Geothermal Retrofits
Almost every home can be retrofitted with a geothermal heating and cooling system.
The typical site is one-half acre or greater and can accommodate the large drill rig required to drill the borehole(s). These rigs are approximately 40' long, weigh about 70,000 pounds and with the drilling mast raised, are about 40' high. Since the boreholes and pipes are 4' underground, borehole(s) can even be in driveways.
There are generally four categories of homes that affect the cost of installation:
- Homes that use a boiler to generate hydro-air forced hot air heat with central air conditioning and were built after 1975: these homes are the easiest to retrofit. Typically, the boiler and hydro-air heat is left in place to act as auxiliary and emergency heat and the geothermal system is added as the primary heat source. Outside air conditioning condensers are removed since the geothermal system uses the ground as a heat sink. Air handlers are usually changed to accommodate the new R410a refrigerant and to access the variable speed motor for the fan speed. Zone controls and thermostats are changed to accommodate the three stages of heating and two stages of cooling in most of our geothermal heat pumps.
- Homes that use a furnace and forced air heat and were built after 1975: these homes typically have good duct systems and are reasonably insulated. However, every geothermal heat pump needs to backed-up with some form of auxiliary heat and the use of a furnace is not recommended. The reason for this is since the heat source from the furnace is before the geothermal heat coil, the extra heat from the furnace causes the heat pump to short cycle and lock out. Depending on balance point (the point at which the outside temperature drops below a point where the heat pump can not generate enough heat), the system shuts down the geothermal heat pump and all the heat is generated from the back-up source. This can affect the operating cost, depending on how the system has been designed. Usually, the furnace is removed and the system is backed-up with either electric strip heaters installed in the air handlers or hydro-air heat from a fossil fuel (gas or oil) system through hot water coils installed in the ducts. Properly designed systems usually require very little back-up heat since the source of the heat is the ground which, unlike air, is a steady 54 degrees year around.
- Homes that have baseboard heating and either have no central air conditioning or were retrofitted with a central air conditioning system: these homes either require ducts to be installed since a geothermal system needs to distribute heat and cooling via the air (radiant floor systems are typically too cost prohibitive to consider for a geothermal retrofit system) or require some modification to the duct system. Often a home that was retrofitted for air conditioning does not cool bathrooms, and/or the ducts are located on inside walls instead of outside walls needed for even heat distribution, and/or if a two story house, frequently the ducts serving the first floor come down from the attic through closets and are inadequate for heating. Generally, the existing duct system can be modified cost effectively to enable the use of the efficient geothermal heating and cooling system. The boiler and baseboard are typically left in place and used for auxiliary and emergency heat.
- Homes that were built prior to the 1970's energy crisis that have not been renovated: these homes tend to be poorly insulated and have excessively high heating and cooling loads. Typically, we recommend these homes be renovated with insulation and new windows prior to installing a geothermal heating and cooling system. The reason for this is twofold: one, the cost to install is much higher due to the load and two, the operating costs, although much lower than a conventional system, will be much higher than they should be.
