Low refrigerant charge heat pump with microchannel shell and tube heat exchangers.

摘要

The invention, a low refrigerant charge heat pump with microchannel shell and tube heat exchangers, makes it possible to operate an electrically driven compression type heat pump with a heating power of several kilowatts and with a hydrocarbon refrigerant charge of less than 150 gram. The distinguishing feature of the invention concerns the 10 heat exchangers of the heat pump. These heat exchangers have an innovative design in which the refrigerant charge is very low compared to conventional heat exchangers of the same heat exchanging capacity. This innovative heat exchanger design is a microchannel shell and tube heat exchanger. In this design, a secondary liquid that is to be cooled or heated flows 15 through a metal tube with a circular or near-circular cross section. A refrigerant flows through a number of small parallel channels with dimensions in the order of 1mm. diameter (called microchannels) which are located inside the wall of this metal tube (figure 1). Alternatively, the outside of the wall of the central tube may have microchannel grooves, and a second tube that fits closely over the central tube is used 20 to enclose these microchannel grooves (figure 2). Alternatively, the central channel and the surrounding microchannels may be formed inside a block of metal by means of 3D printing or by another means. The length of the heat exchanger can be several meters, and the heat exchanger may be bent or folded several times over this entire length in order to decrease the overall dimensions. 25 The low refrigerant charge heat pump comprises one such heat exchanger as evaporator and one such heat exchanger as condenser. A third microchannel shell and tube heat exchanger mat be present as suction gas heat exchanger, in which case refrigerant vapour instead of a secondary liquid flows through the central metal tube. The low refrigerant charge heat pump furthermore comprises a refrigerant compressor 30 and a means for expansion of the refrigerant leaving the condenser, and optional additional parts and means necessary for the functioning and control of the heat pump.