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Paul Glanville, P.E.
Gas Technology Institute
Field Trial of Residential Ammonia-Water
Absorption Heat Pump Water Heaters
@gastechnology
Motivation for a Gas HPWH: Despite low natural gas prices, Gas HPWH has potential to leapfrog
» Energy/Operating Cost Savings, Fewer Infrastructure Needs, Recent Regulatory Drivers
Condensing Storage: UEF approx. 0.74 – 0.82, ~
20% therm savings with 4-5X
equipment cost and retrofit
installation costs of $1000 or more.
Technology Leapfrog through Direct Retrofit
Baseline:~90% of Gas WHs sold.
At risk with advancing
efficiency, combustion
safety requirements
Tankless and Hybrids: UEF approx. 0.82 – 0.95,
~ 33% therm savings with 2-3X
equipment cost and similar infrastructure
req’s as condensing storage.
Gas HPWH:UEF approx. 1.3, > 50%
therm savings with
comparable installed cost
to tankless.
Mid-Effiency:UEF approx. 0.67 – 0.72,
50-100% greater equipment
costs, simple paybacks
beyond life of product.
HPWH = Heat Pump Water Heater; UEF = Uniform Energy Factor
Describing the Gas HPWH - Specification
GHPWH Units/Notes
Technology Developer Stone Mountain Technologies OEM/GTI support
Heat Pump Output 2.9 kW
Firing Rate 1.8 kW
Efficiency 1.3 UEF Projected
Tank Size 230/300 Liters
Backup Heating Experimenting with backup currently
Emissions (projected) 10 ng NOx/JBased upon GTI laboratory
testing
Commercial Introduction ~2 years Projected
InstallationIndoors or semi-conditioned
space (garage)
Sealed system has a 0.6 kg
NH3 Charge
Combustion Venting ½” – 1” PVC
Gas Piping ½”
Estimated Consumer Cost <$1,800
GHPWH System Specifications: Direct-fired NH3-H2O single-effect absorption
cycle integrated with storage tank and heat recovery. Intended as fully retrofittable
with most common gas storage water heating, without infrastructure upgrade.
Describing the Gas HPWH – How It Works
Simplified Single-Effect Absorption Cycle
Sealed NH3/H2O absorption cycle delivers heat to
the storage tank via two heat exchangers:
1) A closed, pumped hydronic loop extracting heat
from the Absorber and Condenser to a
submerged hydronic coil.
2) A flue gas coil, extracting remaining waste heat
leaving the desorber flue outlet
Describing the Gas HPWH – Challenge in Scaling Down
Custom combustion
system designed to meet
the requirements of the
Gas HPWH using a very
compact premix burner,
fuel/air mixer, and gas
train. Small burner
requires small gas piping,
venting, easing
installation.
For material compatibility and for the
very low charge system, 0.6 kg NH3,
heat exchangers within the sealed
system were primarily custom design.
Several iterations were evaluated by
SMTI during breadboard testing and
within early prototypes prior to field
evaluations.
A HPWH requires a wide operating
range, firing in a cold garage with a hot
storage tank for example, require a
robust expansion valve. Off-the-shelf
options, oversized for this application,
had challenges during field testing and
were the subject of review and redesign.
Field Site Characteristics
Existing WH Seattle Spokane Portland Boise
GHPWH Location Conditioned Basement Garage Garage Garage
Occupants
3-4, Two adults with one
teenager permanently
and one college-aged
child periodically
4, Two adults and
two children under
3 years old
5, Two adults
and three
children under 6
years old
5, Two adults
and three
children
Tank Size (Gal.) 40 34 50 40
Firing Rate (Btu/hr) 36,000 100,000 40,000 40,000
Age 14+ Years 18 Years 0 years 13 years
Rated / Avg. Delivered
EF/TE0.59 / 0.56 96% / 0.91 0.62 / 0.47 0.59 / 0.45
Average Inlet T (°F) 53.3 61.2 54.8 58.7
Average Outlet T (°F) 123.8 122.8 115.2 138.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
2 3 4 5 6
Avera
ge D
aily D
raw
Vo
lum
e (
Gal.)
No. of Occupants
GHPWH Study
EHPWH Validation Study
Compared to typical Pac. NW homes,
GHPWH sites have higher than
average occupancy (> 2.5) and hot
water usage.
EHPWH Validation: Heat Pump Water Heater Model Validation Study, Prepared by Ecotope for NEEA, Report #E15-306 (2015)
F
T
T
F
AmbientT & RH
P
T
T
T
T
T
Power meter
Evap
ora
tor
T
T
Cold water in
Hot water out
Natural GasGHPWH Detail
Mechanical
Heat Pump Performance
> COPHP at lab test targets (1.4-
1.8), near theoretical limits.
> Generally, low COPs from EEV
> With reliable heat recovery,
steady power consumption
(~150W), and minimal backup
heating COPSYS/COPHP has
correlation coeff. of 0.83.
