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Energy Impacts ofEnergy Impacts ofAir-Handling System Leakagein Large Commercial B ildingsin Large Commercial Buildings: Measurements and SimulationCraig Wray, P.Eng.
Buildings and Urban Systems DepartmentEnvironmental Energy Technologies DivisionBerkeley, CA [email protected]@ gTel: 510-486-4021
ASHRAE Winter Meeting, Chicago, IL 23 January 2012
Learning Objectives and DisclaimerSession Objectives:Session Objectives:1. Understand need to determine leakage flows for entire air-handling system, and to understand impacts of leakage flows on zone heating and cooling loads and on whole-building energy use in commercial buildings.2. Estimate energy impacts of system leakage downstream of VAV boxes, and in toilet/kitchen exhaust systems.
f l h h f f l k d d l3. Become familiar with the necessary specifications for system leakage using industry accepted terminology.4. Understand how various codes and standards address system air leakage.5. Understand test protocols for cost-effectively measuring system leakage.6. Recognize it is responsibility of design engineer to specify maximum allowable system leakage percentage.
AIA Disclaimer:ASHRAE is a Registered Provider with The American Institute of Architects Continuing Education Systems Credit earned on completion of this program will be reported toEducation Systems. Credit earned on completion of this program will be reported to ASHRAE Records for AIA members. Certificates of Completion for non-AIA members are available on request.This program is registered with the AIA/ASHRAE for continuing professional education.This program is registered with the AIA/ASHRAE for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Q ti l t d t ifi t i l th d d i ill b dd d t thQuestions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.
Presentation OutlinePresentation Outline
U.S. system characteristicsCommon leakage metricsLeakage test methodsgMeasurement and simulation resultsNext stepsNext steps
Large CommercialSystems
Long, complex pathsL f iLarge fan pressure rises and flowsF d i t dFan-power dominatedSections often outsideconditioned spaceconditioned spaceThermal losses create short circuitshort circuit
Numerous Leakage OpportunitiesSlot Diffuser
Box
Thousands of field assembled joints
VAVBox
L k
T-Bar
assembled joints Leaks
Roof Deck
VAVBox
SupplyDuct
Supply DuctLeaks
LeakCeiling Insulation
System PressuresSystem Pressures
Pressures not uniform or constant
50 to 75% of system might operate at “low”
High pressures upstream of box inlet
pressures
Impossible to know l ti dupstream of box inlet
(100 to 2,500 Pa)
Low pressures
location and pressure difference for each leak
Low pressures downstream of box inlet(10 to 100 Pa)
Common Leakage MetricsCommon Leakage Metrics
Leakage Rate= C (dPreference)
n
A
Leakage Flow Fraction= Qleaks
Q fAduct surface
Reference pressure:not necessarilyoperating pressure
Qreference
Leakage flow: estimated from leakage area and average pressure ORoperating pressure
no standard
ASHRAE Handbook:
and average pressure OR
measured directly
Reference flow:unsealed ducts2.5 L/(s·m2) at 250 Pa
tight ducts5 to 10 times less
Reference flow:fan flow forupstream sections
VAV box inlet flow for downstream sectionsdownstream sections
