22 May 2008

OPERATIONAL RESULTS OF A 10 kW ABSORPTION CHILLER IN HEAT PUMP MODE


A 10 kW H2O/LiBr absorption chiller designed for operating on low-grade driving
heat (solar, tri-generation or district heat) was developed and built jointly with the company
SK SonnenKlima GmbH and the Bavarian Centre for Applied Energy Research (ZAE
Bayern). At nominal conditions the chiller supplies chilled water at 15/18°C using a hot water
driving temperature of 75/65°C and cooling water of 27/35°C with a coefficient of
performance (COP) of up to 0.8. In 2003, a pilot plant was integrated in a solar cooling
system in Berlin where it operates successfully. In the last years several demonstration
plants have been installed in Europe.
To save primary energy also in heating periods as well as to extend the operation time of the
chiller and thus shorten the payback period, the system should also be able to run in heat
pump mode. Traditionally, operation limits of the H2O/LiBr-working pair are the freezing of the
refrigerant at 0°C on the one hand and the crystallisation risk of the LiBr-solution on the
other. Laboratory test results which demonstrate that it is possible to manage both problems,
especially operating below the freezing point of water, will be presented and discussed.