22 May 2002
Low energy houses with an annual end energy heat demand below 160 MJ/m2a (45 kWh/m2a) have several special features, such as a tight building envelope, low supply temperatures for heat distribution, high solar gains and a high ratio for sanitary hot water. The objective of the project was to develop an efficient low-cost heat pump system, where building and heat generation system have been taken into consideration.
In field tests over 2 years it could be proven that a simple hydronic scheme works for low-temperature floor heating systems with supply temperatures up to 30°C very well. The heat pump can be connected directly to the circulation system without heat storage, mixing valves or thermostatic regulators.
A handbook containing the design fundamentals for heat pump heating of residential buildings conforming to the Swiss MINERGY standard has been completed. Main findings are
Two key values describe annual efficiency of heat production and complete system, i.e. heat production efficiency (SPFprod) and system efficiency (SPFsys)
There are non-negligible differences between SPFprod / SPFsys, e.g. the ground source heat pump for heating and tap water achieved SPF of 4.8/4.1 and the air water heat pump for heating 3.0/2.7
Furthermore new control strategies have been tested, to cover the heat demand. Energy based models have been applied instead of using the return temperature for a two-point control. The new strategies worked well, even no information of a temperature sensor in a reference room has been used.