200-kWh latent heat storage unit using a pillow-plate heat exchanger: demonstration in an office building

An innovative latent heat storage (LHS) unit was implemented in the central hydronic heating system of an office building. The LHS unit relies on 24 pillow-plates set in parallel and three tons of phase change material (PCM) CT37 (biowax - melting temperature 37 degrees C) providing about 200 kWh of heat storage capacity. The LHS unit can be charged from the building's main air-to-water heat pump or from the local district heating network. The LHS unit can discharge heat directly to the building's hydronic heating system when heating demand is low or to the heat pump to support it in case of large heating demand. Thus, the LHS unit enables peak shaving during high heating demand, while lowering the nominal output requirement for the heat pump. In addition, the LHS unit can be used as a heat battery in combination with the heat pump to maximize the local use of electricity from the photovoltaic panels installed on the building. After running the LHS unit for several months using a time-based control strategy, results are successful with peak heat output up to 40 kW and sustained heat output above 10 kW for several hours.