Thanks.

The swimming pool does go up in temp just slowly at 1C at a time and maybe a total 3C in a day and just keep going up if i left it overnight until it reached a balance point i guess.  The point i am making is its performance seems to bear no relation ship to temp of water. Whether the input temp is 16C or 26C it will just lift it by 1C

Why cannot a house HP behave just the same. Regardless of air input temp,air output temp, water input temp, water output temp, house temp or anything else you want to think of, it just keeps ticking along at its max COP setting.

In winter this may not reach a satisfactory room air temp and in the shoulder months get say to 25C  but so be it the gas boiler, thermal mass, TOU tariff and PV output will sought it out.

Seems that the trade cannot get their head round it because they are conditioned to suppling heating to a fixed house temp as per MCS.

@kenb they can and they do but only with heat pumps own controllers.

the problem is heat loss and there for load varies as the outside temperature changes. and it changes quite a lot in the U.K. 12-20c temperature swings in winter not uncommon.

This is why out door temp is critical (as temperature drops flow temp rises) as is indoor temperature as room temp rises flow temp drops..

The pool on the other hand you don’t implicitly complain about temperature swings, but your house you would

@kenb the industry is in a muddle because MCS is based around prosaic understandings of heating and NOT the capabilities of heat pumps or even boilers

@alec-morrow 

Yes i get that but i dont want it to behave like that and fully accept the temp swings i will endure.  If the outdoor temp drops i want the output temp to the house drop in line with it.  For eg outside air temp 10C  output  say 45C. Outside temp 0C  output say 30C  ie COP does not change.

I know its a strange concept to many but i think a A2A hp will behave more like this. 

Dont worry the gas boiler will stop me getting cold

@kenb if the out out temp drops the room temps will drop and then people will complain.

Its accepted that stable room temperatures are more comfortable than temperature swings, and indeed a lower stable temperature can be enjoyed if there are no temperature swings

@kenb

yes this is how a hybrid system works.. although you set a threshold temperature on external temp as to when the boiler cuts in

That ensures higher efficiencies pretty well allround

Posted by: @kenb

Not sure where to post this but here goes.

I am thinking that a A2A HP behaves differently from a A2W overall

The A2W seems to be always dictated to by some control somewhere and therefore can be operating a little off max efficiency.

The A2A seems to just do its own thing and operate at conditions which suit it and therefore achieves higher cops.

 

I want a HP which behaves like my swimming pool A2W one in that it takes water in and emits it at 1C higher seemingly for ever.  ie heat the water or air by a optimum for COP not by any other parameter. If that leaves the room/house too cold or hot so be it as i will let the thermal mass of the house deal with it at least up to say 25C

What do you think.

Hi Ken,

Whilst both an A2A and A2W heat pump can be used to heat the air within a home, the way in which they achieve this objective is fundamentally different.

The A2A as the description suggest uses the warmed refrigerant gas to directly heat the air via a heat exchanger, whilst the A2W obviously heats the water which is then used to heat the air in the room by means of heat emitters.

There are therefore distinct differences in the way the two systems work. After a few minutes getting up to speed, an A2A heat pump will start heating the air within a room almost immediately and dependent on the size of the system and the size of the room, it can fairly quickly achieve the desired temperature, whilst on the other hand an A2W system can take several hours to heat up a room. This is dictated by the size and type of the heat emitters and the heat transfer rates at the various temperatures. The heated air coming out of the indoor unit of my A2A system is normally in the region of 40C, but of course this quickly mixes with the cooler air, but in so doing raises the overall room temperature. Radiators at 40C will take some time to raise the room temperature.

Once the room is up to temperature then the required heat input to maintain the temperature should be approximately the same for both an A2A and A2W system.

The only difference that I think could make an A2A system more efficient than an A2W would be the fact that there is less heat exchangers in the heat energy transfer process.

Posted by: @kenb

Thanks.

The swimming pool does go up in temp just slowly at 1C at a time and maybe a total 3C in a day and just keep going up if i left it overnight until it reached a balance point i guess.  The point i am making is its performance seems to bear no relation ship to temp of water. Whether the input temp is 16C or 26C it will just lift it by 1C

Why cannot a house HP behave just the same. Regardless of air input temp,air output temp, water input temp, water output temp, house temp or anything else you want to think of, it just keeps ticking along at its max COP setting.

In winter this may not reach a satisfactory room air temp and in the shoulder months get say to 25C  but so be it the gas boiler, thermal mass, TOU tariff and PV output will sought it out.

Seems that the trade cannot get their head round it because they are conditioned to suppling heating to a fixed house temp as per MCS.

Hi Ken,

The amount of energy required to heat a 100 cubic metre swimming pool by 1C is approximately 3500 times greater than that required to heat a room of the same size by 1C. I certainly hope that you are using solar PV to power your swimming pool heat pump. What is the COP of your swimming pool heat pump?

A heat pump used to heat a home will vary in efficiency dependent upon all the variables that you mentioned above. Even running your heat pump at a fixed water flow temperature of say 35C, will still be less efficient in the Winter compared to other times of the year. This is because the primary energy source for an ASHP is the energy contained in the outside air, so in Winter there is less energy so the heat pump has to work harder. Operating a system as you suggest would probably mean having indoor temperatures of 15C in the Winter and 30C in the Summer.

Alec is perfectly correct that to obtain maximum efficiency from a heat pump requires a control system that matches the heat input to the losses.

Posted by: @kenb

@alec-morrow 

Yes i get that but i dont want it to behave like that and fully accept the temp swings i will endure.  If the outdoor temp drops i want the output temp to the house drop in line with it.  For eg outside air temp 10C  output  say 45C. Outside temp 0C  output say 30C  ie COP does not change.

I know its a strange concept to many but i think a A2A hp will behave more like this. 

Dont worry the gas boiler will stop me getting cold

An A2A will operate in the same manner as a A2W, as the outside air temperature falls it will work harder which will reduce its efficiency.

I can see that you are obviously an environmentalist with you swimming pool, gas boiler and inefficient ASHP.

https://www.designingbuildings.co.uk/wiki/Domestic_heat_pumps_and_the_electricity_supply_system

Posted by: @kenb

Not sure where to post this but here goes.

I am thinking that a A2A HP behaves differently from a A2W overall

The A2W seems to be always dictated to by some control somewhere and therefore can be operating a little off max efficiency.

The A2A seems to just do its own thing and operate at conditions which suit it and therefore achieves higher cops.

 

I want a HP which behaves like my swimming pool A2W one in that it takes water in and emits it at 1C higher seemingly for ever.  ie heat the water or air by a optimum for COP not by any other parameter. If that leaves the room/house too cold or hot so be it as i will let the thermal mass of the house deal with it at least up to say 25C

What do you think.

Ken,

Have you considered installing solar thermal to at least partially if not completely heat your swimming pool?

@alec-morrow 

Yes i understand that as per MCS thinking.

I want it to behave like an electric fire -heat output and efficiency do not change with temp.

Incidentally, going back to my question in the OP, not only do the Swedish test data suggest that A2A's manage 4.0 SCOPs, they also confirm that A2W only manage in the high 2's. The latter corresponds with the EST's field trials. Agreement of results between the Swedish and British A2W stuff was important to give me more confidence in their A2A figures.