Sanitary Hot Water Heat Pumps – A new tube solution developed for R-290 systems operating with max. 150 g charge

The market for Sanitary Hot Water Heat Pumps is growing fast these years due to regulations in EU and UK pushing electrical heaters and gas boilers out of the market in order to lower CO₂ emissions. At the same time refrigerants with high GWP will be pushed out and leaving the industry in the dilemma to switch from typical R-134a to fx. R-290 to meet HFC-gas regulation.

The common solution today is based on a tube wrapped around the water tank. The obvious solution would be down sizing of tube diameter as known from fin&tube heat exchangers, but this will cause an undesired high pressure drop in the system and will destroy a good COP rating. Therefore the solution with one long tube seems to be obsolete in it’s current form. Alternative solutions like Roll Bond or Micro Channel Tubes in parallel solves the technical dilemma and meets low R-290 charge and provides good COP rating, but require changes in the OEM’s manufacturing process and also provides an extra cost per unit. The new tube profile has been developed to utilize maximum heat transfer from the refrigerant, through the tube profile and the tank into the water. In close collaboration with a high end OEM manufacturer, the new tube profile has been tested in a Sanitary Hot Water Heat Pump, and it was possible to reduce the R-290 charge to less than the half reaching 150 g charge at a COP rating 5 % higher than the conventional system. The new tube profile does not ask for major changes in the OEM’s manufacturing process and the extra cost per unit is foreseen to be marginal.