Two decks have been created one for heating mode and one for cooling mode, but the entire year can be simulated all at once. A 10 minutes time step has been selected to promote the convergence of some components, in particular the controllers.

Not many simulations have been carried out up to now. However, some considerable results have come out which already addresses on the way to an optimal planning. In fact, during the first simulations the following aspects have emerged:

• the absorption chiller matches well the cooling peak demand but it often switches on/off at low loads

(Fig. 6.);

• the solar fraction is quite small: boilers are required to run the whole year;

• the tank serving the cogenerator is small: the engine switches on/off whenever low flows are extracted from the top of the tank.

Please note: the on/off behaviour of the cogenerator and the absorption chiller is also due to the fact that thermal inertia effects are not included in both the mathematical models.

Fig. 6. Simulation of the cooling flow demand and the absorption chiller in a typical summer day.

2. Conclusions

SHC-CHP systems seem an interesting project solution but their planning requires a huge effort mainly due to the different behaviour of the solar collectors and cogeneration units. The procedure suggested in this paper is finalised to support the design of such plants in order that the mentioned components do not interfere in their respective operation. This procedure can be applied to whatever kind of building, its demand being known. Once the layout and the control strategy are fixed, the simulations address to the optimal solution in terms of size. The energy consumption corresponding to the final solution will then make clear whether and in which case this sort of project is energetically and economically convenient.

Acknowledgements

The authors would like to gratefully thank the STIFTUNG SUDTIROLER SPARKASSE for the financial support.

References

[1] Dorgan, C. B., Leight, S. P., Dorgan, C. E., 1995. Application Guide for Absorption Cooling/Refrigeration Using Recovered Heat. USA: ASHRAE.

[2] Petchers, N., edited by, 2003. Combined Heating, Cooling & Power Handbook: Technologies & Applications. Lilburn, GA: Fairmont Press.

[3] Troi, A., Filippi, H., Sparber, W., 2005. Practical Experience with Solar-Assisted Cooling in an Office and Educational Building in South Tyrol / Northern Italy. In: Otti, ed., 2005. 1st International Conference on Solar Air Conditioning. Germany, October 2005.

[4] Nurzia, G., 2008. “Design and simulation of solar absorption cooling systems”. PhD Thesis in Energy and Environmental Technologies, Department of Industrial Engineering, Bergamo University.