AAF -HermanNelson Classroom Unit Ventilators

AAF®-HermanNelson®

Classroom Unit Ventilators

Catalog C: UV-1-230E

Models AVS, AVB, AVV and AVR Floor UnitsModels AHF, AHB, AHV and AHR Ceiling Units

Catalog UV-1-230E / Page 2 / (3/01) AAF®-HermanNelson®

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Table of Contents

The AAF®-HermanNelson®

Advantage........................................... 3

Design Features ........................... 4-17Innovative Design Sets Us Apart ....... 4Unit Ventilators Built To Last ......... 5

Extra Strength ........................................ 5Rugged Exterior ..................................... 5

Easy Maintenance ....................... 6-7Good Design .......................................... 6Motor Location ...................................... 7

Comfort You Can Count On ..... 8-12GentleFlo™ Delivery .............................. 8MicroTech® Comfort Control ............... 9Temperature And Humidity Control ... 10Draw-thru Design ................................ 11Face And Bypass Capacity Control ...... 11Outdoor Air For “Free Cooling” .......... 12

Tailored For Adaptability AndGood Looks .............................. 13-17

Built-in Flexibility ................................ 13Extra Adaptability ................................ 14Addressing Window Down Drafts ....... 14Matching Window Sills ....................... 14Outdoor Air Capability ....................... 14Room Exhaust Capability .................... 15Matching Storage Accessories ............... 15Expansive Coil Offering ....................... 16

Application Considerations ...... 18-47Overview ................................... 18-19

Take Control Of Energy Expenditures . 18Why Classrooms Overheat ................... 18

Systems ..................................... 20-23DraftStop™ System .............................. 20Finned Radiation System ..................... 21Part Load Variable Air .......................... 22Demand-Controlled Ventilation (DCV) 22Active Dehumidification Control (ADC) . 23

Temperature Controls .............. 24-32Ideal For Today’s Schools ..................... 24Temperature Control And

ASHRAE Control Cycle .................. 24Typical Temperature Control

Components .................................... 24Direct Digital Control (DDC)

Background ..................................... 25MicroTech® Direct Digital Control

(DDC) Operating Functions ........... 26MicroTech Components ...................... 27Basic Unit Components ....................... 29Status/Diagnostic Capability ................ 30Split System DX Operation ................. 30

Face And Bypass SequenceOf Operation ................................... 31

Modulating Valve SequenceOf Operation ................................... 32

Field Installed TemperatureControls By Others ................. 33-35ASHRAE Cycle II ................................ 33Required Control Sequence ................. 34DX Low Temperature Limit ................. 34End-Of-Cycle (EOC) Operation ......... 34Water Coil Low Temperature

Limit (Freezestat) ............................. 34Face And Bypass Damper Control

Applications ..................................... 35Valve Control Applications .................. 35

DX Split System ........................ 36-37DX Split System Applications .............. 36System Installation ............................... 36Typical System Wiring and Piping ....... 37

Outdoor Air ............................... 38-47Wall Structures .................................... 38Ventimatic™ Shutter Assembly ............. 39

Floor Units ................................. 41-43Arrangements ...................................... 41

Ceiling Units .............................. 44-47Duct System ........................................ 44Arrangements ...................................... 46

Nomenclature ............................. 48-52Floor Units – AV Available

Combinations .................................. 48Ceiling Units – AH Available

Combinations .................................. 50Coil Combinations .............................. 52

Typical Capacities.................... 53-142Quick Selection ................................... 53Coil Selection Procedure ...................... 54Selection Procedure Example ............... 55Hot Water Heating Selection ............... 56Capacity Correction Factor

For Hot Water Heating .................... 58Hot Water/Steam Heating ................... 60Electric Heating Capacities .................. 61Chilled Water Capacities ...................... 62

750 CFM ........................................ 621000 CFM ...................................... 781250 CFM ...................................... 941500 CFM .................................... 1102000 CFM (Ceiling Only) ............. 126

Direct Expansion Cooling Coils ......... 142

Valve Selection ....................... 143-146Face And Bypass End-Of-Cycle Valve 143

Modulating Valve ............................... 144

Steam Valves ...................................... 145

General Data .................................. 147

Details and Dimensions ........ 148-176Floor AV Units 165⁄8˝ Deep ........... 148Floor AV Units 277⁄8˝ Deep ........... 149Floor AV Unit CoilConnections ......................... 151-153

Heating Only ..................................... 151Cooling only ...................................... 151Heat/Cool .......................................... 152Reheat ................................................ 153Condensate Drain .............................. 153

Ceiling AH Unit AirArrangements ........................ 154-160

Discharge Air Arrangements ................ 154Inlet Air Arrangements ........................ 155Arrangement AU ................................. 156Arrangement AJ .................................. 157Arrangement AT ................................. 158Arrangement AH ................................ 159Arrangement BD................................. 160

Ceiling AH Unit Coil Combinationsand Connections ................... 161-163

Heating Only ...................................... 161Cooling Only ...................................... 161Heat/Cool ........................................... 162Reheat ................................................ 163Condensate Drain ............................... 163

End Panels and EnclosureApplications .................................. 164Valve Dimensions ......................... 165Wall Intake Louver And Grille .... 166Ventimatic™ Shutter .................... 167Accessories ......................... 168-172

Sink and Bubbler Cabinet .................. 168Filler Sections and Utility

Compartment ................................ 169Shelf Storage Cabinet with

Painted Metal Tops ........................ 170Shelf Storage Cabinet with

Laminate Tops ................................ 171Finned Tube Radiation Cabinet ......... 172

Wiring Diagrams .................. 173-176Typical Power Wiring Diagram .......... 173Typical MicroTech Control

Wiring Diagram ............................. 174Typical Wiring Diagrams ................... 175Typical Wall Sensor Diagrams ............ 176

Guide Specifications ............. 177-179

©2001 AAF®-HermanNelson®

The information in this catalog supersedes and replaces previous catalogs/bulletins with regard to AAF-HermanNelson unit ventilators. Illustrations cover the generalappearance of AAF-HermanNelson unit ventilators at the time of publication. AAF-HermanNelson reserves the right to make changes in design specifications and constructionat any time without notice. AFF®-HermanNelson® and MicroTech® are registered trademarks of AAF-McQuay Inc. Windows® is a registered trademark of Microsoft corporation.

Catalog UV-1-230E / Page 3 / (3/01)AAF®-HermanNelson®

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Model AH (Ceiling)

If you’re looking for an economical, energy-effi-cient, and versatile solution to your heating andcooling requirements, AAF-HermanNelson UnitVentilator systems can adapt to virtually any set-ting. That’s why our unit ventilators have becomethe system of choice for schools. Since HermanNelson received the original patents in 1917, unitventilators have proven to be one of the mostreliable energy-efficient systems available formaintaining proper ventilation and precise tem-perature control in the classroom.

Because we know that a comfortable classroomenvironment creates a better climate for learn-ing, we’ve continually adapted our systems toaddress the changing requirements of modernschool buildings.

AAF-HermanNelson Unit Ventilator systemshave an economical first cost and an economicallife-cycle cost. The Model AV Floor and ModelAH Ceiling Unit Ventilators were designed toprovide optimal comfort levels with minimalenergy consumption. This is made possible bystate-of-the-art controls and superior outside aircapabilities, which allow the unit to supply “freecooling” a large percentage of the time. Both the

The AAF®-HermanNelson® AdvantageQuality Counts

pan so that heating-only units can be readily con-verted to heating-cooling units at a later date.

Model AH Ceiling UnitThe horizontal ceiling-mounted unit ventilator,Model AH, provides chilled-water or refrigerantcooling and hydronic or electric heating. Like theModel AV, it can also be supplied for “heating/ventilating-only,” “cooling/ventilating-only,”“heating/cooling/ventilating,” or with the optionof adding cooling at a later date.

Model AH is designed for rooms where floorspace is at a premium. It can be installed with avariety of exposures, including completely exposed,partially or fully recessed, or completely concealed.

Responding To Your NeedsSolid construction, reliability, and innovationhave remained the cornerstones of our productdevelopment. We recognize the requirements ofschools are constantly changing and remain com-mitted to helping you prepare for the future.Whatever your application, there is a AAF-HermanNelson unit ventilator for you.

Model AV and Model AH are available with fac-tory-furnished, fully automatic controls. Thesecontrols adjust quickly to compensate for changesin activity and occupancy so the proper learningenvironment can be maintained.

Model AV Floor UnitThe vertical floor unit, Model AV, utilizes chilledwater or refrigerant for cooling, and hot water,steam or electric heat for heating. Refrigerant cool-ing is accomplished by using a remote condens-ing unit piped to the internal refrigerant coil.Model AV can also be supplied as a “heating/ven-tilating-only” unit, using either hot water, steamor electric heat; or a “cooling/ventilating-only”unit using chilled water or refrigerant cooling;or with “heating/cooling/ventilation.”

Model AV is just right for new construction andretrofit applications. With the Model AV, olderbuildings with baseboard radiant heat or someother form of hydronic heating system can beeasily adapted to work efficiently with the unitventilator. Additionally, chilled-water or refrig-erant cooling can be added, making the unit aheating and cooling unit that provides year-roundcomfort. All floor units come with a built-in drain

AAF-HermanNelsonUnits Optimize ComfortAnd Minimize Costs.

Take A Closer Look At The Best Unit Ventilator Ever Built . . .For Over 80 Years!

Model AV (Floor)


Design FeaturesInnovative Design Sets Us Apart

� Welded One-piece Chassis offers supe-rior strength, durability, and vibrationreduction.

� Large Fan Wheel with aerodynamicallyshaped blades moves air more quietly.

� Fan Housing utilizes logarithmic expansionfor quieter operation.

� Advanced Heat Transfer Coil Designprovides extra capacity.

� Integral Drain Pan, standard on allunits, permits future cooling on heating-onlyunits.

� Unique Draw-thru Design provides uni-form air distribution across the coil to delivereven discharge air temperature.

� Face And Bypass Damper provides supe-rior dehumidification and reduces the chanceof coil freeze-up.

� Two Hinged Top Access Doors provideeasy access to motor and end bearing. Specialtamper-resistant fasteners deter unauthorizedaccess.

Fan Motor Location provides for easy re-moval and maintenance. Placing motor out ofthe air stream (and away from the heating coil)reduces heat exposure to prolong life.

Three Sectionalized Front AccessPanels provide easy access to unit interior. Allpanels can easily be removed by a single personand front side panels can be removed while unitis running. Special tamper-resistant fasteners de-ter unauthorized access.

� Sturdy Cabinet Construction includes hid-den reinforcement, a non-glare textured surface,and a tough, scuff- and mar-resistant finish tomake the top sturdy enough to support mainte-nance personnel.

Superior Design And Engineering And A FirmCommitment To Quality Result In OutstandingPerformance. . .For Years To Come.

� Single Full-length Air Filter is efficient andeasy to replace. All air delivered to classroom isfiltered.

Indoor Room Air Damper blocks unwantedgusts of outdoor air on windy days. Its nylonbearings are quiet and maintenance free.

� Insulated Double-wall Outdoor AirDamper seals tight without twisting.

� Sampling Chamber provided on each unitfor unit-mounted room sensor provides accu-rate sensing of room temperature.

� MicroTech® Digital Direct Control usestime-proven algorithms to provide superior com-fort control. It can function either as a stand-alone or networked control.

� UL/cUL Listed.

� Rated in accordance with ARI 840.

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DesignFeatures


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• End and front panels are available in a pleasingarray of architectural colors.

• The Oxford brown steel kickplate is coated andbaked with a thermosetting urethane powderpaint to blend with floor moldings and pro-vide years of service.

• Ceiling units are finished with an off-white, bakedthermosetting urethane on all exterior panels andbar stock steel discharge grille, which blends wellwith most ceilings.

• Finally, each unit is painstakingly inspectedbefore boxing, then encapsulated in a clear plas-tic bag to prevent chafing, surrounded by anextra heavy duty cardboard box, and secured toa skid permitting damage free shipment.

• We know the next inspector is the customerand we want you to be satisfied.

Superior Design AndSolid Construction MakesThe AAF®-HermanNelson®

Unit Ventilator The BestUV On The Market.The AAF-HermanNelson Unit Ventilator is trulyengineered and manufactured using industrialdesign concepts to resist abuse over the years.Our solid construction promotes continued align-ment and structural strength. They can remain asstrong and rigidly assembled decades after theyare installed.

Extra StrengthPromotes Long LifeAAF-HermanNelson’s exclusive unitized weldedframe (Figures 5-1 and 5-2) is far superiorto the fastener-type construction (Figure 5-3)used by other manufacturers. Loosened fastenerscan allow vibration, rattles and sagging panels.With reinforced welded construction, there areno fasteners (screws or bolts) to come loose.

The unique benefits of the welded-frame corrosion-resistant galvanized-steel foundation, combinedwith AAF-HermanNelson’s extra-strength steel bargrilles and heavy-gauge metal cabinet panels, pro-vides trouble-free operation and long life. Metal-forming techniques add rigidity for superiorstrength. The extra-strength pipe tunnel stiffensthe structure while adding aerodynamic air flowwithin the unit. Hidden reinforcement providesadditional built-in support for the top panel aswell as better support for the fan assembly. Thisreinforced surface is strong enough to supportmaintenance personnel without fear of damag-ing the top.

Rugged ExteriorWithstands The TestOf TimeInstitutional quality cabinets offer durability andgood looks. The superior finish fosters long-last-ing beauty, as well as resistance to abuse and cor-rosion.

We apply the very highest standards at every step ofthe finishing process to reinforce a lasting high qual-ity finish.

Design FeaturesUnit Ventilators Built To Last

• High-quality furniture steel is carefully inspectedbefore painting. Scratches and marks thatmight show through the finish are removed.

• After fabrication, the metal undergoes a five-stage cleaning and phosphatizing process toremove cutting oils and forming compounds,and prepare the surface for painting. This pro-vides a good bonding surface and reduces thepossibility of peeling or corrosion.

• A specially formulated environmentallyfriendly thermosetting urethane powder is ap-plied electrostatically to the exterior panels.This film is then oven-cured to provide cor-rect chemical cross-linking, which gives maxi-mum scuff- and mar-resistance.

• The top of floor units is finished with a textured,non-glare and scuff-resistant, charcoal bronze elec-trostatic paint.

Figure 5-2. AAF-HermanNelson’sWelded Construction

Figure 5-3. Competitor’sFastener-type Construction

Figure 5-1. AAF-HermanNelson Welded Chassis

Built-inPipe Tunnel

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Extra-strengthPipe Tunnel

Reinforced Top Support

Motor Mount

FanPartitions

One-pieceEnd Frame

Strong, Formed, Vertical End Back Bracingwith Built-in Access Knockouts

One-piece, Heavy-gauge, Full-length KickPlate

Full-lengthStrong Channels


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Figure 6-1. Easily Accessible With Tamper-resistant Fasteners

Design FeaturesEasy Maintenance

Good Design MakesRoutine MaintenanceQuick And Easy.AAF®-HermanNelson® Unit Ventilators are de-signed to provide a safer and easier access formaintenance and service personnel. Our unitshave several access panels and doors that allowdirect access to the motor, fan housings, bear-ings, filter, and temperature controls. This allowsfor easier maintenance that typically can behandled by a single person.

