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Ground Source Heat Pump; same as a coal stove?

03 Jan 09 | Conservation, Environment, Geothermal

I read a lot of information on a daily basis.  A few months ago, somebody commented that a Ground Source Geothermal Heat Pump is the same as using a coal stove to heat your house.  The notion is that by purchasing and installing a GSHP, a homeowner is only pushing the problem further away (to the electrical generation plant), not actually reducing pollution.

Is that right?  Perhaps a little research is in order.

First, a little background.  A Ground Source Heat Pump (GSHP) uses a refrigeration cycle to move heat either to or from a heat sink which is typically a large coil of PEX pipe burried in the ground.  Wells, ponds and other sources can be used also.  The idea is that using the ground (or other source), which is a constant temperature of around 50 degrees F, a heat pump can be much more efficient than using resistance heating.

GSHPs are rated by a coefficient of performance, known as COP.  This is a comparison of the amount of electricity used by the heat pump vs. electricity used in resistance heating.  Thus a COP of 5 means the heat pump is producing 5 KW of heat for 1 KW of electric used.  The highest COP is about 6, or 600% efficiency compared to electric resistance heating. A COP of 5 is considered very good.

The electrical distribution system in the US is about 31.2% efficient.  Therefore, a head to head comparison of power used vs. heat produced would look something like this:

1 kWh = 3413 BTU

A GSHP using 1 kWh of electric with a COP of 5 produces 17,065 BTU heat.

The electric plant producing the current to run the GSHP burned 10,939 BTU of fuel to produce 1 kWh.  Therefore, a very well designed, well installed GSHP is about 156% efficient when all the energy requirements are considered.

A typical coal stove is about 60-65% efficient, therefore it would require 26,254 BTU to generate 17,065 BTU of usable heat.

Conclusion: A Ground Source Heat Pump ≠ a coal stove.  GSHPs are energy efficient and a good way to heat a home where solar resources are not available.  They are not 500% efficient, as some companies would have you believe, but are greater than 100% efficient if properly designed and installed.

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03 Jan 09 | Conservation, Environment, Geothermal | Comments (10)