Combined heating, cooling and power systems for buildings

Combined heat and power systems are gaining ground and co-generation units (CHP) in the small capacity range are available today on the market. Such systems supply buildings with heat while generating electricity at the same time. The electricity can be used on-site or fed into the public grid. Up to now, this technology has been restricted to the heating period, because this is the time when use of the CHP waste heat can be made. One possible solution towards a year-round, and thus more efficient, operation is the following: Through an additional, thermally driven chiller, the waste heat of the co-generation system is converted to cold, which is used to air-condition buildings. In the EU-project PolySMART 32 partners from research and industry are working on combined heating, cooling and power systems in the small and medium power range under the direction of the Fraunhofer Institute for Solar Energy Systems ISE. The results of this European-wide cooperation as well as other information in this field were presented at a workshop on Tuesday, May 18, 2010 at the Freiburg Concert Hall. The basic principle of the combined heating, cooling and power systems has been well established for a long time. System concepts, however, are available only in the very large power range for industrial use and for large buildings or districts. The future of combined heating, cooling and power systems also lies in their application in commercial buildings, hospitals, small hotels and office buildings, in which both cooling and heating demands exist. The goal of the project PolySMART (Polygeneration with advanced Small and Medium scale thermally driven Air-conditioning and Refrigeration Technology) is to further develop the CHCP technology in the small and medium power range and to present suitable market solutions. In the four year project, the focus is on the construction, operation and evaluation of twelve actual systems each with different specifications and applications.
The performance characteristics and operating data of the test systems were evaluated using a self-developed procedure. One of the systems was installed at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg to air-condition several office rooms with a high cooling demand. The particular feature of this system is that some of the office rooms are air-conditioned with fan-coil units during the day. In the other rooms, the CHCP is operated during the night to discharge the storage, made up of phase change materials integrated into the ceiling. During the day, the PCM cooling ceiling is able to absorb heat without having to be actively cooled at the same time. With this procedure, it is possible to increase the hours of operation as well as the efficiency of the installed system. The field test results showed that the system components used – especially the co-generation unit powered by natural gas and the thermally driven chiller with a cooling power from 5 kW up to 25 kW – have achieved a high level of technical maturity. The most promising economic niches for market entry exist when the system installed is to cover the base load and is supplemented by additional systems to meet the peak loads for heat (e.g. gas boiler) and cooling (electrically driven chiller). The planning and operating process involved in order to join the system components still presents a challenge. This challenge will continue to exist until a standardization for wide-range use is established.

Source : Energ�tica XXI - Actually news of energy sector