The total investment cost of the solar cooling system is calculated adding the cost of the solar thermal field and the cost of the sorption chiller, plus a 20% of cost installation. The first one is determined from the specific solar cost [8] and the computed surface in the previous section. The cost of the thermal chillers is much more difficult to obtain. Table 3 shows some specific costs found in the literature ([5], [6]) for the absorption chillers. Fortunately in the case of the adsorption chiller the manufacturer itself provides the economic data that could be seen in table 4.

The results obtained (tables 5 and 6) indicate that the systems with high selective Flat Plate Collectors would achieve the 700 MWh at a lower price. Among them, the systems with absorption chillers are the best option with a cost around 780.000 €. Compared to this, the more economical FPC-adsorption system is 12% more expensive. If subsidies of the Polycity project for solar collectors and adsorption chiller are taken into account, the absorption-FPC systems are still the most economical option but with the adsorption-FPC with an additional cost of less than a 5 %.

The main drawback of FPC systems is that they require more area to be installed and that also could have important economic implications that are not considered in this analysis.

In the previous study [3] the result was totally different, being the best option the combination of the adsorption MYCOM ADR-80 with FPC collectors. There are several reasons for this change. First of all the absorption chiller considered now has a higher COP which leads to lower collectors areas. Secondly, in the case we are dealing with now, the specific cost of the adsorption chillers are 15 — 30 % higher and the specific cost of the absorption chillers 25 % lower. Finally, we used another model to simulate the thermal chiller that brings more accurate results.

Then it is evident that it is necessary to be aware that the economic results are very sensitive to the specific costs of the solar collectors and thermal chillers. Then the final decision will depend of the specific values of these parameters in each particular case.

4. Conclusions

The results obtained in this study suggest that the best system configuration to produce the required 700 MWh of cooling consist of a selective FPC field of 1888 m2 with a tilt angle of 35° and using the absorption chiller of 663 kWc driven at a temperature of 85 — 90°C. The total cost of solar cooling plant using an adsorption chiller is around 770.000 €, 595.000 € if potential subsidies are included. Despite this result, it is necessary to be aware that the economic results are very sensitive to the specific costs of the solar collectors and thermal chillers. Then the final decision will depend of the specific values of these parameters in each particular case.

From the point of view of energy efficiency, the absorption-ETC-CPC system is the best option, with a maximum annual performance of 606 kWh/m2y of chilled water production. The important disadvantage of this system is the high cost of the ETC-CPC collector technology.

Also it has been demonstrated that the new thermal chiller TRNSYS model (type 811), developed specifically for this analysis, could be used to simulate both absorption and adsorption chillers with enough accuracy.

Acknowledgements

The authors acknowledge the support of the European Commission under the Concerto Programme to the Polycity Project n°:TREN/05FP6EN/S07.43964/51381.

References

[1] POLYCITY — Energy Networks in Sustainable Cities. Sixth Framework Programme. Concerto Programme. http://www. polycity. net/en/cerdanyola-barcelona-project. html.

[2] A. Kuhn, F. Ziegler, Operational results of a 10 kW absorption chiller and adaptation of the characteristic equation, Solar Air Conditioning Conference 2005, Shaftelstein, Germany.

[3] J. Lopez-Villada, J. C. Bruno, A. Coronas, Analysis of solar thermal cooling technologies in district heating and cooling networks. Solar Air Conditioning Conference 2007, Tarragona, Spain.

[4] TRNSYS 16 Program Manual, Solar Energy Laboratory, University of Wisconsin, Madison, USA, 2004.

[5] CHOSE — Energy Savings by Combined Heat Cooling and Power Plants (CHCP) in the Hotel Sector. European Commision. Save II Programme.

[6] H. M. Henning, (2004). Solar Assisted Air-Conditioning in Buildings, Springer-Verlag, Wien

[7] MYCOM — AdSORPTON CHILLER, Construction and Data Catalogue. Albring GmbH — Industrial Agency

[8] Institut fur Solartechnik SPF. Solar Thermal Collector Catalogue 2004.