03.21.13

Harvesting the Energy Stored in the Ground Below Us

Posted in Uncategorized at 6:22 am by Administrator

In an earlier blog posting I discussed ways that residential and commercial electricity consumers can reduce their draw on the utility grid either by generating some of their own electricity or by using geothermal heat pumps (now more commonly referred to as geoexchange systems) to provide heating and cooling. Because space heating in the winter and air conditioning in the summer represent the most significant drivers for peak electricity demand the ability to use the energy stored in the earth to “clip” these peaks is very significant.

But how does geoexchange really work? It is somewhat counter-intuitive to think that the ground which is at a temperature of approximately 50 degrees Fahrenheit can heat a home to 70 degrees.

In this case the “secret sauce” is the use of a refrigerant, most commonly a substance with the romantic and memorable name R-410A. The boiling point of R-410A is highly dependent upon pressure and varies within a temperature range which matches human comfort zones. By using a closed system with two different pressures it is possible to cause the fluid to evaporate and condense at specific temperatures as shown in the graphic below.

The low pressure zone including the evaporator is located outside the home. Refrigerant fluid is at a temperature warm enough to evaporate but needs to absorb heat from the ground in order to make the transition from fluid to vapour (1). During this process the mixture of fluid and vapour warms up to the ambient temperature of the ground, in this case about 50 degrees Fahrenheit.

An electrically powered compressor is then used to rapidly increase the pressure of the vapour in order to raise it’s condensation temperature(2).

The high pressure zone including the condenser is inside the home and the transition from gas to fluid releases heat into the home (3). During this process the mixture of fluid and vapour cools to the ambient temperature inside the home, in this case about 70 degrees Fahrenheit.

The fluid then passes through an expansion value which drops the pressure in order to reduce the evaporation temperature(4).

The low pressure produced by the expansion value is chosen so that the R-410A will evaporate at a temperature significantly lower than the ambient ground temperature. The high pressure produced by the condenser is chosen so that the R-410A will condense at a temperature significantly higher than comfortable room temperature. A typical configuration is shown in the graphic below.

In cooling mode the flow of the fluid is reversed. The fluid is evaporated by the hot home and the hot gas is compressed to bring it to the upper condensation pressure and temperature. The hot gas is then circulated through the ground where it condenses, releasing heat. The expansion valve is then used to bring the fluid to the lower evaporation pressure and temperature.

It is important to note that it does take electricity to run a geoexchange system – for the compressor, one or more pumps for the fluid, and usually a fan to force the warmed/cooled air through the home. However, a system that is designed well and installed properly should be able to deliver 2-3 times as much heating/cooling as a comparable electric system and even more when compared to a natural gas system.

So why isn’t everyone doing geoexchange? The main reason is cost. For a typical single family dwelling the cost of installing a geoexchange system is in the range of $25,000, at least twice a comparable furnace/air conditioning combination and probably 3- 5x a furnace only system. Most home-owners are not prepared to make that kind of investment. That’s why I argued in my earlier blog that the local electrical utility should own the geoexchange system (just as they own the traditional electrical distribution equipment like transformers).

Costs/home would be greatly reduced if geoexchange was installed for an entire neighbourhood. And regardless of how many times a home changes hands the utility would continue to benefit from a lower electricity demand for decades to come. I personally would like to see building codes modified so that geoexchange was required for every new housing development – just like electricity, water, and sewer services.

The case for geoexchange in large commercial buildings is even more compelling. Here again short-term cost is the barrier and here again a utility company can make a great long-term return on this type of investment.

In the meantime Post-Secondary institutions are demonstrating just how effective geoexchange can be. With multi-building campuses that often already have central heating plants these institutions are in a great position to show leadership with this technology and recent headlines indicate that is starting to happen in a big way.

On March 3, 2013 the Board of Governors of the University of Maine at Farmington approved a $1.55 million geoexchange project which will replace aging oil-fired boilers and eliminate the burning of 28,000 gallons of oil yearly. The system will pay for itself in 8-10 years after which both heating and cooling of the campus will be essentially free for decades to come.

Perhaps the most encouraging aspect of the UMaine project is that it is built upon past successes with geoexchange. Earlier projects implemented this technology for the education center and a swimming pool and fitness center.

February 13, 2013 marked another geoexchange milestone as the Missouri University of Science and Technology closed on funding for a $2.5 million geoexchange project which will provide heating and cooling for 2/3 of the buildings on the campus in Rolla, Missouri.

Missouri S&T Chancellor Cheryl B. Schrader stated that “the system is one of the most comprehensive ever undertaken by a college or university”.

Post-Secondary institutions in Canada are also making use of geoexchange to reduce campus carbon footprints.

The University of British Columbia plans to use geoexchange for its entire Okanagan campus home to more than 8,000 students.

In 2007 the British Columbia Institute of Technology formally adopted the concept of transforming BCIT’s campuses into living laboratories of sustainability. Theory was transformed into practical application that year as the new Aerospace Technology Campus was opened incorporating geoexchange and other technologies designed to minimize the environmental impact of this state-of-the-art facility. The concept was applied to the Gateway project which saw a major renovation of one of the most important campus buildings, again incorporating geoexchange.

Geoexchange technology has developed to the point where it represents the best solution for commercial and institutional heating and cooling. By reducing the electricity loads that cause almost all of the highest consumption peaks (heating on cold winter days and cooling on hot summer days) geoexchange can “clip” these peaks providing relief to regional generation and transmission systems.

Widespread adoption of geoexchange is such an obvious choice that I hesitate to characterize it as a “Black Swan”. However, the potential to dramatically smooth out power consumption curves makes this technology one that could radically change the electricity supply/demand balance – in a very positive way.


17-Apr-2017 Update: A company in Vancouver, Canada is selling a different form of geoexchange which makes use of roof-mounted panels to provide heat by extracting energy from the ambient temperatures outdoors.

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