Basic Principles

Background: Cooling demand in Germany

Currently, electrically operated compression refrigeration systems are almost exclusively used to provide cooling; therefore, approximately 15 percent of the electrical energy consumed in Germany is expended to operate cooling or air conditioning systems. [1] This value will rise in the future, because the demand for air conditioning in Germany is expected to increase by 50 percent by the year 2030. [2] This shows that in order to meet environmental and climate goals, the potential presented by sorption cooling to increase energy efficiency should be fully tapped, where it is economically feasible. Sorption cooling systems can generate cooling from waste heat. Therefore, the electrical energy required to operate compression refrigeration systems can be cost-effectively replaced by exploiting already available waste heat. Consequently, overall electricity consumption can be reduced as well as CO2 emissions by approximately 30 percent.

Basic principles of refrigeration

Chillers are designed based on the principle that cooling is generated when a liquid evaporates; and inversely, condensation releases heat. In order for a liquid to evaporate at a low temperature (e.g., 6°C) and condense at a higher temperature, different pressures must predominate within the system. A liquid refrigerant is evaporated, compressed, liquefied and expanded in a cycle. The refrigerant can release absorbed heat through the compression and subsequent condensation at a higher temperature. With sorption technology, a “thermal compressor” provides the compression by using a heat source. In conventional chillers, the compression is generated by an electrically driven pump

Chiller Efficiency

Chiller efficiency is expressed by the performance value, the energy efficiency ratio (EER). Efficiency is also often denoted by the coefficient of performance (COP). The EER and the COP express the relationship between cooling capacity and the power input. Typical EER values for simple lithium bromide/water absorption refrigeration machines are between ca. 0.55 – 0.70. [3] This means that ca. 1.5- to 2-fold the amount of cooling must be input into the system as driving heat. In electrically driven compression refrigeration machines, EER values are in the range of 2 – 5. [4] In this range, 2- to 5-fold the amount of cooling can be generated by electrical energy.


[1]: Müller W. (2011), Beitrag der Kältetechnik zum Klimaschutz, Bundesumweltministerium, Berlin.

[2]: Berliner Energieagentur GmbH (12/2007) Summerheat – Meeting cooling demands in summer by applying heat from cogeneration. Berlin

[3]: Henning Hans-Martin, Urbaneck Thorsten, Morgenstern Alexander, Nunez Thomas, Wiemken, Edo, Thümmler, Egbert, Uhlig, Ulf (2015) Kühlen und Klimatisieren mit Wärme. Bine-Fachbuch.

[4]: DIN V 18599-7 (2007), Energetische Bewertung von Gebäuden – Teil 7, Beuth-Verlag, Berlin.