The Thermo Chemical Accumulator (TCA) is a chemical heat pump driven by low temperature heat that has integral heat storage with high energy density. This makes the device very suitable for solar cooling. The working pair consists of Lithium Chloride and water, and energy is stored and released by desorption and absorption of water under near vacuum conditions. In contrast to most absorption processes and chemical heat pumps, the TCA works with three phases: solid, solution and vapour. This results in near constant operating conditions during charge and discharge, independent of state of charge. This paper describes the fundamental working principles of the TCA as well as a simple steady state model for the TCA. A temperature difference between theoretical and effective temperature in the reactor during absorption and desorption was required in order to get reasonable agreement with measurement data of a prototype TCA machine. For absorption, this value for subcooling was 15°C, which is significantly higher than has been found for low-temperature absorption chillers, indicating potential for improvement. For desorption the value was 7.5°C. The TCA has desorption temperatures of below 100°C for ambient temperatures below 40°C, which is relatively low. The temperature lift depends on the cooling rate supplied and varies from 15°C for the design cooling rate of 5 kW per TCA unit and 30°C inlet temperature to the reactor, to 20°C for a cooling rate of 2.5 kW. The energy density for storage was 180 kWh/m3 for the tested prototype.