HVAC SYSTEM DESIGN PROCESS - …wtgzik.pairserver.com/courses/373f15/373-HVACDesign.pdf · HVAC System Design Process Establish HVAC ... red = architect blue = engineer with ... you’ve

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Ball State Architecture | ENVIRONMENTAL SYSTEMS 2 | Grondzik 1

HVAC SYSTEMDESIGN PROCESS


HVAC System Design ProcessEstablish HVAC-related owner’s project requirements (OPR: design issues/intents/criteria;

including code/standard compliance)Establish zoning requirementsMake a preliminary system selection based on the aboveCalculate preliminary design heating/cooling loadsSelect appropriate source equipment (to meet loads, intent, and context)Select appropriate distribution approach (to meet intents and to fit context)Coordinate HVAC components with other building systemsRough-size equipment (fans, pumps, valves, dampers, pipes, ducts, condensers, air-

handlers, tanks, …) Run energy analyses to optimize equipment selections and system assembliesFinal-size equipment based upon optimization studiesCoordinate final individual equipment selections into a cohesive wholeDevelop appropriate control logic and strategiesDevelop commissioning tests and checklistsWitness systems installation and verificationDevelop systems manuals for the ownerProvide benchmark performance data for the ownerConduct POE validations of systems outcomes on site

red = architect blue = engineer with architect black = engineer

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HVAC System Selection Process

Carefully consider potential design issues

Clearly define design intents

Establish meaningful design criteria

Compare potential systems against criteria

Select best system

Validate system selection

collectively, the first three become the Owner’s Project Requirements (OPR) for climate control and IAQ


Common HVAC Selection Issues

• First cost• Life-cycle cost• Durability• Maintainability• Reliability• Appearance• Zoning capabilities• Flexibility• Energy efficiency• ODP and GWP

• Greenness• Noise• Space requirements• Smoke control

capabilities• Fuel options• Owner dictates• Demand charges• Many others

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Common HVAC Design Intents

• “Provide” thermal comfort• “Provide” acceptable IAQ• Low first cost• Good energy efficiency• No equipment located in occupied spaces• A “green” system• Highly reliable operation• Easily maintained equipment• Low life-cycle costs• And such …


Establish Design Criteriafor Each Intent

• Low first cost means no more than $xx.xx / sq ft• Energy efficient means xx% better than the requirements of

ASHRAE Standard 90.1• Provide thermal comfort means meets the requirements of

ASHRAE Standard 55 (“bettering” this standard is not necessarily meaningful; comfort is comfort)

• Provide good IAQ means meets the requirements of ASHRAE Standard 62.1 (“bettering” is expensive to verify and may be energy intensive)

• Easy to maintain means janitorial staff can do the job• No equipment in occupied spaces means as stated• Aesthetically pleasing means meets three visual precedents

the criteria shown above are simply examples, from a world of possibilities

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Selection Matrix (a design tool)

311297OVERALLRATING

7285469 **Good IAQCapabilities

5493666CleanAppearance

8081001010 *HighFlexibility

5677298Good EnergyEfficiency

4973557Low First Cost

WEIGHTEDSCORE

SYSTEM B

SCORE

SYSTEM B

WEIGHTEDSCORE

SYSTEM A

SCORE

SYSTEM A

PROJECT WEIGHT

INTENT

* most important attribute/intent; ** second most important; etc.

and the most logical system to use—in this context—is B

POSSIBLE SYSTEM “A” POSSIBLE SYSTEM “B”


Key HVAC Coordination Issues

• Equipment Locations– Source equipment (noise, maintenance access, access for

replacement, access/connection to utilities)– Condenser (must be exterior, noise, appearance, airflow, spray)– Air-handlers (length and placement of air supply and return paths,

outdoor air access, noise, vibration)– Terminal devices (maintenance access, noise, space incursion)– Outdoor air intakes (located to provide unpolluted outdoor air)

• Floor Area for Equipment– Main mechanical room(s), satellite AHU room(s), condenser

• Volume for Distribution (and for Equipment)– Ductwork (by itself and in coordination with beams, lighting

fixtures, sprinkler piping, electrical and signal runs)

• Aesthetics– Exposed elements (especially diffusers)

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Desired Equipment Locations

The Architect’s Studio Companion: 3rd Ed.

this is a jointarchitectural/mechanical

decision

these 4 examples all “work” … butone will usually make more sense

in a given project context

a 5th option (not shown) wouldbe “fan room on roof”


Required Equipment Locations

zonecontrol

diffusers are laid out for

reasonable air distribution


box MUSTbe in this

area

undifferentiatedsupply air;

not yet controlled for specific zones

zone-differentiatedsupply air

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Large Equipment

Areas

for schematic planning: can estimate central plant at 7% +/-of conditioned floor area



AirHandling Unit

Areas


USE these simple tools in studio—don’t just guess

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Consider Volume (not just floor area)

The Architect’s Studio Companion, 3rd Ed.


Volumeworking in and around structure

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Volume

plenums are neveras deep as they seem


Provide for Access who will know thisstuff is up there?

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Estimating Duct Sizes (another option)

• For schematic design, assume 1 cfm per square foot (for an all-air system; 0.1 for an air-water system)

• Duct volume (in ft2) = airflow (in cfm) / air speed (in fpm)– cfm = cubic feet per minute (airflow rate)– fpm = feet per minute (air speed in ducts)

• Assume (as a starting point) 1000 fpm air speed– higher air speed is possible and fairly common, but it uses more

energy and generates more noise (and we’re just estimating)

• Estimate duct dimensions as needed for the area served by a given duct (main ducts, branch ducts, …)


Estimating Duct Sizes (Examples)

• For a 200 sq ft office (all-air HVAC)

– (200 sq ft)(1 cfm/sq ft) = 200 cfm– 200 cfm / 1000 fpm = 0.2 sq ft – duct size might be around 12” x 3” or 6” x 6” or ….– and a similar size return air duct may be required

• For a 3000 sq ft classroom wing (all-air HVAC)

– (3000 sq ft)(1 cfm/sq ft) = 3000 cfm– 3000 cfm / 1000 fpm = 3 sq ft – duct size might be 36” x 12”– and a similar size return air duct may be required

message: ducts can get quite large, and there are often two of them

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The Aesthetics ofAir Delivery

register

diffuser

diffuser

diffuser

all devices do not have equal visual impact


The Aesthetics of Air Delivery

diffuser grille register

grille

a diffuser provides sophisticated control of air delivery; a register the same but not quite so sophisticated; a grille basically just covers up a hole

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Aesthetic Potential

of ExposedSystems


The Messy Stuff Is Usually Hidden

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Big Stuff: Plan for It

chiller

cooling tower

you’ve got to give innovation credit for the partially earth-bermed cooling tower


Really Big Stuff: Seriously Plan for It

< penthouse mechanical room >

OA “duct”

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Creative Design

student work: Oklahoma State University


Creative Design

student work: Oklahoma State University

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HVAC SYSTEM DESIGN PROCESS - …wtgzik.pairserver.com/courses/373f15/373-HVACDesign.pdf · HVAC System Design Process Establish HVAC ... red = architect blue = engineer with ... you’ve