Catalitic converter

[culzean]

And because the hot water temperature achieved by the heat pump is only 45C compared to 60C from a gas boiler...

Ooh! Legionnaires Disease here we come!

Apparently the answer is to have electric immersion heaters in the water tanks to heat up the water to >65degC once a week...  but in the meantime you will use tepid water for everything,  and the amount of hot water that can be stored at 45degC is less than at 65degC, so when you run a mixer shower at 40 degrees it will be taking all hot water from the tank and no cold water,  so the tank of hot water that used to be OK for a family will either run out a lot sooner or have to be a lot bigger volume ( which is another cost and you will lose your airing cupboard space.

You can get heatpumps that will give a higher temp than 45deg, but they need a larger motor and a higher pressure compressor and take more energy to run ( are less efficient). 

[Expatman]

Having lived with a heat pump I can tell you that you realise very quickly that the only way to get hot water is to leave the immersion heater on permanently.
Doesn't do much for your energy consumption or bills however!

[culzean]

Having lived with a heat pump I can tell you that you realise very quickly that the only way to get hot water is to leave the immersion heater on permanently.
Doesn't do much for your energy consumption or bills however!

How fast the water in DHW tank heats up depends on heat gradient between the temperature in heating coil tube and the water in tank,  when water in tank if say 20degC and flow in coil from heatpump is 45degC there is quite a difference in temperature so heat will travel fairly quickly into water,  but when hot water in tank is 40 deg and flow from heatpump is 45 deg,  the transfer of heat from coil to water is very slow, so to get that last 5 deg C will take ages,  if it ever happens.... so water in tank will probably be nearer 40degC than 45   

[Downsizer]

We’re well off-topic, but immersion heaters make very efficient use of electricity if the tank is well insulated, and are economic if you can get off-peak electricity.  I would be inclined to heat water this way if I ever fit a heat pump for space heating.  I did the same when I replaced night storage heaters with an oil boiler.

[Lord Voltermore]

Partly back on  topic.  Someone on  another forum  had a fox chewing the exhaust  sensor wires on his VW van. (initially he though someone had been after  the catalytic converter. )

If a fox tries that on our HV wires its in for a shock .   Or a cat licking it  (cat 'l lick it converter  )