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Fig. 29: Screenshot of PCMexpress at www.valentin.de

Fig. 34: Low-temperature latent heat storage unit for the “SolCool” project.
© ZAE Bayern
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In practice

Innovative recooler concept using PCM

Conventional systems for solar heating and cooling using absorption cooling equipment involve the release of waste heat by means of a wet cooling tower, which leads to considerable water consumption and a large amount of maintenance work. For this reason, the “Solar heating and cooling with compact absorption coolers and latent heat storage” (SolCool) research project is taking a completely new approach: In place of the wet cooling tower, a patented recooler concept using a dry air cooler and an innovative latent heat storage device is being tried out. The latent heat storage device with a phase change temperature of 29 °C stores a part of the waste heat during the day and then releases it at night. In addition, this high-capacity storage unit is available to provide short-term buffering of the solar yield during the heating period. Test runs at ZAE Bayern have shown that the use of a latent heat storage device means that recooling of the absorption cooler during cooling operation can be maintained at the required temperature level of 32 °C even when there are high outside temperatures. The increased power consumption caused by night-time discharging of the storage unit is small here, and is more than compensated by the shifting of the peak electricity requirement for recooling into low-load periods.

The solar fraction rises significantly during heating operation thanks to the use of the storage unit. On the one hand, excess heat can be buffered during the day for night-time use, and, on the other, losses from the collector drop during the charging process. The most significant factor here is the storage of latent heat at a constantly low temperature. In this way, increases in the collector temperature and the associated drops in the coefficient of performance – which occur with conventional sensible heat storage equipment – can be avoided. Over its two years in operation, the storage unit has completed around 300 heating and cooling cycles without any faults occurring. The unit leads to a significant improvement in system efficiency, especially during heating operation, thanks to its low storage temperature. The system is now being optimised with regards to the control policy and minimisation of the auxiliary energy requirement. The target is an electric COP – the ratio of the average electricity consumption to the useful cooling generated – of over 10 during cooling operation and around 8 during the heating period.

Simulation software

The PCMexpress simulation software was developed and released as part of the “PCM active” joint research project. This software makes it possible to obtain a quick initial estimate of the comfort gains that can be achieved by using a PCM building material. It makes recommendations on the PCMs that could be employed, how they could be used, and also gives initial estimates regarding financial viability. The simulation software contains a comprehensive databank regarding building materials, construction and weather conditions, and this databank can be added to by the user. PCMexpress is available at no charge from Valentin Energiesoftware GmbH’s website. It is not a substitute for EnEV certification, however.

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