Ovo Isto Treba Za Dokumentaciju

8/4/2019 Ovo Isto Treba Za Dokumentaciju

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March 2010

Brian FiegenSystems Engineering ManagerTraneLa Crosse, Wisconsin

Shane LabuzanAccount ManagerTrane Central Indiana DistrictIndianapolis, Indiana

High Performance Chilled Water VAV Systems,An Unconventional Look at System Design


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Indiana Building Green Symposium2

ASHRAE 90.1Moves Toward Net-Zero

100

80

60

40

20

Net Zero

Bu

ildingEQ(

EUIb

uilding

/EUIm

edian

)

LEED

2.1LEED

2.2LEED2009

Building Stock Median

ASHRAE 90.1-2007

ASHRAE 90.1-2010?

ASHRAE 90.1-2004

ASHRAE 90.1-1999


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Golden Rule ofReducing HVAC Energy Use

First, reduce the load.

Glazing: Avoid glazing which faces eastor west, shade exterior glazing, useinsulating low-e glass, and make all

glazing as small as possible (consistentwith use of daylighting)

Daylighting/Lighting: Design envelopeand glazing so the sun provides interiorlighting at perimeter, and design efficient

supplemental interior lighting thatmodulates when not needed

Envelope: Design and construct exteriorenclosure to be as airtight as possible


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high performance chilled water VAV systems

Agenda

Cold air systems Benefits Common concerns

Optimized VAV system controls Energy performance comparison

Chilled WaterVAV systems


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Lower Supply-Air Temperature

Benefits Reduces supply airflow

Less supply fan energyand less fan heat gain

Smaller fans, air handlers,VAV terminals, and ductwork


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SA Temperature vs. Airflow

= 1.085

spacesensiblecooling

load

supplyairflow (Tspace Tsupply)

same (75F 55F)100%cfm

(75F 50F)80%

cfm

same

(75F 45F)67%cfm

same


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Can reduce HVAC installed cost Can reduce building construction cost


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lower supply-air temperature

Can Reduce HVAC Installed Cost

Lowering supply-air temperature from 55F to 48Freduces supply airflow (cfm) by 26%

Ducts can be smaller VAV terminal units can be smaller Diffusers can be smaller Air-handling units can be smaller

(plus smaller electrical service and VFDs)


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example

HVAC Installed Cost Savings

Twelve-story office building in Atlanta, GA(30,000 ft2 per floor)

One VAV air-handling unit per floor Base design: 55F supply-air temperature Alternate design: 48F supply-air temperature


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example

Air-Handling Unit Selections

AHU equipment costs (12 units, including VFDs) Base = $204,962 Alternate = $167,345 ($38,000 savings, or $0.11/ft2)

If ductwork and VAV boxes are downsized also: Less sheet metal, insulation, and labor = $50,370 ($0.14/ft2) Smaller VAV terminals (300 units) = $7,800 ($0.02/ft2) Total HVAC cost savings = $96,170 ($0.27/ft2)

cfm size ESP TSP bhp motor HP MBh (total)Base 25,600 50 3.5 in. 4.21 in. 28.4 30 919

Alternate 20,000 40 3.5 in. 4.97 in. 22.2 25 961


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Can Reduce Building Cost

Smaller indoor air-handling units can allow forsmaller equipment rooms and more usable floor space

Smaller ductwork can allow for a shorterfloor-to-floor height, reducing the cost ofbuilding materials and labor


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potential reduction in duct size

55F supply air (10000 cfm) vs. 48F supply air (7400 cfm)


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55F supply air 48F supply air

concrete slab floor

What if you could save 5 in. per floor, in a 30-story building?

What if you could save 5 in. per floor, in a 3-story building?

5 in.

ceiling


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Can reduce HVAC installed cost Can reduce building construction cost Improves occupant comfort

Lowers indoor humidity levels Lowers indoor sound levels


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180

160

140

120

100

80

60

40

20

humidityra

tio,grains/lbofdryair

11030 40 50 60 70 80 10090

dry-bulb temperature, F

80

70

50

4030

60

SA

MA

OA

OA

48F SA

84F DB76F DP

RA 75F DB49% RH

MA 81F DB

SA 48F DB

(670 cfm)

SA

RA

84F DB76F DP

75F DB57% RH

79F DB

55F DB

(900 cfm)

55F SA


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Lower Indoor Humidity Levels

Conventional system(55F supply air)

Low-temperature system(45F to 50F supply air)

Indoor humidity levels of55% to 60%

Indoor humidity levels of45% to 50%

Lower humidity improves occupant comfort, which can

increase employee productivity and student alertness.


