August 22, 2014

Ground Source Heat

Section diagram of the Washington Square Park House.

OVERVIEW
Ground source heat systems, sometimes refered to as geothermal exchange systems, use heat pumps to capture the stable temperatures of the earth in order to pre-heat and pre-cool a building, reducing the strain on conventional comfort systems. Notably, this is a different strategy than geothermal power, which is a direct energy source typically found in areas of the world near tectonic plate boundaries.

BENEFITS
+ Highly efficient
+ Cost-effective and durable relative to other heating and cooling systems
+ Can reduce heating & cooling costs up to 75% compared to conventional systems
+ Low maintenance
+ Low or zero emissions
+ Quiet operation

CHALLENGES AND OPPORTUNITIES
+ Not practical for all sites
+ Open systems do present risks due to unknown geological conditions
+ High initial costs, specifically related to drilling and site exploration
+ Federal tax credits incentives exist (through 12/31/16) to offset installation costs
+ Special financing is available from Energy Star®, among other organizations

PROCESS
Using a ground source heat approach requires a heat pump, a heat exchange component, and a delivery system; this can be in the form radiant surfaces (water-to-water) or forced air (water-to-air). The heat exchange component uses two thermally conductive materials – a source and a sink – to transfer energy, heat, or cooling.

Water-to-water systems use water as a thermal conduit to deliver comfort throughout the building. Examples include: radiant cooling panels, radiant under-floor heating, baseboard radiators, and conventional cast iron radiators.  Water-to-water systems are the most efficient for of thermal exchange and are preferred for pool heating and domestic hot water pre-heating.

Water-to-air systems are slightly less efficient than water to water, due to the energy loss between conductors. Water-to-air systems are often used to replace forced air furnaces and central air conditioning systems. Variable designs allow for split systems, high-velocity and ductless systems.

 

CASE STUDIES
Washington Square Park House
BKSK Architects
New York, NY
2,000 square feet

Historic Front Street
COOKFOX
New York, NY
150,000 square feet

 

ADDITIONAL RESOURCES
NYC Geothermal Heat Pump Manual [PDF]
NYC Department of Design & Construction