Experimental diagnosis of the influence of operational variables on the performance of a solar absorption cooling system M. Venegas a,⇑ , M.C. Rodríguez-Hidalgo a , R. Salgado b , A. Lecuona a , P. Rodríguez a , G. Gutiérrez a a Dpto. Ingeniería Térmica y de Fluidos, Universidad Carlos III de Madrid, Avda. Universidad 30, 28911 Leganés, Madrid, Spain b Dpto. Ingeniería Mecánica, Universidad Interamericana de Puerto Rico, Recinto de Bayamón, 500 Carretera Dr. John Will Harris Bayamón, PR 00957-6257, United States article info Article history: Received 28 July 2010 Received in revised form 6 October 2010 Accepted 6 October 2010 Available online 30 October 2010 Keywords: Solar cooling Weather variables Statistical analysis Absorption Flat plate collectors abstract This paper presents the analysis of the performance of a solar cooling facility along one summer season using a commercial single-effect water–lithium bromide absorption chiller aiming at domestic applica- tions. The facility works only with solar energy using flat plate collectors and it is located at Universidad Carlos III de Madrid, Spain. The statistical analysis performed with the gathered data shows the influence of five daily operational variables on the system performance. These variables are solar energy received along the day (H) and the average values, along the operating period of the solar cooling facility (from sunrise to the end of the cold-water production), of the ambient temperature ( T ), the wind velocity mag- nitude (V), the wind direction (h) and the relative humidity (RH). First order correlation functions are given. The analysis of the data allows concluding that the most influential variables on the daily cooling energy produced and the daily averaged solar COP are H, V and h. The period length of cold-water produc- tion is determined mainly by H and T . Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Increasing the use of renewable energy resources is one of the society’s main targets nowadays and it will be in the foreseeable near future. Absorption-cooling machines are employed broadly worldwide when solar thermal energy is used for air-conditioning purposes [1]. Mugnier and Quinette [2] presented a methodology based on a checklist for the correct integration of a solar cooling system in buildings. The checklist is based on the feedback of Euro- pean solar cooling experiences in the framework of the IEA Task 25. IEA Task 38 is still improving the dissemination of the state of the art, evaluation procedures and overview of this sector [3]. The most common working fluids used in absorption machines are H 2 O–LiBr and NH 3 –H 2 O pairs, the former being better and risk- less for air-conditioning applications. In these machines, refriger- ant vapor is separated in the generator thanks to the heat transferred by the external driving fluid, which is supplied by the solar plant. The vapor enters into the condenser and evaporator in a similar way as in a conventional electricity-driven compres- sion machine. The vapor produced in the evaporator incorporates to the solution in the absorber, releasing the absorption and dilu- tion heats to ambient. If only one generator is used, the system is named single-effect. This is the most common technology utilized for solar cooling, allowing the use of conventional flat plate collec- tors [4,5]. Nowadays small-scale systems receive increasing attention for their potential application to single-family housing or to small buildings. For example, Desideri et al. [6] describe different techni- cal installations for solar cooling, their way of operation, advanta- ges and limits, analyzing their technical and economic feasibility. The dissemination of the solar cooling systems depends much on the economy, real energy saving and emission reduction. Thus, real operating data summarized in manageable figures of merit are required. The global performance of the solar cooling facility depends on the way the solar energy is managed in the daytime. The variability of weather conditions and solar radiation also contribute to the dif- ficulty in obtaining conclusions from real facilities monitoring campaigns, especially on the dependence from the meteorological parameters such as solar radiation, temperature, humidity and wind. In particular, wind effect on operating solar facilities has not been satisfactorily documented. The instrumentation currently available in commercial solar cooling facilities is not what is needed for the determination of the wind heat transfer coefficient, namely the on-surface wind velocity of each solar collector and the superficial temperature of the glass cover. Only an on-site weather station is currently available and in some cases even not; only the hourly or day averaged weather data is available from a neighbor public station. Many researchers in the last years have studied the effect of wind over the thermal losses of single solar collectors, obtaining different heat transfer correlations, e.g. [7–9], but with varying re- sults, because of the different operating conditions. More recently, 0306-2619/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2010.10.011 ⇑ Corresponding author. Tel.: +34 91 624 8465; fax: +34 91 624 9430. E-mail address: mvenegas@ing.uc3m.es (M. Venegas). Applied Energy 88 (2011) 1447–1454 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy