I was listening to the radio the other day where the topic of discussion was a migration path away from using fossil fuels for heat. The guest was from a part of the world where apparently they don’t have a season called “winter”, and was claiming that geothermal heat pumps could “easily” replace all the fossil fuel burning heating systems pretty much anywhere in the world, as well as provide “all the cooling needs” you could ever need in the summer.
It would be a fascinating discussion if they were talking about another planet, but what started to cause my blood to boil was the fact that this nut was talking about making it mandatory over the next 30-50 years to remove what he called the “inefficient, fossil fuel burning, carbon-emitting natural gas furnaces” in [our] homes with ground source heat pumps.
First of all, I’ve looked into this concept with great interest for my own education. In fact, I am subscribed to a number of newsletters and online magazines aimed specifically at alternative energy and “green” building concepts. I’ve read many articles dating back to the 1980’s on geothermal, or ground-sourcing your heat for home envelope conditioning. The fact that most of these tree-huggers always seem to neglect is that in order to run a heat pump system, you need to have a PUMP, and that pump takes a considerable amount of energy to move the volume of glycol (or similar) solution through the hundreds or thousands of feet of tubing buried in your back yard to extract or dump heat from or into the ground. Often this electrical demand is actually HIGHER than that of your forced air, natural gas furnace, so your electrical need is actually higher – not lower – with a ground source heat pump system.
Second, one of my friends owns his own HVAC company and has a customer who prided themselves on using a ground source heat pump to acquire all the heat they thought they needed for a new building they had designed – a boast that was augmented by the fact that this customer deliberately did not install a natural gas connection to their facility when it was under construction. Now, after two years in operation, they have cooled their ground loop to 34 degrees Celsius, effectively draining it of all heat energy. Not only have they had to rent portable, temporary propane-powered boilers, costing in excess of $4,000 / month to maintain their operation, they are having to pump heat back INTO the ground to try to replenish their ground loop’s energy supply. The current estimates are that with the boilers running at the current rate and cost, it will take 17 years to return the ground temperature to it’s original level when they began to extract heat from it TWO YEARS AGO. Simply put, it has been a colossal failure.
He explains the reason for this failure: All of the energy estimates that were used to design the building assumed the earth temperature was a constant, and would remain so indefinitely. In reality the energy stored as heat within the ground is also a finite resource. If you dig a well and then pull all the water out of that well, it will take time for it to replenish – and it usually takes a lot more time to replenish the water than it does to extract the water. Heat is no different – in fact – it’s almost worse. Because of the insulative properties of the upper layers of the earth’s crust, the soil and clay that ground source heat systems are integrated into are very well insulated from the surface. The daily and seasonal fluctuations that affect the surface temperature take YEARS longer to affect the ground temperature. When you extract all the heat from the ground deep beneath the surface of the earth, all that insulation now works against you in preventing new energy from the sun from replenishing it, and the ground essentially remains cold. Now the ground source heat pump is useless as a heat source. Of course, it would be significantly more effective now as a heat sink, but this customer’s needs for heat far exceed it’s ability to replenish the energy they extract, and now it is costing them even more than the original installation due to their lack of foresight and the missing natural gas connection – now prohibitively expensive to install “after the fact.”
The simple truth is that no alternative energy source is even close to being as efficient as fossil fuels. If we are ever going to get off fossil fuel dependency it is not going to be by finding alternative energy sources that provide as much energy yield as fossil fuels, but will be by drastically reducing our appetite for energy – not something many people talk about these days.