Tamper-resistant AccessFront panels and top access doors are held in placeby tamper-resistant fasteners using positive posi-tioning fasteners, which are quickly removed oropened with the proper tool but deter unautho-rized access to the unit’s interior (Figure 6-1).

Sectionalized Access Panels And DoorsAll floor units have three separate front panels,sized for easy handling by a single person. Thisfeature allows easy, targeted access to the compo-nent that needs servicing (Figure 6-1).

Two 12"-wide front panels (Figure 6-2), conve-niently located at each end of the unit, provideaccess to piping, temperature control componentsand the fan High-Medium-Low-Off switch. Un-like units that have full-length front panels, thesesmaller front panels can be removed without dis-turbing the normal operation of the unit. Theshort center front panel (Figure 6-1) providesaccess to the filter and discharge grille.

Hinged top access doors allow easy access intothe end compartments to facilitate convenientservicing of the motor and shaft bearing (Figures6-2 and 6-3).

Single-filter DesignWith AAF-HermanNelson’s single-filter design,filter changeout takes only seconds. Change only onefilter instead of several. One-piece filter designdirects the mixture of outdoor air and room airthrough a single unit filter. This eliminates thepossibility of uneven dust loading, common tounits with separate filters for room air and out-door air or units that restrict air through thefilter by a metal partition between the return airand outside air. Because there are no gaps betweenindoor and outdoor air, the single-filter designalso increases filter life so filter maintenance is lessoften.

12" Left FrontAccess Panel

Filter

Motor

Figure 6-4.Renewable Media Filter

RemovableDischarge

Grille

Center Front Access Panel

Discharge Screen

Figure 6-3.Filter Access

12" Right FrontAccess Panel

Renewable Media (Single-use And PermanentWire Mesh Filters Also Available.)

Tamper-resistantFasteners

Tamper-resistant Fasteners

Tamper-resistantFasteners

StructuralFrame

12" Left FrontAccess Panel

Fan ShaftBearing

Figure 6-2. Left FrontAccess Panel

Top AccessDoors

Discharge GrilleMounting Bracket(s)


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ing the motor away from the coil (Figure 7-4) hasthe added benefit of extending motor life. Ourdirect-coupled motor and self-aligning motormount facilitate motor changeout. The motorcomes with a molex plug that fits all sizes, whichfurther simplifies removal.

Multi-tap TransformerThe auto-transformer (Figure 7-5) provides mul-tiple fan motor speed control through the speedswitch. The motor is independent of supply volt-age, which allows stocking of one motor (schooldistrict-wide) for various voltage applications.

Long-life BearingsThe floor unit rotating element has only onelarge, self-aligning, sleeve-type end bearing (Fig-ure 7-6) and two motor bearings for smootheroperation. The location of the bearing at the endof the shaft (out of the airstream) (Figure 7-4)makes for easy access and convenience, shouldthis become necessary.

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Figure 7-5. Multi-tap Transformer

Design Features Easy Maintenance (Continued)

Filters are included in all units. AAF®-HermanNelson® single-use filters are standard onall but electric heat units, which come with per-manent wire mesh filters. Permanent wire meshand renewable media (Figure 6-4) filters are avail-able for non-electric heat units, in lieu of single-use filters.

• Single-use filters feature Amerglas media.They are designed to be used once and dis-carded.

• Permanent filters are metal filters that maybe removed for cleaning and reused numer-ous times.

• Renewable media filters (Figure 6-4) consistof a heavy painted metal structural frame andrenewable Amerglas media

Figure 7-1. Ceiling AccessRetainer Chains

Ceiling Access Retainer ChainsAll ceiling units (model AH) are equipped withretainer chains to facilitate reduced access panelmovement during opening as well as ease ofmaintenance. This feature enables one person toservice the unit—instead of a crew.

Ceiling End PanelsEnd panels ship installed on ceiling units for aclean, exposed finish. Four tamper-resistant fas-teners with exterior access guard against tamper-ing while providing easy access to the interior forauthorized personnel.

Motor LocationSimplifies AccessAnd MaintenanceAAF-HermanNelson Unit Ventilator 115/60/1NEMA motors offer low operating current andwattage. This can result in savings up to hundredsof dollars per year.

The reliable permanent, split-capacitor (PSC) fanmotor (Figure 7-3) features automatic reset, ther-mal-overload protection and has no brushes,contacts or centrifugal starting switches—the mostcommon cause of motor failure. In addition, themotor has a built-in decoupled isolation systemto reduce transmission of vibrations for quieteroperation.

Even “permanently” lubricated motors are suppliedwith recommended lubrication charts calling forlubrication every five or ten years. We recommendthat maintenance instructions of the motor manu-facturer be closely followed.

The large-diameter hollow fan shaft provides quieteconomical performance.

Easy Motor RemovalUnlike many UVs, the motor is separate from thefan assembly and located out of the airstream atthe end of the fan shaft—away from the hotcoil—for easier maintenance and removal. Locat-

Figure 7-2. Discharge Grille

Figure 7-3. Standard Energy-efficient NEMA Fan Motor

PSC

StandardMolex Plug

DecoupledIsolation

Figure 7-4. AAF-HermanNelson Design

Drive shaft solidly anchored and supported onboth ends with motor located out of the air stream

CouplingPartition

EndBearing

Fans Motor

Partition

End CompartmentEnd Compartment

Air Stream�

Figure 7-6. Long-life Bearings

Oilable sleeve bearings on floor units are locatedon fan motor and fan shaft end bearings forquietness and long life—out of the air stream.Maintenance-free permanently lubricated bear-ing are standard on ceiling units (Figure 7-6).

Nylon damper bearings foster quiet, mainte-nance-free operation of room air, outdoor air,and face and bypass dampers.

Removable Bar Discharge GrilleFacilitates cleaning of fans and fan housings. (Fig-ure 7-2 and 6-1) The steel grille is made from extrastrength bar stock promoting long life. A built-in10° angle provides proper air throw to blanket theroom for proper air circulation and comfort.

10° Angle


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Design FeaturesComfort You Can Count On

The AAF®-HermanNelson® Unit Ventilator airdelivery system is engineered and manufacturedto deliver quiet, continuous comfort. Engineer-ing developed and applied leading-edge aerody-namic technology to create a unit that is muchquieter. You will appreciate the difference.

GentleFlo™ Delivery incorporates advances in Air-Moving Technology. The entire air-moving sys-tem is designed for a softer, quieter operation.

Continuous ComfortWith Our GentleFlo™

Delivery

Figure 8-1. Large Fan Wheel

Figure 8-2.Wheel And Fan Housing Design

ExpandedDischarge AirOpening

AerodynamicallyTuned Fan Blades

Fan Housing DesignIncorporates LogarithmicExpansion TechnologyPrecision

Tolerances

Figure 8-4. Flow And Pressure Test Results Of Fan Blade Design

Figure 8-3. Quiet And Comfortable Equals An Excellent Learning Environment.

• Fan wheel blade shape moves the air efficiently(Figure 8-4). Offset aerodynamic blades (Fig-ure 8-1) and balanced precise dimensions re-duce the noise associated with turbulence andresult in lower sound levels (Figure 8-2).

• Fan housing design incorporates the latest“logarithmic expansion” technology forsmoother, quieter air flow. (Figure 8-2) Thelarge fan housing allows the air to expand loga-rithmically after it leaves the fan. This featureworks with the fan’s slow-speed design to pro-mote quieter operation.

• Large, expanded discharge opening (Figure 8-2) minimizes air resistance, lowering sound.Modular fan construction contributes to equaloutlet velocities to promote quiet operation.

• Fan wheels, motor and shaft are pre-balanced,factory balanced after assembly, and factorytested for stable, quiet operation.

GentleFlo™ Delivery is a combination of cutting-edge technologies; delivering gentler, quieter op-eration with smoother air-moving performance.

• Fan wheel is large, wide, and rotates at a lowspeed to reduce fan sound levels (Figure 8-1).The impact-resistant balanced fan wheel pro-vides consistent performance. The large fanshaft of ground and polished steel operatesreliably, well below its critical speed.

Typical Of Older,Smaller WheelDesignsShowing FlowAnd PressureTurbulence

OffsetAerodynamicBlades

AAF-HermanNelsonFan Wheel Blade DesignShows MinimizedFlow And PressureTurbulence Resulting InLower Sound Levels.


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2. CO2 Demand ControlledVentilation CapabilityThe MicroTech controller also has a built indemand controlled ventilation (DCV) algo-rithm that can make sure the system providesexactly the right amount of outside air.

CO2 is an excellent measure of occupancy. Themore people the more CO2 produced. TheAAF-HermanNelson Unit Ventilator enablesventilation compliance at all times using the in-put from a CO2 controller (Figure 9-4) to modu-late the outside air damper based on actual oc-cupancy versus a fixed design level. With thisASHRAE accepted control method, energy useis minimized as only the required amount ofoutside air is introduced to promote good in-door air quality. Humidity levels are improved.Ventilation is optimized, while providing energysavings versus a fixed ventilation strategy. TheCO2 Sensor is either Wall Mounted or FactoryMounted in the unit (See Application Consid-erations pages 22 and 23).

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Design Features Comfort You Can Count On (Continued)

MicroTech® OffersPrecise Comfort ControlThe Direct Digital Control (DDC) packageknown as MicroTech has been designed to pro-vide sophisticated temperature control of AAF®-HermanNelson® Unit Ventilators. The MicroTechpackage can function as a stand-alone controller(Figure 9-1), as part of a MicroTech system (Fig-ure 9-2) or as part of a third-party Building Au-tomation System (BAS) through Open Protocol(Figure 9-3).

UV ControlsASHRAE Cycle II Operation is factory pro-grammed. A room temperature sensor controls heat-ing, ventilation and cooling functions. DischargeAir control can override room temperature controlto prevent discharge air from dropping belowits low setpoint. ASHRAE Cycle II defines thebasic operation of the Outdoor Air Damper, Econo-mizer Functions, and the Discharge Air Tempera-ture Control.

Time Proven AlgorithmsMicroTech uses “Change” and “Step & Wait”algorithms, which work together in a two-stageprocess to maintain room temperature controlwith no overshoot. The “Change” algorithmchanges the actuator (damper or valve) setpoint,in response to deviation of room temperaturefrom its setpoint. The “step & wait” algorithmcauses the actuator (damper or valve) to open orclose to maintain the “change” algorithm calcu-lated position setpoint. The “step” part is theamount of time the actuator is driven either openor closed, and “wait” is the amount of time theactuator holds its position. “step & wait” periodsvary and are dependent on amount of actuatorposition setpoint offset. The “step & wait” algo-rithm thus prevents overshooting and providesbetter comfort control.

Economizer OperationEconomizer operation is facilitated by the outdoorair damper, which automatically adjusts above mini-mum outdoor air to provide free-cooling when out-door air temperature allows for it.

Other control sequences available include:1. Part Load Variable Air Feature

The Part Load Variable Air Feature uses Faceand Bypass control for dehumidification, andPI Loop to calculate percent load. It automati-cally adjusts indoor fan speed based uponroom load and the room temperature algo-rithm. By basing indoor fan speed upon roomload, it provides higher latent cooling capa-bilities and quieter operation during non-peakload periods. The room temperature algo-rithm determines the speed of the fan. Fanspeed varies according to the face damper po-sition. It also provides for built-in “step” and“wait” delays. Based on fan speed, the partload variable air feature adjusts the outdoorair damper minimum position to bring in thesame or constant amount of outdoor air. (SeeApplications section.)

Figure 9-1.MicroTech Stand-alone Architecture

MicroTech System CapabilitiesMicroTech systems (Figure 9-2) and third-partyBuilding Automation Systems (BAS) (Figure 9-3)can directly read and write data, e.g., new setpoints,to MicroTech controllers through network com-munications and Open Protocol respectively.

Unit Ventilator MicroTech ControlsAll Direct Digital Controls (DDC) are factory in-stalled and tested. Communication types includeStand Alone, Master/Slave, and Network. DDCpromotes correct precise sequence of operation. (SeeApplications section.)

The UV software that ships installed is for StandAlone operation. Master/Slave and Network Soft-ware are field downloaded.

3. Active Dehumidification Units (Reheat)During excessive humidity conditions theHumidity Sensor (Figure 9-5) controls the Unitto continue cooling. Wet heat or electric heatthen reheats discharge air. This removes ex-cessive room moisture. During acceptableroom humidity levels the Unit Reheat Func-tion is disabled. The Humidity Sensor is ei-ther Unit Mounted or Remote Wall Mounted.(See Application Considerations page 23.)

Figure 9-4.CO2 Sensor

Figure 9-5.Humidity Sensor

Open-protocol Partner

Level 1Controller MicroTech

Level 2Controllers MicroTech

IntegrationPanel

OpenProtocolMaster

UnitVentilator

UnitVentilator

Air CooledChiller

Figure 9-3.MicroTech Open-Protocol Architecture

Figure 9-2. MicroTech NetworkSystems Architecture

NetworkMasterPanel

LocalMasterPanel

RemoteMonitoringSequence

Panel

Unit

Ventilator

Air CooledChiller


Level 2Controllers MicroTech


UnitVentilator


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Total From From Total From FromBypass Room Outdoors Coil Room Outdoors

0 1500 0 0 0 1500 1050 45010 1500 150 150 0 1350 900 45020 1500 300 300 0 1200 750 45030 1500 450 450 0 1050 600 45040 1500 600 600 0 900 450 45050 1500 750 750 0 750 300 45060 1500 900 900 0 600 150 45070 1500 1050 1050 0 450 0 45080 1500 1200 1050 150 300 0 30090 1500 1350 1050 300 150 0 150100 1500 1500 1050 450 0 0 0

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However, at all other bypass air percentages (partload), significant differences are evident in theroom air and outdoor air compositions of the twounit types. For instance, examine the 1500 cfmdraw-thru unit (Table 10-1) against the 1500 cfmblow-thru (Table 10-2) unit at 70% bypass air.At this point, the draw-thru unit still has all of theoutdoor air going through the coil, while theblow-thru unit is bypassing 315 cfm (70%) ofoutdoor air directly into the classroom—whileonly 135 cfm (30%) of outdoor air is goingthrough the coil.

This illustrates that the most effective way ofmaintaining an acceptable humidity level with achilled-water unit ventilator system is to use a faceand bypass damper controlled draw-thru unit.

Better TemperatureAnd Humidity ControlFace and bypass damper control coupled withdraw-thru unit construction offers maximum de-humidification and optimal temperature control.On the AAF®-HermanNelson® draw-thru unitventilator, the fans are located above the heating/cooling coil, which permits separation of the in-door and outdoor air streams until it is optimal tomix the air streams.

