coastal geothermal: a case study 08/2011

Our client’s 1960’s house, originally conceived for summer use only, was in need of a major upgrade and expansion to accommodate year-round living.  The site’s beauty and location, perched within a stone’s throw of a beautiful salt water marsh in coastal New England, posed many planning challenges, including proximity to coastal wetlands and coastal flooding regulations. Added to the site planning mix was the clients request we minimize energy use with a geothermal system.


coastal geothermal


What is Geothermal: Geothermal, also known as a ground source heat pump, uses the earth’s constant 55 degree temperature to provide much of the heating and cooling energy for a home. Working with Sean Fennessey of Sun Engineering, a closed loop system was specified, where four 350’ deep bore holes are located on the property, providing a below-grade closed loop assembly to be used efficiently by a series of water to air geothermal heat pumps.


Why Geothermal? There are several advantages to a geothermal system:

  • Reduced Energy Use: In conventional homes located in New England, when heating is provided by oil and cooling is provided by electrical outdoor condensers, an annual average of 92 million BTUs from oil and 1600 KWH of electricity are consumed. Since a geothermal system has a number of parts and motors, the electric consumption is reduced very little, but by removing the demand for oil, approximately 850 gallons are saved, for a total cost savings of approximately $3,500/year.
  • Reduced Cost: The high initial cost of a geothermal system is offset by both a 30% Federal tax credit and a $1,750 Rhode Island tax credit, applicable to not only the required geothermal parts and install, but the entire heating/cooling assembly, including ducts, diffusers, hangers, etc. For this project, the total cost of the HVAC system has a 66% additional cost over a conventional high-end system. However, this is reduced by the State and Federal Tax Credits, for a net increase of only 14% for a geothermal system. A home of this size with a conventional HVAC system is expected to consume 1,700 gallons of oil annually, costing $6,000 at today’s energy prices. The geothermal system is estimated to save the client an average of $4,000 per year, paying back the original investment in approximately 3 years, along with peace of mind.
  • More Beauty! Conventional home cooling systems require several exterior condensers, unsightly boxes that are also noisy and occupy valuable land. Geothermal eliminates the need for the exterior condensers and pads, replacing them all with the above-mentioned internal heat pumps, located in the building’s available basement.

System Particulars: The engineered design called for a well field, composed of four 350’ deep bore holes, located outside of the adjacent sensitive wetlands. A closed-loop 1 ¼” plastic pipe, surrounded by high conductivity grout, circulates a safe, food-grade glycol/water mixture, and is connected to a heat exchanger. The geothermal interfaces with conventional efficient water to air heat pumps, where a balance of fresh and inside air is circulated over the hot water coils in the winter and cold water coils in the summer. Along with comprehensive humidification, a state-of-the-art air filtration system, and constant outside air supply, this is available technology that has an extensive performance history and adds value to the home investment.