> For all cycles:
• 75% COPHP > 1.4
• 45% COPHP > 1.6
• 68% COPSYS > 1.3
• 42% COPSYS > 1.4
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
Perc
en
tag
e o
f C
ycle
sHeat Pump COP Bins
Portland
Boise
Seattle
Spokane
Rest of Heat Pump
QNG Total
QEvap
QFG Des
TankQHP QFG Out
QHW
Desorber
QHP Des
GHPWH
1
1.25
1.5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
70 75 80 85 90 95 100 105 110 115 120 125
Heat
Pu
mp
CO
P a
nd
Ou
tpu
t (k
W)
Hydronic Return Temperature (F)
COP Output
Heat Pump Performance
COP less affected by ambient
> Known from prior lab testing, GHPWH efficiency is
affected more by storage tank temperature than ambient
air.
• Over one cycle, COP and heat pump output drop as
tank warms
• Over range of ambient air temperatures observed,
COP nearly flat for GHPWHs
Evaporator cooling effect is small
> Function of cycle COP, higher efficiency – greater cooling
effect (same as EHPWHs).
> Observed range from 0.7-1.2 kW
Measured Energy Savings
0.0
0.5
1.0
1.5
2.0
0 5 10 15 20 25 30D
elivere
d E
ffic
ien
cy F
acto
r
Output (kWh/day)
PortlandSeattleSpokaneSpokane wo Feb.Boise
OutputLow Usage
(Seattle)
High Usage
(Portland)
Daily DHW Draw (L) 155 364
Baseline DEF242 L/day 0.59 0.48
318 L/day 0.60 0.50
GHPWH DEF242 L/day 1.21 1.15
318 L/day 1.25 1.18
> Charting daily input/output creates linear
“input/output” relationship, for gas input only.
> In comparison to baseline, all sites showed
greater than 50% savings except for Spokane
with higher eff. baseline.
> Sites had large range of daily hot water usage,
average from 155 – 364 L/day.
𝐼𝑛𝑝𝑢𝑡 = 𝑚 ∙ 𝑂𝑢𝑡𝑝𝑢𝑡 + 𝑏;
𝑂𝑢𝑡𝑝𝑢𝑡
𝐼𝑛𝑝𝑢𝑡= 𝐷𝐸𝐹 = 𝑚 +
𝑏
𝑂𝑢𝑡𝑝𝑢𝑡
−1
Projected GHPWH Economics
$(1,000.00)
$(500.00)
$-
$500.00
$1,000.00
$1,500.00
$2,000.00
50 150 250 350 450 550 650 750
GH
PW
H S
avin
gs f
or
10 Y
ear
Co
st
of
Ow
ners
hip
Average Hot Water Draw (L/Day)
Storage Non-condensing
Storage Condensing
Tankless Non-condensing
Tankless Condensing
For DOE “High Usage” category, GHPWHs have projected
1.2 < DEF < 1.3, > 50% savings versus baseline (except
Spokane), can be competitive for moderate/high usage
homes despite low NG prices. With new min. eff. guidelines
GHPWH leapfrogs condensing storage.
Utility Costs: Assumes OR averages of 11.72 ¢/kWh, $1.11/therm with 1.9% and 1.2% utility escalation rates per EIA 2015 Annual Energy Outlook through 2027.
Conventional Gas Water Heater Data from: Kosar, D. et al. “Residential Water Heating Program - Facilitating the Market Transformation to Higher Efficiency Gas-Fired Water Heating - Final Project Report”. CEC Contract CEC-500-2013-060. (2013) Link:
http://www.energy.ca.gov/publications/displayOneReport.php?pubNum=CEC-500-2013-060
$2,000.00
$3,000.00
$4,000.00
$5,000.00
$6,000.00
$7,000.00
$8,000.00
$9,000.00
$10,000.00
50 150 250 350 450 550 650 750
10 Y
ear
Co
st
of
Ow
ners
hip
Average Hot Water Draw (L/Day)
GHPWH - Conditioned
GHPWH - Semi/Unconditioned
Baseline GWH - High DEF
Baseline GWH - Low DEF
GHPWH - Next Steps
> Continued laboratory-based reliability testing
and field trials of “next generation” design in
different climate zones and housing types.
> Improvement of components based on
lab/field findings.
> Evaluation of technology by interested
OEMs.
> Parallel program evaluating larger gas
absorption heat pump for combination
space/water heating applications and
commercial water heating.
Published Materials:
• Garrabrant, M., Stout R., Glanville, P., Fitzgerald, J., and Keinath, C., (2013), Development and
Validation of a Gas-Fired Residential Heat Pump Water Heater - Final Report, Report
DOE/EE0003985-1, prepared under contract EE0003985, link:
http://www.osti.gov/scitech/biblio/1060285-development-validation-gas-fired-residential-heat-
pump-water-heater-final-report
• Garrabrant, M., Stout, R., Glanville, P., Keinath, C., and Garimella, S. (2013), Development of
Ammonia-Water Absorption Heat Pump Water Heater for Residential and Commercial
Applications, Proceedings of the 7th Int’l Conference on Energy Sustainability, Minneapolis, MN.
• Garrabrant, M., Stout, R., Glanville, P., and Fitzgerald, J. (2014), Residential Gas Absorption Heat
Pump Water Heater Prototype Performance Results, Proceedings of the Int’l Sorption Heat Pump
Conference, Washington, DC.
• Glanville, P., Vadnal, H., and Garrabrant, M. (2016), Field testing of a prototype residential gas-
fired heat pump water heater, Proceedings of the 2016 ASHRAE Winter Conference, Orlando, FL.
Further information:
http://www.stonemountaintechnologies.com/