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Geothermal HVAC and the “Negatherm” Factor

Posted by Jay Egg

May 15, 2014 12:59:00 PM


In our first geothermal book, Geothermal HVAC, Green Heating and Cooling (McGraw-Hill Professional, Geothermal_HVAC_Textbook2010, p16), Brian Clark Howard and I shared a dialogue from an article wherein a commenter said that switching from a gas furnace to ground sourced heating is increasing the burning of fossil fuels, because the power plant producing the electrical power is probably burning coal, natural gas or other fossil fuels.  The argument seems valid until you understand what we call the “Negatherm Factor”.

 “Negatherm” is a term that was coined to refer to energy that would or could have been used from fossil fuel consumption, but was never used.  “Nega”, root of “negative”, meaning unused, and “Therm”  a unit of energy equal to 100,000 BTU’s, usually measures the combustion of fossil fuels for heating a home or business.  When heating from an appliance using electricity, we use “kilo-watt-hours” (kWh).  Electricity comes from many different fuel sources including hydroelectric, solar, wind, hot rock geothermal, nuclear, natural gas, coal, and diesel to name a few.  We are certainly seeing an increase in the renewable sources, the first four in particular.

When a consumer is using a fuel heating appliance, he is consuming fossil fuel.  When that consumer switches over to an electric appliance, he may be eliminating his CO2 footprint if the electrical power is coming from one of the renewable sources.  And with an interconnected grid, we are all increasingly partakers of renewable energy.

Fuel prices, whether for natural gas, propane, or coal may go down, and they may go up.  Electricity prices also fluctuate, but since electric power comes from coal, natural gas, solar, wind, nuclear, hydro (and the list goes on…), electricity is not subject to the supply and demand “commodity like” fluctuations of any one individual fuel source.

Electric_is_stable.jpgPrice fluctuations driven by supply and demand and other market forces are dampened by the abundant sources of fuels available to power the grid.  The electric grid is also becoming increasingly powered by renewables like solar and wind, etc. Last winter, the “Polar Vortex” caused propane and fuel oil prices to skyrocket, and yet the cold caused relatively little fluctuation in electricity prices, even in areas hardest hit.

Right now, natural gas is favorable to many. It’s abundant, clean burning and cheap.  Investors will be taking profits eventually, but they’re patient. This report from Sustainable Plant says, we will end up paying more sooner or later.

A good financial practice is to buy something before the demand for it peaks. Earth coupled systems are "all-electric" powered. They heat, cool, generate domestic hot water, heat pool, spas, driveways, and much more. Ground sourced systems are the most efficient heating and cooling systems available. Ground coupled heating costs about the same per BTU as natural gas at the current price point of about $0.60/therm. But natural gas is for combustion heating, and does not provide cooling. Here’s a thought to ponder:

We need cooling and heating.  A geothermal heating and cooling system is environmentally friendly, and superior to other types of systems in efficiency, comfort, longevity, and safety. So, when prices go up for fossil fuels, financially we’re already poised to reap the rewards.

Slide1Geothermal heating and cooling is renewable to begin with. A Geothermal Heat Pump (GHP) converts stable earth temperature into usable BTU’s, just as certainly as a photovoltaic cell converts light into electricity. But geothermal eliminates one step in the conversion process.  Electricity from PV still needs to be converted to BTU’s in order to heat and cool, and Geo does not.  A Geothermal Heat Pump is what the name implies, a pump that moves heat either into or out of a structure or “process” (“process” meaning things like domestic water heating).

For comparison, consider that a combustion furnace can come close to being 100% efficient in delivering One_Unit_Electricity_to_Five_Units_Heatheat, meaning for every unit of fuel applied, you get about .9 units of usable heat (about 90% to 97% efficient). For each unit of fuel consumed by a GHP (electricity is the fuel for heat pumps), the GHP delivers 5 units of heat, making it 500% efficient (owing to the renewable nature of geothermal).  It works the same way in heating or cooling. It’s just a matter of which way were moving the heat; in or out.

If we use combustion heating, then we have little or no choice what we pay for fuel.  Go with geothermal heating and cooling, and we let the ever improving electrical grid make the choice.  And the bonus is that with every solar, wind, or other renewable improvement to the grid, we are doing our part to help the environment.

While all geothermal technologies have great promise, Geothermal Heat Pumps (GHP’s) emerge as the most accessible and cost effective technology to install and operate.  That’s good news for us. 

Industry Stakeholders have created a website with vast resources to educate the public on geothermal heat pumps.  The “Geothermal Day” Website aims to raise awareness about environmental and economic benefits of geothermal energy and its vital role in building a clean and secure energy future. We are inviting industry partners, communities, businesses and educators to join efforts to advance further understanding and acceptance of geothermal technology as an unlimited, renewable form of energy. Join us by co-creating and sharing educational resources and participating in interactive activities in local communities and on-line.

National Geothermal Day is October 20th 2015.

Geothermal 101 Video


-Jay Egg is a geothermal consultant, writer, and the owner of EggGeothermal. He has co-authored two textbooks on geothermal HVAC systems published byMcGraw-Hill Professional. He can be reached at   

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