Solar Assisted Cooling and Heating with Multi Stage Absorption Chiller
Abstract
Resorting to commercially available components solar cooling installations are commonly based on hot water-driven single-effect absorption chillers. This configuration yields a considerable solar cooling performance, when solar heat is applied as driving heat source only. Yet in commercial installations requiring reliable supply of cooling with no regard to the current availability of solar driving heat, fossil fired boilers are applied as back-up heat source. In this case a rather poor utilisation of the driving heat is accomplished as measured by the exergetic content of the fossil driving heat. For improved utilization of the fossil fuel serving as backup driving energy input for the absorption chiller an integrated double/single-effect chiller is applied. Solar driving heat is supplied to the conventional single-effect sub-cycle, whereas fossil back-up firing drives the double-effect stage of the chiller when indicated, allowing for a more efficient utilisation of the fossil energy. During the transitional period the plant can serve for simultaneous cooling and heating. In the cold season the system operates as heat pump enhancing low temperature heat provided by the solar collectors or any other ambient heat source to useful heat. This concept offers higher efficiency of the chiller and results in lower primary energy consumption compared to a single effect chiller backed-up by conventionally produced heat using fossil fuels in a hot water boiler. By integration of the backup heating device into the absorption chiller no additional backup device is required and thus a reduction of the complexity of the overall system is achieved. Additionally, this energy system can also be operated self-sufficiently in heating mode. Ideally the machine functions as a heat pump using an ambient heat source like low temperature solar heat or ground water. If this ambient source is not available or not sufficient, the machine can be run in heat-pipe mode where the high temperature stage is used as a boiler vessel while the lower stage is not operating. Currently a first pilot installation is under construction with commissioning in August 2010.