With a draw-thru design (Figure 10-1) and dur-ing most part-load conditions, the majority of thehumid outdoor air passes through the cold coil(coil surface below the dew point), where the mois-ture is removed, and the previously treated, lesshumid room air bypasses the coil, providing maxi-mum condensate removal. Consequently, humid

outdoor air is not bypassed around the coil untilthe amount of air going through the coil is lessthan the amount of outdoor air that is enteringthe unit.

On the other hand, with blow-thru construction(Figure 10-2), the amount of humid outdoor airthat is bypassed around the coil at part-load con-ditions is directly proportional to the percentageof the total air stream that is being bypassed sincethe air is mixed in the fan.

The tables below compare the composition of theair streams through the coil and air streamsbypassing the coil at various bypass air percent-ages for draw-thru and blow-thru unit ventilatorsusing 450 cfm of outdoor air. At both “0% bypassair” and “maximum bypass air” no differenceexists in the composition of the air streams when


OutdoorAir

Figure 10-1.AAF-HermanNelson Design

Face andBypassDamper

RoomAir

Table 10-1. 1500 cfm Draw-thru Unit

IncreasedDehumidification

Bypass Air Stream (cfm) Coil Air Stream (cfm)%Bypass

Air

TotalUnitcfm

AAF-HermanNelson Design

Table 10-2. 1500 cfm Blow-thru Unit

Total From From Total From FromBypass Room Outdoors Coil Room Outdoors

0 1500 0 0 0 1500 1050 45010 1500 150 105 45 1350 945 40520 1500 300 210 90 1200 840 36030 1500 450 315 135 1050 735 31540 1500 600 420 180 900 630 27050 1500 750 525 225 750 525 22560 1500 900 630 270 600 420 18070 1500 1050 735 315 450 315 13580 1500 1200 840 360 300 210 9090 1500 1350 945 405 150 105 45100 1500 1500 1050 450 0 0 0

Bypass Air Stream (cfm) Coil Air Stream (cfm)%Bypass

Air

TotalUnitcfm

ReducedDehumidification

Competitor’s Design

Figure 10-2.Competitor’s Blow-thru Design

RoomAir

Filter

R.A./O.A.Divider

OutdoorAir


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3. Direct a portion of the air through the coilsand allow a portion to bypass the coils (Fig-ure 11-4).

AAF-HermanNelson’s modulating controllerautomatically adjusts the damper so that maximumenergy efficiency and maximum comfortare achieved. Face and bypass damper control(Figure 11-5) eliminates the frequent problem ofincorrectly sized modulating control valves. Im-properly sized control valves often result in “two-position” valve cycling, resulting in poor com-fort (temperature and humidity) control and valvewear.

largely humid outdoor air, resulting in uncondi-tioned air being bypassed and creating poorcomfort conditions.

With a blow-thru design the positive pressure ofthe fan discharge can create areas across the coil ofvarying temperatures and airflow. In addition,Blow-thru face and bypass damper constructionpicks up heat by wiping the coil creating over-heating conditions. Also the sound in a blow-thrudesign will vary based upon the position of theface and bypass damper.

Face And Bypass OffersInfinite Capacity ControlThe AAF-HermanNelson face and bypass dampercontrol units utilize standard unit ventilator cyclesof temperature control and can allow maximumoutdoor air into the room for cooling. The faceand bypass damper can be positioned to:

1. Direct all the air through the heating orcooling coil (Figure 11-2).

2. Direct all the air to bypass the heating orcooling coil. (Figure 11-3)


Room AirDamper

Coil

Outdoor AirDamper

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Draw-thru DesignProvides Even DischargeTemperatures And BetterHumidity Control

The AAF®-HermanNelson® Draw-Thru principlesets the AAF-HermanNelson Unit Ventilator apartfrom most competitive models. With this system,fans draw air through the entire heat transferelement (Figure 11-1), rather than blowingit through highly concentrated areas of the coilelement.

AAF-HermanNelson’s draw-thru design is moreeffective because:

(1) Draw-thru design provides uniform dischargeair temperatures.

(2) Draw-thru fans allow complete, even, heat trans-fer over the entire face area of the coil for moreefficient unit ventilator operation.

Draw-thru vs. Blow-thruWith AAF-HermanNelson’s draw-thru construc-tion, situations requiring less than full coolingcan be controlled with accuracy. The face andbypass damper directs the humid outdoor airthrough the cooling coil and allows the low hu-midity room air to bypass the coil. In addition,in a draw-thru design the air is drawn evenlythrough the entire coil fostering even tempera-ture across the coil and maximizing coil surfaceutilized for dehumidification.

Blow-thru designs cannot provide comfort likethis. With blow-thru designs, the humid outsideair is pre-mixed with the room air before it can gothrough the coil. Dehumidification occurs onlyto the portion of the air that is directed throughthe cooling coil. The air that bypasses the coil is


Figure 11-1. Draw-thru Design WithEven Air Distribution

Coil

Air Flow Shaded

Face And Bypass DamperThe AAF-HermanNelson modulating face andbypass damper assembly has twist free reinforcedaluminum construction for durability. Aluminumis used because it is lightweight and noncorrosive,resulting in low torque and easy movement. Theend seals are wool mohair and the long closingedges of the damper use a cushion formed ofwoven glass fabric-coated silicone rubber. Thisseal is free from deterioration and retains itsmemory for a tight seal.

Nylon damper bearings foster quiet, maintenance-free operation of the face and bypass damper.

OutdoorAir


RoomAir

Figure 11-5. Face And Bypass Damper

Figure 11-3. Full Economizer Opera-tion With 100% Outdoor Air

Figure 11-4. Portion Of Air ThroughCoil And Bypassed

Notice natural bypassing oftreated room air

Figure 11-2. 100% Room Air

Flexible Air Seal

Metal Formed ForExtra Rigidity

OutdoorAir

Room AirDamper

RoomAir

Wool MohairEnd Seal

Outdoor AirDamper


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Dampers on AAF-HermanNelson Unit Ventilatorsuse the turned-metal principle on the long clos-ing edges (Figure 12-3), which provides positivesealing by embedding into wool mohair (no metalto metal contact). This superior design preventsoutdoor air from entering (Figure 12-4). Thereare no plastic gaskets to become brittle with time,sag with heat or age, or require a difficult slot fitto seal.

Room Air Balanced Damper DesignThe AAF-HermanNelson room air damper de-sign is free floating and prevents intermittentgusts of cold air from blowing directly into theclassroom on windy days (Figure 12-5). It isconstructed of aluminum with built-in rigidity.The metal forming technique resists twisting andincorporates a full-length counter weight for easyrotation.

Delivering Outdoor AirFor “Free Cooling”It is well recognized that cooling, not heating, isthe main thermal problem in school classrooms.The typical classroom is cooled by outdoor airover half the time, even in cold climates.

It is therefore essential that unit ventilatorsefficiently deliver outdoor air when classroomconditions call for “free” or economizer cooling.With AAF-HermanNelson Unit Ventilators, youcan have outdoor air whenever it is needed.

Cold Weather Outdoor Air DamperThe standard AAF-HermanNelson outdoor airdamper is made of galvanized steel to inhibitcorrosion, with double-wall welded constructionfor rigidity, and encapsulated insulation (Figure12-2). The outdoor damper has additional in-sulation on the exterior of the outdoor air damperblade and on the outdoor air entry portion ofthe unit.

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Figure 12-5. Room AirDamper Design


OutdoorAir

RoomAir

Figure 12-2. Full Economizer Opera-tion With 100% Outdoor Air

Maximum DehumidificationThe design of the AAF®-HermanNelson® face andbypass damper control has been carefully engi-neered to provide maximum dehumidification atall times. Constant water flow through the coil ismaintained to keep the surface temperature at, orbelow, the dew point. Directing all the air throughthe cooling coil may result in short cycling or anover-cooled condition. Directing all the air aroundthe coil may result in overheating and no dehu-midification.

AAF-HermanNelson’s sophisticated DDC con-trols monitor room conditions and modulate theface and bypass damper to obtain maximum de-humidification and optimal temperature control.

Ease Of System BalancingWith a face and bypass damper, the water in thesystem is constantly circulating, which maintainsa desirable head pressure to the pumps. With fluc-tuating head pressure eliminated, balancing thesystem can enable the correct quantity of water inall circuits.

Increased Coil Freeze ProtectionWith face and bypass damper control, there is nochange in the flow of water through the coil. Coilsthat have a constant flow of hot water cannotfreeze. Additionally, the AAF-HermanNelson as-sembly has a double-walled insulated outdoordamper with an encapsulated insulation and woolmohair seals to prevent unwanted cold air fromentering the unit. This cold-weather air-tight con-struction further decreases the chance of coil freeze-up, if waterflow is inadvertently interrupted.

Furthermore, a low-temperature Freezestat (Fig-ure 12-1), factory installed on all hydronic units,significantly reduces the chance of coil freeze-up.Its wave-like configuration senses multiple loca-tions by blanketing the leaving air side of the coilto react to possible freezing conditions.

Figure 12-1. Freezestat Figure 12-3. Turned-metal Seal

Figure 12-4. Cold Weather Outdoor Air Damper

TurnedMetal

Full-lengthWool Mohair

SealWool Mohair

End SealFull-length Wool

Mohair Seal

TurnedMetal

AdditionalInsulation

Insulated Double-wall Construction

The simple principle of an area exposed to a forceis used to prevent gusts of cold air. The largerarea closes the damper. The return air damperuses turned-metal sealing concepts with a mo-hair seal.

Both the room air and outdoor air dampers havenylon damper bearings to foster quiet, mainte-nance-free operation.

Room AirDamper

Coil

Freezestat

Wool MohairEnd Seal

Turned-metalDamper Stop

Full-lengthWool MohairDamper Seal

Turned-metalDamper Blade

AdditionalInsulation

Wool MohairEnd Seal

RoomAir Damper


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Protective Metal Wire RaceBuilt-in metal wire race for extra protection thatruns from one end of the unit to the other so wiresare not exposed to unit air (Figure 13-3).

Auto TransformerAuto transformer provides multi-speed fan motorspeed control through speed switch. Motor is inde-pendent of supply voltage to unit.

Easy Fit-up To ShelvingEasy fit up to shelving cabinets is realized by a weldedslot in the floor unit top front rail, which receives aspline from cabinet shelving (Figure 13-4).

Reversible Bar Discharge GrilleReversible bar discharge grille’s optimum 10° up(standard) or 10° down vertical deflection on ceilingunits provides architecturally pleasing appearance.Standard on 30" units. Optional accessory on 36" units.

Adjustable Double DeflectionDischarge GrillesCeiling units with front (36" unit) and bottom(40" unit) discharge are available with four-waydouble deflection discharge grilles (Figure 13-5) so that air distribution patterns may be ad-justed on the job to meet room requirements.Both the horizontal front vanes and vertical rear

Built-in FlexibilityAAF®-HermanNelson® unit ventilators havemany standard features with flexible options thatmake them just right for retrofit applications andwell suited for new-construction. It is this atten-tion to detail and understanding of school appli-cations that make AAF-HermanNelson units theproduct of choice.

Add Cooling At A Later DateAll units (heating-only, cooling-only, heating/cooling) come with an insulated, galvanized-steeldrain pan. (Figure 13-1) The drain pan is insu-lated on the bottom to help prevent condensateformation. Some manufacturers eliminate thedrain pan on heating-only units. Because werecognize that some schools may wish to addcooling at a later date, we include a built-in drainpan on heating-only units as standard.

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Design FeaturesTailored For Adaptability And Good Looks

Figure 13-2. Adjustable Leg Levelers

Reversible Drain ConnectionThe insulated drain pan has drain connections atboth ends. One drain is shipped open. This canbe reversed in the field.

Ceiling Unit Drain ConnectionCenter-line located 5" above unit bottom forproper drainage.

Figure 13-1. Insulated,Galvanized Steel Drain Pan

Adjustable Leg LevelersFront adjustable leg levelers on floor units com-pensate for floor irregularities. (Figure 13-2)

Built-in Pipe TunnelBuilt-in pipe tunnel on floor units allows field cross-over of hot-water or chilled-water piping, electricalor refrigeration tubing (Figure 13-3).

Figure 13-6. Ceiling Unit Ventilators

Return Air Static BalancerReturn air static balancer is used whenever theoutdoor air static pressure is 1⁄8" greater thanreturn air static pressure (ceiling model only). Inapplications where significant external static pres-sures are encountered due to outside air ductwork, the return air static balancer may be used tobalance air flow between outdoor air and returnair. A balancer is included in the return air ple-num of the unit that may be manually set so thatthe room air fan motor is not subject to overloadconditions as the outdoor air/return air dampertravels during the normal cycle.

Accurate Response To RoomTemperature ChangeA sampling chamber is provided on each unit forhousing the unit-mounted temperature sensorwhenever the unit mounted temperature sensor isprovided with MicroTech® controls. A represen-tative sample of room air is continuously drawninto the sampling chamber when the fan is run-ning, to provide an accurate response to roomtemperature changes.

Figure 13-4. Fit-up Shelving

Exposed Partially Recessed

Soffit Concealed

Wire Race

vanes of the double deflection discharge grilles areadjustable to provide both side deflection andupward or downward deflection.

Finished AppearanceCeiling unit ventilators can be mounted in anexposed position, in a soffit, partially recessed,fully recessed, or concealed (Figure 13-6). Forpartially- and fully-recessed units, recess flanges(Figure 13-7) are a standard accessory to pro-vide a finished appearance to help finish off theceiling and provide a break to isolate the unitfrom the ceiling.

OutdoorAirRoom

Air

Figure 13-3.Built-in Pipe Tunnel And Wire Race

Room AirDamper

Built-inPipe Tunnel

OutdoorAir Damper

Front AlignmentBar

ShelvingCabinet

Unit Ventilator

Figure 13-5. Double DeflectionDischarge Grille

Figure 13-7. Recess FlangeRecess Flange

LegLevelers


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used for recessing into the building masonry wall.Louvers are sized to match the unit outside airopening to maximize outdoor air. Drainage is lo-cated in the exterior side of the frame. All alumi-num construction is standard, with a decorativegrille optional. The 1⁄2˝-square mesh bird screen(Figure 14-3) located on the leaving air side pre-vents birds and other small animals from enter-ing. The strong aluminum mesh is designed tominimize air pressure drops, unlike expandedmetal.

Horizontal And Vertical Blade LouversHorizontal blade construction turns the air to keepmoisture from entering. The bottom weep holesdrain moisture to the outside (Figure 14-4).Vertical-blade multiple-break configuration pro-vides positive water impingement and entrapment.The bottom lip drains moisture to outside(Figure 14-5).

GrilleAAF-HermanNelson decorative intake grilles areavailable in heavy-gauge aluminum. The squareholes are designed to match the blades of the AAF-HermanNelson louver, maximizing the air open-ing. The grilles come in either painted or un-painted AQ 5005 aluminum with holes formounting to building exteriors (Figure 14-6).

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1˝ End Panels1˝ End Panels finish off stand-alone floor units.They are individually wrapped in plastic andboxed to prevent damage during construction.

