Modelling of a Commercial Absorption Heat Pump with Integral Storage

The thermo-chemical accumulator (TCA) is a closed absorption batch process that uses a working pair, not only in the liquid, vapor and solution phases but also with solid sorbent, so called triple state operation. It was patented in 2000 (Olsson et al., 2000). Since then the TCA process has been developed in a relatively short space of time by the Swedish company ClimateWell via five generations of prototypes and is now commercially available under the name ClimateWell 10 (CW10). The majority of the 500 machines sold since 2007 are for relatively complex solar heating and cooling systems in the Mediterranean. They provide cooling during summer, space heating during winter and hot water year round. Although in principle both common absorption and adsorption processes can include significant heat storage, this is not used in commercial products. The ClimateWell machine is the first thermally driven heat pump with integral storage on the market. It uses LiCl and water as the working pair. Several prototypes have been developed, with different characteristics and operating principles (Bales et al., 2004). The first simulation model was derived for the 3rd generation of prototypes (Bales and Nordlander, 2005; Bales, 2006). The 4th generation of machines differs significantly from the previous generations, and was the first to be sold commercially, as from 2007. As a result the simulation model for the 3rd generation had to be rewritten. This paper describes the basic operating principles of the machine, the model as well as the identification of model parameters. Finally the paper describes a series of parametric studies highlighting the influence of a number of parameters on the COP and storage capacity of the machine.