04 July 2008
In apartment buildings and block of flats of such buildings of low-energy and passive house standard, the annual energy demand for heating of domestic hot water (DHW) typically constitutes 60 to 85 % of the total annual heating demand of the building. Since the DHW heating is the dominating heat load, a centralized DHW system that meets the entire demand can be a very profitable installation. Possible heating systems include electric immersion heaters, solar collectors in combination with electric immersion heaters for supplementary heating, gas- or pellet-fired boilers and heat pump water heaters (HPWH) utilizing e.g. outdoor air, exhaust ventilation air, groundwater, boreholes in crystalline rock or grey water as a heat source.
A HPWH using carbon dioxide (CO2, R744) as the working fluid will typically achieve 20 % higher COP than the most energy-efficient HPWH system on the market using HFC or propane as working fluid. Air-to-water and water-to-water CO2 HPWHs in the capacity range from about 5 to 60 kW have now become commercially available in Japan and Europe from a number of Japanese manufacturers (www.R744.com).