This project has developed and tested a series of 1G mini-heat pumps of the brine/water type (geothermal heating type) which will become important in future low-energy houses. Three proto-types of a mini-heat pump of the brine/water type have been produced. Two of these were tested in a laboratory, whereas the third type was listed for field testing in Energy Flex Hous at the Danish Technological Institute. The proto-types are based on a new compressor from Danfoss Compressors. Laboratory tests showed good COP values for the proto-type. A dynamic simulation programme was developed in the project which is used to analyse possible control strategies for mini-heat pumps..
Project description
The need for and possibility of using mini-heat pumps for well-insulated houses will be investigated. Their possible use in summer houses will also be investigated. The tendency towards more well-insulated buildings will result in a need for small and efficient heat pumps for room heating and for the production of domestic hot water. In this project, small liquid/water and liquid/air heat pumps will be developed. They will take energy from ground coils and/or other heat sources such as collectors, and the heat from the heat pump will be discharged for room heating in the house with COP values of app. 4, depending on the precise temperatures etc. Such a product is not available today and the new heat pumps will use natural refrigerants (R290 - propane). The heat pump is based on special, efficient compressors from Danfoss
Results
New residential houses are better insulated, and this reduces the need for heat during the winter period. In addition to this many new houses have floor heating systems. This combination is favorable for small heat pumps which can produce heat to central water systems with low water temperatures in the area 25 to 35 C. This low temperature will result in a high efficiency of the heat pump. Simultaneously the governments in Denmark and in many other countries want to reduce the use of fossil fuel and enforce the use of heat pumps. This is the reason why the Danish Technological Institute started a developing project with the goal to develop and test a small heat pump for high insulated residential houses. The project has received economic funding from the Danish Energy Agency. 4 prototypes of mini heat pumps of the brine/water type was build and tested in the refrigeration laboratory at the DTI. The prototypes are using a variable speed compressor (Danfoss SLV12) which originally is developed for plug-in supermarket cabinets. The heating capacity of the prototypes can vary between 1.0 and 2.1 kW. The refrigerant charge is 150 grams of R290 (propane). Two prototypes are charged with 375 grams of R134a. Test were conducted following EN14511 at 0/+35 C and COP was measured to between 3.2 and 3.6 depending of the compressor speed and the type of plate heat exchangers used. This is quite good for such small machines. One of the prototypes was installed in the Energy Flex House which is a new highly insulated test house build at the DTI. The house was equipped with two heat pumps: 1. An exhaust air heat pump taking energy from exhaust air and producing hot tap water and heating the intake air; 2. A mini heat pump for floor heating taking energy from ground source outside the house. A family with four persons lives in the house. During the cold winter 2009/2010 the mini heat pump showed good performance and the COP varies between 2.0 and 4.0. The lower value was caused by a fault in the floor heating hoses, which made it necessary to increase the temperature of the central heating water, which decreased the efficiency of the heat pump during the coldest winter period. The floor heating system has been repaired, and a new prototype heat pump with a slightly bigger compressor has been installed for the heating season 2010/2011. A heat pump manufacturer is now producing this combination of exhaust air heat pump and mini heat pump for floor heating and several systems have been installed in Northern Europe
