Choices… Geothermal Heat Pump

There is some confusion in terminology: “Geothermal heating” “Heat pump” “Ground source heat pump” and other combinations of words. What is all of this stuff and how does it relate to heating and cooling in our homes? All of these can be proper descriptions of the various ways to use a heat pump, so let’s start by defining what a heat pump is.

Through air to air transfer, the conventional HVAC expels heat in the summer and gathers heat in the winter. A heat pump uses the same principle but with water. Like a car radiator, a piped loop of water gathers heat from the heat source then takes it to the cooler source to expel the heat and cool down. Although the heat pump is commonly used for cooling, adding the components for heating is a nominal $100 – 200 additional expense. In the winter, the process is inverted; it gathers heat outside and expels the heat inside your home instead.

The most common way to use a heat pump is a ground source, or geothermal heat pump. In Texas, the primary climate control in our homes is cooling and to take maximum advantage of the cooling capabilities of the earth we need to go deep. Drilling is the best way, through 5-6” diameter bore holes about 250’ deep. Two polyethylene pipes with a U-bend at the bottom creating a “loop” are placed into the bore hole all the way to the bottom. An expansive clay grout is used to fill the bore hole and stays flexible while maximizing contact from the pipe to the earth.

At the surface, lateral trenches connect bore holes with a continuous loop to the pump connected to the unit. The pump uses minimal power, usually about 2 amps and is only powered when the unit is running. The ground temperature is in the mid 60’s and the heated water leaving the home is about 85deg. With the proper design and calculation of bores and pipes for the water loop for your specific home, the water temperature leaving the earth will be about 10 – 15 degrees cooler than when it leaves your home.

In a residential neighborhood, an installation can be easily done. The contractor will locate all underground services, plumbing, sewage, utilities etc. by contacting www.texasonecall.com before digging. The 5-6” bore hole is so small compared to all other pipes that it is very simple to find a safe location for the bore holes. The lateral pipes are installed not too deep but deep enough to keep them safe from landscaping and general surface digging at about 3’. Sometimes if the soil is rocky, heavier equipment is used to get through the rock.

If you live near water, the water loop can be placed in the water to avoid the need to drill. This is called a water source heat pump. This would be a much cheaper possibility, however with some risks. The water level is a factor as well as boat anchors or other hazards in open water. If the water level falls too low to effectively transfer heat, literally nothing can be done to fix the system. Your options are to wait for the water level to increase to normal, or start drilling bores for a new location for the water loop. If you have a reliable water source, do consider this option as an alternative to drilling. Be creative, do you have an abundant source of rain water collection? Or a maintained water source for animal habitats?

The cost of installing a ground source heat pump is more than the conventional unit. The equipment price is comparable, but it is the labor and additional materials that increase the cost. For the excavation, pipe, grout, pump and additional labor the cost difference is about $2500 per ton. Depending on the tonnage, it can be twice the cost of the conventional air to air unit. The pay back in dramatic energy cost is quick and is worth considering the investment.

The advantages of investing in a heat pump are many. The equipment has a long life span considering Texas summers will kill a convention air to air unit in 10 – 12 years, much shorter than they were designed in a milder climate. A ground source heat pump is much more reliable because the temperature under the ground is constant rather than a wildly fluctuating ambient air temperature. There is no outside condenser making noise or taking up space. The unit is completely assembled at the factory where a conventional unit requires on site assembly with the outside condenser, inside unit and all the piping and wiring that must connect them. With the condenser and the unit combined into one piece, good manufacturers have taken great care to insulate for sound. It is, however, important to consider the location of the unit inside your home for sound. The greatest advantage is that using a water loop in lieu of air to air transfer is a highly effective way to cool air in your home and is usually doubly more efficient than air.

All of this wonderful information about heat pumps has come direct from Michael Scher of

All Year Heating and Cooling. Michael was one of the most gracious educators I have had the pleasure of talking to and was a wealth of information. He has spent time educating himself by being diligent with research and by attending a 3 day seminar at the OSU campus. “Water Oklahoma” is the home of the International Ground Source Heat Pump Association and has been the founders of research in the industry.

Michael also says that his favorite companies who manufacture the heat pumps are Water Furnace International (in business for ~65 years) and Florida Heat Pump (who are accustomed to dealing with higher temperatures). Michael started his career with a degree in architecture, then in 1986 had an opportunity to buy All Year Heating and Cooling. Since then, he has made heating and cooling his passion. You will see Michael with his company, All Year Heating and Cooling, at many of Austin’s “Green” events hosted by the Austin Energy Green Building and other sponsors. He takes care to design the best system for you and your budget and always uses correct calculations to design the right sized unit for your home. Next time you need heating and cooling service of either a heat pump or conventional type, please contact Michael at michael@allyearaustin.com

Good green building starts with good design and construction for little to no extra expense. With the proper design and building team, your budget can allow for sound energy systems like a heat pump.

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