6˝ End Panels6˝ End Panels with kick plates can be used to addextra space for piping with stand-alone floor units(Figure 14-1). They are individually wrapped inplastic and boxed to prevent damage during con-struction.

Take The Chill Out OfWindow Down DraftsAAF®-HermanNelson® DraftStopTM is designedto minimize cold window downdrafts.Downdrafts can be generated in classrooms withrelatively large windows during prolonged peri-ods of cold outside temperatures. For comfortduring such conditions, some form of downdraftprotection should be provided.

The AAF-HermanNelson DraftStop System isone of the best systems available to address thedowndraft problem. Our unique DraftStop Sys-tem intercepts falling cold air at the window silllevel and recirculates it back to the unit ventila-tor. It then enters the unit’s air stream throughthe room air damper and becomes part of thenormal air circulation pattern. This is accom-plished by blocking the return air grille at thefront of the unit ventilator to cause the return airto be drawn in through the ends of the unit.

Sub-base Available ToMatch Window Sills OrExisting CabinetsAAF-HermanNelson sub-bases are used to pro-vide additional height to the floor unit ventilator.This allows the unit to match the window sill orexisting cabinets’ heights. Prior to 1968, unitventilators came in 28˝, 30˝, and 34˝ heights. Theindustry standardized on the 30˝ height of the

Functional UnobtrusiveOutdoor Air CapabilityWith today’s increased emphasis on outdoor airfor ventilation and proper indoor air quality, AAF-HermanNelson louvers are especially important.They allow outdoor air to be drawn in whileblending with the building architecture.

The AAF-HermanNelson Louver is constructedwith heavy blades in a rugged frame. Both lou-vers and frames are made of heavy-gauge alumi-num, which is available either painted or un-painted. For painted louvers and grilles a speciallyformulated environmentally friendly thermoset-ting urethane powder is applied electrostaticallyand baked for long lasting beauty as well as resis-tance to corrosion. The paint is then oven curedto provide correct chemical cross-linking, whichprovides years of service. The alloy used for lou-vers and grilles, AQ 5005, is suitable for color an-odizing by others. Louvers can be supplied with orwithout a flange. The optional flange can be usedfor a panel wall finish. The unflanged louver is

Design Features Tailored For Adaptability And Good Looks (Continued)

Figure 14-5. Vertical Blade Louver

Lip Drains

Figure 14-2. Sub-base

AAF-HermanNelson unit. Sub-bases (Figure 14-2) are available in five different heights: 1˝, 2˝, 4˝,6˝, or 12˝ with 165⁄8˝or 217⁄8˝ depths. Their Oxfordbrown baked thermal setting urethane powderpaint matches the unit’s bottom section andwithstands cleaning of floors. In addition, the unit’sleg levelers can be used to level the entire unit/sub-base assembly, compensating for uneven floors.

The AAF-HermanNelson sub-base can also beused to raise the outside air opening above floorlevel to reduce blockage of outside louvers andreduce louver soiling from rain splash.

Figure 14-4. Horizontal Blade Louver

Weep Holes

Figure 14-6. Outdoor Grille

Figure 14-1. 6˝ End Panels

Figure 14-3.Bird Screen On All Louvers

(Indoor View)

Weep Holes

Sub-base

Louver Flange

Bird Screen


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Figure 15-2. Ventimatic Shutter FrontFigure 15-1.

Ventimatic Shutter With Louver

Louver

VentimaticShutter

Exhaust Room Air


Matching Storage Accessories Available To Meet Your Needs

Figure 15-3. Sink And BubblerCabinet With Stainless Steel Top

Shelving cabinet tops are furnished with a tex-tured, non-glare and scuff-resistant charcoalbronze electrostatic paint. Optional laminate topsare available. Also available for field-supplied andinstalled countertops.• Adjustable kickplates with leg levelers are stan-

dard on all units and functional accessories. Eu-ropean cabinet design has adjustable leg level-lers on each corner that adjust to compensatefor variations in the floor.

• Adjustable height metal shelves for flexible storagespace. Shelf adjusted without tools by reposi-tioning the four concealed shelf holding clips.

• Optional easy sliding door with bottom glidetrack for good alignment. Bottom glide trackprevents door bottom intrusion into the stor-age space. Optional door locks.

• Door pulls added for convenience and finishedappearance.

• Front alignment bars fit into welded notchespermitting alignment of storage accessories withthe Unit Ventilator.

Figure 15-4. Shelf Cabinets

FrontAlignmentBarAdjustable Kick Plate

And Leg Levelers

Unit Ventilator

Shelving Cabinet

Alignment Slot

Simple RoomExhaust CapabilityVentimaticTM ShutterThe Ventimatic shutter is a continuously variable,gravity-actuated room exhaust vent that operates indirect response to positive static air pressure (Fig-ure 15-1 and 15-2). Unlike other non-poweredvents, it opens at extremely low positive pressure(0.005"). Outdoor air introduced by the unit ven-tilator must leave the room in some way. In somestates, exhaust vents are required by law or codeto accomplish this. The Ventimatic shutter is amore economical solution to the problem.

The operation of the Ventimatic shutter isinherently silent. The shutter flaps are made oftemperature-resistant glass fabric impregnated with

silicone rubber for flexibility and long life. Thisfabric retains its original properties down to -50°F.The Ventimatic shutter’s ability to exhaust onlythe amount of air required results in considerableenergy savings. In the heating mode, the unit ven-tilator brings in the minimum percent of outside

air required. The Ventimatic shutter, in turn, ex-hausts the minimum amount. In cooling mode,the unit ventilator brings in outdoor air for fullnatural cooling when conditions allow; theVentimatic shutter responds by exhausting anequal amount.

Storage cabinets are designed to complement theAAF®-HermanNelson® classroom Unit Ventilatorand provide adequate storage. Heavy gauge steelfinished with environmentally friendly thermo-setting urethane powder electrostatically appliedand oven-cured in a pleasing array of matchingarchitectural colors.• The one-piece stainless steel top has stainless

steel bowl(s), a raised front lip, and formed backand end splashboards.

• Comes with chrome fittings, a choice of singleor double bowl and optional door locks to con-ceal storage and piping.

• Adjustable kickplates with leg levelers are stan-dard on all units and functional accessories. Eu-ropean cabinet design has adjustable leg level-lers on each corner that adjust to compensatefor variations in the floor.

• When the sink and bubbler model with adapterback is furnished, the adapter back has a char-coal textured finish.


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Air Vent And Drain FeaturesA manual air vent and drain is provided on allhydronic coils. The vent allows air to be purgedfrom the coil during field start-up or duringmaintenance. The manual air vent is located onthe top of the coil header of all floor (AV) hy-dronic coils. (Figure 16-2) Ceiling (AH) unithydronic coils come with auto air vents.

The manual drain plug (Figure 16-2) is located atthe bottom of the coil header of hydronic coils.Others may not provide drainage of coils.

With AAF-HermanNelson unit ventilators, theextensive choice of coil combinations means thatroom conditions can be met using almost anycooling or heating source.

Des

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AAF®-HermanNelson® offers a complete andflexible coil selection. All coils are located safelybeneath the fans and designed for draw-thru airflow to provide maximum efficiency of heat trans-fer. All water, steam and direct expansion coilsare constructed of aluminum fins with a formedintegral spacing collar, mechanically bonded tothe seamless copper tubes by expansion of thetubes after assembly. Fins are rippled or embossedfor strength and increased heat transfer surface.Coils and unit are ARI capacity rated.

Quality Coil DesignThe coil design (Figure 16-1) relies on advancedheat transfer to provide extra cooling capacity fortoday’s increased ventilation requirements. Tunedinternal water flow and balanced header designwith additional surface area in the air streamincreases heat transfer to satisfy the increasedneed for dehumidification.

Figure 16-1. Typical Coil

Figure 16-2. Manual Air Vent AndDrain Plug

Figure 16-4. Hot/Chilled Water Coil2-Pipe System

Figure 16-5. Chilled Water Coil4-Pipe System


Maximize Heat TransferHeat transfer is maximized (promoting comfortand reducing operating costs) by ensuring that allcoils have their own individual unshared fin sur-faces. Some manufacturers use a continuous finsurface sacrificing proper heat transfer. An airbreak between coils in all AAF-HermanNelsonunits is used to enhance decoupling of heat trans-fer surfaces, providing full capacity output, com-fort and reduced operating costs.

Electric CoilsWith a draw-thru design electric coils are directlyexposed to the air stream and come with a built-in dead front switch to de-energize the coil whenthe center front panel is removed. A unit mounteddisconnect switch is included. A continuous elec-tric sensory element for high temperature is notrequired because the air is drawn smoothly andevenly across the coils, prolonging life. A blow-thru design uses cal rods inserted into the tube ofa fin tube coil that results in reduced heat transfer.The constant movement of the electric heatingcal rod within the tube shortens life.

Steam Distributing CoilsSteam distribution coils allows even distributionof steam and even discharge air temperature.

Vacuum BreakerThe vacuum breaker relieves the vacuum in thesteam coil to allow drainage of condensate fromthe coil. This eliminates water hammer and greatlyreduces the possibility of coil freeze-up.

Drain

Air Vent

Standard CapacityHigh Capacity

2 Row 3 Row 4 Row 5 RowU D E F1 2 3 4

Standard CapacityHigh Capacity

2 Row 3 Row 4 Row 5 RowV S W Y5 6 7 8


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Figure 17-3. DX CoilClose-up of factory installed TEV (Thermal Expansion Valve)

suction line and equalizing tube

Figure 17-5. Electric Resistance Heating Coil

Figure 17-1. Hot Water Coil


1 Row 2 Row 3 Row65 66 671 2 3

ThermalExpansion

Valve

BulbEqualizingTube

3 RowG

Figure 17-2. Steam Coil With Opposite End ConnectionsWith factory supplied pressure equalizing and check valve assembly

Opposite End Connections

1 Row 2 Row68 69

1 Row 2 Row78 79

Low Heat High Heat12 13

Dead Front Switch

Connector

Staging

Figure 17-4. Electric Heat Control Panel

Steam Coil

Electric HeatDisconnect


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Why ClassroomsOverheatOverheated classrooms occur every day in schoolsin every area of the country. When you considerthe consequences of an overheated classroom, theproblem is obvious to all who have been evenremotely associated with schools. The most seri-ous result of an overheated classroom is its detri-mental effect on students’ ability to concentrateand learn. Research has determined that the abil-ity to learn and retain knowledge decreases rap-idly as the temperature exceeds recommendedclassroom temperatures. Overheated rooms alsorepresent wasted fuel, resulting in excessive oper-ating costs. This is a needless waste of school op-erating funds.

Correcting an overheating problem in an existingbuilding is very difficult and expensive. It calls forredesign and alteration of the heating and venti-lating system, necessitating considerable renova-tion. This potential problem should be recognized,understood and planned for when heating andventilating systems are designed for new and ex-isting buildings.

Take Control OfEnergy ExpendituresSchools consume more than 10% of the totalenergy expended in the United States for comfortheating and cooling of buildings. As energy costsincrease, educators are placed in a difficult positioncaught between rising costs and irate taxpayers andthe requirements to raise educational standards.

Fortunately, the technology and the system (i.e.the unit ventilator) exists to enable schools to takecontrol of their energy expenditures while pro-viding a comfortable environment for learning.

Energy use in schools is actually determined moreby hours of operation and system selectivity thanby building design. Most of the school heatingcosts are accounted for by unoccupied spaces.Because lights, computers and students give offconsiderable heat, occupied spaces require littlesupplemental heat. In fact, the removal of heat isusually required in occupied classrooms whenoutside temperatures are moderately cold (i.e.:35-40°F). However, all cooling energy is typicallyrequired during occupied periods. The AAF®-HermanNelson® Unit Ventilator is designed to de-liver natural air or free cooling (economizer op-eration) directly into the classroom, reducingenergy usage and lowering operating costs.

Central systems (i.e. all air types using rooftopsor air handlers) waste energy by bringing in out-side air, heating and cooling the air and deliver-ing it to unoccupied spaces. Contrast this wasteto the unit ventilator located in each classroom.The unit ventilator can be turned on whenneeded, cycled off during unoccupied periods,bring free natural air cooling directly into thespace, and provide individual classroom controland comfort. In addition, each unit ventilator hasits own air-moving device (fan and motor), whichuses about as much energy as two 100-watt lightbulbs. Contrast this with the energy consumedby the large horsepower motors (20hp-plus) ofcentral air systems, which pump supply air andreturn air to a central source from unoccupied oroccupied classrooms, and then exhaust the air.

Ideally a school should be able to turn on heating,cooling, and ventilating equipment only when itis needed and use free economizer cooling to keepeach classroom at a comfortable temperature.Unit ventilator systems provide this kind of energy-efficient, cost-effective incremental operation.

Schools Have Special NeedsSchools have unique heating and ventilating needs,in large part because of their variable occupancyand usage patterns. Fewer cubic feet of space isprovided per student in a school building thanany other type of commercial or public building.School classrooms are typically occupied six hoursa day, five days a week for only three-fourths ofthe year, with time out for vacations. All in all,this represents approximately 15% of the hoursin a year that a classroom is occupied.

To understand the overheating problem in schools,one must first realize that the excess heat that causesthe classroom to become too warm comes fromwhat is commonly termed “uncontrolled heatsources.” To gain some perspective on how thisaffects heating and cooling decisions, let’s take a lookat a typical classroom in the northern section of themidwestern United States. Let’s suppose we havea classroom that is 24 by 38 feet long with 10-foot ceilings and 100 square feet of window areaalong the outside wall. At an outside temperatureof 0°F and a desired room temperature of 72°F,let’s assume the normal amount of heat loss fromthe room to the outside is 55,000 BTUs per hour.

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Figure 18-1. Heat Gain vs. Heat Loss

-10

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TU

/HR

.

7,800 BTU/HR.Heat Gain FromStudents

Outside Air Temperature, °F.

}

Temperature On RoomHeat Loss Line AboveWhich Cooling Is AlwaysRequired

}}

10,000 BTU/HR.Possible Heat Gain FromSun – Direct And Reflected8,500 BTU/HR.Heat Gain From Lights10,000

20,000

30,000

40,000

50,000

60,000“A”

“B”

“C”

“D”

ROOM HEAT LOSS LINES

0 10 20 30 40 50 60 70

Note: Figure 18-1 shows the Room Heat Loss and Uncontrolled Heat Gains plotted to showreason for overheating of school classrooms. During occupied day, classroom is more likely torequire cooling than heating in very cold weather.

Application ConsiderationsOverview


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Application Considerations Overview (Continued)

As the outside temperature changes, so does theamount of heat that the room loses. This is repre-sented in Figure 18-1 by the line marked, RoomHeat Loss Line “A”, which ranges from 55,000BTUs per hour at 0°F outside air temperature to0 BTUs at 70°F. Obviously, if the heating systemwere the only source of heat in the classroom, theproblem would be simple. The room thermostatwould cause the heating system to supply exactlythe amount of heat required to maintain the roomat the room thermostat temperature setting. Inreality, however, the introduction of excess heatfrom a variety of uncontrolled source makes theproblem considerably more complex.

