Opportunities Hidden in Plain Sight
With relative certainty, it can be assumed that energy is wasted in nearly all large industrial facilities, often unknowingly. Due to the inherent nature of the operating systems, much of the wasted energy cannot be harnessed (or become useful) no matter how hard one tries. Don’t be deterred, there is still wasted energy, ripe for the picking and waiting to be harvested in chilled water and refrigeration systems.
As heating, cooling, and process loads become larger, so does the opportunity. Refrigeration systems require the removal of heat to operate. The heat is simply rejected via a cooling tower or condenser into the atmosphere where it is thrown away.
Application, Application, Application
Just as location is the key to success in real estate and many businesses, the application in which a heat recovery chiller may be used determines its practicality and return on investment. Industrial facilities with a combination of year-round process heating and cooling demands are ideal. Food processing plants are the obvious candidate and can fit the mold perfectly. Foodstuffs are often heated in the process to kill bacteria (i.e. pasteurizing, blanching) and later cooled or frozen to preserve freshness.
The heating portion of the equation is almost always provided by a natural gas fired boiler and can be offset by a chiller’s heat rejection. Instead of being sent to the cooling towers, the heat from the refrigeration compressors can be delivered to the processes via a heat recovery chiller. This creates 140°- 160°F water on the condenser side and removes heat from the evaporator side before sending it back to the refrigeration or process cooling units, completing the cycle. Depending on operating temperatures, a COP of 3.0 – 5.0 can be expected. If the water cannot be used to supply 100% of the process or sanitation water, it can be used to pre-heat it, thereby recovering nearly all of the rejected heat from the refrigeration system. Excess heat can still be sent to the cooling tower, which will now operate much more efficiently with a reduced load.
Barriers and Bottom Line
So, why aren’t heat recovery chillers commonplace? The price of natural gas is a big reason; so is the cost of equipment, design, and installation. It’s just not as easy as plopping down a boiler and operating business as usual. Heat recovery chillers are best suited for use in new facility construction or plant expansions that increase heating loads. In these cases, an incremental cost analysis is used and may provide a better return when compared to purchasing a new boiler.