I have a Trane water to water heatpump and am considering doing this; My closed loop gets down into the 30's during heavy use and so my thought is that if I run the ground loop through a vacuum tube solar collector any heat that I add to bring the loop closer to the optimum 50d would help the efficiency of the HP. In the summer I would just shunt that part off and use it for domestic HW. I have two concerns 1) can I make the loop water too hot and cause a problem and 2) should I warm the water as it goes into the HP or after it comes out? I can see arguments for both options? Thanks for your input.

With only 2000 lf of pipe on a 6 ton heat pump, I can understand why your loop gets cold.

The solar collector sounds like a good solution. Heat pumps can handle incoming temps up to 90° in the cooling mode, so you should be okay up to 90°.

If the water gets hotter than 90°, I would run it into the ground first. If less than 90°, your heat pump will be able to heat your house very efficiently.

Let me know how it works.