Heat From StudentsBody heat generated by students in a classroom isone of the three primary sources of uncontrolledheat. In a typical classroom of 30 students, theamount of heat given off at all times will vary ac-cording to factors such as age, activity, gender, etc.A conservative estimate is 260 BTUs per hour perpupil. Multiply this by 30 and you get a total of7,800 BTUs per hour added to the room by thestudents alone. This excess heat is noted in Fig-ure 18-1 as “Heat Gain from Students.”

Heat Gain From LightsHeat emitted by the lighting system constitutesa second uncontrolled heat source. Artificial light-ing is needed in most classrooms even during day-light hours to prevent unbalanced lighting andeye strain. A typical classroom requires approxi-mately 2,500 watts of supplemental lighting toprovide properly balanced lighting. Fluorescentlights add heat to the room at the rate of 3.4 BTUper watt per hour or a total of 8,500 BTU perhour. This extra heat is represented in Figure 18-1 as “Heat Gain from Lights.” Add the heat gainfrom lighting to the 7,800 BTUs introduced bystudent body heat and we now have an extra16,300 BTU/HR being introduced into the class-room by uncontrolled sources. This heat gain re-mains constant regardless of the outdoor air tem-perature.

Solar Heat GainThe sun is a third source of heat—and, becauseit is neither positive nor constant, calculating itscontribution to the overall heat gain is difficult.Solar heat gain can be the worst offender of thethree in classrooms with large windows. Indirector reflected solar radiation is substantial even oncloudy days, even in rooms with north exposure,as a result of what is termed “skyshine.” To get

an idea of the potential effect of the sun, let’s as-sume that the solar heat gain in our hypotheticalclassroom will peak at 240 BTU/HR per squarefoot of glass area. If we then assume a glass areaof 100 square feet and at least 100 BTU/HR persquare foot of glass for solar heat gain, we cancalculate a very conservative estimate of 10,000BTU/HR heat gain through windows. If we addthis to the heat from the lights and body heat,total heat gain adds up to 26,300 BTU/HR fromsources other than the heating and ventilating sys-tem. This is indicated in Figure 18-1 by the tophorizontal line, which intersects Room Heat LossLine “A” at approximately 37°F. This is a reason-able estimate of the maximum uncontrolled heatgain that can be received in the typical classroomfrom these common heat sources.

The AnalysisFrom Figure 18-1 it is evident that at an outsidetemperature of 48°F or higher, the heat given offby 30 students and classroom lighting is suffi-cient to cause overheating, requiring the heatingand ventilating system to provide some form ofcooling at all times. This is true even if the class-room was occupied at night when solar heat gainis not a factor. But, since classrooms are occu-pied during the day, solar addition provides heatin varying amounts even in classrooms with northexposures. Consequently, the heating and venti-lating system in our typical classroom must pro-vide cooling at all times when the outdoor tem-perature is above 48°F, and at any time duringcolder weather when the solar heat gain exceedsroom heat loss.

If we assume an average winter temperature ofapproximately 33°F in the region where our typi-cal classroom is located we know that half of thetime, both night and day, the outside tempera-ture will be above 33°F. However, since it is gen-erally warmer during the day, when school is insession, the heating and ventilating system willbe required to provide cooling for this classroomduring much of the time that the room is occu-pied.

In this example, we’ve assumed that our class-room had a room heat loss of 55,000 BTU/HRat a design outdoor air temperature of 0°F (RoomHeat Loss Line “A”). Bear in mind, however, thatthe recent trend in “energy-saving” building designoften results in rooms with lower room heat loss,as indicated by Room Heat Loss Lines “B”, “C”and “D.” At 0°F design outdoor air temperature,

Room “B” has a room heat loss of 45,000 BTU/HR, Room “C” has a room heat loss of 35,000BTU/HR, and Room “D” has a room heat lossof 25,000 BTU/HR. Note the lowering of the tem-perature above which cooling will always be requiredas the room heat loss decreases.

We’ve noted that cooling is always required inClassroom “A” when outdoor air temperatures ex-ceed 48°F. In Classroom “B” we see that coolingis always required when outdoor temperaturesexceed 44°F. In Classroom “C” cooling is alwaysrequired when outdoor temperatures exceed 36°F.In Classroom “D” cooling is always required atan outside temperature of 23°F or higher. Low-ering room heat loss means that classroom “D”requires cooling most of the time that the room isoccupied.

Now that we understand the reason for class-rooms overheating, the solution is simple. Theheating and ventilating system must provide coolingto take care of the heat given off in the classroomby uncontrolled heat sources.

Cooling of the ClassroomThe AAF®-HermanNelson® Unit Ventilator hasbecome a standard for heating and ventilatingsystems in schools because it provides thesolution to this very problem. The unit ventilatorcools as well as heats. During the heating seasonthe outdoor air temperature is nearly alwaysbelow the desired room temperature. It stands toreason then that the outside air should be usedto provide the cooling necessary to keepclassrooms down to thermostat temperature.The classroom unit ventilator does just that.By incorporating an automatically controlledoutdoor air damper, a variable quantity ofoutdoor air is introduced in the classroom,metered exactly to prevent overheating. This au-tomatically controlled damper is capable of bring-ing in outside air as needed to prevent classroomoverheating. Since our problem is more one of cool-ing than of heating, it is evident that more thanjust the room heat loss must be determined todesign a good heating and ventilating system. Thecooling requirements should be assessed as well,and the free-cooling capacity of the equipmentspecified along with the heating capacity required.If this is done, the optimum learning tempera-ture can be maintained in each classroom.

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DraftStop™ System/Window Down DraftProtectionOver the years the unit ventilator system hasproven to be the most effective system inmaintaining excellent comfort conditions inclassrooms. This is still true today.

Cold window down drafts are a common prob-lem in classrooms with relatively large windows,particularly during prolonged periods of coldoutside temperatures. The AAF®-HermanNel-son® DraftStop System is designed to address thisproblem. Because down-draft conditions causediscomfort to the room’s occupants, some formof down-draft protection should be provided.

Window down-draft protection is recommendedfor classrooms where the following conditionsexist:

1. Window area exceeds 40% of the total outsidewall area.

2. Single-pane glass is used.3. Outside temperatures are below 35°F for a

significant portion of the occupied period.

The need for window down-draft protection willnot always be so clear cut. Where uncertaintyexists, a further check can be made by calculatingthe window heat loss at an outdoor temperature

of 35°F. If estimated window heat loss exceeds250 BTUH/FT, window down-draft protectionis recommended. If estimated window heat loss isless than 250 BTUH/FT, the need for down-draft protection is marginal but should not bearbitrarily dismissed.

The “DraftStop” system can be employed even inthose marginal applications to assure theoccupants’ comfort without the material installa-tion and operating cost penalty associated with“auxiliary radiation.”

How DraftStop WorksMorning Warm-up (Figure 20-2)During this period, no outdoor air is admitted.The cold air from the windows flows into theDraftStop slot and is drawn toward the unitventilator. This air enters the unit through theroom air damper, passes through the heatingelement and is discharged into the room.

Falling Cold Air

from Window

Figure 20-1. DraftStop System

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Down-drafts

OptionalVentimaticExhaust

Unit Ventilator

Outdoor Air

Figure 20-3.Normal Operation,

Minimum % Outdoor Air

Normal Operation (Figure 20-3)During much of the day, the unit ventilatorcirculates a mixture of outdoor air and room air,proportioned to maintain thermal comfort in theclassroom. The return air continues to be drawnoff the windows, providing the DraftStop action.We now see the impact of the optionalVentimaticTM gravity exhaust. The Ventimaticshutter concealed behind the cabinets allows airto be expelled to the outdoors. This preventsexcessive room pressurization, which would in-terfere with the ventilation cooling capability ofthe unit. This exhaust action also enhances theDraftStop effect since the air to be exhausted isforced into the DraftStop slot at sill level.

Maximum Ventilation Cooling (Figure 20-4)During these periods, the unit ventilator willoperate with the outdoor air damper fully open.In this mode, there will be little or no return airto the unit and little or no DraftStop action. Theunit ventilator will not operate at maximumventilation cooling when the outdoor tempera-ture is low enough to create cold windowdowndraft conditions. Therefore, the lack ofDraftStop action is of no consequence. Theoptional Ventimatic exhaust continues to pro-vide an effective means of relieving the room ofexcess pressure.

Unit Discharge

Down-drafts

Unit Discharge


Unit Ventilator

Figure 20-4.Maximum Ventilation Cooling

Down-drafts


Unit Ventilator

Outdoor Air

Figure 20-2. Morning Warm-up

Unit Discharge

Application ConsiderationsSystems


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Consult Table 21-1 for recommended minimumand maximum DraftStop grille lengths. Note thatthe maximum lengths are based on maintainingoptimum velocity through the DraftStop grille. Ifthe maximum lengths are exceeded the system willremain operational; however, the efficiency will becorrespondingly reduced.

DraftStop EnclosuresDraftStop wall enclosure or DraftStop cabinets arefitted to the ends of the unit ventilator so that thereis a continuous elongated return air grille locatedbeneath the windows.

These cabinets have a built-in 3" or 513⁄16" cavitybetween the rear of the cabinet and the wall, whichforms the return air path to the unit ventilator.Cool air from the windows is drawn into the ple-num before it is allowed to reach the occupants.Either a steel bar-type inlet grille or a stamped in-let grille is fitted to the rear of the cabinet, flushwith the cabinet top. In applications where cabi-nets are intended to be included as part of class-room equipment, the DraftStop feature can beadded to the cabinets and unit ventilator at noincrease in material cost over a standard cabinetinstallation without draft protection. The instal-lation labor cost would be the same in either case.Both shelf-type cabinets (165⁄8" or 217⁄8" deep) andsink bubbler cabinets (217⁄8" deep) are available inthe DraftStop configuration. Filler sections areavailable to complete the installation; however, theydo not have inlet grilles and their use under win-dows should be held to a minimum.

A manually adjustable damper is located beneatheach section of DraftStop grille. This damper isprovided so that a uniform air velocity can beachieved throughout the entire length of theDraftStop grille. This simple adjustment is madeonce by the installer during the final stage of in-stallation. Figure 21-2. Typical Finned Radiation Piping

Application Considerations Systems (Continued)

Wall enclosures are used to form the return air pathto the unit ventilator when DraftStop cabinets arenot used. The enclosures are available with stampedinlet grille or with an aluminum bar-type inletgrille.

Enclosures can be 14", 20" or 24" high and areavailable in 1´ through 8´ lengths in 6" increments.Accessories such as wall trims and end caps areavailable to complete the installation. Normalmeasures should be followed concerning instal-lation when using DraftStop enclosures orDraftStop cabinets. If the grille length limitationsare adhered to and the DraftStop grille dampersare adjusted to achieve a uniform velocity in the150 FPM to 500 FPM range, the system will befunctional. Radiation elements can be installedbehind storage cabinets or in separate wall hungenclosures.

Finned Radiation SystemFinned radiation down-draft control is availablefor those who prefer it. Made of furniture-qualitysteel and designed to complement the unit venti-lator styling, it is particularly appropriate for abuilding with very large expanses of window wherethe DraftStop system is not used, and for use inother parts of the building (Figure 21-1).

Table 21-1. DraftStopTM Grille Length

20” High DraftStopWall Enclosure

24” High DraftStopWall Enclosure orStorage CabinetsUnit

Nom.CFM

MinimumLength (Ft.)Each Side

MaximumLength (Ft.)Each Side

MinimumLength (Ft.)Each Side

MaximumLength (Ft.)Each Side

750

1000

1250

1500

3

4

5

6

13

18

22

25

3

4

5

6

22

30

36

42

Figure 21-1. Typical Finned RadiationEnclosure (left) And Typical DraftStop

Enclosure (right)

There will be many periods during the heatingseason when window down-draft protection is re-quired even though the unit ventilator is no longeradding heat to the space. In fact, the unit ventila-tor will most likely be attempting to cool the spacewith outside air due to the heating effect of theoccupants, solar load and lights. This presents anobvious control dilemma when using radiation aswindow down-draft protection. Auxiliary radia-tion is normally controlled so that the radiation isturned off whenever the unit ventilator heatingelement is off (Figure 21-2). This control se-quence is required to prevent the costly additionof heat that is not required by the space. It is usedto prevent serious overheating problems that canoccur if the radiation capacity exceeds the ventila-tion cooling capability of the unit. However, thisis a compromise solution since cold window draftscan definitely exist even when no further heat isrequired in the room. In fact, a well-heated roomcan accentuate the draft problem due to the largerdifference between room air and window drafttemperatures. In order to conform to the abovesequence, steam or hot-water radiation will requirean additional field-installed control valve. (seeMicroTech Controls page 26 for auxiliary heatcontrol function and setup).


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Part Load Variable AirControl: SatisfiesRequirements, ReducesOperating CostsSatisfying School RequirementsThe AAF®-HermanNelson® Unit Ventilator offersa unique opportunity to combine the best featuresof a unit ventilator system for schools.

Schools require:• Easy to maintain systems• Simple operation• Even comfort• Fresh outside air brought directly into the

space for a good learning environment• Low operating cost• Low capital cost

All these requirements are satisfied by AAF-HermanNelson 2-pipe Face and Bypass Unit Ven-tilators with part load variable air control.

Using AAF-HermanNelson Unit Ventilators witha 2-pipe Face and Bypass System, central equip-ment can be sized smaller using building diver-sity. This results in a low capital-cost system. Fur-ther savings can be realized in renovations or newconstruction by piping. Piping installations useless space than duct systems. This is important inexisting buildings and also in new constructionwhen floor to floor heights can be reduced, savingon overall building costs.

Better Learning EnvironmentWe invented unit ventilators in 1917 specificallyto satisfy the school requirements for a durableunit that delivers fresh air right to the classroom.AAF-HermanNelson Unit Ventilators are locatedin each classroom so the outdoor air is drawn inthrough the building wall directly into the space,unlike central systems that deliver outdoor air in-directly. This promotes student attentiveness anda better learning environment.

Humidity ControlA draw-thru unit ventilator using face and bypasswith a 2-pipe system provides superior humiditycontrol and overall comfort. The coil is selectedfor cooling. With face and bypass, during mechani-cal cooling the coil is always dehumidifying dueto water being pumped continuously to keep thecoil surface below the dew point. With face and

bypass control, humidity in the space can be main-tained in the 30% to 60% relative humidity com-fort zone. The result is improved humidity con-trol, a key concern in schools today. Valve controlsystems are unable to do this consistently.

EconomyIn the 2-pipe system with the coil selected for cool-ing during the heating season extra coil heat trans-fer is available. Since the water is always beingpumped with face and bypass, boiler water tem-perature can be modulated rather than fixed, re-ducing the hot water temperature to better matchthe heating load. This is an opportunity to reduceoperating costs. By resetting the boiler hot waterto 90°F and modulating upward to 140-160°F fordesign conditions, boiler economy results in sav-ings. Better room temperature control is availableat low heating loads and the system can be quicklyand easily changed over from heating to coolingor vice versa.

