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

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

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

Geothermal Power Production of electricity Requires unique geology

Vapor Compression Refrigeration Cycle Cooling Mode

Vapor Compression Refrigeration Cycle Heating Mode

Vapor Compression Refrigeration Cycle Idealized Carnot Cycle

Vapor Compression Refrigeration Cycle Actual Refrigeration Cycle Lines of constant pressure

Vapor Compression Refrigeration Cycle

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

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

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

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

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

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

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

Geothermal Field Design

Pressure testing Reverse return Direct Return Reverse Return

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

Residential Applications Direct replacement for conventional systems

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

Commercial Applications Distributed heat pump system

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

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

Commercial Applications Central geothermal systems

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

Efficiency Gains

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

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

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

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

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

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: $ per ton

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

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

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 Central Geothermal Systems Design and Control. Trane. Geothermal Heat Pumps. Department of Energy. DOE/ GO September Geothermal Heat Pump Design Manual. McQuay Air Conditioning pGuide/AG_31-008_Geothermal_021607b.pdf pGuide/AG_31-008_Geothermal_021607b.pdf US Department of Energy Efficiency and Renewable Energy.