Cooling demands in districts

Where do cooling demands occur?

Around 70 TWh of electricity is used annually in Germany for the provision of cooling. In the future, the cooling demand will continue to increase, with annual growth rates of up to 5% [1]. Cooling is used in various sectors: industrial refrigeration applications include process cooling, storage of temperature-sensitive products, cooling of server infrastructure, or air conditioning of control cabinets. Building air conditioning includes, for example, the air conditioning of office buildings, educational institutions (schools and universities), residential buildings, and retail and wholesale trade (e.g. shopping centers and department stores).

Full load hours of space cooling

Applications in the field of air conditioning have only low full load hours in Germany. The guidelines for energy demand certificates in non-residential buildings (EnEV 2009 edition) indicate full load hours of 500 h/a for office buildings and 350 h/a for educational buildings. A study by the Federal Environment Agency indicates full load hours in the range of 400 to 520 h/a. Measurement data collected in the EvaSolK research project indicate full load hours between 170 and 430 h/a for air-conditioning systems. Overall, it can be observed that due to safety margins and climatic conditions, the refrigeration technology is often overdimensioned.

Cooling technologies

Refrigeration technology can be electrically or thermally driven. For small refrigeration applications, electrically driven units are more common. In industrial applications with high thermal capacities, thermally driven chillers are also used. In these systems, for example, heat from combined heat and power units (CHP) is converted into cooling in absorption chillers, allowing efficient use of CHP heat even in summer operation.

Compression chiller

The electrical supply is compression chillers (also called split and multi-split units). Decisive for the calculation of the electrical power consumption is the coefficient of performance (COP) or the averaged annual value, the so-called seasonal coefficient of performance (SCOP). According to DIN V 18599-7, a reference value of 2.9 can be assumed for multi-split units. However, this depends strongly on the boundary conditions (especially temperature levels) and should be determined individually for each project.

Absorption chiller

Thermally driven refrigeration technology involves absorption chillers. They use heat at a high temperature level to generate cold. Furthermore, a waste heat flow is released at ambient temperature. The ratio of thermal input energy and generated cold is expressed by the heat ratio. Typical heat ratios range between 0.6 and 0.8. For H₂O-LiBr absorption chillers, a heat ratio of 0.71 is reported in DIN-V-18599 for a chilled water temperature of 6/14°C, a cooling water temperature of 27/33°C, and an input heat temperature level of 80/70°C.

Sources

1. Ecodesign, 2008.Lot 10 Chapter 1: Preparatory study on the environmental performance of residential room conditioning appliances (airco and ventilation) – Task 2: Economic and Market analysis (Entwurf),
2. Preuß, Guntram, 2011. Energiebedarf für Kältetechnik in Deutsch (Entwurf), VDMA - Fachverband Allgemeine Lufttechnik
3. Nachhaltige Kälteversorgung in Deutschland an den Beispielen Gebäudeklimatisierung und Industrie. Umweltbundesamt. 2014.
4. Leitfaden für Energiebedarfsausweise in Nichtwohngebäuden.
5. Wiemken, E., Elias, A.R.P., Nienborg, B., et al., 2012. EvaSolk - Evaluierung der Chancen und Grenzen von solarer Kühlung im Vergleich zu Referenztechnologien - Analyse von solarthermischer und photovoltaisch gespeister Kälteerzeugung, AP 4 Vergleichsstudie - Modellansätze.
6. Wittig, S., Safarik, M. & Zachmeier, P., 2012. Monitoring und Effizienzermittlung - Vier Kompressionskältesysteme in unterschiedlichen Anwendungen. In DKV-Jahrestagung 2012.

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