System Pressurization TestsSystem Pressurization Tests
Supply FanSupply FanCabinet
PressurizationAirflow
U DownstreamSections
UpstreamSections
System Pressurization Results50
Oth S t
41
40
45
L
Other System Branches
n=30ASHRAE Unsealed Leakage Rate (2.5)
31 30
30
35
eakage Rate Test Building
2220
1715
1815
17
22
25
11
20
25
@ 250 Pa [L/(
Test BuildingBranches(B2) n=6
Averages
MainM i
106
512 10
511 11
55
1112 11
5
79
106 6 6
5 5 5
13
413
9
5
10
15
(s·m2)]
Ductsn=6
Mainsn=6
4
5 5
3 4
53
5 5
4
20.5
0.3
0
5
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B5 -
B3 -
B3 -
B3 -
B9 -
B10
B10
B11
B11
B11
B11
B8 -
B8 -
B8 -
B4 -
B4 -
B4 -
B2 -
B2 -
B2 -
B2 -
B2 -
B2 -
B1 -
B9 -
B9 -
B4 -
B5 -
B2 -
All b
B2 b
All mVA
V Fan1VA
V Fan2VA
V1VA
V2VA
V3VA
V4VA
V5VA
V6VA
V7VA
V8VA
V9VA
V10VA
V11VA
V12VA
V1VA
V2VA
V3VA
V- VA
V1- VA
V2- D
ualDuct1
- DualD
uct2- D
ualDuct3
- DualD
uct4C
AV1
CA
V2C
AV3
VAV1
VAV2
VAV3
VAV Fan1
VAV Fan2
VAV Fan3
VAV Fan4
VAV1
VAV2 Slots
CA
VC
AV
VAV
VAV
VAV
VAV
ranchesbranchesm
ains
System Pressurization Results100%
80%
90%
Sweden (n=69)France (n=21)Belgium (n=12)US Main Ducts (n=6)
Leakage Rate f400
(L/s·m2 @ 400 Pa)
Average [Std Dev]S d 0 27 [0 13]
US Mains (n=6)
60%
70%
O
US Branch Ducts (n=36) Sweden: 0.27 [0.13] France: 2.7 [1.6] Belgium: 5.8 [6.3] US Main Ducts: 5.1 [3.0] US Branch Ducts: 17 [12]
US Branches (n=36)
40%
50%
Occurence
EUROVENT 2/2 Class D: 0.05 Class C: 0.15 Class B: 0.44
20%
30%
Class A: 1.33
ASHRAE Unsealed: 3.3
0%
10%
Class D
Class C
Class B
Class A
3*Clas
s A
9*Clas
s A
27*C
lass A More
Measuring Leakage Airflowsg gQout,i
Qleak = Qin -ΣQout,i
Qin
Qout iQout,i
Airflow Measurement TechnologyAirflow Measurement Technology
Status:Rapid response CO2 tracer gas system2developed (better than 2% accuracy)
CA, MN, & FL pilot field tests well received(pitot-static tube traverses within 4%)
Five flow hoods tested in lab & field,,more than 1000 lab tests over wide rangeof flows and grille types, found one suitable hood (3% accuracy)hood (3% accuracy)
Tracer Gas System
High Pressure CO2I j t D t il
AirflowSampler
Duct wall
Injector DetailWhip injector
Sampler
Mixing fan
Tracer-gas Airflow Measurement Analysis1200
CO2 tankCO2 analyzer
888 888
800
900
1000
1100
tion
(ppm
)
= COave mQ 2 414 415500
600
700
800
CO2 C
once
ntra
t
( )∫ −= T
updownCO
air
dtCCQ
02
ρ 300
400
0 60 120Elapsed Time (second)
Tracer Gas System - Lab Test Results5%
%)
3%
4% Straight ductT-ductL-ductur
emen
t (%
AVG Error: 0.2%RMS Error: 1%
1%
2%
Flow
Mea
su
-1%
0%
1%
Gas
-Bas
ed F
3%
-2%
-1%
of T
race
r-G
-4%
-3%
ativ
e Er
ror o
-5%500 1000 1500 2000 2500 3000 3500
Reference Nozzle Flow (cfm)
Rel
a
30%
Flow Hood Test: Good Results
20%
25%
30%ABCD
10%
15%
ood
1 (
%) E
5%
0%
5%
or O
f Flo
w H
o
-15%
-10%
-5%
Rel
ativ
e Er
ro
-25%
-20%
R
A B C D E
-30%50 100 150 200 250 300 350 400 450 500 550 600
Reference Nozzle Flow (cfm)
Flow Hood Test: Biased Results30%
20%
25%
30%ABCD
10%
15%
ood
4 (
%)
DE
5%
0%
5%
or O
f Flo
w H
o
-15%
-10%
-5%
Rel
ativ
e Er
ro
-25%
-20%
-30%50 100 150 200 250 300 350 400 450 500 550 600
Reference Nozzle Flow (cfm)
Flow Hood Test: Scattered Results30%
20%
25%
30%ABCD
10%
15%
ood
5 (%
) E
5%
0%
5%
or O
f Flo
w H
o
-15%
-10%
-5%
Rel
ativ
e Er
ro
-25%
-20%
-30%50 100 150 200 250 300 350 400 450 500 550 600
