Vestia is a large housing corporation, mainly active in the Rijnmond and Haaglanden regions. Vestia has chosen to use four Caldameg 140kW heating systems in two residential complexes in Zoetermeer to make its technical installations more sustainable. The current collective gas boilers are only used in extreme cold and in case of calamities. The first is the use of a CO2 heat pump in combination with phase change materials (PCM) in the buffer tanks for the storage of heat. The phase chage materials increase the storage capacity of the buffer tanks to cope with peak demand.