Posted by: @kenb

@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.

Ken,

As I explained in a previous post an ASHP cannot behave like an electric heater or even gas boiler because the calorific value of its primary fuel source (the outside air) is not constant, but varies with temperature. If you can arrange for the outside air temperature to remain constant then you would get your wish. I'm afraid the basic laws of physics prevail.

@derek-m 

"Operating a system as you suggest would probably mean having indoor temperatures of 15C in the Winter and 30C in the Summer."

yes thats right and thats what i am thinking is preferable to flogging a HP down to a low COP.  Use the gas boiler when its 15C to get it to 18C  (my winter house temp) and switch the HP off when it gets to 20C.

A HP rated at 50% of what MCS says is required will cater for 80% of the heating season.

Instead of the gas boiler it may be more preferable when we have close to 100% RE grid to have storage heaters powered by TOU tariff.  But many people are starting off already having a working gas/oil boiler

I am not a newbie to all of this just thinking outside the box.

Yes swimming pool HP powered by PV with a COP of 10  -very little grid power if any

Yes i am a enviromentalist and have a EV again powered by PV dont be to quick to pre judge.

The chinese have a saying “ask the wrong question get the wrong answer” which could be changed to “write the wrong policy get a undesired out come.

Many people with a naciente interest in energy conservation think they are being smart. But they aren’t. Countries where products are designed like Germany have done considerable research into energy optimisation and produce products that cannot be optimised.

The difficult part for a “brit” is to accept their understanding is not aligned with the manufacturers. And they frequently go down rabbit holes, as MCS does

@kenb

What you are suggesting is what I am actually doing, though with an A2A heat pump rather than an A2W one. When there is sufficient solar PV energy from my system and heating is required I run the A2A heat pump to raise the indoor temperature  to approximately 23C. When there is insufficient solar PV to supply the heat pump I divert any excess to a 2kW electric convection heat in the hallway, which adds further heat energy into our home. When the indoor air temperature falls to 20.5C the gas boiler is fired up to maintain the indoor temperature.

I doubt that you would be able to use both an A2W heat pump and gas boiler at the same time, since they are both probably using the same heat emitters, but you can have a hybrid system than switches over from heat pump to gas boiler as the heating demand increases.

@derek-m 

Brilliant, as that is what i had in mind. In the OP i did say that the A2A is probably the best choice but for the reason that it has a better COP because it is not being controlled by all manor of parameters.

Do you just let the HP do its own thing and any idea what COP you might be achieving or indeed how is the total system working out. What size HP and how many days does the gas come on- i guess a lot in Dec with low PV.

@kenb

Our A2A heat pump is rated at a maximum 2.6kW, which is adequate for our small bungalow. It consists of a single outdoor unit and a single indoor unit which is mounted in the hallway above the front door. Heat distribution relies upon leaving all the doors in our home open. For larger homes it would be possible to have two or three indoor units.

It is not possible to measure the COP of an A2A heat pump, but I estimate that it varies from 3 to possibly 5 or 6, which is dependent upon the heat demand and the outside air temperature. Just like an A2W heat pump the COP reduces as the heat demand increases and the outside air temperature reduces.

I have not recorded how often the heat pump has operated in preference to the gas boiler, but on a sunny day during Autumn, Winter or Spring I will run the heat pump when there is sufficient solar PV generation. Dependent upon the outside air temperature and hence heat demand, the heat pump will often increase the indoor air temperature to the point where the gas boiler no longer operates. When the solar PV output falls I switch off the heat pump and the gas boiler fires up when the indoor air temperature eventually falls. By raising the indoor air temperature above the setpoint during heat pump operation, it extends the period when the gas heating is not required.

My next objective is battery storage, so that I can extend the period of heat pump operation.

@kev-m Hi. You mentioned "BTW you can get a remote room temperature sensor for the FTC off ebay for about £15." Please, can you post a link to it. I can't find anything. 

What I would like is wireless alternative to PAC-SE41TS-E

@damijand 

the PAC-SE41TS-E is the one I meant.  Although it's wired it comes with a long cable. If you want wireless, you'll need a PAR-WR51R-E and a PAR-WT50R-E.   These are much more expensive and I had trouble finding  them at all.  

Ahh. Stupid me - somehow I understood word "remote" in a wireless sense 😀

Thx. Yes these wireless options for Mitsubishi are very pricy.

One additional question if someone might know: FTC main controller can be used as a room sensor. And I see it's reading in melcloud. But Room temperature is not displayed on main controller even though I set room temp + DHW temp for the display option. 

Posted by: @damijand

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One additional question if someone might know: FTC main controller can be used as a room sensor. And I see it's reading in melcloud. But Room temperature is not displayed on main controller even though I set room temp + DHW temp for the display option. 

 

Where is your FTC controller located?

@derek-m Inside inner unit (I don't know how it is called: inside metal box with FTC board )