By Melissa Aho, Ultra Geothermal Inc.
New Hampshire Sustainable Energy Association newsletter
NH Energy Connections | July/August 2009 | Volume 3, Issue 4
Geothermal heat pumps have been used to heat and cool homes since the 1940’s when Robert Webber converted a freezer into a heating & cooling system for his house. Heat pumps now provide many homeowners a comfortable way to maintain constant temperatures throughout the home. There are several considerations, however, that should be looked at prior to installing a system here in New England. A majority of the information available on the web regarding geothermal is written from the southwest and the geothermal application in those areas is very different then here in New England.
New England seasons have large temperature variances. The winter temperatures consistently reach below zero so the heat pump needs to be sized according to the heat loss, not heat gain. We also have rocky and low soil conductivity to contend with which makes horizontal ground loops costly and difficult to install. There is a closed loop system that works very well here in New England, the vertical loop. This is a series of bore holes that have a glycol and water solution circulating between the ground loop and system to obtain temperature.
Several differences between the open loop (standing column well) and closed loop systems lead customers to choose one over the other. Water temperatures entering the system from an open loop range from typically 47 to 50 degrees in the Southern NH region. Entering glycol and water fluid temperatures on a closed loop system is between 30 and 34 degrees. This temperature difference means that you are able to size the geothermal heat pump smaller for the open loop application, costing less up front. The installation cost of a closed loop is slightly higher than the standing column well since it requires drilling more holes. The other advantage to the open loop is you have the ability, here in NH, on new construction to use the ground source for your domestic water which is a huge cost savings.
The geothermal heat pumps allow you to heat your home in one of two ways; through radiant floor tubing or forced hot air ducting. Water-to-air systems will allow you to take advantage of the cooling mode of the geothermal, whereas the water-to-water option does not operate in cooling mode unless you install a ducting system and air-handler. The Co-efficient of Performance (COP) value on the water-to-air system will be slightly higher since it takes less energy to heat air than water. Both systems are very efficient, running COP’s of 3.8-5.0.
If you are looking at installing a geothermal system in your new construction or existing home, now is a great time. The federal government is offering a 30%, no cap tax credit for all qualified geothermal installations.
Copyright ©2009 New Hampshire Sustainable Energy Association