Heat Pump Water Heaters:
Interior, Ducted Installations
Presentation to the
Regional Technical Forum
December 13, 2011
Ben Larson, Ecotope
ben@ecotope.com
1
Background
• In October 2011, Provisional UES approved for
heat pump water heater (HPWH) for:
– Northern Climate Specification Tier 1
• Buffer space installs
• Interior (non-ducted installs)
– Northern Climate Spec Tier 2
• Buffer space installs
• Northern Climate Spec Tier 2 Interior Installations
require exhaust ducting
– Left as “TBD” in October
– Today’s presentation covers ongoing analysis
2
Overview
•
•
•
•
Equipment airflows and installation
Analysis method
Analysis output and findings
Discussion and continued research
3
Equipment Exhaust Airflows
– 4” duct, 10 feet long with 3
elbows at 160 cfm creates
0.72” static pressure
120
350
100
CFM
80
250
200
60
150
40
100
20
50
0
Fan Power (W)
300
Power(W)
Poly. (CFM)
Linear
(Power(W))
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Static Pressure (in. W.G.)
Voltex Fan Characterisitcs
500
450
400
350
300
250
200
150
100
50
0
104
102
100
98
96
94
92
90
Fan Power (W)
• Field airflows will depend on
specifics of each installation
400
Airflow (CFM)
– Static pressure variation
created with damper at duct
outlet
– Different models have
different fans and flow
characteristics
ATI66 Fan Characteristics
Airflow (CFM)
• Flow range of interest:
350cfm to 150cfm
• Flow measurements in lab:
Airflow
(CFM)
Fan Power
(W)
88
0.00
0.10
0.20
Static Pressure (in. W.G.)
0.30
4
Analysis Inputs
• Used the same assumptions as with earlier
HPWH analysis
– 45 gallons per day of hot water
• water temperature rise: 72.5F
• results in a little less than 4 hrs per day of runtime for indoor
temperatures ranging from ~64F – 78F
– house characteristics the same
• tightness: 7ach50
• ducts: sealed
• 4 HVAC system types
– baseline tank EF: 0.92 (50 gallon size)
5
Analysis Updates
• Using updated version of SEEM which allows
direct infiltration modeling in combination with
exhaust airflows
• HPWH exhaust air ducted outside
• Water heater runs based on draw schedule
• Water heater COP varies as indoor temperature
changes
– Ex: higher inside T in summertime for houses without
cooling gives better performance than wintertime
situations
6
HPWH COP versus Ambient Temperature
Tier 1, <= 55 gal
Tier 1 > 55 gal
Tier 2 (both sizes)
3.00
2.50
COP
2.00
1.50
Interior installation
temperature range.
1.00
0.50
0.00
27
32
37
42
47
52
57
62
67
72
77
82
Ambient Temperature (deg F)
7
DHW Energy Use Only –
No HVAC System Interactions
• Baseline DHW Energy Use: ~3100 kWh/yr
• Measure DHW Energy Use: 1130-1280 kWh/yr
– varies because indoor temperature varies with
season and climate
• DHW Energy Only Savings: 1820-1970 kWh/yr
– Houses without cooling have higher summer
temperatures and therefore better water heater
performance so more savings
• HPWH Interior Install Annual COP: 2.3-2.5
8
Overall Savings Estimates
• Impact on house heating + cooling system
depends on climate, exhaust airflow, and HVAC
system type
• Combining DHW energy savings with heating +
cooling impact produces the overall energy
savings estimate
• 5 scenarios in 5 climates considered on next slide:
– Interior non-ducted (0 cfm flow to outside)
– 4 levels of exhaust ducting to outside
• 150, 200, 250, and 300 cfm
9
Heating System Interaction
Zonal Resistance Heat (kWh/yr)
Electric Resistance Furnace (kWh/yr)
CFM
PDX
SEA
SPO
BOI
KAL
CFM
PDX
SEA
SPO
BOI
KAL
300
-1143
-1210
-1529
-1263
-1764
300
-1296
-1374
-1758
-1450
-2036
250
-913
-967
-1234
-1014
-1431
250
-1037
-1099
-1413
-1162
-1641
200
-707
-747
-970
-793
-1130
200
-801
-847
-1104
-903
-1288
150
-530
-558
-730
-597
-853
150
-597
-630
-827
-678
-969
0
-1334
-1455
-1491
-1316
-1597
0
-1511
-1647
-1702
-1501
-1830
Heat Pump HSPF 7.9 (kWh/yr)
