Heat Pump Water Heaters for Single and Multifamily Residential Buildings

October 10, 2014

Learning Objectives 

Understand important concepts governing heat pump performance

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Present range of available heat pump water heater technologies currently available

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Learn about critical code and design issues to ensure good heat pump water heater performance in residential applications

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Review case studies and lessons learned from actual installations

Regional Residential Baseline

Superinsulation and DHP

Low Flow Fixtures

Energy Star Appliances

LED

Occupant Conservation

Refrigeration Cycle

Coefficient of Performance

1 Unit of Electricity + 3 Units of transferred heat = COP of 4

Source vs. Load Source  Indoors or Outdoors?  Air or Water? Load  Domestic Hot Water  Hydronic Space Heating?

Source vs. Load Temperatures

Refrigerant 410a Minimum Source Temperature -20F Maximum Load Temperature 115F

134a 744 (CO2) 40F

-10F

150F

150F

Storage vs. Heating Capacity

Back-up or Finishing Fuel

Double Walled Heat Exchanger

http://encyclopedia.che.engin.umich.edu/Pages/HeatTransfer/HeatExchangers/HeatExchangers.html (Copyright of Alfa Laval, Richmond, VA)

Legionella

Hot Water Recirculation

Hot Water Recirculation

Packaged Residential Equipment

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Rated COP ~2 Actual COP ~1.8

Manufacturer Comparison

Refrigerant Operating Range Features # Showers 1st hour rating Cost Problems

Voltex

Voltex

Rheem

GeoSpring

AirGen

(60, 80)

(50)

(50)

(50)

(66, 80)

R134a

R134a

R410a

R134a

R410a

45°F min

42°F min

42°F min

45°F to 120°F

32°F min Duct-able

Ducting Kit 3,4

2.5

2.5

2.5

3,4

67.8, 87

63.5

55.8

66

67.9, 79

$1495

~$1300

~$1200

$1109

$2268

Cannot efficiently handle large or frequent draws

R410a can have trouble heating to setpoints above 135

Cannot efficiently handle large or frequent draws

See discussion

None noted

AirGenerate ATI66 

Recently de-listed from Northern Climate Qualified products list due to reliability problems. 

Units exhibited signs of leaking refrigerant 

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No refrigerant = no heat pump cycle

AirGenerate is addressing the problems

Biggest HPWH Energy Problem 

“Hybrid” design 

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Packaged HPWHs have a resistance element and heat pump When resistance element runs, there is no energy savings over a standard tank

Solution  

Change control strategy to heat pump only Get a unit with a big tank, 60 gallons or greater

Northern Climate Specification Designates equipment which will perform in colder climates:

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Climates with 4,000 heating degree days + and average ambient temperatures below 60 degrees Fahrenheit. Roughly locations in North America with latitudes above 40 degrees. In these climates, use the Northern Spec Equipment. Found at the link: http://neea.org/northernclimatespec

HPWHs: Ducting?

Where installation location impacts performance of heat pump

Small Closet Installation

Where installation location impacts comfort in a conditioned space

Conditioned Basement Installation

HPWHs: Space Heat Interactions 

Integrated HPWHs will scavenge heat from the house 

You save energy on water heating but lose some (not all) to added space heating

HPWHs: Exhaust Venting is not a Panacea 

Added infiltration load can cool house in winter requiring more space heat

HPWHs: Solutions/Design Options 

Garage  

No space heating interaction Air temperatures are cooler so pick the best HPWH performers 

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Unconditioned Basement  

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Rheem, AO Smith (large tanks), AirGenerate

Temperatures mild compared to garage Small space heating interaction

Inside  

If using a heat pump for space heating, this is a great option Tiny closet 

Consider ducting to exterior to guarantee a supply of warm air to the HPWH

Multifamily - Preheat • Cheap method to shave off load • Integrates well if there is waste heat available • Requires Back-up

Sanden CO2 Heat Pump Sanden (40) COP

3.0

Refrigerant

R744 (CO2)

Water Temps

149° F

Operating Range

Down to 5° F

Features

GWP of 1

# Showers

4

1st hour rating

58 gallons

Cost

+$3000

Problems

UL

NEEA NextStep Homes

R410a –Altherma    

Operate down to sub-zero ambient temp. Produce up to about 115F water Annual COP ~2-3 Retrofit with existing central electric

Small Multifamily

VRF – Refrigerant to Water  

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Mitsubishi and LG Operate down to subzero ambient temp. Produce up to about 115F water Annual COP ~2? Can integrate with VRF space heat systems

Puyallup Phase 2 VRF Heat Plant

Reverse Cycle Chiller (RCC) R134a  Operate down to ~40F airsource  Produce water up to 130-160F  Single Pass Design  Annual COP ~2.6 for garage 

RCC Schematic

Sunset Electric, Stackhouse, Stream

Geothermal: Water-to-Water

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COP ~3

Geothermal: Phase 1 Puyallup

Sewage Heat Pump • Potential for very high COP (5-6) • Sewage Handling Issues • Well-matched Source and Load

Questions? [email protected]