Heatpump efficiency/reuse
 

Hi. Can anyone comment on what improvements have allowed heatpumps to become more efficient ? Older ones were delivering maybe 3x electric power, while newer ones are > 5x. I live on a boat in a tidal harbour, and am thinking of building a water to water pump to store heat when the tide is in. Is it worth extracting the pumps from the old systems, they have had minimal use.

Thanks in advance.

The biggest and easiest improvement is to upsize the heat exchangers.

Do you mean the tube arrays ? Am I right in thinking that a much smaller array would be required for water to water than air to air ?

Water/refrigerant heat exchangers are significantly smaller than air coils due to more efficient heat transfer. Tube in tube exchangers are the least expensive for your application. A shell over tube exchanger might be needed for the sea water unit so you can clean it. Sea water heat exchangers are expensive.

The newer rotary compressors are somewhat more efficient than piston units. Yours may be rotary if the system isn't very old. As Mike said, the biggest gain in efficiency with the latest systems is primarily due to larger heat exchangers. This mainly applies to air coils where the difference in size can be significant.

I already have 400W of PV, and a home-made CHP unit for higher power AC power and battery charging. I am about to rewind a 7kVA generator to charge 24V batteries and supply AC power from the same unit. A wind turbine and standby cord-start power will follow for battery charging if main batteries get too depleted to start the CHP unit. My plan is to be completely fossil-fuel free by next winter,except for some heavier power tools. Excess power from that turbine will be routed to a resistive load, controlled to either use for heating, or overspeed control. Slowing the turbine will dramatically reduce the power that it collects from the wind. I will also experiment with an exhaust turbine driving a high-speed PMDC motor.