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TRANSCRIPT
March 2010
Brian Fiegen Systems Engineering Manager Trane La Crosse, Wisconsin
Shane Labuzan Account Manager Trane Central Indiana District Indianapolis, Indiana
High Performance Chilled Water VAV Systems, An Unconventional Look at System Design
Indiana Building Green Symposium 2
ASHRAE 90.1 Moves Toward Net-Zero
100
80
60
40
20
Net Zero
Bui
ldin
g EQ
™ (E
UI bu
ildin
g/EU
I med
ian)
LEED 2.1
LEED 2.2 LEED
2009
Building Stock Median
ASHRAE 90.1-2007
ASHRAE 90.1-2010?
ASHRAE 90.1-2004
ASHRAE 90.1-1999
Indiana Building Green Symposium 3
“Golden Rule” of Reducing HVAC Energy Use First, reduce the load. • Glazing: Avoid glazing which faces east
or west, shade exterior glazing, use insulating low-e glass, and make all glazing as small as possible (consistent with use of daylighting)
• Daylighting/Lighting: Design envelope and glazing so the sun provides interior lighting at perimeter, and design efficient supplemental interior lighting that modulates when not needed
• Envelope: Design and construct exterior enclosure to be as airtight as possible
Indiana Building Green Symposium 4
high performance chilled water VAV systems Agenda
• Cold air systems – Benefits – Common concerns
• Optimized VAV system controls • Energy performance comparison
Chilled Water VAV systems
Indiana Building Green Symposium 5
Lower Supply-Air Temperature
Benefits • Reduces supply airflow
– Less supply fan energy and less fan heat gain
– Smaller fans, air handlers, VAV terminals, and ductwork
Indiana Building Green Symposium 6
SA Temperature vs. Airflow
= 1.085 ×
space sensible cooling
load
supply airflow × (Tspace – Tsupply)
same (75°F – 55°F) 100% cfm
(75°F – 50°F) 80% cfm
same
(75°F – 45°F) 67% cfm
same
Indiana Building Green Symposium 7
Lower Supply-Air Temperature
Benefits • Reduces supply airflow
– Less supply fan energy and less fan heat gain
– Smaller fans, air handlers, VAV terminals, and ductwork
• Can reduce HVAC installed cost • Can reduce building construction cost
Indiana Building Green Symposium 8
lower supply-air temperature Can Reduce HVAC Installed Cost
• Lowering supply-air temperature from 55°F to 48°F reduces 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 VFD’s)
Indiana Building Green Symposium 9
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: 55°F supply-air temperature – Alternate design: 48°F supply-air temperature
Indiana Building Green Symposium 10
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
Indiana Building Green Symposium 11
lower supply-air temperature Can Reduce Building Cost
• Smaller indoor air-handling units can allow for smaller equipment rooms and more usable floor space
• Smaller ductwork can allow for a shorter floor-to-floor height, reducing the cost of building materials and labor
Indiana Building Green Symposium 12
potential reduction in duct size… 55°F supply air (10000 cfm) vs. 48°F supply air (7400 cfm)
Indiana Building Green Symposium 13
55°F supply air 48°F 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
Indiana Building Green Symposium 14
Lower Supply-Air Temperature
Benefits • Reduces supply airflow
– Less supply fan energy and 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
Indiana Building Green Symposium 15
180
160
140
120
100
80
60
40
20
humidity ratio, grains/lb of dry air
110 30 40 50 60 70 80 100 90 dry-bulb temperature, °F
80
70
50
40 30
60 SA
MA
OA
OA 48°F SA 84°F DB 76°F DP
RA 75°F DB 49% RH
MA 81°F DB
SA 48°F DB (670 cfm)
SA
RA
84°F DB 76°F DP
75°F DB 57% RH
79°F DB
55°F DB (900 cfm)
55°F SA
Indiana Building Green Symposium 16
Lower Indoor Humidity Levels
• Conventional system (55°F supply air)
• Low-temperature system (45°F to 50°F supply air)
• Indoor humidity levels of 55% to 60%
• Indoor humidity levels of 45% to 50%
Lower humidity improves occupant comfort, which can increase employee productivity and student alertness.
