Earlier in this series of articles, I discussed
using the waste heat in available on-site water-based sources to heat water. Essentially, you just add a water-to-water heat pump system that allows you to move a lot of heat to a useful function with the expenditure of just a little energy.
Wouldn't it be nice if you could do this sort of transfer of heat from a waste source to a useful function without requiring the addition of a compressorized system?
Well, in existing refrigeration systems, there already exists a source of heat that is usually of a temperature that can provide useful heating for a domestic hot water application without need for additional compressors: The compressor superheat.
In a refrigeration process, where
cooling is the desired function of the compressorized system, this compressor superheat is essentially waste heat, and serves no useful purpose. It is simply thrown away to the environment through whatever heat rejection process the system employs. But this compressor superheat was put into the system by the energy used to run the compressor, and therefore was paid for once by the operator of the equipment. Instead of paying for it again in the operation of the heat rejection fan or cooling tower, why not instead use it for something, saving the heat rejection costs and reaping a real benefit?
It was this sort of thinking that prompted Florida Heat Pump to develop their
HRP Heat Recovery Package (pdf). This is an add-on heat exchanger that transfers the compressor superheat directly into a domestic hot-water source--using double-walled heat exchangers to protect the potable system.
The heat from the desuperheater system provides supplemental heat to the domestic hot water system any time the compressor operates--in heating or in cooling. This can greatly reduce the amount of electric or gas heat required for water heating--even completely displacing this direct heating during many times of the year, depending on the building loads and use of the space.
(Note, however, that the compressor superheat is lost to the heat pump space heating process and therefore the space heating capacity of the heat pump will be reduced by the capacity of the desuperheater. As long as this is taken into account in the sizing of the heat pump, this presents no problem to operation.)
But water-source heat pumps represent only a small part of the compressorized systems that are exisiting or installed every year. It seems there is an opportunity for taking advantage of this same heat source on many other systems and on existing equipment, too.
That is where the
Heat Harvester Heat Recovery System can be used to great effect. This heat recovery system is a stand-alone desuperheating device that is pre-designed for various compressor system capacities and is available for retrofit on existing or new systems.
How much heating potential is there? Well, Heat Harvester has provided an
interesting analysis of the desuperheat capacities of compressorized systems:
| Size of Air Conditioning
System tons | Gallons of Hot
Water per Hour | Gallons of Hot
Water per Day |
| 3 | 15-to-25 | 180-to-300 |
| 5 | 25-to-40 | 300-to-480 |
| 10 | 50-to-80 | 600-to-960 |
| 20 | 100-to-160 | 1200-to-1800 |
| 30 | 150-to-240 | 1800-to-2880 |
These systems can be economically installed into just about any compressorized systems using positive displacement compressors: Scroll and Screw air-cooled chillers, Rooftop packaged units, Condensing units, CRAC units, you name it. Since the Heat Harvester heat recovery system consists of a package with a heat exchanger and a pump, the installation basically involves a little refrigerant and water piping. And in a cooling-only application, all of the heat recovered would have otherwise been lost to the environment.
