ovo isto treba za dokumentaciju
TRANSCRIPT
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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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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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Lower Supply-Air Temperature
Benefits Reduces supply airflow
Less supply fan energyand less fan heat gain
Smaller fans, air handlers,VAV terminals, and ductwork
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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lower supply-air temperature
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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Lower Supply-Air Temperature
Benefits Reduces supply airflow
Less supply fan energyand less fan heat gain
Smaller fans, air handlers,VAV terminals, and ductwork
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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Lower Supply-Air Temperature
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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lower supply-air temperature
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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lower supply-air temperature
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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lower supply-air temperature
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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lower supply-air temperature
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
Lower Supply-Air Temperature
Benefits Reduces supply airflow
Less supply fan energyand less fan heat gain
Smaller fans, air handlers,VAV terminals, and ductwork
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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ventilation optimization
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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ventilation optimization
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