Heat pump hot water system

I have built a heat pump hot water system which uses two sealed unit compressors which have a rated cooling capacity of 3750 watts each. I am using S/S plate heat exchangers for condensers.

The source of heat for the pump is 5000 liters of water contained in a tank located on the ground underneath my home. I am hoping to be able to heat enough water for domestic use and to heat several rooms with hydronic radiators. The evaporators consist of three meters of 18 mm copper tubing contained in cylinders which have the tank water slowly circulating through them with the aid of a very small pump.

I started the system yesterday and only succeeded in heating water to 30 degrees celcius. I am using Hychill Propane refrigerant HR/22 502. My problem is that the water in the tank is only about ten degrees celcius and my system was running with a low discharge pressure of 140 psi and a suction pressure of 40 psi.

I am considering discarding my home made static evaporator and using a stainless steel plate heat exchangers with a much larger circulation pump in the hope that this will be more efficient in extracting heat from the water in the tank.

I am relying on the water in the tank warming up each day when the heat pump will not be in use.

I know I haven't provided much information about my system but I wondering whether the water tank is large enough to be my source of heat.

I think you'll need to get a much bigger heat source. A 5000L tank at 10C will become a lump of ice very quickly.

Within 14 hours, the temperature in you tank will drop to +1°C. This is not sufficient for heating, although it could be used to make domestic hot water.

Thanks for your responses.


I guess the next thing I could consider would be to heat the water in the tank during the day using solar energy.

There are commercial hot water heat pumps sold in Australia that extract heat from the air and which have a defrost cycle when the evaporator builds ice. I didn't go this way thinking the 5000 liters of water would contain far more heat than air.:eek:

I'm sure if you used r22 and got your head pressure up you would have much different results. But as previously stated you are limmited by your heat source. If your going to try solar preheating your tank you could used black polythene pipe spiralled on your roof, there is plenty of this info in the Renew magazineor on the ata website. Good luck and good effort