Thermo-chemical accumulator (TCA) is chemical heat pump integrated high energy density heat storage. It could be used for heating or cooling. The purpose of this thesis work is to find out the suitable low temperature source which is between 5ºC to 30ºC. And size the system to find out the required collector and proper amount of lithium chloride for 3 climates (Stockholm, Zurich and Carpentras) The studies of low temperature source were base on the literature survey. 3 kinds of low temperature source were studied, which are domestic waste water, domestic exhaust air and group heating. System sizing was carried on by using simulation program called TRNSYS version 16. The charging process and discharging process was simulated separated. The reference house used in simulation was SFH30 from IEA-SHC task 26 and the weather data for Stockholm, Zurich and Carpentras were used in simulation. The results show that seasonal storage requires both large stores and relatively high source temperatures of free heat. For Carpentras the space heating load can be supplied with a machine with 1400 kg of LiCl salt together with 20 m2 flat plate collector and low temperature heating whereas 9650 kg and 30 m2 were required in Stockholm. In Stockholm, the source temperature needed to be above 15°C in order to get more than 95% of the space heating load delivered, whereas in Carpentras 8°C was sufficient. The conclusion is that ground heat is the most suitable heat source compare with other 2 sources. And the TCA have better performance and smaller size in Carpentras due to the relative higher solar radiation and smaller heat demand.