I'm having a geothermal heating system installed in my home, and the contractor recommended heating my water using a buffer tank and desuperheater, which is a device that cools the refrigerant lines of the heat pump (when the heat pump is in heating mode) and uses the heat it captures for heating the drinking water in the buffer tank.

However, when the heat pump is in heating mode, the exiting refrigerant line is actually colder, not hotter, than when it enters. As a result, you cannot heat water during the winter.

I recently became aware of water-sourced heat pump water heaters, which basically act just like the heat pump for the home, except their only job is to heat a water tank. This seems to make a lot of sense for a house, however, because you could use the same geothermal water loop in the summer or winter to heat water; I would lose the "free" water during the summer and would have to pay for running the heat pump, but during the winter the price of hot water would remain the same low amount, instead of rising due to the need for full-time use of an electric or gas hot water heater.

Am I missing something important, or is there some reason why the internet and contractors seem to only suggest the desuperheater approach?