Wednesday, November 22, 2017

The False Claims of Ground Source Heat Pumps

In 2010 I emailed an employee of a Midwestern state energy agency, following a public conference call about a state energy-efficiency spending plan, which the employee helped present,
I want to follow up on my concern about referring to ground source heat pumps (GSHP) as "geothermal."  This term has been incorrectly applied to GSHPs since the 1990s.  The term is extremely misleading and at least some people who use it actually believe that is makes use of the renewable geothermal energy resource in the earth, which it does not.  I'm was particularly concerned when I thought I heard you say on the call that [state agency] plans to report on renewable energy recovered through its agricultural GSHP program.  I hope I misunderstood.  GSHPs are the most efficient electric heating technology.  They do not use renewable energy unless they use electricity generated from renewable resources.
I made a couple of typos, but I think the state employee's reply has a couple of non sequiturs,
Ted, I don't think we are reporting geo as an alternative;
However, common nomenclature claims  ground source as "geo". 
change is like trying to  rename Kleenex.

False Claim: Ground Source Heat Pumps Use Geothermal Energy

The first non sequitur changed the subject from geothermal to "geo." "Geo-" means earth and the ground is part of the Earth; using "geo-" with ground source heat pumps is not the issue. It's the "-thermal" part of "geothermal heat pump" that's the issue, which the employee did not type. Maybe they were in a hurry, unaware "-thermal" is a false claim, or wanted to defend it without typing it. The reason also can be "willfully unaware," as I was following up on a comment I made during the call when state employees used the term "geothermal heat pump." I explained how it was misleading and why they needed to stop using it. The reply also avoided the words I wrote concerning another false claim made on the call, that ground source heat pumps provide "recovered" renewable energy, instead "thinking" they aren't reported as "alternative." After I discuss the second non sequitur, I'll show how energy at ambient temperatures, transferred from the ground by cooler heat pump evaporators, is regularly updated and reported as consumption of renewable energy, alongside hydroelectric, solar, wind, and others in Section 10, Renewable Energy, of the U.S. Energy Information Agency (EIA) Monthly Energy Review.

When I read the state employee's email I thought, "Nobody ever tried to rename Kleenex, but probably not the meaning they intended. They probably think of geothermal as a brand, like Kleenex." The word geothermal originated in the 1870s. Scientific knowledge of the nature of the geothermal gradient and its resources increased and geothermal is the word used to describe the outward flow of thermal power from the interior of the Earth. Like solar and tidal, it's the adjective for a unique, natural power source, it's not a trademark that got confused with generic substitutes so it now includes local average ambient temperature. I understood the meaning of their last two lines as, "I don't know what geothermal means, nobody knows what geothermal means, the cat's out of the bag and all facial tissues are Kleenex to everybody." Then I wrote,
Kleenex is a brand of facial tissue paper, which marketing convinced people to use in place of washable, cloth handkerchiefs while also, through poor trademark protection, make it synonymous with facial tissue paper in general.  Your analogy would be more apt if people began calling all geysers Old Faithful, or even all geothermal features Old Faithful. Geothermal is the facial tissue paper in your Kleenex analogy.  It's a generic definition for a thing, not the specific name for one of the many global features of this natural phenomenon.
This was worse than my original email since I gave an unqualified legal opinion about trademark protection, another typo, and then I denigrated the aptness of his simile, which I called an analogy. My attempt to explain why I thought the state employee was wrong also hasn't aged well for me because I've since seen the first geyser known to modern Europeans, located in Iceland and named Geysir. Its name became the English word "geyser" for all similar hydrothermal features, including Old Faithful. It became the Kleenex of geysers, or Kleenex became the Geysir of paper facial tissue since Geysir's name was borrowed before paper facial tissue existed. Either way, since I couldn't find the email thread until recently, I had developed another analogy where ground source heat pumps are paper facial tissue.

  • ground source heat pump = paper facial tissue
  • WaterFurnace® = Kleenex®
  • geothermal power systems = cloth handkerchief
  • geothermal heat pump = cloth paper facial tissue

The terms "geothermal heat pump" and "cloth paper facial tissue" are each an oxymoron, like "stored heat." While geothermal power systems and ground source heat pump systems both touch the Earth, only geothermal power systems are designed to touch ground temperatures that can do useful work. Kleenex and handkerchiefs both touch noses, but only handkerchiefs can be renewed by the work of washing. My analogy might work better if one cloth handkerchief were worn out for every 4800 paper facial tissues since 1:4800 is the ratio of geothermal power (0.082 W/m^2) to infrared power (398 W/m^2) emitted by the Earth's surface. Geothermal power does not maintain the temperature of the ground, which is the source/sink of ground source heat pumps, the Sun and the atmosphere do.

False Claim: Ground Source Heat Pumps Use Renewable Energy

The U.S. EIA regularly reports on renewable energy production and consumption in Section 10 of its Monthly Energy Review. Table 10.1 is titled, "Renewable Energy Production and Consumption by Source (Trillion Btu)." Footnote "a" describing Production begins, "For hydroelectric power, geothermal, solar, wind, and biomass waste, production equals consumption." Geothermal Consumption is described by footnote "f" as "Geothermal electricity net generation (converted to Btu by multiplying by the total fossil fuels heat rate factors in Table A6), and geothermal heat pump and direct use energy."

The renewable geothermal energy consumption column from Table 10.1 is the top (blue) line in the following chart legend, and is the sum of consumption by the residential, commercial, industrial, and electric power sectors reported in Tables 10.2a, 10.2b, and 10.2c. The electric power sector geothermal consumption data, Table 10.2c, the second (teal) line, is equal to the product of the geothermal data in Table 7.2b, "Electricity Net Generation: Electric Power Sector (Million Kilowatthours)" and the total fossil fuels heat rate factors in Table A6 (BTU/kWh), divided by 1,000,000 to convert to trillion BTU.

