Description of the solar cooling plant

1.1. Design of the solar cooling plant

The Fraunhofer institute UMSICHT in Oberhausen has operated a solar cooling plant since summer 2002. The solar cooling plant supplies cold water via a cold water network for space cooling. The cooling power of the solar cooling plant is provided by an absorption chiller with a target cooling power of 58 kWth. The absorption chiller is hot water driven, which is heated up by a solar collector field with a size of 108 m2. Figure 1 shows the process scheme of the solar cooling plant.

solar collector field

he cold capacity of the solar cooling plant is generated by a single-effect LiBr-absorption chiller type WFC-10 from the manufacturer Yazaki. The cold capacity of the absorption chiller is variable from 25 to 58 kWth that based on the cooling water temperature. The chiller COP is 0.65 to 0.75 at nominal operation condition and cooling water temperature of 24/31 °C, reported by the manufacturer. The refrigerant of the absorption chiller is water and the absorbing agent is a LiBr-solution. The solar collector field consists of nine field parts with a total collector size of 108 m2 Each part consists of eight vacuum tubes collectors type Lux 2000 from the manufacturer Soleado, Germany. The installation is on the roof of the institute building C orientated in southern direction. In its present stage of extension, the solar collector field provides 50 kWth heat power on the temperature level of 105/98 °C at a solar irradiation of 900 W/m2. In the final stage of extension, the solar collector field will be still enlarged and the heat power will rise to 78 kWth. The heat transfer fluid flows directly through the vacuum tubes (no heat pipe system). The stagnation temperature of the solar collectors is 223 °C. In order to prevent damage from the solar collector by overheating, surplus heat can be discarded by a stand-by cooler, which is installed in parallel to the solar collector field. An evaporative cooling tower is used as re-cooling device for the absorption chiller and serves also as cooling device for free cooling. The re-cooling power of the cooling tower is 134 kWth at a wet bulk temperature of 21 °C and cooling water temperature of 24/31 °C. The volumetric flow rate of the cooling water over the cooling tower has max. value of 15 m3/h. An additional heat exchanger, which is installed parallel to the absorption chiller enables to use the cooling tower for free cooling. The solar cooling plant is equipped with a 6.6 m3 solar energy storage in the hot water cycle and a 1.5 m3 cold water storage in the cold water cycle. The solar energy storage has a heat capacity of 230 kWhth at max. temperature of 115 °C and the cold water storage 7 kWhth at min. temperature of 6 °C. The total electrical connecting load of the solar cooling plant including all auxiliary drives and devices is 10 kWel, but the electrical power input is smaller than 3.5 kWel.