airconditioning heat recovery for hot water

Hi Brian - this feature is fairly common in air to water heat pumps (ASHP) or ground source heat pumps (GSHP). The bad parts of the feature are:

1.additional cost for the heat exchanger involved as you mentioned. This is not an add on but must be a built in feature of the design as it affects the operation of the entire system.

2. In the winter you have to use additional kW to use the feature - there is no free heat being dumped to the atmosphere - still not too bad as the heat pump is far more efficient that an electric water heater as long as the electric resistance feature of the heat pump does not come into use. At zero degrees C (32 deg F) start to worry. 

3. In the summer the heat is free as long as you are using the air conditioning. If not then the heat pump must be run to get hot water. Still better than the typical electric hot water heater. If the hot water accessorie caused frequent starts/stops of the heat pump there would be concern over excessive wear & tear.

4. Thermal solar panel for hot water are far more effective. I turned off the power supply to our hot water tank the end of March and will turn it on again in November. Even during the winter months substantial hot water is available free. 

In building our new home (we move in this week) I opted for the solar panel solution. We typically operate the A/C unit very little due to our location. Here on the West coast of Turkey it gets hot but at our site we generally have breezes for natural cooling. There will be a few nights in August when A/C is necessary for comfortable sleep. In our situation I felt it was of no real value.

If the heat pump were to operate all summer then it is a good feature. Saves electricity as the COP/SEER of a new heat pump is far better than the 1-1 of electric resistance water heaters.