More and more people are using geothermal heating and cooling for their homes, offices, buildings, and industrial processes.
What is geothermal energy?
How is it used?
What locality is best suited for its application?
Why would you use it to meet your needs?
Let's take the first question...
Geothermal energy is a thermal energy within the earth's crust.
Much of this energy is the result of the radioactive decay from various elements. This radioactive decay produces huge amounts of heat.
How hot does the earth's crust get?
Well the temperature increases about 14 F per 1000 feet of depth.
Just like the thermostat in your home, the earth is able to modulate that heat to maintain a near constant ground temperature 6 feet below the surface of the ground.
Below is a map of the United States that is used to present average ground temperatures in various locations. This is an important factor in determining whether a geothermal heating and cooling system is right for you.
(The above map was taken from the report GEOTHERMAL HEAT PUMP UTILIZATION IN THE UNITED STATES, by John W. Lund, Research Associate, at Geo-Heat Center. Click on this link, geothermal heating and cooling to read this highly informative research report).
The reason that this energy is so useful for geothermal heating and cooling is the fact that, for our purposes it is virtually limitless.
Fossil fuels, such natural gas, propane, and oil, are limited resources. So our dependency on them will eventually be a problem.
Also, as we all know, fossil fuels cost money...and lots of it.
However, geothermal energy is free for us all to use.
Refer to the diagram below for a pictorial rendering of how geothermal heating and cooling works.
In order to understand how geothermal heating and cooling works, we need to see the difference between a heat source and a heat sink.
A heat source can be a solid, liquid, or gas substance (or composite of substances).
In the case of geothermal, the heat source is either the ground soil, ground water, or both.
In either case, when the ground temperature is greater than the temperature of the medium (water, refrigerant, etc) it is in contact with, then it is a heat source. This is because the temperature of the heat exchange medium increases and therefore, absorbs heat (geothermal heat) from the ground.
The same but opposite holds true for a heat sink. If the ground temperature is less than the temperature of the medium it is in contact with, then it is a heat sink. Heat is rejected from that medium into the ground.
So, how is this concept applied to heat pumps?
The heat pump ensures that, during the winter, the temperature of the heat exchange medium is less than the temperature of the ground. In that way, heat is absorbed from the ground and rejected into the house (or other building).
During the summer, the heat pump ensures that the temperature of the heat exchange medium is greater than the temperature of the ground. In this way, heat absorbed from the house is rejected into the ground. (Thereby, cooling the home.)
In general, a geothermal heat pump is capable of operating in areas with a ground temperature between 35 F - 100 F.
Again, they are capable of operating between those temperatures.
An argument can be made that a heat pump is capable of operating at any range of ground temperature.
This is true. However, if you want to use a commercially available, inexpensive heat pump, the 35-100 F range is acceptable.
If you reference the above ground temperature map, you will notice that all average ground temperatures are between the 35-100 F range.
So does that mean that geothermal heating and cooling is ideal for all areas in the United States?
For energy efficiency purposes, it is ideal to be 15-20 F above and below the extremes.
So the ideal ground temperature for heat pump operation would be between 50 - 80 F.
Again, take a look at the map to see what locality benefits the most from using a geothermal heat pump.
At the risk sounding contradictory, we have to remember that geothermal heating and cooling is very efficient.
So even in areas with a lower ground temperature (between 40-50 F) you are still saving an immense amount of money in comparison to conventional heating and cooling methods.
The only issue to consider here:
Is the installation cost of excavating buried pipe (to absorb/reject heat) worth the payback for saving on energy costs?
This analysis requires the services of a professional geothermal installation contractor. They will survey your situation and give you the installation cost versus the payback cost.
Another factor to consider in cooler climates is the need for secondary heating. Often in areas with this 40-50 F range in ground temperature, the winters can get quite cold. It is very possible that (if the heat pump and ground loop was undersized for economy purposes) you many need an auxiliary heat source (such as a conventional furnace or electric duct heater).
Again, a personal analysis of your situation can help you determine if you are a prime candidate for geothermal heating and cooling.
If you live in an area where the ground temperatures are within an acceptable range and you are interested in saving money....
a geothermal heat pump is definitely worth a look.
Let's start with an example of a 2000 sq. ft residence in Michigan, U.S.A.
Standard heating and cooling costs for a typical 2000 sq. ft. residence in Michigan usually ranges between $1500-$2000 per year.
The ground temperature usually ranges between 42-50 F in Michigan. Using a ground temperature of 47 F, geothermal can save a homeowner between 55-75%.
Using the conservative numbers of 55% savings and $1500 annual heating and cooling costs using conventional equipment:
The example homeowner can expect to save at least $825 per year (as much as $1500 per year!)
As you can see, the savings is significant. But now imagine if your home or building is 4000 sq. ft.....5000 sq.ft.
....Now we're talking into the thousands of dollars per year of cost savings!
So, why control the climate of your home using geothermal heating and cooling?
Huge cost savings!
As you can see, if your home is between 1000-2500 sq.ft it may be many years before you get the payback.
So, is it worth it to use geothermal energy for your particular case?
Contact a professional geothermal contractor for further assistance.