Engineer’s View

Solar and geothermal energy systems are based on sound engineering principles. But, instead of burning fossil fuels to produce heat the sun and earth provide from 60 to 100% of the same requirements, but without producing hydrocarbons, carbon monoxide, carbon dioxide, and atmospheric warming.

Solar energy systems are most efficient with 90 – 100% of their delivered energy coming directly from the sun. The other 10% is from electrical energy to store or distribute this free energy. If the economics warrant even this 10% can come from solar photo voltaic direct conversion of sunlight to electricity.

Geothermal low level systems use the energy stored in the earth in the form of ground water. In the Northeast our density of bedrock allows us very good heat transfer between ground (well) water and the earth. Every pound ( approx. 1 pint ) of this water has stored in it 10 BTU’s of potential energy.

Our earth freezes down from 3 to 6 feet deep each Winter, making the horizontal geothermal loops shown in some manufacturers booklets impractical for us in the Northeast. The same goes for pond and lake loops from shallow sources of water. The water is not the source of the heat, only the heat transfer medium. The earth is the source and the sink of the heating and cooling.

From a pure physics point of view there is much more heat available in a pound of water at our earth’s average temperature of 50°F than there is in frozen earth at 32°F, or colder. Once you get below the frost and it’s effect, at least 15 feet down, the temperature is this relative constant 50’F for many hundreds of feet.

The reverse is also true in Summer. Cooling is much more efficient with a heat sync at 50°F than one at 77-95°F, as it would be with a buried horizontal loop.

Also, with a vertical system (sometimes referred to as a vertical standing water column, VSWC) there is no need for an antifreeze solution, and it’s associated loss of heat transfer efficiency and changes in viscosity, or ground water pollution potential, as some fluids have shown in the past. Simply stated If you use water as your heat transfer medium all of these potential problems are avoided.

In the Northeast VSWC systems give higher COP’s in Heating and SEER’s in Cooling than their closed loop counterparts.

This can be easily be verified by viewing the Air Conditioning Research Institute (ARI) operating conditions of closed loop (ARI-330) vs. open loop or VSWC (ARI-325) for any of the major geothermal heat pump manufacturers equipment. Under the ARI conditions the water pumping penalty is always included in all calculations. And remember with geothermal systems there is no boiler or cooling tower on a loop.

A geothermal unit running on ARI-325 produces higher levels of both heating and cooling than the same unit operating on ARI-330, thereby requiring less run time to satisfy space temperature requirements. Given the advantage of the clean water ( fuel ) source and the high density bedrock we have throughout the Northeast why would anyone throw away this clear performance advantage and opt for a closed loop open ( or VSWC) system.

Following IGSHPA standards you can also see why the VSWC system operating under ARI-325 conditions outperforms the vertical closed loop (ARI-330) simply by the size of their respective heat exchangers.

  • Vertical closed loop (ARI-330)- 150 ft./ton of grouted bore with 300 ft.of 3/4″ plastic pipe, making a total surface area of aprox. 75 sq.ft./ ton of heat pump capacity. This heat exchange with the earth has to take place through a poly plastic with an antifreeze solution. The anti freeze alone drops the heat transfer efficiency to less than 90%. The anti freeze is required as the loop usually goes below 32’F during the heating season.
  • VSWC open loop (ARI-325) – 100 ft./ ton of 6″ bore into either steel well casing or high density bedrock. Using 100 ft. of water standing column per ton of unit capacity makes a total surface contact of aprox. 150 sq.ft./ton of heat pump capacity. This is water with a heat transfer ratio of 1:1, or 10 BTU / LB. of water for a 10’F delta T.

Today’s state-of-the-art geothermal heat pump units operate with 70 to 75% of their output energy being supplied by the earth. The other 25 to 30% from the electric utility or solar photovoltaic array.

Where else can you get a heating and cooling energy system that is 70 to 75 % independent of any fuel source or utility and only 25 to 30% dependent on a public service regulated electric utility? Literally all fossil fuel systems are 95% dependent on OPEC or a similar source, not regulated within each state.

Contact us if you are interested in working together on your client’s project.