Solar cooling: Experiences and lessons learned with two different systems

The aim of this study is to report the performance as well as the gained experiences and lessons learned with two different solar cooling systems. The first cooling system is an integrated cooling plant having both free cooling system and solar powered single-effect lithium bromide-water absorption chiller in operation since August 2002. A floor space of 270 m² is air-conditioned by the plant. The plant includes 35.17 kW cooling absorption chiller, vacuum tube collectors´ aperture area of 108m², hot water storage capacity of 6.8 m³, cold water storage capacity of 1.5m³ and a 134 kW cooling tower. For this solar driven cooling plant, the performance data show that free cooling in some cooling months can be up to 70% while it is about 25% during the 5 years period of the plant operation. Moreover, for sunny clear sky days with equal incident solar radiation, the daily solar heat fraction used to drive the chiller ranged from 0.33 to 0.41; collectors´ field average efficiency ranged from 0.352 to 0.492 and chiller COP varies from 0.37 to 0.81, respectively. The monthly average value of solar heat fraction varies from 31.1% up to 100% with five years average value of about 60%. The monthly average collectors´ field efficiency value varies from 34.1% up 41.8% and the five-year average value amounts about 28.3%. The second solar driven cooling system is a steam jet ejector chiller (SJEC) driven by parabolic trough collector. The chiller has a capacity of one kW cooling. The experiments show that the particular characteristics of a SJEC with the strong influence of the condenser cooling water temperature and evaporator temperature on the system coefficient of performance. The coefficient of performance reaches high values in part load and at good re-cooling conditions, so that the mean efficiency is clearly higher than the nominal efficiency of the system. A first calculation of profitability leads to specific cold cost of 0.- 2 €/kWh in Germany and 0.15 €/kWh in Egypt.