In summary, the results from the experimental evaluation show that the storage can provide hot water with a temperature of 40 °C for more than two hours, at an average power of 3 kW. The control strategy for discharging according to a specific load requirement is however presently under development.

It is possible to charge the 140 liter HEATPACK prototype with close to the theoretically calculated value of 15 kWh. Hence, this is a PCM storage solution with a storage capacity of over 100 kWh/m3 which is a good value for accomplishing overall cost effectiveness as compared to a stratified hot water storage.

It is desirable to further increase the heat transfer rate within the HEATPACK prototype. One measure is to include finned tubes in the next generation, although here care must be taken not to significantly increase the cost of the tank while doing this. Discussions with potential manufacturers are underway. The next generation design will also be configured for a lower pressure drop on the water side such that the water flow rate can be increased while still using a reasonable sized pump.

The conclusion is thus that with some changes in design, the HEATPACK concept is promising, and after further evaluation it should be ready for taking the project into the commercial phase during 2008 and 2009.

References

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[4] W. Streicher (editor), (2007), Laboratory Prototypes of PCM Storage Units, Report C3 of Subtask C within the IEA Solar Heating and Cooling Programme Task 32, May 2007, www. iea-shc. org/task32

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