Carrier running strip heaters often
My father in law just built a new house in South Dakota with a Carrier ground source heat pump. He is having some trouble with it, as the auxiliary strip heaters keep coming on and he is spending a lot more money heating than he expected.
I don't know all the details (I live far away), but here's the basics:
It's a Carrier 3 ton model 38-something
His water source is 52F groundwater, with waste dumped into a separate well.
The return water is 9 degrees cooler, indicating that heat exchange is occurring.
He has an insulated crawlspace of a few feet, with the ductwork running uninsulated under the house. He had some crawlspace vents that were accidentally left open, but they are closed now without a great improvement.
When outside temperatures are in the 30s and 40s, the crawlspace is a comfy 65F.
The pump is rated at 10 gallons per minute, but the installer put in a choke to 3 gal/min because he said the manf. called for it. (Why not open this up?)
So, the basic question is, why do the strip heaters keep coming on and running up the electric bill? Is too much heat being lost to under the house? He had a ductwork guy out, but he said the ductwork should not be insulated under the house. We were thinking maybe he was losing too much heat to the environment under the house.
It's a new house and well-insulated. He is disappointed in the whole project and isn't getting anywhere with the contractor or subcontractor. Any thoughts on this? Thank you, experts.