The third (red) and fourth (tan) lines in the chart legend are California geothermal electric generation statistics. Increases in geothermal electric power production in other states have offset recent decreases in California. The third line uses a constant heat rate and the fourth line uses Table A6 heat rates to convert Gigawatthours to trillion BTU.

The fifth (grey) line, the difference between the total geothermal consumption (Table 10.1, blue) and the electric power sector geothermal consumption (Table 10.2c, teal), is the sum of the geothermal energy consumption by the residential, commercial, and industrial sectors (Tables 10.2a & 10.2b), which are plotted individually as the last three solid lines in the chart legend (maroon, olive, & blue).

The dashed lines in the chart are data from Table 4.17, "Geothermal energy consumption by direct use of energy and from heat pumps, 1990-2009 (quadrillion Btu)" from the Renewable Energy Annual 2009 (REA), published January 2012, the last edition of this discontinued EIA report. The total geothermal energy consumption reported (dark grey dashed) is equal to the sum of the geothermal energy consumption from the residential, commercial, and industrial sectors reported in Tables 10.2a and 10.2b. The green dashed line is "geothermal consumption from heat pumps;" the red dashed line is "geothermal consumption by direct use of energy."

In the same section of the REA, Table 4.11 reports manufacturers' shipments of ground source heat pumps in 2009 totaled 338,689 rated capacity in tons. From Table 4.17, the increase from 2008 to 2009 of "geothermal consumption from heat pumps" is 0.0085 quadrillion BTU. Assuming a heat extraction rate of 10,000 BTU per ton, those new heat pumps would need about 2500 full load heating hours to cool the ground by 8.5 trillion BTU. The EIA Monthly Energy Review sources for the data in Tables 10.2a & 10.2b are similar, "1989–2011: Annual estimates by EIA based on data from Oregon Institute of Technology, Geo-Heat Center. 2012 forward: Annual estimates assumed by EIA to be equal to that of 2011," excepting the last year of Geo-Heat Center data for the industrial sector is 2009, rather than 2011 as it is for the residential and commercial sectors.

The "geothermal consumption from heat pumps" reported in the REA, from the Geo-Heat Center, is an estimate of the heat extracted from the ground by the population of installed ground source heat pumps during the heating season. This is a false claim, repeated regularly by the EIA as consumption of renewable geothermal energy in its Monthly Energy Review.

Some interesting consequences of this false claim:
  • After annual updates of Table 4.17 "geothermal consumption from heat pumps" ended around 2010, the EIA assumed annual "geothermal consumption" by direct use and from heat pumps would remain constant thereafter. One impossible explanation for this is that ground source heat pumps manufactured since about 2010 are using the ground only as a heat source/sink while older ground source heat pumps continue to find renewable geothermal energy with their ground loops, as reported in the EIA Monthly Energy Review.
  • The geothermal energy accounting scheme used by EIA for ground source heat pumps does not account for the heat rejected to the ground when the heat pumps are in cooling mode.
  • If the growth of "geothermal consumption from heat pumps" from Table 4.17 had not stopped in 2011, it might now exceed the geothermal consumption by the electric power sector in Table 10.2c.

Grade school children are taught about the potential energy resources consumed by our built environment; fossil fuels, hydroelectric, nuclear, solar, geothermal, and others, and they are taught, "energy is the ability to do work." When they get to high school physics they learn, "energy can be neither created nor destroyed," the first law of thermodynamics, and they learn not all energy can do work, the second law of thermodynamics. The only useful work done by the ambient, climate dependent temperature of the ground is heating the cooler atmosphere. The surface of the Earth is a high temperature reservoir relative to the average temperature of the atmosphere, but it is a low temperature reservoir relative to our winter indoor environment. Most people who call ground source heat pumps "geothermal heat pumps" or claim GSHPs use geothermal or renewable energy don't have a basic understanding of thermodynamics or the geothermal nature of the Earth, but those that do understand know they are lying.


  1. The "geothermal" heat energy in soil is a product of the original accretionary (gravitational) energy of the planet's formation, solar radiation, and nuclear fission. The lowest temperature geothermal source currently used for electricity production is 53 C (326 K) at Chena Hot Springs in Alaska. Solar radiation provides ~255 K (as it would for any object with Earth's albedo at Earth's distance from the Sun) and the remaining ~71 C is provided by heat energy generated from the original accretionary (gravitational) energy of the planet's formation and from nuclear fission of heavy elements in the mantle and crust. All three of these forms of energy contribute to the subsurface temperature and can be considered "geothermal energy".

  2. I am surprised and disappointed to see this blog being circulated in the geothermal community, as it shows a clear lack of understanding about GSHP systems.

    In your email to the state energy agency, you claim that "They do not use renewable energy unless they use electricity generated from renewable resources.", demonstrating a clear lack of understanding between "electricity" and "energy". GSHPs never claimed to provide electricity, they provide heat - thermal energy. For someone who tries to summarize high school physics, you yourself are clearly missing some fundamentals.

    You go on to make the claim that the heat in the subsurface, tapped into by the heat pumps, is a result of the surface climate. While this may be the case in some shallow systems, in many (I would like to say "the majority") systems, particularly in northern climates, the temperatures are higher than the mean surface temperature. The heat is available because of the Earth's natural heat flux - therefore, "geo"-"thermal".

    You and your article by saying that "Most people who call ground source heat pumps "geothermal heat pumps" or claim GSHPs use geothermal or renewable energy don't have a basic understanding of thermodynamics or the geothermal nature of the Earth, but those that do understand know they are lying.". Clearly it is you who is spreading misinformation, and I hope that the reason is the former, rather than a delibate attempt at lying.