Ralph Waldo Emerson never said “Build a better mousetrap, and the world will beat a path to your door.” The mousetrap that likely inspired the misquote was invented seven years after his death. Unfortunately, many people take it literally. GHPs have all the hallmarks of a better mousetrap: They do the job of heating and cooling a building more efficiently than any other option. Despite the larger up-front cost, they are a mature technology and usually the most economic option for buildings that can accommodate them.
Not only can GHPs cut energy costs for heating and cooling by up to 80%, they can also provide other benefits such as essentially free hot water when in cooling mode, lower reliance on fossil fuels, and the elimination of above ground outdoor equipment. These advantages have earned GHPs a small but dedicated cult of true believers, but not broad market acceptance.
The world has not yet beaten a path to the GHP door. Instead, GHPs have a slim and only modestly growing market share. A study by Frost and Sullivan projects the market for GHPs in North American commercial buildings to grow at a 7.8% annual rate from 2012, 4.7% faster than the North American climate control market as a whole. An industry representative pointed me to a Navigant study which projects the world installed base to grow from 13.3 million tons to 36.2 million tons in 2020, see chart below.
Unfortunately, growth in installed base is not comparable to industry sales. For a young industry with a low installed base, sales are approximately the increase in the installed base. I eyeballed the chart to get annual estimates of world sales from the chart, and found that Navigant is projecting less than 5% sales growth in 2013 to 2015, followed by rapid growth (20-30 percent) in the 2016 to 2018 time frame. Navigant’s discussion makes clear that the later rapid growth rates require a revival of the economy and easier access to capital.
In the short term, Navigant’s study seems less optimistic than Frost & Sullivan’s, while it is more optimistic in the medium to long term. Using either projection, the near term less than 5 percent annual market share growth is clearly not the type of market transformation many would expect from a “better mousetrap.” Does the rapid market growth Navigant expects after 2015 have to depend so greatly on easy access to capital? Are other factors holding the GHP market back?
I struck a few raw nerves when I asked if air source heat pumps are a threat to geothermal heat pump suppliers last month, despite the fact that I answered my own question with a “no.”
Except in moderate climates, super-insulated homes, or situations where the installation of a geothermal heat pump (GHP) would be particularly difficult, GHPs have the better economics. This is despite recent advances in air source heat pump (ASHP) technology, which led me to ask the question in the first place. ASHPs don’t provide hot water, while many GHP systems can. Also, as the recent heavy snows in the Northeast demonstrated, there are some advantages to having a heat exchanger which is not exposed to the elements (see pic).
One advantage of a geothermal heat pump’s ground loop compared to the air source heat exchangers shown is that you don’t have to dig them out after a snowstorm. This pic also shows an installation problem which is allowed under manufacturer specs, but may lead to less than optimal performance if both pumps are operating simultaneously: one heat exchanger blows air directly at the other. This problem is analogous to poor ground loop design for GHPs.
ASHPs in Net-Zero Buildings
Given all these advantages, why the raw nerves? I suspect it’s because geothermal heat pump sales continue to disappoint and proponents are looking for someone to blame.
Another target of geothermal advocates’ ire is Marc Rosenbaum (who teaches the online Net Zero Energy Homes course in the Northeast Sustainable Energy Association’s Building Energy Masters Series.) He also raised hackles when he recommended minisplit air source heat pumps (ASHPs) for most single family net zero homes (I quoted Rosenbaum extensively in the previous article.)
He relates the story of the Putney School’s 16,000-square-foot Net-Zero Field House. The team designing this building modeled its heating costs using a GHP, and also using ASHPs with additional solar photovoltaics sufficient to provide the extra electricity needed to run the ASHPs. They found that it was cheaper to expand the solar system to power the ASHPs than it would have been to pay the extra installation costs of a GHP. Furthermore, the price of solar has fallen significantly since the Putney Field House was built; the price of the ground loop for a GHP has not.