Application of customized absorption heat pumps for utilization of low-grade heat sources

Based on established and proven technology of water/lithium bromide absorption chillers, customized single-stage and double-stage heat pump cycles adapted to specific applications can be designed, especially aiming at medium and large heating capacities of 500 kW and above. These heat pumps can either be fossil fired or driven by heat from combined heating and power (CHP) systems or other sources. In terms of primary energy saving, in many cases this is the most suitable technology to utilize the available heat sources. This is demonstrated by three examples of current installations in southern Germany. An analysis of the energetic performance and of the economic situation has been performed. At a municipal composting plant, waste heat is generated at a temperature level of about 40-50 degrees C. Previously, this waste heat had to be rejected to the ambient by means of a cooling tower. A direct-fired single-stage absorption heat pump has been installed which lifts the waste heat to a temperature level of 82 degrees C enabling its utilization in the local heating network of a commercial area. At a spa with various swimming pools located next to a thermal spring, a CHP engine plant is installed. The reject heat of the gas engine drives a novel two-stage absorption heat pump that utilizes the spring water as renewable heat source to provide heating of the pools and the building. In Munich, a solar-assisted local district heating system is installed in a new housing development area with about 300 accommodation units. At this site, a seasonal hot water storage for the solar system of about 5700 m(3) is erected. At the beginning of the heating season, it serves the local heating network directly and afterwards - at a lower temperature level - it is utilized as heat source for an absorption heat pump that is driven by the municipal district heating network. By that concept two effects are accomplished: the available temperature change of the hot water storage is increased and the mean temperature of the solar system is decreased. Thus an increase of the annual efficiency of the solar collectors and finally an increase of the annual solar gain is accomplished. (C) 2008 Elsevier Ltd. All rights reserved.