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Robbin Garber-Slaght, PE Cold Climate Housing Research Center Fairbanks, Alaska [email protected]

Conference Paper Session-Ground Source Heat Pump System Performance Case Studies in Different Climates Around the World

Ground Source Heat Pump Efficiency in Cold Climates

2014 ASHRAE Annual Conference Seattle ©2014 ASHRAE

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Session Learning Objectives Provide an overview of the performance of GSHPs in cold climates Describe how finite element modeling can be used to aid in the design of a GSHP in a cold climate Understand renewable energy possibilities in buildings Describe new technologies in heat pumps Feasibility air-to-air and geothermal heat pump systems in residential buildings with different insulation level located in different climates • Significance of the insulation level of the building and the climate to the SCOP (HSPF) of heat pump systems • Explain the barrier of adopting ground source heat pumps (GSHPs) with respect to incentives and rebates in each scenario • Compare ground source heat pumps (GSHPs) to conventional natural gas furnaces and air conditioners (NGF & A/C), and air source heat pumps (ASHP) in terms of energy consumption and economics ASHRAE is a Registered Provider with The American Institute of Architects Continuing Education 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. 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. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

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Acknowledgements Co-authors: Dr. Ronald Daanen, Geohydrologist for the Department of Natural Resources, Division of Geological and Geophysical Surveys for the State of Alaska and Andy Roe of Alaska Geothermal, LLC

This project is jointly funded by the Alaska Energy Authority and the Denali Commission through a grant from the Emerging Energy Technology Fund and the Alaska Housing Finance Corporation

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Fairbanks, Alaska Fairbanks is at 64.8°N, in the cold dry Interior of Alaska On December 21 the sun is up 3 hours and 42 minutes On June 21 the sun is up 21 hours and 46 minutes 13,517°F HDD (7,509°C) 99.6% design temperature is -43.5°F (-41.9°C) 65 inches (165 cm) snow fall annually

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Fairbanks, Alaska

Did I mention permafrost?

• Soil at or below freezing for 2 or more years • Fairbanks has discontinuous permafrost, most of it is warm 30 to 32°F (-1 to 0°C) • It is melting in cleared areas and under heated structures • The permafrost under the research center has been melting for 60 years; since the vegetation was first cleared • Test bore holes in 2011 did not find permafrost in the first 30 ft. (9.4m) where it had been at 24 ft. (7.3 m) in 2006 • Frozen bedrock (20°F, -6.7°C) starts at 64 ft. (19.5 m) under the research center Does heat extraction in the winter create more permafrost? Or can the ground recover enough heat in the summer sun?

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Extracting heat from the soil in Alaska • Has anyone really done it successfully? • Sure – it’s a way to preserve permafrost under a structure • A GSHP ground cooling system has been keeping a foundation stable in Fairbanks since 1993 (McFadden, 2007) Not this foundation

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GSHP Studies in Cold Climates

that analyze heat production and efficiency • GSHP work in cold climates in the short term (Mueller and Zarling, 1996) • COPs during the heating season can be effective in the first 2 years, 2 to 3.89 (Meyer et. al, 2011) • Freezing the soil around a ground loop adds the energy of phase change (Eslami-nejad and Bernier, 2012)

But what happens 4, 5, 10 years down the road?

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GSHP at the Testing Facility Meyer et. al. (2011) found that GSHP can be cost effective if COPs are greater than 2.5 and heating fuel is sufficiently more expensive than electricity We began a study of a GSHP in Fairbanks in November 2013

• A ten year study in a severe cold climate • Evaluating the ground thermal regime and how it affects the efficiency of the GSHP • Studying ways to mitigate thermal degradation in the soil

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GSHP at the Testing Facility

• Heating a 5,000 ft2 (464 m2) office space with in-floor hydronic delivery • The design heat load is about 60,000 BTU/hr (17.6 kW) • The in-ground heat exchanger is above thawing permafrost • The initial soil temperature at 9 ft. (2.7 m), the depth of the in-ground heat exchanger, was approximately 34°F (1.1°C)

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GSHP at the Testing Facility 3 ft 6 ft (1m)(1.8m)

Dark Gravel

Sand

Ground Loops NW corner of property

Grass

100 ft (30.5 m)

Plowed driveway area

working fluid is water

to in-floor heat

Buffer Tank

working fluid is 20% methanol

Water-to-Water Heat Pump

not to scale Key Circulator Pump

Datalogger

Ball Valve

Heat Exchanger

Compressor Flow Meter Temperature Sensor

Mechanical Room

Current Sensor Temperature String

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Initial Simulations

2-D model of temperature at 10.5 ft.. (3.2 m) under 1 coil in the ground heat exchanger

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Initial Simulations

3-D model of temperature 4 years after the heat pump starts The black isotherm indicates permafrost formation under the ground heat exchanger

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First Heating Season Data • The heat pump came online in November 2013 • It’s seasonal COP for the first year was 3.7 • The incoming fluid temperature dropped from 34°F (1.1°C) to 31°F (-0.5°C) over the heating season • The soil temperature at 9 ft. (2.7 m) was 2.7°F (0.6°C) colder then the temperature outside of the heat exchanger field 4

Monthly COP

3.9 3.8 3.7

A warm spring brought the temperature required for the heat delivery water down, improving efficiency

3.6 3.5 3.4

December-2013

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January-2014

February-2014

March-2014

April-2014

May-2014

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First Heating Season Data Center of the Ground Loop

Undisturbed West Edge

0

-0.5

0 -1.6

-0.5

-3.3

-1

-1

-1.5

-1.5

-2

-2

-6.6

-2.5

-2.5

-8.2

Depth (m)

-4.9

Depth (ft.)

0

level of in-ground heat exchanger -3

-3

-3.5

-3.5

-4

-4

-9.8 -11.5 -13.1

Temperature (F) 26.6 -4.5 -3

30.2 -2

-1

33.2 0

37.4

3 2 1 Temperature (C) October 2013

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41 4

5

44.6 6

December 2013

7

26.6 -4.5 -3

Temperature (F)

30.2 -2

Feburary 2014

-1

33.2 0

37.4

2 3 1 Temperature (C)

April 2014

May 2014

41 4

5

44.6 6

7

-17.8

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Conclusions • This is just the first year of a 10 year project • We will keep studying the system • If the heat pump starts to fail due to low temperature in the ground we could use the heat pump for summer cooling • Data will be used to refine the model • Data will be verified and errors corrected this summer

©2014 ASHRAE

© 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission.

References

ASHRAE. 2013. ASHRAE Handbook-Fundamentals. Atlanta: American Society of Heating Refrigeration and Air Conditioning Engineers, Inc. Eslami-nejad, P. and M. Bernier. 2012. Freezing of geothermal borehole surrounding: a numerical and experimental assessment with applications. Applied Energy 98: 333-345. McFadden, T. 2007. Supplemental research report on the foundation stabilization using a heat pump cooling system at 728 Constitution Drive Fairbanks, Alaska. Permafrost Technology Foundation. Fairbanks, AK. Meyer, J., D. Pride, J. O’Toole, C. Craven, and V. Spencer. 2011. Ground source heat pumps in cold climates. http://cchrc.org/docs/reports/Ground-Source-Heat-Pumps-in-Cold-Climates.pdf. Mueller, G. and J. Zarling. 1996. Ground source heat pump monitoring: final report. Matanuska Electric Association. Alaska. Rettig, M. and N. Wiltse. 2012. Cold challenges. High Performance Buildings: 18-29.

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© 2014 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission.

Questions? Robbin Garber-Slaght [email protected]

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