Geothermal

Siting and Feasibility  |  Financing  |  Case Study  |  This is Just the Beginning...

Geothermal systems, or ground source heat pumps (GSHPs), use the constant temperature of the earth to heat and cool buildings and heat hot water. While Massachusetts experiences seasonal temperature extremes, the ground just a few feet below the surface remains at a relatively constant temperature. This ground temperature is warmer than the air above it during the winter and cooler in the summer. A GSHP takes advantage of that variant by exchanging heat with the earth through a ground heat exchanger – heat is sunk from the building into the ground in the summer, and heat is taken from the earth in the winter. The GSHP’s air delivery system delivers heated or cooled air through a building in the same manner as a typical HVAC system.

According to the U.S. Environmental Protection Agency, geothermal systems can reduce heating energy consumption (and greenhouse gas emissions) up to 44%. And geothermal systems use 72% less energy than comparable cooling systems.

Siting and Feasibility

The specific geological, hydrological, and spatial characteristics of your land will help determine if geothermal is right for your site, and which kind of system would work best. Composition of soil, presence of surface water, and availability of land all determine geothermal cost effectiveness. It’s important to test the condition and temperature of the site and groundwater. Drilling a test bore hole can be an important step before installation.

Heat pump systems are designed to transfer heat to and from the ground; the exchange of heat over the year should be net zero. Relying on the system for cooling or heating exclusively could create a temperature imbalance within the well field. Richard Stockton College has done extensive work on how temperature balance affects optimal geothermal system performance. See more information on the Stockton College website.

There are two kinds of geothermal heat pump systems – closed loop and open loop. Closed loop systems use the earth as the heat source and heat sink by moving a water and anti-freeze fluid mixture through loops buried deep in the ground.

(Courtesy U.S. Department of Energy: Energy Efficiency and Renewable Energy)

 

Open loop systems use underground or surface water as the heat source and the heat sink. Standing column wells (shown below) are one form of open loop system.

The last siting consideration for geothermal systems is a recognition for what ISN’T there. Geothermal systems eliminate the need for large HVAC systems or cooling towers on roofs.& And they are much quieter than conventional heating and cooling systems

(Standing column well at Harvard.  Courtesy Harvard University.) .

 

Financing

There are currently no financial incentives available for the installation of geothermal
systems, but geothermal systems can be an economical choice.

• Systems can be costly but first costs are generally paid back within 5 to 10 years. System life of the underground components is typically 50 years or more, much longer than a comparable HVAC system.
• Geothermal systems require less ongoing maintenance than conventional systems, making long-term savings from geothermal installations much more significant.
• GHP heating efficiency is measured by its coefficient of performance (COP). The COP is the ratio of heat provided in Btu per Btu of energy input. Cooling efficiency is indicated by the Energy Efficiency Ratio (EER), the ratio of the heat removed (in Btu per hour) to the electricity required (in watts) to run the unit. Look for a GHP with a COP of 2.8 or greater and an EER of 13 or greater.
• Many schools heat with oil in the winter, but cool with electricity in the summer. Geothermal systems can do both. It's important to evaluate the cost benefits of geothermal in terms of thermal and electrical load.

Case Study

The Noble and Greenough School in Dedham installed a geothermal system in 2007. Projected savings for the middle school are $17,000 a year. Although the system cost $723,000 (about $100,000 more than a conventional HVAC system) the additional first costs will be recouped in six years.

Richard Stockton College boasts one of the world’s largest single closed loop geothermal HVAC systems, totaling 1,741 tons of installed geothermal heating/cooling capacity. The college in Pomona, New Jersey, now uses 400 heat exchange wells and water source heat pump (WSHP) units to serve the heating and cooling needs of a growing campus.

The closed loop system of wells (each 425 feet deep) are arranged in a grid at 15 ft. intervals. The majority of the wells are located under a 4-acre parking lot.

The college initially projected that a geothermal system would cost about $1.2 million more to install than a conventional HVAC system, but that it would be expected to save $330,000 in energy costs. Thus, the simple pay back of the extra costs of the geothermal system would be about 3.5 years.

Furthermore, because the reduced peak electrical demand would reduce the need for Atlantic Electric Company to install new generators, the utility offered an $800/Ton rebate for installing the geothermal system.

Since its installation, the school confirms that it has reduced its electric consumption by 25% and natural gas consumption by 70%.

However, since its initial design, the college has made changes to the system to increase its efficiency. The college operates a cooling tower in the winter months (to waste heat) in order to precondition the field for the college’s increased need for summer-time cooling.

Find out more about Richard Stockton’s impressive geothermal system at the Stockton College website.

Heat diagram of Richard Stockton College's
geothermal well field. (Courtesy Richard Stockton College.)

This is Just the Beginning…

Oberlin has included their campus’s geothermal system in its web-based computer monitoring system (See online performance graph, below.). Faculty, staff, and students can check on the system’s heating and cooling capacity in real time. Find out more at Oberlin's website.

Harvard has installed multiple heat source pumps on campus. Find out more about their robust geothermal plan at http://www.greencampus.harvard.edu/cre/index.php.

The U.S. Department of Energy has great descriptions of geothermal heat source technology. Go to their website to learn more.