Air Source Heat Pump limit of Coefficient Of Performance being less than one?

For heat pumps the input and output temperatures are critical to the COP, given underfloor heating as the output and a warm day as input the COP can be very high, 10 or maybe more. BUT if the cold end temperature is -10C and the output to radiators at 60-70C (less than normal CH BTW), the COP will be less than 2 with practical working fluids. 

That's why nobody with any sense would run a heat pump that hot.  Something like 40C is more sensible.  If it's for space heating, run it at a lower temperature for a longer time.  If it's for hot water, give the hot water tank a boost to 60C with an immersion heater perhaps once a week to kill off any bugs that live at 40C.

But do you realise how big a conventional radiator needs to be to be useful at 40C or less? It is monsterous! In other words it is completely unsuitable unless it is a new build and can have underfloor heating throughout. Now look and see what the Government says, because they haven't even considered any of these things. The downside of underfloor is that it has a high thermal capacity and takes a long time to heat up. Thus it needs to operate for long periods, even 24/7 to work. All this means that the only useful heat pump system is air to air, meaning real aircon.is the only proper option if it must be reasonably silent.

I stayed in a hotel recently with an air to air system in an older building. The room was cold for more than an hour until the miniscule heat input managed to heat the room, probably 1kW, and that was it on a not very cold day and the fan was quite noisy.

We have a local swimming pool and can heat pump a stream that runs 5 metres behind the plantroom.

Now if the stream is 10 degrees cooler than the 27 degree pool will it be economical to install a heat pump or better to run on gas??

We have a local swimming pool and can heat pump a stream that runs 5 metres behind the plantroom.

Now if the stream is 10 degrees cooler than the 27 degree pool will it be economical to install a heat pump or better to run on gas??

The heat pump is probably a bit cheaper but the capital cost is more. With a 17 degree differential the COP could be 7 or 8 and electricity is about 6 times as expensive, so a long payback period. Good luck. Ask the manufacturer for an accurate figure and actual electricity consumption. Assume a gas boiler is 90% efficient,(although probably a bit more) and compare.