04 July 2008


Low-energy and passive houses are superinsulated and airtight buildings where the space heating demand is much lower than that of buildings constructed in accordance with current building codes. Due to the low space heating demand, the annual heating demand for domestic hot water (DHW) typically constitutes 50 to 85 % of the total annual heating demand for the residence.

A heat pump system can be used to cover the entire heating demand in a low-energy or passive house. It can be designed as a stand-alone system, i.e. a heat pump water heater in combination with a separate unit for space heating, or can be an integrated unit for combined space heating and hot water heating. Due to the more compact design, the latter system is most likely to achieve the lowest investment and installation costs and therefore the best profitability.

Integrated residential heat pump systems using carbon dioxide (CO2, R744) as the working fluid can achieve a particularly high Seasonal Performance Factor (SPF) in low-energy and passive houses due to the unique characteristics of the CO2 heat pump cycle. However, the energy efficiency is very dependent on the design and operation of the heat pump unit and the secondary systems.