Since conditions of full heating or full cooling areonly achieved 1-2% of the time, savings are innu-merable with today’s “fuzzy logic” chillers that areair cooled, load rates at changeover of 100°F plusare limited and the chiller protected. And,McQuay chillers have this state-of-the-art system.Couple the cooling with today’s high-efficiencycondensing boilers (which can accept 45°F enteringwater without damage), the elimination of boilercirculating pumps, mixing valves and isolationvalves considerable savings can be realized.

Part Load Variable Air ControlIt all starts with the unique Part Load Variable AirControl system that is available on AAF-HermanNelson 2-pipe Face and Bypass Unit Ven-tilators with MicroTech® DDC (4-pipe also avail-able). The Part Load Variable Air feature uses PIloop algorithms to calculate room load, face andbypass control for dehumidification, and it auto-matically adjusts indoor fan speed based uponroom load and the room temperature algorithm.By basing indoor fan speed upon room load, itprovides higher latent cooling capabilities andquieter operation during non-peak load periods.The room temperature algorithm determines thespeed of the fan. Fan speed varies according to theface damper position. The “change” algorithmchanges the Direct Digital Control (DDC)damper actuator setpoint, responding to roomload. The “step & wait” algorithm causes the ac-tuator to open or close. The “step” is the calcu-

lated movement/time the actuator is driven eitheropen or closed. The “wait” is the amount of timethe actuator holds its position. The system con-stantly samples to prevent overshooting for bettercomfort control.

With Part Load Variable Air, air delivery is basedon the face damper position or the degree to whichroom load is being satisfied. When the face damperposition is 0-15%, the unit ventilator runs on lowspeed. When the face damper is 15-30%, air isdelivered at medium speed. For face damper posi-tions greater than 30%, the fan runs on high speedto satisfy the room load. During the Part LoadVariable Air operation, fresh air is maintained atthe set minimum. The Part Load Variable Air con-trol adjusts the outdoor air damper to bring inthe same or a constant amount of fresh air to pro-mote student comfort and attentiveness.

Easy MaintenanceThe AAF-HermanNelson Part Load Variable AirUnit Ventilator 2-pipe face and bypass controlheating/cooling system is easy to maintain. It hasfewer moving parts: one pump, one motorizedvalve, two or three small modular condensing boil-ers, one or two air-cooled chillers, and, in eachclassroom, one outdoor air damper actuator, oneface and bypass damper, and one fan. Simple pe-riodic filter changing promotes filtered air in eachclassroom. The system can deliver the lowest util-ity cost—and with AAF-HermanNelson UnitVentilator’s long, durable life, replacement/main-tenance costs can be deferred. These low costs aredesirable to taxpayers and school officials so lim-ited resources can be used to support teaching.

This unique Part Load Variable Air concept is theproduct and system schools need and expect fortoday’s and future schools. It satisfies school re-quirements for a quality environment while ad-dressing the need to contain costs.

Demand-ControlledVentilation (DCV) ForProper Air ControlUsing AAF-HermanNelson Unit Ventilators withbuilt-in Demand Controlled Ventilation (DCV)enables the ventilation system in your classroomsprovides the right amount of outdoor air. Thissaves money and energy by preventing costlyover-ventilation.



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Figure 23-1. Daily CO2 And Occupancy Level With DCV


How It WorksThe AAF®-HermanNelson® Unit Ventilator usesinput from a CO

2 controller to ventilate the space

based on actual occupancy instead of a fixed de-sign occupancy. The CO

2 Demand Controlled

Ventilation system monitors the amount of CO2

produced by students and teachers so enough freshoutdoor air is introduced to maintain good airquality. The system is designed to achieve that atarget ventilation rate (e.g., 15 cfm/person) ismaintained based on actual occupancy.

By using DCV to monitor the actual occupancypattern in a room, the system can allow code-spe-cific levels of outdoor air are delivered when needed.Unnecessary over-ventilation is avoided during pe-riods of low or intermittent occupancy. This savesmoney by minimizing the conditioning of outdoorair. Instead of providing a fixed ventilation rate basedon an assumed occupancy, this system automati-cally delivers the proper amount of outdoor air atthe proper time. This means that you can be confi-dent that your school is meeting ventilation stan-dards for Indoor Air Quality and that your studentsare receiving adequate air to be attentive to instruc-tion. At the same time, you are saving money inearly morning hours, in between classes, or after hourswhen classrooms are heated and cooled but not al-ways fully occupied.

As Simple as a ThermostatDemand Controlled Ventilation is easy to apply.Simply mount the DCV CO

2 sensor near the re-

mote MicroTech® room sensor or use the unit-mounted DCV CO

2 sensor and unit-mounted

room temperature sensor. The system does the rest.If desired, the ventilation control setpoint can beadjusted through the MicroTech Controller.

Acceptance By Codes And StandardsASHRAE Standard 62-1999 Ventilation for In-door Air Quality recognizes CO

2 based DCV as a

means of controlling ventilation based on occu-pancy. The ASHRAE standard has been referencedor adopted by most regional and local buildingcodes. This standard references ventilation on aper person basis. Using CO

2 control will some-

times lower the absolute amount of outside airdelivered into a room but will maintain the perperson rate. For example, if a classroom is designedfor 30 students, the ventilation rate is 450 cfm(30 students X 15 cfm/student). However, whenthere are only ten students in the classroom, theCO

2 control will adjust ventilation to 150 cfm

(10 students X 15 cfm/student). A minimum base

ventilation rate (typically 20% of design levels) isprovided when in the occupied mode. This pro-vides outdoor air to offset any interior source con-tamination while allowing for proper space pres-surization.

Active DehumidificationUnits (Reheat)In high-humidity applications in which valve con-trol reheat units are used, the Active Dehumidifi-cation Control (ADC) sequence should be con-sidered. During excessive humidity conditions, theHumidity Sensor controls the unit to continuecooling. Wet heat or electric heat then reheats dis-charge air, removing excessive moisture. Duringacceptable room humidity levels, the unit reheatfunction is disabled. The humidity sensor is ei-ther wall mounted or remote wall mounted.

Dehumidification unit ventilators with ADC uti-lize the proper control management of a coolingcoil with a post-conditioning reheat coil coupledwith a humidity sensor. PI loop algorithms are de-signed to govern both classroom temperature andrelative humidity. MicroTech algorithms minimizethe amount of reheat needed to maintain relativehumidity below a preset limit. Reheat is used onlywhen required and in the most energy-efficientmanner for this system type.

The MicroTech ADC sequence uses a humiditysensor, unlike others which use a humidistat. Ahumidistat is an open-close signal based on the level ofrelative humidity detected, which indicates whetherthe humidity is above or below a certain level.

The MicroTech ADC humidity sensor issues a sig-nal proportional to the classroom’s humidity level.This enables a control sequence that manages boththe temperature and the relative humidity. Whenthe relative humidity exceeds a preset value, themodulating chilled-water valve opens fully to de-humidify the mixture of outdoor and return airentering the cooling coil. The reheat modulatingwater valve then opens to reheat the air leavingthe cooling coil, as required to maintain the class-room setpoint. Active dehumidification startswhen the indoor relative humidity exceeds thepreset relative humidity upper setpoint and con-tinues until the room humidity falls 5% belowthe endpoint. During active dehumidification, theeconomizer operation is disabled (and the outdoorair damper reset to its minimum position) unlessthe outdoor air temperature is below 55°F andmaintained until dehumidification is completed.

When the indoor humidity level is satisfied, theMicroTech control reverts to its normal sequencesto satisfy the classroom temperature setpoint.

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CO2 Concentrations And Occupancy Using CO2 Proportional Control Strategy

Application = ClassroomDesign Density = 30 people/1000 sq.ft.Proportional Control Starts @ 200 ppm > OAOutside Air Ventilation Rate = 15 cfm/personCO2 Upper setpoint = 965 ppm

Daily CO2 and Occupancy Level with Demand Controlled Ventilation

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AAF®-HermanNelson®

UVs: Ideal ForToday’s SchoolsIAQ DefinedThe issue of indoor air quality (IAQ), which hascaused great concern for the health hazards posedin the home and at work, is no less a threat tostudents and faculty.

For the past several years, efforts to reduce en-ergy costs in new school buildings have seen theuse of tighter construction, sealed windows andheavier insulation. While these construction tech-niques have helped reduce energy costs, tightlysealed buildings, or “envelopes,” when combinedwith increased use of recirculated air, have led toa condition known as sick building syndrome.

In a poorly ventilated school building, fumes andvapors from plastics and other synthetics are oftennot properly exhausted, while mold, fungus, and bac-teria are able to flourish. These conditions can causevarious ailments, including nausea, smarting eyes,and coughing, as well as increased student absen-teeism and diminished productivity.

In fact, the American Society of Heating,Refrigeration and Air Conditioning Engineers(ASHRAE) now recommends 15 cfm of outdoorair per pupil, and no longer endorses the prac-tice of little or no usage of outdoor air.

AAF-HermanNelson Unit VentilatorsSolve The IAQ ProblemAAF-HermanNelson unit ventilators have beenfound to do a more thorough job of maintaininga healthful and productive classroom environmentthan other systems through the introduction ofplenty of filtered fresh air directly into the class-room. This unique feature, which has always beena significant factor in reducing energy costs, isnow more important than ever in the promotionof a healthful environment for learning.

It should be kept in mind that a properly designedexhaust system is essential for avoiding indoor airquality problems. Simply put, if room air is notbeing exhausted in a prescribed fashion, freshoutside air cannot be introduced into the room.Likewise, an excessive amount of outside air willbe admitted, wasting energy.

The AAF-HermanNelson VentimaticTM shutter(see page 15), a gravity-actuated room exhaust

vent, solves both these problems. The Ventimaticshutter allows that the correct amount of out-door air is brought into the room while main-taining a slight positive pressure in the room. Thisslight positive pressure, maintained during nor-mal operation, can also help prevent the infiltra-tion of undesirable gases into the classroom.

Temperature ControlAnd ASHRAEControl CycleControl ImpactHow well a unit ventilator performs its intendedfunction is governed largely by the performanceof the automatic temperature controls. In orderto achieve optimum unit ventilator operation, itis imperative that temperature controls be prop-erly applied, installed, calibrated and maintained.

ASHRAE Control Cycles-HeatingUnit ventilators are normally controlled accord-ing to ASHRAE Control Cycle II. ASHRAEcontrol cycles apply only to heating, heating andventilating and free cooling operation.Cooling control is discussed in later paragraphs.

ASHRAE Cycle IIDuring warm-up, the outdoor air damper isclosed. As the room temperature approaches thethermostat setting, the outdoor air damper opensto a predetermined minimum percentage ofoutside air. The heating coil capacity controllerthen modulates to maintain the thermostatsetting. If the room temperature rises above thethermostat setting, the heating coil is turnedoff and the outdoor air damper opens beyondthe minimum position to maintain the thermo-stat setting.

amount of outdoor air is heated and free outdoorair—natural cooling—is available to offset thelarge internal heat gain associated with the denseoccupancy of classrooms.

EXAMPLE: For a 60°F entering air mixturetemperature and 70°F room temperature, with30°F outdoor air temperature, 25% outdoor airwill produce the 60°F mixture air temperature.When the outdoor air temperature drops to 10°F,12.5% outdoor air will produce the 60°Fmixture air temperature.

Night SetbackSubstantial fuel savings can be realized by oper-ating the unit ventilator system at a reduced roomsetting at night and during other unoccupiedperiods, such as weekends and holidays. Unitswith steam or hot-water coils will provide con-vective heat during the setback period. If the spacetemperature falls below the setting of the unoc-cupied thermostat, the unit fans will be broughton to provide additional heat. Units with electricheat coils do not provide convective heat. Theelectric coil and the unit fans will be brought onto maintain the thermostat setting.

Typical TemperatureControl ComponentsIn general, unit ventilators require thefollowing basic DDC electrical components inorder to operate on any of the standard unit ven-tilator ASHRAE cycles of control. The controlcomponents listed in this section are for familiar-ization purposes only and should not be construedas a bill of material.

Outdoor Air Damper Actuator This is amodulating device, under the control of the roomand discharge sensors, which positions the out-door air damper to admit the amount of outdoorair required at any given point in the control cycle.The room air damper is mechanically linked to theoutdoor air damper, which permits the use of asingle actuator. Electric actuators should be ofthe spring-return type so the outdoor air dampercloses whenever the electric power supply to theunit is interrupted.

Discharge Airstream Sensor This deviceoverrides the room sensor and modulates theoutdoor air damper toward the closed positionwhen the unit discharge air falls to a potentiallyuncomfortable temperature.

Application ConsiderationsTemperature Controls

Figure 24-1. ASHRAE Cycle II

ASHRAE Cycle II is a very economicalsequence of control, since only the minimum

+2°FSetPoint

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Application Considerations Temperature Controls (Continued)

Capacity Controller For Heating OrCooling Coils:

a. Face and Bypass Damper ControlThis modulating damper actuator, under controlof the room sensor, positions a face and bypassdamper to control the amount of air that passesthrough or around the unit coil.

b. Valve ControlThis modulating valve, under control of the roomsensor, regulates the flow of steam, hot water orchilled water through the unit coil.

c. Electric HeatStep Controller This modulating step controller, un-der control of the room sensor, steps individual elec-tric heating elements on and off as required. Stagingrelays are sometimes used in lieu of step controller.

Contactors/Relays When unit ventilators contain-ing electric heat are ordered without controls(controls by others) the contactors and relays usedfor staging the electric heat are not provided. Thisis because the number of stages varies based onthe type and manufacturer of the control devices.It is not possible to pre-engineer contactors andrelays for all these variables. The control contactoris responsible for making certain that the con-trols correctly control the unit’s functions.

Room Sensor A temperature-sensing device thatmodulates the intensity of a pneumatic or electricsignal to the controlled components within the unitin order to maintain the comfort setting of the roomsensor. Room sensors can be mounted on the wallor within the unit in a sampling chamber.

Additional components may be required depend-ing on the specific application. They include:

Sampling Chamber This device is requiredwhenever the room sensor is to be mountedwithin the unit ventilator rather than on the wall.The sampling chamber is located behind a seriesof holes in the unit front panel. The sensing ele-ment of the room sensor is positioned within thesampling chamber. The unit fans draw a repre-sentative sample of room air over the sensingelement at a relatively high velocity, which is nec-essary for rapid control response. Sampling cham-bers are furnished with MicroTech® controls.

Low Temperature Protection A low tem-perature limit or freezestat senses the dischargeair temperature off the hydronic coil. If the tem-

perature drops below 38°F, the unit ventilator willshut down, closing the outdoor air damper andopening the heating valve.

DX Cooling Control This sequence switch inthe cooling control circuit energizes the condens-ing unit contactor on a call for mechanical cooling.