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Common concerns Increases reheat energy, reduced

economizer savings

Minimize comfort problemsdue to cold air dumping Avoid condensation on air

distribution system components


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Maximize Energy Savings

Use supply-air-temperature reset (ex: from 48F to 55F)during mild weather Reduces reheat energy use Recovers lost economizer savings

Raise space setpoint by 1F or 2F Lower indoor humidity often allows zone dry-bulb temperature

to be slightly warmer

Further reduces supply airflow and fan energy use

Keep same size ductwork Further reduces fan energy use Allows SAT reset in systems that serve zones with

near-constant cooling loads

Capable of delivering more airflow, if loads increase in future


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Supply-Air-Temperature Reset

Benefits Decreases mechanical cooling Increases economizing Decreases reheat energy

Drawbacks Increases fan energy Raises indoor humidity levels


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SA temperature reset

Example #1: OA Temperature

50 55 6045 757065

outdoor dry-bulb temperature, F

SAtemperature

setpoint,F

60

58

56

54

52

50

48


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Minimizing Comfort Problems

Use linear slot diffusers

and supply-air-temperature reset(example: from 48F back up to 55F)

linear slotdiffuser

dumping

conventionalconcentric diffuser


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Avoiding Condensation

Properly insulate and vapor-sealductwork, VAV terminals, and supply-air diffusers


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surface temperatures on duct insulation (wrapped metal duct)

44F supply air (Trane district office in Dallas, TX)fully-ducted return air path (85F dry bulb above ceiling)

trunk duct (2 in. insulation)outer surface temp = 82F

branch duct (1 in. insulation)outer surface temp = 77F


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Avoiding Condensation

Properly insulate and vapor-sealductwork, VAV terminals, and supply-air diffusers

Maintain positive building pressure to minimizeinfiltration of humid outdoor air

Use linear slot diffusers to increase air motion Monitor indoor humidity during unoccupied periods

and prevent it from rising too high

During startup, slowly ramp down the supply-airtemperature to gradually lower indoor humidity


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examples

Humidity Pull-Down Sequences

SAT ramp-down schedule

SAT ramp-down based on indoor dew point SAT = current indoor dew point 3F

supply airflow supply-air

limit temperature

2 hours before occupancy 40% of design 55F1 hour before occupancy 65% of design 51F

Scheduled occupancy no limit 48F

or

Source: ASHRAE Cold Air Distribution System Design Guide (pp 138-140)


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summary





Can reduce HVAC installed cost Can reduce building construction cost Improves occupant comfort

Lowers indoor humidity levels Lowers indoor sound levels


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Optimized VAV System Controls

Supply-air-temperature reset Optimal start/stop Fan-pressure optimization Ventilation optimization

Demand-controlled ventilation at zone level Ventilation reset at system level


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VAV boxes

staticpressure

sensor

Traditional VAV Fan Control

Psupply

fan

VFD


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VAV boxes

staticpressuresensor

supplyfan

Fan-Pressure Optimization

P

BAS

with DDCcontrollers

VFD


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surge

fan-pressure optimization

Part-Load Energy Savings

airflow

staticpressure

fan-pressureoptimization

duct static

pressure control


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fan-pressure optimization

Benefits

Part-load energy savings Lower sound levels Reduced risk of fan surge Less duct leakage Factory-installation and -commissioning

of duct pressure sensor

Operator feedback to "tune the system" Typical applications: any VAV system!


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6.5.3.2.3 Setpoint Reset. For systems with DDC of

individual zone boxes reporting to the central controlpanel, static pressure setpoint shall be reset based on

the zone requiring the most pressure; i.e., the setpoint isreset lower until one zone damper is nearly wide open.

Required by ASHRAE 90.1

Since 1999


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lounge restroom

storage office

office conference rm computer roomreception area elev

ators

vestibule corridor

demand-controlled ventilation

CO2 Sensor in Every Zone??

CO2

CO2

CO2

CO2

CO2 CO2

BAS


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lounge restroom

storage office

office conference rm computer roomreception area elev

ators

vestibule corridor

ventilation optimization

Zone Level: DCV

CO2

CO2

OCC

OCC

TOD TOD

BAS


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System Level: Ventilation Reset

CO2 OCC

Required ventilation (TOD, OCC, CO2) Actual primary airflow (flow ring) Calculate Vent Ratio

DDC/VAV controllers

SA RA

air-handling unit withflow-measuring dampers

Reset outdoor airflow

CO2TOD TODOCC

BAS New OA setpoint

per ASHRAE 62


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Benefits

Saves energy during partial occupancy Lower installed cost, less maintenance, and more

reliable than installing a CO2 sensor in every zone

Use zone-level DCV approaches where they best fit(CO2 sensor, occupancy sensor, time-of-day schedule)

Combine with ventilation reset at the system level Earn LEED EQc1: Outdoor Air Delivery Monitoring

Typical applications: any VAV system!


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Example TRACE700 Analysis

High Performance VAV system

48 F supply air Optimal start Fan-pressure optimization SA temperature reset Ventilation optimization

DCV at zone level Ventilation reset at system level


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2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

AnnualBuilding

EnergyUse,

kBtu/yr

Pumps

Fans

Heating

Cooling

Plug Loads

Lighting

Houston Los Angeles Philadelphia St. Louis


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High Performance VAV System

Reduced energy Reduced materials of construction and first cost Improved comfort Lower sound


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Questions

Documents

Ovo Isto Treba Za Dokumentaciju