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:

Paul.glanville@gastechnology.org

http://www.stonemountaintechnologies.com/