Geothermally Speaking
by Denis Collet

Since the mid-19th century, fossil fuel based heating systems have been used to heat our homes. Wood and coal have given way to oil and natural gas, but we haven't replaced the furnace as the primary heating mode in the US. Faced with a global energy crisis and the prospect of environmental collapse precipitated by our continued exploitation of fossil fuels, many of us are rethinking how we consume energy, and have begun to upgrade our homes to support our personal and environmental commitments. Research into heating system alternatives has proved to me that geothermal or ground source heat pumps promise to be a viable sustainable heating alternative to burning fossil fuels. A properly installed, moderately efficient geothermal heating system can yield the same heat output of a highly efficient oil furnace, for about one third the operating cost.

A word about the principles of geothermal heat exchange. These principles are based on the fundamental law of physics that energy can neither be created nor destroyed, but only changes form. Some of the sun's light energy is transformed into heat energy and stored as heat energy (measured in British thermal units or Btus) in the earth. A heat pump simply brings Btus from the earth, whose temperature is relatively constant, to a cooler space or, conversely for cooling, transfers unwanted heat energy from that space into the earth.

The heat pump is not a new technology. The invention of the rotary compressor, however, constituted a real breakthrough in the efficiency with which heat pumps convert electrical energy into mechanical energy. It has made geothermal exchange a viable sustainable alternative to traditional furnaces while simultaneously eliminating the greenhouse emissions associated with fossil fuel combustion.

Based on operating costs alone, one might conclude that converting from oil or gas to geothermal should be a no-brainer, even if the installation cost runs ten or 20 times as high as purchasing a new oil burner. Alas, converting is not as easy as buying a system and turning it on.

An Incremental Approach
By 2005, the rising cost of fuel, the improvements in geothermal technology, and the omnipresent crisis of global warming converged in a way that made it clear to me and my wife that it was time to take action. My wife and I approached our objective of living in a carbon free home incrementally. Our first step was to invest in photovoltaic panels to generate electricity for our home. This effort allowed us to generate a surplus of electricity in anticipation of our intention of adding a geothermal system. The 12-kilowatt solar system we installed proved to be able to satisfy all of our electrical energy needs including lighting and the electrical power required by a geothermal heating and air conditioning system.

We installed the solar panels in April of 2005. Six months later, the engineer we had chosen to give us an estimate for converting our heating system from oil to geothermal explained the prerequisites. For his design to work, we would need to upgrade the insulation in the attic and tighten the building envelope, work that he himself would not do. After his recommendation for an insulation contractor didn't pan out, we went through several false starts before we found an insulation contractor to air seal the fixtures and possible leaks between the attic and second floor bedrooms, and to create a conditioned space that would be used to house the upstairs geothermal unit. This contractor also added a couple of feet of non-toxic cellulose insulation—a step that should have been done regardless of whether or not we converted to geothermal. (Improving the efficiency of the home by properly insulating may improve the efficiency of any heating system up to 20 or 30 percent.)

After insulation came the well. The design for our geothermal system called for using the domestic water well as the ground source heat exchanger, and for that purpose we had to change the type of well pump we used to a variable speed, constant pressure pump. The bottom line: installation of a new pump, as with the insulation, was not included in the quoted price of the geothermal system. I had to hire a pump specialist to replace the existing pump and wire in the special inverter required to control it. An additional requirement: a return line to the well needed to be installed to complete the water loop. This required digging a trench in the front yard to accommodate the return line (however here the geothermal contractor excavated the trench as part of his work). The installation of the geothermal heat pumps went in without incident. We turned the system on and voilà, it worked. Yet, as I watched the taillights of the installation crew disappear over the horizon, I had a premonition that I would be seeing these folks again.

Twists and Turns Along the Way
Now we had replaced our oil furnace with a ground source heat pump or geothermal system as our primary heating and air-conditioning source. Although the cost of converting our home from oil to geothermal had not been without complications or expense, the first day that we turned up the heat without hearing the muted roar of the furnace we were thrilled. It is hard to describe the sensation of walking into a warm home without hearing the background sound of the furnace. But the sensation was also eerily familiar—it was the same sensation I had the first time I stopped at an intersection in my Prius and wondered if the engine had stalled because the electric motor was still.

Today the benefits of the new geothermal heating system to our household budget and our health are undisputed, even though we still use the oil furnace to supply domestic hot water and supplemental heating in case of failure or extreme conditions. Our total annual energy bill now amounts to less than $800. Equally important: in the three years since installing solar panels and geothermal, our household has produced 80 tons less CO₂ than we would have otherwise!

There were, however, some further twists and turns to get to this point. The geothermal work was completed in mid September, 2005. A cold spell that lasted about a week in November brought on the first indication of a problem: The system suddenly shut down—the result of a safety device that locks the heat pump out when an event requiring immediate attention occurs.

I called the engineer who designed the system. He was responsive and spent considerable time trying to determine the root cause. Unfortunately, there was nothing obvious to blame. So, he reset the system and bid me adieu. The system seemed to be okay for a week or so, then it happened again. After several attempts to recreate the problem in order to nail down the cause, the sensor was identified as the culprit. The engineer replaced it twice before determining that it probably wasn't the problem after all. Next step was to contact the manufacturer's engineering support. They were on vacation for the holiday beginning Christmas week and not returning till January 5.

Luckily we could rely on the heat provided by the oil furnace as an emergency backup. Still, our first "geothermal" season was spent with an intermittent lockout, continually resetting the system, and continued use of oil. Finally, after an entire season of trial and error, we identified the problem as well water temperature so cold that it locked out the system—a situation the design engineer never anticipated. After an additional expenditure of $2,000, the problem was resolved.

What are we to conclude from these experiences? Clearly the suppliers of geothermal heat exchange technology for home use constitute a fledgling new industry and are still stuck on a learning curve. Insufficient manufacturer's technical support, the lack of diagnostic tools or an established routine for finding the root cause of problem are real hindrances to its further development. Unlike oil companies, which offer low cost service contracts as a way of locking in the home owner into purchasing fuel from them, solar and geothermal providers get no income from the solar or geothermal energy their systems allow us to tap. System efficiency and performance for the geothermal provider are critical to their success.

Another concern I have about the current geothermal industry is the warranty period usually offered. Often the coverage is not aligned with the product. An engineering design problem may go unnoticed until the system has run under the varying load conditions during the heating or cooling season. If the system is installed in the spring, an error may not be observed until the following winter. When the time comes for you to select a geothermal system and installer, make sure that the manufacturer guarantees that the installer will be supported and that they will send a field representative to fix a problem if the installer cannot. Amend the contract to extend the warranty coverage to cover a complete heating and cooling season.

Entering our fourth heating season with geothermal as our primary heating and cooling system, I am convinced that the decision to invest in geothermal in 2005 was the right one despite some aggravation and additional cost. We are now looking forward to a new addition to our sustainable energy portfolio: adding solar thermal to generate domestic hot water. This will bring us even closer to a carbon free home.