Geothermal

Geothermal, or ground source, heat pumps provide cost-effective, eco-friendly heating and cooling for homes and buildings with energy savings of 25-50%, according to the International Ground Source Heat Pump Association.

If you’ve ever visited an underground cave or cavern, you know that the air there is a constant—cooler than aboveground air in the summer, warmer than aboveground air in the winter. In Maryland, the earth maintains a constant 55°F, below frost level (from 4-8 feet deep).

This reservoir of energy can be converted for heating and cooling. To tap into it trenching or drilling equipment drills down into the earth in two closed loop configurations:

  • Horizontal loops are used when trenches are easy to dig and available open area is plentiful. Workers use trenchers or backhoes to dig the trenches 3-6 feet below the ground, in which they lay a series of parallel plastic pipes. Fluid runs through the pipe in a closed system. A typical horizontal loop will be 400-600 feet long for each ton of heating and cooling.
  • Vertical loops are used where there is little yard space, when surface rocks make digging impractical, or when you want to disrupt the landscape as little as possible. Vertical holes 150-450 feet deep are bored in the ground, and a single loop of pipe with a U-bend at the bottom is inserted before the hole is backfilled. Each vertical pipe is then connected to a horizontal underground pipe that carries fluid in a closed system to and from the indoor exchange unit.

The Union of Concerned Scientist’s website has more information on geothermal resources, applications, costs, and benefits.

Geothermal Heat Pump Conversion Systems

Conventional Systems

As illustrated at right, geothermal, or ground source, heat pump systems use the constant temperature of the earth to heat and cool homes and buildings by exchanging heat with the earth:

  • In the winter, they move the heat from the earth into the house or building.
  • In the summer, they pull the heat from the house or building and “dump” it into the ground.

Geothermal heat pump systems can be equipped with a device called a "desuperheater" that can heat household water, which circulates into the regular water heater tank.

  • In the winter, the desuperheater can reduce water-heating costs by about half, while a conventional water heater meets the rest of the household's needs.
  • In the spring and fall when temperatures are mild and the heat pump may not be operating at all, the regular water heater provides hot water.

The U.S. Environmental Protection Agency now includes geothermal heat pumps in the types of products rated in the ENERGY STAR® program. On average, ENERGY STAR qualified products covered under the Agency’s 2009 specification will be over 45% more energy efficient than standard options. Its Tier 2 specifications, effective as of January 2011, can be found at its Geothermal Heat Pumps Key Product Criteria website.

Hybrid Systems

The U.S. Department of Energy, Alliant Energy, and Madison Gas & Electric, and the Energy Center of Wisconsin studied Hybrid Ground-Source Heat Pump Installations: Experiences, Improvements and Tools demonstrating hybrid ground-source heat pumps – which tie in to existing/conventional HVAC systems – as a cost-effective solution to reduce energy use in commercial and institutional buildings.

This group offers free analytical software for building engineers and owners to assess hybrid systems for their buildings.

The below websites offer much more information on geothermal heat pumps:

Geothermal Heat Pump Market Trends

The U.S. Department of Energy (DOE) recently highlighted a report – Hybrid Ground-Source Heat Pump Installations: Experiences, Improvements and Tools – demonstrating hybrid ground-source heat pumps (GSHP) as a viable solution to reduce energy use in commercial buildings. The report finds that new hybrid systems dramatically decrease up-front costs while delivering financial and environmental benefits nearly equivalent to standard ground-source heat pumps. With its lower price, hybrid GSHP technology could be deployed widely, saving energy and money in new and existing commercial, industrial, and institutional buildings, according to the report.

Click here to read the DOE article.

Geothermal Heat Pump Projects

The Holly Hall Elementary School in Elkton, Maryland—built 50 years ago—was recently expanded to increase capacity by 22,424 square feet to the building’s existing 33,718 square feet to accommodate anticipated student enrollment. Another addition to this school is the geothermal heating and cooling system. The system uses a total of 108 borings that act like a heat exchanger in the ground. This system taps the earth’s subsurface energy to preheat and precool fluids that supply the building’s heating and air-conditioning system.

For more information, download the County’s Annual Report.

Apply for a Geothermal Heat Pump Grant

Questions

Contact Clean Energy Program Manager Doug Hinrichs via email at dhinrichs@energy.state.md.us or telephone 410-260-7543.