Gas Furnace AFUE 90 (therms/yr)
CFM
PDX
SEA
SPO
BOI
KAL
CFM
PDX
SEA
SPO
BOI
KAL
300
-619
-660
-1277
-962
-1700
300
-59
-64
-84
-70
-98
250
-487
-527
-993
-749
-1325
250
-47
-50
-67
-55
-78
200
-369
-400
-754
-570
-1018
200
-36
-39
-52
-43
-61
150
-271
-292
-552
-421
-750
150
-26
-28
-38
-32
-46
0
-558
-598
-833
-690
-997
0
-59
-65
-65
-58
-69
•
•
CFM is airflow ducted to outside (“0” corresponds to no ducting)
Negative values are a heating system debit
10
Cooling System Interaction
• None for houses without cooling system (Zonal
Resistance and Electric Furnace)
• Cooling savings for ducted installations nearly negligible
but not so for nonducted ones
Heat Pump SEER 13 (kWh/yr)
•
•
Gas Furance: A/C SEER 13 (kWh/yr)
CFM
PDX
SEA
SPO
BOI
KAL
CFM
PDX
SEA
SPO
BOI
KAL
300
25
27
16
-1
19
300
24
27
16
-1
19
250
22
24
15
2
18
250
22
24
15
2
18
200
20
20
14
5
17
200
20
20
14
5
14
150
17
17
13
7
13
150
17
17
13
7
13
0
166
116
148
197
125
0
165
115
147
195
123
CFM is airflow ducted to outside (“0” corresponds to no ducting)
Positive values are a cooling system benefit
11
Analysis Outputs: Savings Estimates
DHW Savings Combined with Heat+Cool Interaction
Electric Resistance Furnace
2000
1750
1500
1250
PDX
1000
SEA
750
SPO
500
BOI
250
KAL
0
0
50 100 150 200 250 300
Airflow Ducted to Outside (CFM)
350
PDX
SEA
SPO
BOI
KAL
0
Estimated Savings (kWh/yr)
Heat Pump HSPF 7.9 / SEER 13
50 100 150 200 250 300
Airflow Ducted to Outside (CFM)
350
Gas Furnace 90 AFUE w/ SEER 13 Cooling
2000
1750
1500
1250
1000
750
500
250
0
2000
1750
1500
1250
PDX
1000
SEA
750
SPO
500
BOI
250
KAL
0
0
50 100 150 200 250 300
Airflow Ducted to Outside (CFM)
350
0
-20
-40
-60
-80
-100
-120
0
50 100 150 200 250 300
Airflow Ducted to Outside (CFM)
350
Therm Interaction (therms/yr)
Estimated Savings (kWh/yr)
Zonal Resistance Heat
2000
1750
1500
1250
1000
750
500
250
0
PDX
SEA
SPO
BOI
KAL
PDX (therms)
SEA (therms)
SPO (therms)
BOI (therms)
12
KAL (therms)
Analysis Caveats
• Caution: as yet, analysis does not include performance
variation of HPWH with airflow
– Performance at lower airflows could be expected to
decrease but what is the critical airflow where
performance drops significantly?
• Space heating heat pump sizing
– Analysis used constant size for both measure and base
– Ducted HPWHs sometimes increased house load enough
to trigger auxiliary resistance heat which shows as a
nonlinear response in the heating interaction
• Especially relevant for 250-300cfm flows and coldest climates
13
Measured Airflow Variation Effects
•
•
NEEA lab testing of ATI66 at 40F ambient found a decrease in COP of 10% for an
airflow decrease from 338 to 177cfm
BPA HPWH lab evaluation observed Voltex compressor performance for 3 flow
scenarios at 67F ambient temperature
– Full flow:
475 cfm
– ⅓ filter area blocked: 372 cfm
– ⅔ filter area blocked: 284 cfm
 Small changes in performance
14
Analysis Discussion
• Space heating impact (and therefore overall
savings) is highly dependent on amount of
exhaust airflow
– Also, climate dependence due to increased
infiltration rate: more outside air at lower
temperatures increases heating load
• Is there a optimized airflow which might
reduce HPWH performance but at the same
time provide a minimal space heating impact?
15
Continued Research – Next Steps
• Field Measurements:
– NEEA project with 10-15 ducted, indoor installations will
measure airflow as installed
– Project will also provide incremental install cost estimates
• Lab Measurements:
– Plans to measure AirGenerate compressor performance at
200cfm and 150cfm at 67F ambient air.
• Installation Specification:
– Is it desirable to write a spec to limit airflow upon installation?
• Analysis for houses with Ductless Heat Pumps
– Where is the HPWH? Is it heated by the DHP or the resistance
heating system?
16