Reference Nozzle Flow (cfm)
Leakage Flow Fractions – 10 Systems40
Measured
30
35
Measured
Estimated from leakage area &duct average pressure
Branches
Before
25
30Leakage Flo
Whole SystemsSealing
15
20
ow Fraction (%
5
10
%)
AfterSealing
0
B1 -
(10,00
B2 -
(11,50
B3 - V
(6,700
B4 - V
(1,900
B5 - V
(7,000
B6 - V
(1,100
B7 - V
(1,300
B8 - C
(700
B8 - C
(1,200
B8 - C
(900
B9 - C
(400 LCA
V00 L/s)
VAV
00 L/s)
VAV
0 L/s)
VAV
0 L/s)
VAV
0 L/s)
VAV
0 L/s)
VAV
0 L/s)
CA
V1L/s)
CA
V20 L/s)
CA
V2L/s)
CA
VL/s)
System ID and Duct Inlet Flow
Measured Leakage FlowsMeasured Leakage Flows
Ten systems:Three “tight” (<5%)Seven “leaky” (10% and more)
Potentially a substantial duct leakage problemPotentially a substantial duct leakage problem in U.S. buildings
Need to train installers to use industry best practices and to test for system leakage
Measured Leakage ImpactsMeasured Leakage Impacts
LEED Platinum building in Sacramento, CATwo identical floors: intervention and controlVAV single-duct reheat systemsParallel fan-powered boxes for perimeter zonesSummer 2002 cooling season testsSummer 2002 cooling season tests
Supply leakage increased from:5% to 20% (operating conditions: 14,000 cfm)( p g , )4% to 13% (design conditions: 24,400 cfm)
35% supply fan energy increase25% net effect due to reduced box fan operation
Measured Fan Power: “5%” Leakage
Measured Fan Power: “20%” Leakage
Air Distribution System Modely
Return FanRelief1620 W
Air
ReturnAir
ReheatBoxes
22.4 C
23 5 C
11.7 C
5.79 kg/s
0 64 kg/s0.71 kg/s
5.79 kg/s
22.7 C
79% flow
Supply FanCooling CoilAir Filter
CP
Zone P1
Zone P2
Air
22.7 C
11.7 C
23.5 C
23.2 C
11.7 C
11.7 C
0 kg/s
5.79 kg/s
0.64 kg/s
0.87 kg/s
0.96 kg/s
1.11 kg/s
0 W
0 W
4500 W
7630 W
9970 W
83% flow
79% flow
79% flow
MixingBox
Ceiling
PlenumZone P3
Zone P4
SupplyAir10.9 C
19.9 C
21.9 C
23 C
11.7 C
11 7 C
5.79 kg/s
1 kg/s
0.97 kg/s1.08 kg/s
1 22 kg/s
-82800 W0 W
0 W
10270 W
11100 W
91% flow
80% flow
MinimumOA
Zone C1
DownstreamL k
24.9 C
11.7 C
19.9 C
1.04 kg/sMassFlow
Temp.
1.1 kg/s1.22 kg/s
0 W 6350 W
Coil Load
L d
14650 W71% flow
Legend
EconomizerOA
Leakage
UpstreamLeakage
0.51 kg/s
0.71 kg/s
Load
Power
19.9 C
4.75 kg/sLighting
VAV Duct Leakage Case: 10% Upstream / 10% Downstream (7 am, July 29)
Modeling Resultsg
Single-duct VAV reheat system; unpowered VAV boxesCalifornia Title 24 VSD fan modelsSupply leakage increased from 5% to 20%at design conditionsAnnual energy consumption impactsgy p p(Sacramento, Oakland, Pasadena):
Supply & return fan electricity up 40 to 50%
Chiller & cooling tower electricity up 7 to 10%
Boiler (reheat) natural gas down 3 to 10%
Total HVAC site energy up 2 to 14%
Ceiling Conduction Effects
Cool PlenumWarm Plenum Cool PlenumWarm Plenum
Fan Component Models
ƞ at 40% full-flow (660 Pa):
0.89 x 0.80 x 0.69 x 0.50 = 0.250.89 x 0.80 x 0.69 x 0.50 = 0.25
Next StepsNext Steps
Further evaluation of diagnostic tools
Flow measurement device calibration standardsFlow measurement device calibration standards
System commissioning guidelines
Identify “tight system” installation procedures(ultimately eliminate leakage testing?)V lid d l d i l iValidate new models and simulate impactsEvaluate combined retrofit opportunities
fReduce system leaks/flows/pressuresImprove component efficiencies and sizing
