I believe that to get peak efficiency from a geo system, it must be understood, monitored, adjusted on an as needed basis. Many changing factors continually determine the adjustment frequency. Any of you who have paid an electric bill where the emergency heat strips were on more than they should have been will agree.
Since the heat pump can do more than heat/cool your house the control system should allow you to take advantage of it. Example:
The heat pump can heat HW four times cheaper than direct electric heat and heat it for free when AC is running. Therefore the control system should be smart enough to turn the direct heat ON only when the HP is not available due to failure, being turned off etc.
The main challenge is to match the HP and the controls to particular house. Ideally the HP should run continuously at extreme condition while still maintaining sufficient temperature inside the house. That is the American way designing it.
In the Europe they design it for about 70-80% load and then cover the deficit by direct heat. The thinking is that the peak load is required less than 10% of heating/cooling time while the HP, ground loop and total cost of installation is significantly less. Additionally the smaller HP cycles less.
When the system is new it should be mandatory to check not only if it meets expectation but if there is room for improvement in efficiency and/or comfort.
Example: Typical setting for floor heating temperature is 110 F. But I found that it works as well at 90F. While ago the HP run almost continuously for few days during very low temperatures and high wind. It was able to maintain only about 90F of liquid entering the floor because almost all loops were ON. But the temperature in the house was still maintained at the desired SP. Therefore I set the HP set point to 90F. Since efficiency of the HP is proportional to inverse of the temperature differential I expect that the lower temperaure rise will save some energy.
