GeoExchange or Ground Source Heat Pumps are one of the most efficent ways in which to heat a building. The idea is to take advantage of the heat storage capabilities of the earth and leverage that using a heat pump to create ultra efficient heating and cooling.
Properties of the Earth
The earth can be thought of as a solar battery, collecting and storing the energy of the sun over the course of the year. The temperature gradient of the earth several meters below the surface has 2 properties that make it an ideal source for heating and cooling. The deeper we go into the ground, we find that the variation in temperature decreases compared to the temperature of the surface and secondly the seasonal temperature swings below the earth lag behind the temperature change up on the surface. The resultant effect of these conditions is that 3m-10m below the surface the mean earth temperature is relatively constant at around 10˚C.
In geothermal terms this is considered low-grade heat but when leveraged with a mechanical heat pump it is very useful and efficient source for heating and cooling.
How it Works
At a mean temperature of approximately 10˚C, the earth is cooler in the summer than average air temperature and warmer in the winter than the average air temperature. As such, it can act as a sink and source for our cooling and heating needs.
Using the same mechanical process as a refrigerator, the geoExchange heatpump can draw heat from one source and dump it to another.
In the Ground: There are several methods to draw heat from the ground.
Horizontal Trench – If there is land available, horizontal trenches can be dug and slinky loops of HDPE pipe can be laid and buried. This length of pipe is sized to accommodate the heating and cooling needs of the building.
Ocean/Lake Loop – Similar to a horizontal trench, if there is a large body of water available, loops can be anchored down into the body of water which is an excellent source
Vertical Borehole – if space is a problem, a vertical borehole can be drilled and a pipe runvertically into the ground
Vertical Well – if there is abundant ground water source available a ‘pump and dump’ system may be possible, pumping water from one source, through a heat exchanger then returning it back to the ground.
Heat Pump - the heart of the system
The Heart of the system is the heat pump. The heat pump is a mechanical system utilizing the vapour compression cycle to move heat from one location to another in the same process as a refrigerator. What is unique with a heat pump is that it is reversible and can move heat from the ground to the building or in reverse remove heat from the building to the ground. The heat pump requires electricity to operate but no other fuel source.
Delivery System – A geoExchange heat pump systems can deliver heat to either (or both) a forced air or hydronic heating system and can also provide heating for domestic hot water making it a flexible system for both new construction and retrofits.
The main advantage of using geoExchange heat pumps are their efficiency. For every one unit of electrical energy used to run a heat pump, 3-5 units of heat energy are created. Compared to an electric baseboard heater (1:1 efficiency) it's 3-5 times more efficient. In comparison, natural gas or oil fired heaters have a efficiency of 0.5-0.85.
Apart from their efficiency, geoExchange heatpumps are quiet, housed indoors for a long lifespan, and only require electricity to run. Removing the reliance on fossil fuels for heating is both environmentally friendly and provides energy security.