DX Cooling Low Ambient Lockout Mustbe used on DX split systems to lockout the con-densing unit when the outdoor air temperatureis below 55°. This device must be integrated intothe control system so that the unit has full ven-tilation cooling capability during the lockout period.

DX Low Temperature Limit Must be usedon DX split system cooling units to de-energizethe condensing unit (compressor) when the re-frigerant falls below freezing.

Direct Digital Control(DDC) BackgroundMicroprocessor-basedDirect Digital Controls (DDC) are microproces-sor-based devices that measure variables (inputs),process those variables with application programsand produce actions (outputs). They can bethought of as instruments that measure a con-trolled variable and respond by producing an out-put signal which is proportional to the differencebetween the set point and the control point.

Inputs and Outputs (I/O)There are two types of Inputs and Outputs (I/O) Di-rect Digital Control (DDC) uses; binary or digital, andanalog. Digital describes a signal with only two states(e.g.,“on” and “off ”) or a device such as a compressor ora fan which is either on or off. Each state is constantover time. Analog describes a signal that has manyvalues (e.g., 60, 61, 62, etc.) or a device such as a tem-perature sensor or a humidity sensor that reports manyvalues. The values generally change over time. Float-ing point devices are digital devices that simulate ana-log devices by using positions that float based upontwo digital signals. One signal is used to push the de-vice open and the other to push the device closed. Whenboth signals are off, the device remains in its last posi-tion. Some floating point devices, such as damperactuators or valve actuators that use two digital signals,are provided with springs that force them to a “home”position when power is lost, e.g., when an outdoorair damper is closed or a hot-water valve opened duringloss of power.

ProtocolsSimilar to languages such as English or French that

people use to communicate information, proto-cols are “languages” controllers use to communi-cate information. They are defined by a set of rulesthat govern data exchange between microproces-sors and facilitate communications between con-trollers using the same protocol.

Proprietary protocols are unique — typically notshared, not exposed, not published and usuallyunable to be utilized by different Building Auto-mation Systems (BAS) without specific informa-tion from the original manufacturer. Communi-cations between different proprietary BAS is usu-ally not possible without cooperative efforts to-ward translation.

Open, proprietary protocols, such as theMicroTech protocol, have proprietary informationpublished, usually under a license agreement, forothers to use. Once the protocol is translated, cer-tain types of information, such as monitoring andcontrol points, are made available for use by par-ticipating third-party BAS. Other types of infor-mation, such as specific sequences of operation toprotect equipment, remain inaccessible. Becausethey can create interfaces that use the proprietaryprotocol, participating BAS providers establishdirect communications with controllers providedby the original manufacturer, which can be a costeffective means of exchanging information.

Open, standard protocols have information pub-lished, usually without license, for others to use.Because this information is shared openly, any-one can use it to create native devices or to trans-late between it and proprietary devices in a sys-tem. Open, standard protocols are usually devel-oped by committee or by independent companies,and are becoming widely used. They are evolvingwithin the HVAC industry to facilitateinteroperability between devices provided by dif-ferent BAS manufacturers.

In the same way a person speaking English to aperson speaking French will require a languagetranslator, mixing protocols, regardless of whetherthey are proprietary, open proprietary or open stan-dard protocols, will require the use of a commu-nications translator, or gateway.

Electrical Communication StandardsMany Direct Digital Control (DDC) devices com-municate using standards from the Electronic In-dustries Association for serial communicationssuch as EIA-485 (RS-485). Generally, this pro-vides communications networks with 4000-5000foot limitations.


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MicroTech® DirectDigital Controls (DDC)Direct Digital Control (DDC) SystemThe MicroTech unit ventilator control on AAF®-HermanNelson® units is a complete Direct Digi-tal Control (DDC) system. It provides comfort-able classroom environments through configura-tion flexibility that allows the unit ventilator tobe set up in any of several operating modes.

Modes Of OperationStand-Alone OperationWhen operating in stand-alone mode, theMicroTech unit ventilator controller performscomplete room temperature and ventilation control.

Occupied/Unoccupied ChangeoverOccupied/unoccupied changeover on stand-aloneunits can be accomplished manually by a unit-mounted day/night switch, automatically by aunit-mounted day/night time clock or automaticallyby a remote-mounted time clock operating unit-mounted day/night relays. If a school has morethan one zone, a separate remote time clock regulateseach zone. In this case, the remote-mounted timeclock energizes or de-energizes an external (24-volt or 120-volt) control circuit which operatesthe unit-mounted day/night relays in that zone. Thecontrol circuit is de-energized during occupiedcycles and energized during unoccupied cycles.

Master/Slave OperationWhen operating in master/slave mode, theMicroTech unit ventilator control provides coor-dinated operation for up to 6 stand-alone units.Master/slave control is used in large spaces, suchas school libraries, or where multiple in-room unitventilators are operating together. The objectiveof master/slave control is to maintain a uniformtemperature throughout the space.

In master/slave mode, each slave unit ventilatorhas its own room air temperature sensor enablingit to maintain a common room heating or cool-ing setpoint dictated by the master unit ventila-tor. Communications between the master and itsslaves is accomplished with RS-485, twisted-pairwiring. Master/slave operation is not intended tobe used in place of network operation.

Master UnitThe master unit initiates communications andprovides control inputs to the slaves that desig-

nate common room heating and cooling setpoints(occupied and unoccupied), minimum outdoorair damper position setpoint and operating mode(occupied, unoccupied, or tenant override).

Slave UnitsSlave units do not initiate communications, butrather respond by acknowledging they have re-ceived control inputs from the master unit. Slavesoperate independently as if in stand-alone mode,however, they ignore their own three on-boardsetpoint potentiometers. In the event communi-cations between the master and a slave fail, theslave unit triggers an alarm, reverts to using itslocal potentiometers for setpoints and remains inits current operating mode until communicationsare restored.

Occupied/Unoccupied ChangeoverA master/slave configuration requires only oneday/night changeover device, as described previ-ously under stand-alone operation, for the masterunit only.

Network OperationWhen operating in network mode, the MicroTechunit ventilator controller provides building opera-tors the capability to perform advanced equipmentmonitoring and control from a central or remotelocation. Network mode provides capabilities suchas heating and cooling setpoint adjustment, mini-mum outdoor air damper position, setpoint ad-justment, ventilation lockout, a network change-filter indication for preventative maintenance,demand limiting, scheduling and occupied/unoc-cupied changeover through communications. Inthe event network communications fail, the unitventilator remains operational using the last oper-ating mode and setpoint information received overthe network. Communications between the unitventilators and other MicroTech system control-lers is accomplished with RS-485 twisted-pairwiring. Communications between the MicroTechcontrollers and a MicroTech or other BuildingAutomation System (BAS) is accomplished withRS-232 or RS-485 wiring.

Operating FunctionsRegardless of the mode of operation selected(stand-alone, master/slave or network); theMicroTech unit ventilator control offers manyadvanced operational functions.

Economizer OperationEconomizer operation is facilitated by the outdoor

air damper, which automatically adjusts aboveminimum outside air position to provide freecooling when the outdoor air temperature isappropriate.

Exhaust Fan OperationAn output signal, Exhaust Fan Control, can beused to operate a remote exhaust fan when theoutdoor air damper opens. It provides a triac sig-nal for use with a field-provided, pilot duty, 24-VAC relay and associated diode. The Exhaust FanControl output signal defaults to an energized re-lay coil, which equals the exhaust fan being on.

Exhaust Fan InterlockThe Exhaust Fan Interlock (reset condition–Out-side Air Ventilation Lockout Control) provides ex-ternal capability to fully open the outdoor airdamper. A personal computer (PC) loaded withMicroTech Monitor™ for Windows® software canbe used to reconfigure the Ventilation Lockout in-put signal using a field-provided, pilot duty24-VAC relay. When the input is energizedthe outdoor air damper will be fully opened. All“safeties” remain in effect to override this func-tion for equipment protection.

Auxiliary Heat OperationA triac output signal, Auxiliary Heat Control (re-set condition–Exhaust Fan Control), can be usedto operate a normally open hot-water valve. A PCloaded with MicroTech Monitor for Windowssoftware can be used to reconfigure the ExhaustFan Output signal. The output signal is activatedwhen the room temperature is less than the heat-ing setpoint minus the auxiliary heat differentialsetpoint (default=2°F). This condition de-ener-gizes a field-provided, pilot duty 24-VAC relay andthe hot water valve is opened. A room tempera-ture 1°F above the heating setpoint energizesthe relay and the hot-water valve is closed. Theauxiliary heat differential setpoint is adjustable.

Ventilation LockoutAn input signal, Outside Air Ventilation Lockout(default), provides external capability to fully closethe outdoor air damper. A field-provided, pilotduty 24- VAC relay with normally open contactsis factory wired to the DI-1 input on the unit con-troller. The relay is field wired to a signal devicecapable of controlling a 24- VAC relay (115-VACaccessory relay coil available). When the relay isenergized, the outdoor air damper is closed. Al-ternatively, in the network mode of operation, theNetwork Ventilation Lockout variable is used.


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Night Setback ControlThe MicroTech® unit ventilator control offers nightsetback options to match the operation of the AAF®-HermanNelson® unit ventilator to building require-ments. Occupied (day) is the normal, or default,mode of operation. During unoccupied mode theoutdoor air damper is closed, night setback and setuproom setpoints are maintained and the fan is en-gaged when either heating or cooling is required.The unit controller uses a single room air tempera-ture sensor for both occupied (day) and unoccu-pied (night) control, which eliminates the require-ment for a separate night-setback thermostat. Steamand hot-water unit ventilators provide convectiveheat during unoccupied operation but remain un-der the control of the room air temperature sensorto help prevent “convective overheating.” Whenconvective heat is insufficient to maintain the un-occupied heating setpoint, the fan is engaged untilthe room air temperature exceeds the unoccupiedheating setpoint. The outdoor air damper remainsclosed during unoccupied operation.

Stand-Alone and Master/Slave OperationUnits operating in stand-alone mode, and the mas-ter in master/slave applications, establish and main-tain unoccupied (night) operation by closing thecontacts of the DI-2 input on the unit controller.Alternatives for closing the contacts include field-provided, pilot duty 24-VAC relays (115-VAC re-lay accessory is available), manual day-nightswitches, time clocks and holiday switches, andpneumatic-electric (PE) switches or relays.

Network OperationUnits operating in network mode establish andmaintain occupied (day) and unoccupied (night)operation according to a time schedule establishedfor each unit. A PC loaded with MicroTech Moni-tor for Windows software or signals from third-partybuilding automation systems (BAS) can be used toconfigure the time schedules.

Control SystemComponentsUnit Ventilator Controller (UVC)The “brain” of the MicroTech DDC system in AAF-HermanNelson Classroom unit ventilators is themicroprocessor-based model 325 unit ventilatorcontroller (UVC). It is located in the left end com-partment of the unit ventilator. The UVC (Figure27-1) utilizes digital control algorithms to main-tain adjustable heating, cooling and ventilationsetpoints. It is factory-mounted, capable of stand-alone, master/slave or network operation, can in-terface with a personal computer (PC) running

Figure 27-1. The MicroTech UnitVentilator Controller (UVC) – Model 325

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LED RELAY OUT AUX OUT STATUS POWER PWRG 0 H 1 2 3 4 5 6 7 8 V 9 10 G 24V

1 2 3 1 2 3 4 5 6 R 5 4 3 2 1 0 G S G S G S G S G S G S G S G S G S1 S0COMMB COMM A DIGITAL INPUT IN 13 IN 12 IN 7 IN 6 IN 5 IN 4 IN 3 IN 2 IN 1. 0

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MicroTech®

325 ControllerThis devise complies with Part 15 of the FCC rules.Operation is subject to the following 2 conditions:(1) This device may not cause harmful interference.(2) This device must accept any interference received, including interference that may cause undesired operation.

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File E159169Model 325

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MicroTech® Monitor™ 2.0 for Windows® soft-ware, or in network mode, with either Monitor orthird-party “front-end” software.

The UVC is pre-programmed with application soft-ware that provides heating and cooling control ofthe unit ventilator by sending outputs to actuatorsand auxiliary equipment in response to various in-puts such as that from a unit or wall mounted roomtemperature sensor. The UVC supports 20 inputs(14 analog, 6 digital) and 10 outputs (8—binary—electromechanical relays, 2—analog— solid-staterelays). Input and output connections are of theInsulated Displacement Connector (IDC) type.Heating and cooling setpoints, offset and the mini-mum outdoor air setpoint are adjustable by meansof on-board potentiometers except in the networkmode of operation where these potentiometers aredisregarded. The UVC provides a visual means offault detection through the use of on-board statusLEDs and has self-diagnostic capability to providereliability.

Heating and Cooling SetpointsThe UVC utilizes separate heating and coolingsetpoints. This energy-saving feature permits “one-time” setting of the desired heating and cooling tem-peratures and eliminates the need to make seasonalthermostat adjustments. The room heating setpointadjusts unoccupied heating setpoint. The unoccu-pied offset is the delta temperature between occu-pied (heating minus occupied setpoint). On unitsoperating in stand-alone or master/slave (masterunit) mode, the heating setpoint is determined bythe room temperature adjustment potentiometer.On units operating in network mode, setpoints areadjusted using PC-based software and the tempera-ture adjustment potentiometer is disregarded. Thecooling setpoint is determined by adding a deadband to the heating setpoint, and is typically offset6°F (default). Typical setpoint values for a heating/cooling unit would be 70°F heating and, conse-quently, 76°F cooling. Thus, a room temperaturebelow 70°F will cause heating to be initiated while

a room temperature above 76°F will initiate me-chanical cooling. When the room temperature isbetween 70°F and 76°F, the “dead band,” heatingor mechanical cooling will not be permitted. Otherthan for the fan, no energy is expended during thismode. The room temperature can be held between70°F and 76°F during a substantial portion of theschool year by simply admitting more or less out-door air to offset the high internal heat gains associ-ated with school classrooms.

Minimum Outdoor Air SetpointOn units operating in stand-alone or master/slave(master unit) mode, the minimum outdoor air po-tentiometer located on the UVC allows for the ad-justment of the minimum outdoor air setpoint from0-100%. On units operating in network mode, thefactory setting is 20% (default), setpoints are ad-justed using PC-based software and the minimumoutdoor air potentiometer is disregarded.

ActuatorsActuators used on AAF-HermanNelson Classroomunit ventilators utilize “floating-point” control withposition feedback for damper and valve modula-tion. The actuators are controlled using “Change”and “Step-and-Wait” control algorithms running inthe UVC. The outdoor air damper is normally closedand the face-and-bypass damper is normally open-to-face. Heating valves are normally open (includes2-Pipe). Cooling valves are normally closed.

Self-CalibrationWhen power is restored or applied, damper andvalve actuators calibrate full-open to full-close.The status (amber) LED blinks 3 seconds on, 3seconds off, until calibration is complete.

