Don’t throw that away, we can use it
Think of all the improvements we make in our daily lives to reduce waste and our negative impacts on the planet. Take recycling, for example — the last I heard, Americans recycle about half of our aluminum. That means we are taking 50% less aluminum from mines and putting 50% less aluminum into landfills; not bad but there is room for improvement. It’s easy to recycle aluminum cans, paper, plastic, and even heat… yes heat. Heat is one of the most efficient resources to recycle and one of the most commonly wasted resources today.
Chillers, not just for chilling anymore
Contrary to what you may think, it is possible to “recycle heat” and do it efficiently, especially in industrial processes. Many industries employ processes and space conditioning that use large amounts of heating and cooling simultaneously: food processing facilities, printing facilities, and facilities that house both offices and industrial areas, just to name a few. In a standard chiller plant, the chiller takes heat out of the chilled water loop and sends it outdoors to the cooling tower where the heat is dissipated into the atmosphere. In many industrial cases, that heat can be recycled. In conventional chiller control, heat rejection occurs at 85-90F, which may not be warm enough for many uses; but there are solutions.
How it works
A heat recovery chiller is basically another chiller that can take the 85-90F water that would normally go out to the cooling tower and recycle it for use in the process or in space conditioning. These chillers typically produce a heat recovery loop with temperatures varying from 110 -130F, which is much more useful than 85-90F water. Take, for example, a 200 ton chiller. A heat recovery chiller installed on the condenser loop can expel 200 tons or 2,400,000 Btu/hr, plus the energy used by the chiller, in to the heat recovery loop. Plus the cooling tower has to reject 2.4 million Btu/hr less, resulting in reduced cooling tower energy consumption, or in a new system, a smaller, less expensive cooling tower. This recovered heat can then be used to heat make-up air, reheat make-up air after dehumidification, preheat boiler make-up water, preheat domestic hot water or process hot water. The options are endless.
It should be noted that not all chiller types can produce this hot of water on a continuous basis with out being damaged, so it is important to install a chiller type that can handle these temperatures (which is why you shouldn’t increase your condenser water temperature on the chiller you have). Most heat recovery systems use multiple scroll or screw chillers for both longer life and efficiency at the higher temperatures.
Basically, for the electrical cost of running the chiller, you get some or all of the heat you are removing from your chilled water, a reduced load on the cooling tower, and all the power you put into the chiller back as heat. Sounds like a win, win to me. Paybacks vary greatly due to process types and utility rates, but facilities that have a year around chilled water load and a steady process heat or space conditioning load are good candidates. Savings for these systems can be upwards of $250/ton annually. This doesn’t sound like much but for the 200 ton chiller mentioned above, that’s $50,000 a year! A properly designed and installed heat recovery system is like finding a pile of money in your back yard, Jackpot!!