Fig. 8. shows the typical heating power and stored heat on a day in fall. On sunny days, the storage can be fully loaded. However, most days, as shown in fig. 8, the storage is only partly loaded. In daytime the total energy demand of the building is rather low, therefore the solar heat must be stored and used in night time. At night time the storage almost completely covers the heating power demand (fig. 8), unless the night time outside temperatures are extremely low. In that case the auxiliary heater is used. During the heating period 2007 / 2008 a significant increase of the solar gain in the system has been observed; this is due to the low temperatures using the LHS.

space heating solar heat
kWh
stored heat
/contribution
contributor single storages
0.00
14:00	18:00	22:00
2:00	5:00

time

Fig. 8. Typical heating power and stored heat on a day in fall.

3.2 Storage capacity

The storage is now installed and used in the system for one and a half years. During that period, a total of over 250 charge and discharge cycles of the storage were completed. About every two months, a separate cycle just to test the storage is performed. These tests have shown no degradation of the storage capacity or storage power.

2. Conclusion

As part of a demonstration project a pilot installation of a solar heating and cooling system was installed in the R&D building of the ZAE Bayern in Garching. The system includes a latent heat storage that stores about 120 kWh in the temperature range from 25 °C to 33 °C. As PCM, 2 t of CaCl26H2O melting at 28-29 °C are used. Stand-alone tests of the storage showed that it fulfils the designed heat storage capacity and power. First operational results of the system since summer 2007 confirm the general feasibility and the design of the system. During the heating season, the latent heat storage allows a low operating temperature of the solar collectors thereby increasing the solar gain. In the cooling season, the latent heat storage supports the heat rejection of the absorption chiller. Analysis of system operation and performance will continue until end of 2009.

Acknowledgement

The project is supported by funds of the German Federal Ministry of Environment (BMU) under contract number 0329605D.

References

[1] H. Mehling, S. Hiebler, C. Schweigler, C. Keil, Development of a Latent Heat Storage for a Solar Heating and Cooling System, Proceedings EUROSUN 2006

[2] Schweigler, C., Hiebler, S., Keil, C., Kobel, H., Kren, C., Mehling, H.: Low temperature Heat Storage for Solar Heating and Cooling Applications. ASHRAE Transactions, ASHRAE Winter-Meeting, 2007

[3] M. Helm, B. Potz, C. Keil, S. Hiebler, H. Mehling, C. Schweigler, Solar heating and cooling system with low temperature latent heat storage — energetic performance and operational experience, International Sorption Heat Pump Conference 2008, 23-26 September, 2008, Seoul, KOREA