I've seen homes with old units out by the A/C that heats the water for the hot water tank and want more info.

Question

I live in Florida and on some of the homes there are these units out near the A/C that heats the water by using the exhausted heat from the A/C and sends it in to the hot water tank. Does anyone know what these units are called and do they still make them?

Answer 1

That product is called a heat recovery unit. The hot refrigerant gasses are circulated through a loop of copper pipes and the home's water supply is circulated in a loop as well, abutting the hot refrigerant gas. Theoretically, the heat given off by the hot gasses is transferred in part to the cold water, heating it up.

This saved energy on two counts. Less conventional water heating was required, and cooler refrigerant gas was being sent to the compressor. Sales of this product were driven by rebates from utility companies and big energy savings. They are still manufactured, but not an investment I would recommend on a modern a/c system.

As split systems became more efficient, the energy savings from these units diminished, and utility companies stopped the rebates. Now, the numbers don't make a lot of sense. This rather expensive device has fallen prey to the law of diminishing returns, to be replaced by more modern energy-saving methods, such as dual-speed compressors and variable-speed blower motors.

Here is a scientific look at heat recovery from the University of Florida. It indicates, among other things, that a relatively inefficiant unit is required for this process to be effective:

http://www.p2pays.org/ref/08/07362.pdf#search='heat%20recovery%20unit%20air%20conditioning'