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Geothermal Heat Pumps in residential and commercial HVAC systems Dan Winters 4/18/11.

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Presentation on theme: "Geothermal Heat Pumps in residential and commercial HVAC systems Dan Winters 4/18/11."— Presentation transcript:

1 Geothermal Heat Pumps in residential and commercial HVAC systems Dan Winters 4/18/11

2 Outline Review of refrigeration principles Geothermal field design Geothermal HVAC system design Energy efficiency Economics Question and answer

3 What is Geothermal Heating and Cooling? Geothermal HVAC systems incorporate the earth as a heat source or heat sink to provide heating and air conditioning to a desired space Geothermal systems take advantage of the relatively constant temperatures year around in the earth’s crust

4 Geothermal Power Production of electricity Requires unique geology

5 Vapor Compression Refrigeration Cycle Cooling Mode

6 Vapor Compression Refrigeration Cycle Heating Mode

7 Vapor Compression Refrigeration Cycle Idealized Carnot Cycle

8 Vapor Compression Refrigeration Cycle Actual Refrigeration Cycle Lines of constant pressure

9 Vapor Compression Refrigeration Cycle

10 Refrigerants Chlorofluorocarbons (CFCs): R-12 Hydrochlorofluorocarbons (HCFCs): R-22 Hydrofluorocarbons (HFCs): R134a, R410a

11 Geothermal Heat Pumps Employ refrigeration cycle and another fluid as a heat transfer medium to exchange heat between the system and the earth Not a new technology, can be a direct replacement for existing systems

12 Complete Geothermal HVAC System Required components o Heat Pump o Geothermal Exchange Field o Secondary Energy Distribution System Video

13 Field Type - Vertical Benefits: o Most consistent temperatures o Compact footprint Restrictions: o Most complex installation o Restricted by local geology o Expensive to fix

14 Field Type - Horizontal Benefits: o Take advantage of high water table Restrictions: o Large area o More variable temperature

15 Field Type – Open Loop Benefits: o Useful in settings with continuous water use Restrictions: o Water use restrictions o Often not allowed to return water to aquifer

16 Field Type - Submerged Benefits: o Takes advantage of evaporative cooling Restrictions: o Limited by body of water location o Limited use in cold climates

17 Geothermal Field Design


19 Pressure testing Reverse return Direct Return Reverse Return

20 Geothermal Field Design Grout: Bentonite Clay o Seals bore hole o Increases heat transfer Antifreeze o Required in cold climates

21 Residential Applications Direct replacement for conventional systems

22 Commercial Applications Distributed heat pump system Required Components o Geothermal heat pumps o Dedicated outdoor air unit o Building exhaust system

23 Commercial Applications Distributed heat pump system

24 Commercial Applications Distributed heat pump system Advantages: Modular and expandable Simple design Drawbacks: Need for separate outdoor air system Noise Maintenance

25 Commercial Applications Central geothermal systems Required components: o Central chiller plant o Variable air volume distribution system

26 Commercial Applications Central geothermal systems

27 Commercial Applications Central geothermal systems Advantages: Centralized Maintenance Ability for heat recovery Increased efficiency Ventilation air through VAV system Drawbacks: Equipment failure affects whole building Redundant equipment Skilled Maintenance

28 Efficiency Gains

29 EER: Energy efficiency ratio [btu/hr/W] o btu capacity/running wattage SEER: Seasonal energy efficiency ratio [btu/hr/W] o annual btu output/annual watt hours COP: Coefficient of performance [-] o EER = COP*3.41 Energy Star: o Air source: EER >12 o Geothermal: EER >14

30 Efficiency Gains Residential: Air source heat pump: up to 13.7 EER Geothermal heat pump: up to 27.0 EER

31 Efficiency Gains Commercial Trane Central Geothermal System 20-30% reduction in total HVAC building energy use

32 Efficiency Gains Residential: 25-50% reduction in energy consumption Commercial: 10-25% reduction in energy consumption

33 Equipment Costs Residential: geothermal only slightly more expensive Commercial: utilize conventional water cooled refrigeration equipment

34 Drilling Costs All of cost premium due to the geothermal exchange field Costs vary greatly o Local geology o Local contractor expertise Residential: $1,250-1,500 premium per ton Commercial: $900-1300 per ton

35 Tax Credits and Incentives Federal tax credit (expires 2016) Residential 30% of system cost Commercial 10% of system cost o Must be energy star equipment o Includes installation costs States offer incentives as well

36 Savings and Payback Simple Payback: o Retro-fit: 9-12 years o New construction: 5-10 years


38 Sources Geothermal Heat Pumps Deliver Big Savings for Federal Facilities. US Department of Energy Efficiency and Renewable Energy. Cost Containment for Ground-Source Heat Pumps. Steve Kavanaugh. University of Alabama. December 1995. Central Geothermal Systems Design and Control. Trane. Geothermal Heat Pumps. Department of Energy. DOE/ GO- 10098-652. September 1998. Geothermal Heat Pump Design Manual. McQuay Air Conditioning. 2002. pGuide/AG_31-008_Geothermal_021607b.pdf pGuide/AG_31-008_Geothermal_021607b.pdf US Department of Energy Efficiency and Renewable Energy.

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