I’m always surprised when clients don’t move forward with a heat recovery chiller when it’s a good fit with solid advantages. I hope that when you finish reading this, you too will see why this is a no-brainer.
What is a Heat Recovery Chiller?
The physics of HVAC is simply the removal (if cooling) or addition (if heating) of heat energy. The Law of Conservations of Energy states that energy can neither be created nor destroyed only converted from one form of energy to another. Whether water-cooled or air-cooled, a chiller removes the heat energy from the water that enters its heat exchanger and expels it to another place, usually the atmosphere. Instead of expelling this heat into the atmosphere, the process of heat recovery transfers that heat energy to your hot water loop, taking waste energy and converting it to useful energy.
Again, The Law of Conservation of Energy comes into play. The boiler is your most inefficient piece of equipment. So, anything we can do to unload the boiler or use less energy will dramatically improve the system. The science behind how boilers work explains why this is the case (we can get into how boilers work in a later blog).
A Real-Life Example
One client had a 1,500-ton cooling load demand during peak summer days. In addition to this, they had a continuous boiler demand for domestic hot water and process needs at their facility on the South Carolina and North Carolina border. The client had a big push for energy savings from their umbrella company and asked if we knew any solutions. My first thought was… heat recovery!
Although the plant did not require another chiller, they came to understand the value of adding a heat recovery chiller. The client expected payback in less than two years. The energy savings met their corporate initiative, and they were soon sold on the idea.
We sized the chiller for their minimum needs on both the hot water side and chill water side to stay on continuously. This came out to be about 300 tons of constant demand. We tied the evaporator loop into their main chill water header and connected their condenser water loop into the domestic water line just before it entered the boiler. Water from the street typically came into the boiler at 70℉, and the boiler performed the work to heat it to the required temperature for the building. By running the 70℉ water through the chiller’s heat exchanger, we could then heat it to 125℉. So, the boiler’s delta to heat the water improved by 55℉, making it drastically unload and waste far less energy.
The best news of all? After measuring kilowatt-hours at all points, we found that the additional chiller had a payback of only one year! The clients were ecstatic.
Why Shouldn’t you Pursue Heat Recovery?
As you may have guessed from this blog post, you must have a simultaneous heating and cooling need. In some cases, when you have a heating demand most of the time, you can add a bypass to reject the chiller’s heat to a cooling tower instead of the boiler loop when there are little to no heat needs. You should add heat exchangers so that you aren’t mixing treated water with domestic water, but we can figure all of that out to keep everyone safe. Keep in mind that if the simultaneous need is not there, the payback diminishes, and you may be better off with a high-efficiency chiller solution. But we can dive into that together if this might be a better solution for your needs.
Lastly, the advancements in chiller technology have allowed the heat recovery concept to expand beyond water-cooled to include air-cooled chiller options. If you have a water-cooled or air-cooled chiller plant and would like some outside-of-the-box ideas, don’t hesitate to contact us at: firstname.lastname@example.org or 1-855-761-HVAC. We have staff all over Virginia, Tennessee, North Carolina, South Carolina, and Georgia.