Damper ActuatorsDamper actuators are of the compact electric/hy-draulic type (Figure 27-2) and are factory mounted,wired and adjusted. They implement floating-pointcontrol with position feedback. A digital output sig-nal from the UVC controller moves the actuator inone direction, another digital output signal movesthe actuator in the opposite direction. When bothoutputs are de-energized, the damper actuator holds

Figure 27-2. Damper Actuator


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Figure 28-3.Wall Mounted Room Sensor

Figure 28-2. Modulating Valve

ing-only and chilled/hot water (2-pipe) units thatare face and bypass controlled can optionally have a2-position, 3-way, EOC valve to shut off the hotwater flow at the end of the heating cycle. When ahot water reset schedule is used, the EOC valve isnot required. Any two-coil unit with a chilled watercoil that is face and bypass controlled requires a 2-position, 3-way, EOC valve to shut off the chilled-water flow at the end of the cooling cycle.

its position. Damper actuators position the outdoorand room air dampers, and face and by-pass damp-ers (when furnished).

On shutdown, the outdoor air damper will closeand the face and bypass damper (when used) willreturn to the “full-face” position, allowing airthrough the coil. During loss of power, the outdoorair damper will spring-return to closed position andthe face and bypass damper actuator will spring-return to “full-face” position. This combination pro-tects the unit and prevents outdoor air frominfiltrating the space when the unit ventilator is notin use.

ValvesValve actuators use floating point control with po-sition feedback. A digital output signal from theUVC controller moves the actuator in one direc-tion, another digital output signal moves the actua-tor in the opposite direction. When both outputsare de-energized, the valve actuator holds its posi-tion. Valve actuators are shipped individually boxed.

End-Of-Cycle Valves(Face And Bypass Control)For face and bypass damper control, the MicroTech®

DDC system requires an End-Of-Cycle (EOC)valve (Figure 28-1) for each hydronic coil. The EOCvalve prevents simultaneous heating and coolingoperation. It uses floating point control with posi-tion feedback. A digital output signal from the UVCcontroller moves the EOC valve in one direction,another digital output signal moves the EOC valvein the opposite direction. When both outputs arede-energized, the EOC valve holds its position.During loss of power, heating EOC valves spring-return to the open position and cooling EOC valvesspring-return to the closed position. EOC valvesship individually boxed.

Figure 28-1. End-Of-Cycle Valve

Modulating Valves(Figure 28-2) Steam valves are 2-way, normally open,angle pattern that spring return to the open posi-tion during loss of power. Hot-water and chilled/hot water (2-pipe) valves can be either 2-way or 3-way and are normally open to the coil. They springreturn to the open position during loss of power.Chilled-water valves can be either 2-way or 3-wayand are normally closed to the coil. They springreturn to the closed position during loss of power.Care must be taken with modulating valves to en-sure proper water flow. In freezing conditions, wa-ter flow must be maintained through the heatingcoil or a suitable freeze-prevention solution em-ployed to prevent freeze-up. Similarly, the coolingcoil should be drained or a suitable freeze-preven-tion solution employed.

Room Air Temperature Sensors(Tenant Override)The MicroTech unit ventilator control systemutilizes Negative Temperature Coefficient (NTC)thermistors for temperature sensing. Only one roomair temperature sensor is required for bothoccupied and unoccupied control. A tenantoverride function allows the user to manuallyoverride unoccupied control for up to two hours.Tenant override, when initiated, operates in accor-dance with occupied control. Contact closureinitiates unit ventilator operation for 120 minutes(default), however, the tenant override value can beadjusted with a personal computer (PC) runningMicroTech® Monitor™ 2.0 for Windows®

software, or in network mode, with either Monitoror third-party “front-end” software. Room airtemperature sensors are available in either unit orwall mount configurations.

Wall-Mounted Temperature SensorsWall-mounted temperature sensors (Figure 28-3)provide electronic (thermistor) sensing of tempera-ture at wall locations and include an LED (green)mode indicator. Options include a tenant overrideswitch, a setpoint adjustment potentiometer (tooffset the current control setpoint by ± 3°F), a com-munications port and a bi-metal thermometer.

Wall-Mounted Sensor LocationLocate the wall mounted sensor in the classroombut not in direct sunlight or directly in the unit ven-tilator air stream. Avoid mounting the sensor neardrafts or “dead spots” behind doors or in corners,near concealed pipes or chimneys, or on outside walls(Figure 28-4).

Unit-Mounted Temperature SensorsUnit-mounted room air temperature sensors (Fig-ure 28-5) provide electronic (thermistor) sensing oftemperature and are positioned in a sampling cham-ber located behind a grouped series of holes in thefront panel of the unit ventilator. A unit-mountedtenant override switch is available.

Units with a face and bypass controlled steam coilrequire a 2-position, 2-way, EOC valve to shut offsteam flow at the end of the heating cycle. Unitswith a face and bypass controlled hot-water coil thatalso have a separate cooling coil require a 2-posi-tion, 3-way, EOC valve to shut off the hot waterflow at the end of the heating cycle. Hot-water-heat-

LED ModeIndicator

Tenant OverrideSwitch

SetpointAdjustment

Figure 28-4. Sensor Locations

SuggestedSensorLocation(about 5 feetfrom floor)

Window

Unit Ventilator•

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Interior Wall

Interior Wall

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Figure 28-5. Unit MountedTemperature Sensor

Unit Left EndCompartment

Room AirTemperatureSensor


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Figure 29-2. Front View, Floor Model AV With Front Access Panels Removed(AH Ceiling Models Similar)

� MicroTech UVC� Room Temperature Adjust� Terminal Strips� Damper Actuators� Sampling Chamber

� Time Clock� Electrical Box� Tenant Override Switch Motor Speed Switch Holiday Switch

A representative sample of room air is continuouslydrawn across the unit-mounted room air tempera-ture sensor in the sampling chamber by the unitventilator fans during occupied operation. This pro-vides excellent room air temperature sensing. Usinga unit-mounted room air temperature sensor con-figuration can also eliminate the problem of deter-mining an optimum location for a wall-mountedroom air temperature sensor.

System ProductsA MicroTech® or third-party control system can beimplemented to provide network support for AAF®-HermanNelson® classroom unit ventilators.MicroTech system controllers are used to constructa control network that ties the MicroTech unit ven-tilator controllers together and to provide a level ofsupervisory control constituting a unit ventilatorsystem. Interaction with the unit ventilator control-lers, or with the unit ventilator system, is providedby means of PC-based software, MicroTech® Moni-tor™ 2.0 for Windows®, or by a third-party Build-ing Automation System (BAS) through Open Pro-tocol™.

MicroTech® System ControllersMicroTech® system controllers are used to coordi-nate communications in a MicroTech network ofunit ventilator controllers (i.e., a MicroTech unitventilator system). These products are seldom usedin an open system application because the third-party BAS would provide their functions.

MicroTech® Monitor™ 2.0 for Windows®

MicroTech® Monitor™ 2.0 for Windows® (Figure29-1) is a PC-based software package that pro-vides a high-level graphical user interface (GUI) toMicroTech unit controllers and system products.Monitor software can be used to commission,troubleshoot, monitor or control stand-alone ormaster/slave configured MicroTech unit ventilatorcontrollers, or systems consisting of network con-figured MicroTech unit ventilators and MicroTechsystem controllers.

Monitor runs on Windows 3.x or Windows 95/98and utilizes the full set of Windows capabilities.Features include password protection, network di-agnostics, trend and alarm logs, group monitoring

and control, time scheduling and facsimile capabil-ity. A PC communications cable kit, includingadapters for AMP, IDC, and Phoenix type connec-tors is required to connect the serial port (DB-9 orDB-25) of a personal computer to any MicroTechcontroller.

MicroTech Open Protocol™MicroTech Open Protocol allows third-party build-ing automation system (BAS) companies to createan interface to MicroTech unit and system control-lers. Every MicroTech unit and system controllercontains a comprehensive set of monitor and con-trol points that are available for system designers touse in meeting the requirements of specific applica-tions. When an existing or specified BAS companyis involved, an Open Protocol Site License allowsthe BAS company to use these monitor and controlpoints in their system. Each BAS company deter-mines the extent to which their interface takes ad-vantage of the monitor and control points availablein the MicroTech controllers.

BAS companies who are Open Protocol partnerswith McQuay International can direct connect toany single AAF-HermanNelson® classroom unitventilator with a factory installed MicroTech unitventilator controller. Multiple unit ventilators withfactory installed MicroTech unit ventilator control-lers can be connected as level-2 controllers directlyto a MicroTech Open Protocol Master (OPM)panel. The OPM panel provides single point accessto the unit ventilator system for the BAS. An OpenProtocol Site License is required when access is pro-vided to any MicroTech unit ventilator controlleror series of unit ventilator and system controllers,.The license serves two purposes; (1) it grants per-mission to establish communications between the

MicroTech controls and another BAS and (2) it isprovided with MicroTech Monitor software that isused in the commissioning process to establish andverify communications between the MicroTechcontrollers and the BAS.

Basic Unit Components“High-Medium-Low-Off”Motor Speed SwitchThis switch allows the user to select the fan speed.The “off” position de-energizes power to the fanmotor and UVC.

Electric Connection BoxThe electric connection box contains the motor speedswitch, motor speed transformer and fusetron(s), whenfurnished. Wiring connections to the day/night relayand vent relay are made in this box. Refer to the unitwiring diagram for specifics.

Right End CompartmentClass 1 wiring required.

Left End CompartmentClass 2 wiring permitted.

Unit Terminal Strips (Left End Compartment)Provides convenient connection points for the fol-lowing:

a. End of Cycle Valve (factory required)b. Modulating steam or water control valve (fac-

tory required);c. Wall-mounted room sensor;d. Condensing unit control circuit (field wired by

others).

1 13

2

4

35 Motor 6 7

11

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� Right End CompartmentClass 1 wiring required.

Electric Heat Disconnect Switch� Left End Compartment

Class 2 wiring permitted.

12Figure 29-1. MicroTech® Monitor™2.0

Software for Windows


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Figure 30-1. Time Clock

AccessoriesDaily and Holiday OperationUsed with Stand-Alone or Master/Slave, the unit-mounted time clock has a 24-hour dial with skip-a-day feature and battery backup. The time clock uti-lizes the unit line voltage power supply. The remotemounted time clock can be furnished by others orby AAF®-HermanNelson®. The AAF-HermanNel-son time clock is 120 volt, 24 hour with skip-a-dayor 7-day and with or without reserve power. It canset daily start/stop times. Voltages available are 115v,460v and 208/230v. The holiday switch places theunit into night setback operating mode.

Status and Alarm IndicationThe yellow UVC status LED and Wall Mounted sen-sor green LED indicate whether the unit status is occu-pied, unoccupied or in tenant override, and any faultcodes.

LED Mode and Fault IndicatorA yellow LED is on the UVC board and a greenLED on the Wall Mounted room air temperaturesensor. Both LEDs indicate the UVC status by flash-ing at predetermined intervals to indicate: “occu-pied” mode, “unoccupied” mode, “tenant override”mode and “fault” conditions. Steady lighted LEDequals “occupied” mode. A flashing LED, on 1⁄2 sec-ond, off 51⁄2 seconds equals “unoccupied” mode.Flashing on 51⁄2 seconds, off 1⁄2 second indicates“tenant override” mode.

The status LED indicates alarm mode conditionsby flashing and blinking for: room temperaturesensor, outdoor air damper position, discharge airtemperature sensor, outdoor air temperature sensor,low leaving air temperature, heat valve positionfeedback, valve or face and bypass damper positionfeedback, high refrigerant pressure, low DX coiltemperature, brownout, water-in temperature sensorand communication failure (Master/Slave only).

Sensor DiagnosticsThe UVC monitors for sensor faults due to failedsensors and/or broken connections. Each sensor faulthas a specific priority, alarm indication and a set ofresponse actions.

Hex SwitchesThese switches determine the address of the unit.For Stand-Alone units, leave AV/AH at 01. ForStand-Alone split system DX units, the hex switchesdefine the random start delay period (up to 63 sec-onds in one second intervals) so multiple units donot start at the same time. On Master/Slave andNetwork units the hex switches determine thecontroller’s address as well as compressor delay.

Split System DXOperationRemote Compressor OperationThe UVC energizes a 24-volt control circuit to theremote condensing unit on a call for DX cooling. Anoutdoor air sensor provides input to the UVC toprevent condensing unit operation in cooling whenthe outdoor temperature is below 60˚F. Brownoutprotection and short cycle protection is included inthe software program.

If the outdoor air temperature is below 64˚F, theoutdoor air damper will modulate for economizercooling. When the outdoor air temperature is above64˚F, the outdoor air damper will be at the mini-mum setting.

Indoor Low Leaving CompressorTemperature Protection With SplitSystems (AV/AH with DX Coils)The DX coil low leaving temperature thermostatdetects an indoor coil low leaving air temperaturecondition and an alarm is indicated and appropri-ate action occurs.

Brownout Protection Split SystemFor DX UnitsThe UVC senses the line voltage of the phase usedto power the 24-vac supply. If brownout failureoccurs and/or line voltage drops by approximately20% below unit’s nameplate value, compressoroperation stops and electric heat operation is stopped.Normal operation resumes when line voltage re-turns to approximately 90% or more of the unit’snameplate value.

Adjustable Power-Up Delayor Random StartThis prevents simultaneous compressor start-upat unit power up during “unoccupied” to “occu-pied” changeover, and brownout condition. TheUVC hex switch setting determines the 1 to 63second delay.

Compressor Short Cycle ProtectionShort cycle protection prolongs compressor life.When the compressor is energized, it runs for atleast 8 minutes before the temperature sequence cande-energize it. An alarm condition can override this.When the compressor is de-energized, it remainsoff for at least 3 minutes before the temperaturesequence can energize.

High Refrigerant ProtectionThis protects the unit from destruction (requiredagency protection). If excessive refrigerant pressureis detected by the external pressure switch (providedby others on remote condensing unit), the com-pressor is de-energized immediately and an alarm isindicated.

Low Ambient LockoutThis prevents damaging unit due to freeze-up andprevents compressor operation in cooling when theoutdoor air temperature is below 60˚F.

Time ClockThis accessory device, field installed behind the rightfront access panel, automatically cycles the unitthrough occupied and unoccupied modes in accor-dance with a user-programmed time schedule. Pro-gramming instructions are included. Time clockshave battery backup, so they will not require reset-ting if electric power is interrupted. A time clock isnot required with network units as this function ishandled through the communications network.

Holiday SwitchThis device is furnished with the time clock as anaccessory. It permits manual changeover tounoccupied (night) control for extended orotherwise unscheduled periods. The switch mustbe manually returned to the normal (automaticcontrol) position at the end of the “holiday” periodfor the unit to operate on the automatic temperaturecontrol sequence. This is not required with Networkunits as this function is handled through thecommunications network.

Status/DiagnosticCapabilityAAF-HermanNelson MicroTech® Control providesadditional benefits of status and diagnosticcapabilities for ease of service, if needed.

Status InformationPower LEDThe green power LED indicates the UVC has power.

Documents

AAF -HermanNelson Classroom Unit Ventilators