Topping 100% Efficient Domestic Hot Water
Recovering useful heat sounds like a no brainer, but suppose you could capture free process chilled water while making hot water. If you have year-round heating and cooling loads, a thermally driven heat pump, which works with a modified absorption refrigeration cycle, may be an excellent solution.
What is it?
Thermally powered heat pumps use ammonia, which is a standard industrial refrigerant, and water in an absorption refrigeration cycle to achieve relatively high hot water temperatures of more than 130F and low chilled water temperatures to 35F produced by the evaporating ammonia refrigerant. In order to run this heat pump, a heat source (fuel sources include natural gas, steam, or waste heat) and a little electrical energy is needed.
Breaking The 100% Barrier
No, this is not a “second law reversing” perpetual motion process. Water heating efficiency is defined as BTUs of thermal energy delivered by the process divided by the BTU content of the fuel or heat source. In this case 100% of the burned fuel is delivered in the process PLUS the heat recovered from the chilled water. Essentially, this is a water heater that is more than 100% efficient by the conventional definition of water heating efficiency AND it makes chilled water as a byproduct of the process.
Thermally powered heat pumps provide process hot water and process chilled water at the same time. Rather than making hot water with a boiler at 80% to 90% efficiency and chilled water with a refrigeration cycle at 0.6 kW/ton, you make hot water at roughly 140% efficiency and the chilled water is virtually free from a fuel input perspective.
Another advantage of using this type of system is that the unit itself consists of very few moving parts; the main part being a pump to pressurize the ammonia.
What Are Good Applications?
Any manufacturing processes that can use a continuous supply of heating and cooling is a good application. Like renewable energy and energy recovery measures, this technology should be applied where there are many hours of demand such as 24 hour-per-day food processing.
And like combined heat and power, you must need the heat that is generated anyway (i.e. you don’t have to build something else substantial that can make use of the heat or chilled water).