The performance of the dry cooler and the cooling tower in the three sites are here evaluated from an economic point of view. The actual interest is to evaluate the effective costs of the heat rejection equipment per kWh of cooling energy produced. This is defined as the ratio between the costs of the heat rejection technology and the cooling energy delivered by the chiller in 20 years of operation. The costs include the initial investment to purchase the equipment (cooling tower or dry cooler) and the operation costs (for electricity and water) in 20 years. Relating the costs directly to the final cooling energy obtained by the system, allows to take into account how the different heat rejection technologies affect the absorption chiller capacity and COP.

The equation 2 defines the previous index.

The results are reported in the following Table 3.

2. Conclusions

In the present work a deck for dynamic simulations in TRNSYS of a small Solar combi+ system has been presented where an EES based code for the dry cooler was integrated. Although the water consumption for evaporative cooling was taken into account, from this first analysis it was observed that cooling tower technology has a much lower effective cost than dry cooler in all the three different locations. However this result has still to be investigated more in details, developing a more detailed model for the cooling tower and spending more efforts in fan control strategies. Different manufacturer data for both the technologies will also be considered, as in the present study the cooling tower had a much lower electrical consumption and still a very good performance for air entering in quasi saturated conditions compared to the dry cooler. Finally other considerations like local legislation on water make-up consumption and legionella disease concerns might be deciding factors for the deployment of dry cooling technologies.

Acknowledgements

The authors would like to gratefully acknowledge the financial support of the STIFTUNG SUDTIROLER SPARKASSE.

References

[1] W. Weiss, Solar Heating Systems for Houses, a design handbook for solar combisystem, Task 26, IEA.

[2] G. Franchini et al, Renewable cooling with solar assisted absorption chiller: system design, 62° Congresso ATI, Salerno, Italy, September 11-14, 2007.

[3] . F. Besana et al “Heat rejection technologies for solar combi plus system”, 2nd International Conference Solar Air-Conditioning.

[4] G. Dierks et al, Technical and Economic Evaluation Of Air-Cooled Cooling Systems Refrigeration And Air Conditioning Technologies, Jaggi/Guentner Report.

[5] D. G. Kroger, Air-Cooled Heat Exchangers and Cooling Towers, PennWell Corp., Tulsa, Oklahoma 2004.

[6] S. A. Klein et al, 1996, “TRNSYS — A transient system simulation program” Solar Energy Laboratory, Univ. of Wisconsis, Madison, USA.

[7] G. Nurzia et al, Combined Solar Heating and Cooling Systems: Simulation and Design Optimization, ASME International Solar Energy Division 2008, August 10-14, 2008, Jacksonville, FL, USA.

[8] W. M. Kays and A. L. London, Compact Heat Exchanger, Third Ed., McGraw-Hill Book., New York.

[9] J. E. Gonzalez, L. H. Alva, Simulation of an Air-Cooled Solar-Assisted Absorption Air Conditioning System, Transaction of the ASME, 276/Vol. 124, August 2002.

[10] ASHRAE Equipment Guide, American Society of Heating, Refrigerating, and Air Conditioning Engineers, Atlanta, 1983.

[11] J. C. Kloppers et al, A critical investigation into the heat and mass transfer analysis of counterflow wet­cooling towers, International Journal of Heat and Mass Transfer 48 (2005) 765-777.

[12] B. Cohen, Variable Frequency Drives: Operation and Application with Evaporative Cooling Equipment, CTI Journal, Vol. 28, No. 2.

[13] H.-M. Henning, Solar-Assisted Air-Conditioning in Buildings, A Handbook for Planners, SpringerWienNewYork.