Indiana Building Green Symposium 17
Lower Supply-Air Temperature
Common concerns • Increases reheat energy, reduced
economizer savings • Minimize comfort problems
due to cold air “dumping” • Avoid condensation on air
distribution system components
Indiana Building Green Symposium 18
lower supply-air temperature Maximize Energy Savings
• Use supply-air-temperature reset (ex: from 48°F to 55°F) during mild weather – Reduces reheat energy use – Recovers lost economizer savings
• Raise space setpoint by 1°F or 2°F – 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
Indiana Building Green Symposium 19
Supply-Air-Temperature Reset
• Benefits – Decreases mechanical cooling – Increases economizing – Decreases reheat energy
• Drawbacks – Increases fan energy – Raises indoor humidity levels
Indiana Building Green Symposium 20
SA temperature reset Example #1: OA Temperature
50 55 60 45 75 70 65
outdoor dry-bulb temperature, °F
SA
tem
pera
ture
setp
oin
t, °
F
60
58
56
54
52
50
48
Indiana Building Green Symposium 21
lower supply-air temperature Minimizing Comfort Problems
• Use linear slot diffusers…
…and supply-air-temperature reset (example: from 48°F back up to 55°F)
linear slot diffuser
“dumping”
conventional concentric diffuser
Indiana Building Green Symposium 22
lower supply-air temperature Avoiding Condensation
• Properly insulate and vapor-seal ductwork, VAV terminals, and supply-air diffusers
Indiana Building Green Symposium 23
surface temperatures on duct insulation (wrapped metal duct) • 44°F supply air (Trane district office in Dallas, TX) • fully-ducted return air path (85°F dry bulb above ceiling)
trunk duct (2 in. insulation) outer surface temp = 82°F
branch duct (1 in. insulation) outer surface temp = 77°F
Indiana Building Green Symposium 24
lower supply-air temperature Avoiding Condensation
• Properly insulate and vapor-seal ductwork, VAV terminals, and supply-air diffusers
• Maintain positive building pressure to minimize infiltration 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-air
temperature to gradually lower indoor humidity
Indiana Building Green Symposium 25
examples Humidity Pull-Down Sequences
• SAT ramp-down schedule
• SAT ramp-down based on indoor dew point – SAT = current indoor dew point – 3°F
supply airflow supply-air limit temperature
2 hours before occupancy 40% of design 55°F
1 hour before occupancy 65% of design 51°F
Scheduled occupancy no limit 48°F
or
Source: ASHRAE Cold Air Distribution System Design Guide (pp 138-140)
Indiana Building Green Symposium 26
summary Lower Supply-Air Temperature
Benefits • Reduces supply airflow
– Less supply fan energy and 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
Indiana Building Green Symposium 27
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
Indiana Building Green Symposium 28
VAV boxes static
pressure sensor
Traditional VAV Fan Control
P supply
fan
VFD
Indiana Building Green Symposium 29
VAV boxes
static pressure sensor
supply fan
Fan-Pressure Optimization
P
BAS
with DDC controllers
VFD
Indiana Building Green Symposium 30
surge
fan-pressure optimization Part-Load Energy Savings
airflow
stati
c p
ress
ure
fan-pressure optimization
duct static pressure control
Indiana Building Green Symposium 31
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!
Indiana Building Green Symposium 32
6.5.3.2.3 Setpoint Reset. For systems with DDC of individual zone boxes reporting to the central control panel, static pressure setpoint shall be reset based on the zone requiring the most pressure; i.e., the setpoint is reset lower until one zone damper is nearly wide open.
Required by ASHRAE 90.1 Since 1999
Indiana Building Green Symposium 33
lounge rest room
storage office
office conference rm computer room reception area elev
ator
s vestibule corridor
demand-controlled ventilation CO2 Sensor in Every Zone??
CO2
CO2
CO2
CO2
CO2 CO2
BAS
Indiana Building Green Symposium 34
lounge rest room
storage office
office conference rm computer room reception area elev
ator
s vestibule corridor
ventilation optimization Zone Level: DCV
CO2
CO2
OCC
OCC
TOD TOD
BAS
Indiana Building Green Symposium 35
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 with flow-measuring dampers • Reset outdoor airflow
CO2 TOD TOD OCC
BAS • New OA setpoint
…per ASHRAE 62
Indiana Building Green Symposium 36
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!
Indiana Building Green Symposium 37
Example TRACE® 700 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
Indiana Building Green Symposium 38
2,000,000
4,000,000
6,000,000
8,000,000
10,000,000
12,000,000
An
nu
al B
uild
ing
En
erg
y U
se,
kB
tu/
yr
Pumps
Fans
Heating
Cooling
Plug Loads
Lighting
Houston Los Angeles Philadelphia St. Louis
Indiana Building Green Symposium 39
High Performance VAV System
• Reduced energy • Reduced materials of construction and first cost • Improved comfort • Lower sound