The heat for our house comes from the ground in our front yard. How is this possible? It is made possible by using a ground source heat pump (GSHP). We have a 650 foot deep well which never produced sufficient water so we decided to use it for heat. We retrofitted our oil fired hot air furnace to use geothermal heat. Thermal Associates of Glens Falls installed our 36,000 Btu Water Furnace Heat Pump in 2005.
The temperature deep in the soil in this area is 50 â€“ 55 degrees F. The idea is to move this heat to the house and concentrate it to produce warm air. Heat naturally moves from hot to cold so some energy (electricity) is required to make it move the other way. Basically it can be thought of as a refrigerator in reverse. Just as a refrigerator removes heat from the food inside and dumps it into the kitchen, a heat pump removes heat from the earth and releases it into the house..
How Does a Heat Pump Work?
In heating mode, water is pumped from the ground and passes through the water-to-refrigerant heat exchange unit (3). In the heat exchanger the 50 F. water causes the refrigerant to change from liquid into gas, thus absorbing heat (latent heat of vaporization) from the water. The refrigerant is then pumped to the compressor (4) where it is pressurized thereby becoming superheated. This â€˜hot gas’ loses its heat in the refrigerant-to-air heat exchanger (1) and warms the air going to the house. As a result, the refrigerant gas is cooled and condenses back to a liquid. In the external loop the water that has been cooled by the water-to-refrigerant heat exchanger is pumped back into the earth to be heated again. Note the external fluid only changes temperature while the internal refrigerant changes both temperature and phase.
How Does GSHP Benefit the Environment?
According to the EPA, a ground source heat pump is the most energy-efficient, environmentally clean and cost-effective way to heat and/or cool a building. (Yes, by reversing the heat pump it becomes an air conditioner.) They say that installing a GHSP system in a home is the equivalent to planting an acre of trees or taking two cars off the road. Roughly 70% of the energy used is coming from the ground (free). The heating efficiency of a GSHP system is 3.4 while the efficiency of the best gas furnaces is only 0.92. (An efficiency greater than 1 indicates that the output energy is greater than the input energy.) If the electricity used is obtained by buying a “green” source, such as hydro, wind, or solar, then the building is being heated without adding any carbon dioxide to the air.
What Are the Possible Configurations?
There are two basic configurations â€“ closed loop and open loop. In a Closed loop system a water â€“ antifreeze mixture cycles through a polyurethane pipe into the ground and back. This can be done vertically, as we have done or horizontally by means of a system of pipe laid out in trenches that are at least four feet deep. A different method is to dig a pit 30′ x 60′ x 6′ into which coils of pipe are laid. If a pond is available, a horizontal system can be laid in the bottom of the pond.
On the other hand, in an Open loop system water is pumped from a well or other natural water source through a heat pump and then the water is discarded. This type of system is only practical if the house is near a high volume source of water, at least 9 gallons per minute.
What Does a GSHP Cost to Install?
Installing a complete new system it will run about 30% more than a conventional furnace. A three ton heat pump costs about $7500. This is the size needed for an average house. (Why tons? Think of the history of cooling! One ton of capacity is equal to the refrigerating power of one ton of ice melting over the course of 24 hours.)
For our gshp to be retrofitted onto our oil â€“ hot air system the cost was about $13,000. Although we did not have to dig a well or trenches, we did have some other special installation problems that boosted the price somewhat.
How Much Can You Save With a GSHP System?
When I compared the electricity bill from our first winter (05-06) with GSHP to the winter before I found an increase of about $900 dollars. The year before we burned 896 gallons of oil. At the price then of $2.59 per gallon, that would have cost us $2321 so there was a saving of $1421 assuming that the winters were comparable. Of course the price of oil is much higher now. It should also be noted that we burn wood in our wood stove most cold evenings.
I believe that our GSHP system payed for itself in seven years or less. I might also note that it has been completely trouble free. Considering the environmental benefits a GSHP system is worth looking into if it is physically possible to install one in your house. You can quickly find more information by googling “geothermal heat pump” on the internet
– Bob Manning
A Garnet Lake resident, Bob Manning is a retired science teacher, a member of PROTECT’s forestry program, and the ALAP water sampling volunteer for Garnet Lake.