400 amp service -- what is required?

[JackMentink]

The units for a given load in the house will run the same amount of time. How could they not?

As I understand it no. If the temp outside is 60F then yes since ground temp is about the same. At colder temps like 32F the geothermal is using 60F water whereas the air heat pump is pulling 32F air. The geothermal will run much less for the same heat output.

You are close to correct, but it amounts to the Coefficient of performance (COP) of the units.

Theoretically a ground source heat pump with 60 degree water should be the same as an air to air heat pump went it is 60 degrees out side , but if you look at the COP's for both at those conditions the Ground source will be considerably more and use considerably less amperage. My ground source has a cop of about 5 at ideal conditions and air to airs typically are around 3 to 3.5.

The COP is actually a ratio of how much heat or cooling is generated for the the current used. I E a cop of 5 means 5 KW of heat is produced for 1 KW of electric used.

Some would say this is impossible as it is impossible be better thasn 100% efficient. But actually it is just transferring some of the energy stored in the 60 degree water to the air to heat or cool your home. That how it does it. You are borrowing the earths energy instead of paying the power company

 

[eepete]

As Jack M points out, the COP is indeed a big factor. A lot of this comes down the accuracy of a hand waving argument. As you start to tear it apart, the COP must be considered. There are also efficient changes when running the compressor at half it's rating, heat exchanger performance and depending on the mechanism used the efficiencies are different. The COP is the way to quantify all of these various system effects.

Here's another way to look at it. My geothermal units is outputting 98 degree air no matter what the outside temperature. My old air to air heat pump put out about 75 degree air when it was 30 degrees out, and that went down to about 68 degrees when it was 15 out. So heating a given room, the unit will run for less time if it's outputting 98 degree air then if it's outputting 75 degree air. ctgoldwing, I hope this makes sense and you can see for a given load in the house, the run times would be different. And as Jack M points out, this is using the heat in earth (the 60 degree water) which has more energy in it than outside air at 30 degrees.

When you start to track down the details, you worry about COP which deals with the efficiency difference of freon to air vs. freon to water heat exchangers, difference between the fan on an air unit and the pump for the water, and multi speed compressor efficiency differences. All the usual problems of how detailed you want to get. Drawing analogies between systems is just a good way to start to understand the differences and advantages of the geothermal system. So I hope this measured temperature data help, and Jacks' comments explain addition reasons why it's a win.

Pete