By Andrew Lake
In a previous post, I described how air source heat pumps can save many homeowners a lot on heating costs. An air source heat pump is capable of removing heat from cooler outdoor air and moving it into your home in the winter. In the summer, it moves heat from the cooler indoor air into the hot outdoor air.
A geothermal heat pump trades heat with the ground instead of the outdoor air. The temperature of the dirt only a few feet under the ground is nearly constant throughout the year. In the winter, underground temperatures are warmer than the outdoor air. In the summer, the underground temperatures are cooler than the indoor air. This allows a geothermal unit to operate extremely efficiently.
In the winter, they provide 3-4.5 watts of heat for every watt of electricity consumed, even on the coldest days of the year. In the summer, the most efficient geothermal units use less than 2/3 as much electricity as the most efficient air conditioners.
A series of pipes must be installed under the ground to trade the heat with the indoors. About 500 feet of pipe must be installed for every 1,000 sq. ft. of home to be heated & cooled. If the yard is very large, the pipes may be buried in 5ft. deep trenches. If the yard is a more typical size, a series of 100-300ft deep wells must be drilled to place the pipes in. Drilling wells is much more expensive than digging trenches.
If you have a good aquifer under your property (if water flows through the rocks such that it can fill up a well), you may be able to install a couple of 100ft. deep wells instead and trade heat with this water instead of the rock. If you have a sizable pond or live on lake or oceanfront property, you may be able to lay the pipes underwater instead of underground. Both of these options are more affordable.
A geothermal heat pump can save most homeowners 50% or more on heating costs. Unfortunately, the costs of installing the ground piping can cost as much as a new automobile. This means that it will take most homeowners more than 20 years to earn back their investment in energy savings. Fortunately, the ground piping is expected to last more than 50 years.
Andrew Lake is a licensed heating and air conditioning technician with Shell Busey's HouseSmart Heating and Air Conditioning in Vancouver, Canada.