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Note 22. Low-Temperature Heat Sources & Sinks for Heat Pumps and Cooling Equipment

The Energy Efficiency Manual provides many energy saving improvements for heat pumps, air conditioning, and other cooling equipment. This Note shows how to improve their efficiency of by using heat sources and heat sinks other than the atmosphere. You will learn the advantages and disadvantages of soil or earth sources; ground water or well water; surface water, including lakes, streams, and rivers; solar collectors; and, waste heat from industrial and domestic sources.

You can increase the efficiency of cooling equipment by lowering the temperature at which the equipment rejects heat. The most common heat sink for air conditioning and industrial cooling is the atmosphere. The disadvantage of the atmosphere as a heat sink is that it gets warmer at the same time you need cooling. You can reject heat at lower temperature by using the soil, well water, or surface water as a heat sink. These alternative heat sinks can typically lower the average condensing temperature by 20°F to 30°F (11°C to 17°C), substantially increasing cooling efficiency.

Similarly, you can increase the efficiency of heating with heat pumps by increasing the temperature of the heat source. Again, the atmosphere is the most common heat source for air-source heat pumps, but the atmosphere gets colder at the same time that you need heating. Soil, well water, and sometimes surface water are warmer heat sources during cold weather. Depending on climate and the nature of the heat source, the average heat source temperature may be 10°F to 30°F (6°C to 17°C) higher than the air temperature.

Heat pumps can also use solar collectors and waste heat as low-temperature heat sources. These sources are available at all times of the year. Certain types of solar collectors offer the possibility of using the collector as a heat radiator at night, so this type of collector can operate as both heat source and heat sink. The Note gives you the details.