Geothermal:  A Green Alternative for Heating and Cooling

The goal of sustainable design or "green development" is to produce buildings that take less from the earth while giving more to people. One way to achieve this goal is to minimize energy consumption. 

Since heating and cooling equipment are a building's primary energy consumers, installing an energy-efficient climate control system will not only take less from the earth but will save in operating costs as well. Of course this all makes sense only if the building has first been built with a tight and well-insulated shell.

One energy-efficient option is the geothermal heat pump. A geothermal heat pump is essentially a reversible air conditioner that uses water as its heating and cooling medium.

Open and Closed Loop Systems

An "open-loop" geothermal unit uses a water well to extract heat from the earth and pump it into the building for warmth in the winter. In summer it pumps heat out of the building and back to the earth to keep the building cool. A "closed-loop" system uses a buried coil of polyethylene or polybutylene pipe filled with water or a solution of water and antifreeze to perform the same tasks.

In colder climates, the ground is much warmer than the air in winter and much cooler in the summer. This helps make geothermal systems much more efficient than air source heat pumps and air conditioners.

Due to the ground excavation and plumbing involved, the installation cost of a geothermal system is greater than for a standard furnace with central air. The operating costs, however, can often justify the investment.

A Local Example

At the Timber-lee Christian Center in East Troy, an open-loop geothermal system was installed for the facility's new 14,000 square foot Science Education Center which we will complete in early August. The heat pump draws water from a new 120-foot private well that was drilled to accommodate the system.  

As Leroy Carlson, Timber-lee's Director of Facilities and Fleet, explained, "This building is a creation science education center, so the guiding philosophy is to communicate the awesome wonders of the design and creation of this earth. We wanted to be very conscious of the environment in the process, so we looked at alternative sources of energy for heating and cooling."

Various programs in Wisconsin encourage the use of alternative heating and air conditioning systems with grants, and that was one of the factors in Timber-lee's decision. Carlson explained that the groundwater temperature at Timber-lee is 45 degrees and that it's warmed further through concentration in the system's heat exchanger. 

Good Things Anticipated

Although the system has been online for only a few months, Carlson said, "The jury is still out but we're anticipating good things.  It's heated the building well during the marginal months of spring. We anticipate that our heating cooling costs will be less than conventional systems."

Factors influencing geothermal heat pump operating costs include the building's size and its annual cooling loads, local electric utility rates, the cost of other heating fuels, and the availability of groundwater. Other considerations are the ease of excavation, experience of the installer, and coordination among subcontractors.

As many as four subcontractors may be required to install a geothermal system: an excavator, a well driller, an electrician, and an HVAC contractor. With this many subs involved, there are plenty of opportunities for miscommunication.

While the owner, architect and builder need to do their homework, Carlson said, "I would recommend this system to others who find themselves in similar circumstances as us. For those who are on municipal water and well systems, it might not be cost effective. But if they have a private well as we do, it's an option worth considering."