To allow the use of a single storage in the heating mode as well as in the cooling mode to reject waste heat, the heat has to be stored in a very narrow temperature range around 30 °C. This makes the use of a latent heat storage with a PCM melting around 30 °C most promising. The development and tests on several functional models of the latent heat storage are described in [1]. After completion of test on functional models, a full scale storage consisting of two storage modules was built in fall 2006. This paper reports on the stand alone tests on the full scale storage, and the tests performed after the storage was integrated into the system during summer operation in 2007 and winter operation 2007/2008.

1.1. Construction of the storage

For the sake of economics, the full scale storage was designed based on standard components. A commercial capillary tube system commonly used for wall heating installations is used as heat exchanger. Despite the total heat exchanger area of 12 m2 the required space for the capillary tubes is less than 2 % of the whole storage volume. The heat exchanger has then been immersed in a commercial polyethylene tank. After the PCM was filled into the tank, the tank was hermetically sealed in order to avoid uptake of humidity from the ambient air which could alter the composition of the PCM and thereby its performance.