Hi - it is hard to be definitive. The house type is key and how much insulation too. We have a Samsung Joule 16 kWh ASHP in a large eco house. During these freezing temps we are using up to 80 kWh/day to keep the house warm and heat the water. We heat the house to 22c in the main rooms and 20c in the bedrooms, which is on the high side. We also heat the water to 52c. So we are pushing it. I know the efficiency of ASHPs can fall off a cliff the more load it is under. 

I would say that your consumption isn’t off the scale but any insulation/draught proofing you can do the better.

Posted by: @johns

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Hello all ... would really appreciate some thoughts and advice. We had our home renovated last year (early Edwardian, about 2000 sq ft, 3 floors, only top floor has insulation) and the gas boiler was replaced with a NIBE F 2040 ASHP. The installer, who fell out with the builders, has been hard to contact/rely on, but we got him round before Christmas because we were freezing - the system couldn't adequately heat the house and everybody was getting sick. The installer added an additional pump and mixer to increase the temperature in the radiators and the house has been warmer, although the ASHP can't meet the temperature set on the thermostat when the outside temperature is below freezing.

Our electricity usage seems extraordinarily high - more than 80 kWh / day when the outside temp is below freezing and our energy supplier wants to put us on a *massive* monthly direct debit. I called in another technician (original installer doesn't respond to messages), he's changed some settings on the 'curve panel', but has not made a huge difference to electricity usage. 

Main questions are, how much electricity should a ASHP be using in a house like this? Should we be doing something different with the ASHP? Is comprehensive house insulation the solution to our problems? How difficult is it to find a reputable insulation firm? (An industry person told me that they have far more work than they can take on). 

sincere thanks in advance for any thoughts, John. 

Hi John, welcome and sorry to hear of your problems. Some more information will help you get the best advice:

- Was a heat calculation done as part of the system design?  You should have heat losses for each room and an assessment of the radiator size and type needed to heat it

- What rating ASHP is your Nibe?

-what flow temperatures are you running the system at currently?  Is it using a fixed flow or weather compensation?

If your ASHP can't heat the house when it's cold then the ASHP itself, or the radiators, could be too small.  But that's not possible to confirm without the above information. It could be something else you can fix by changing settings.

ASHP running costs can go up massively when the average daily temperature drops near freezing, defrost cycles start kicking in, and the house heating load is high. We get maybe 4-6 weeks a year like that typically. ASHPs can't throw huge amounts of heat quickly inside the heated space, but if operated properly they don't need to do that. Insulate the house to the greatest extent possible. Whatever energy source your heating system runs off, a poorly insulated house is heating the street. Have you had a recent EPC survey or an energy assessor in to look at the property? EPCs can be a bit wide of the mark, with some strange recommendations, but that would be a good place to start. Edwardian is probably solid wall (?) - internal insulated dry lining? They may be internal architectural features you don't want to compromise or lose, so it can be challenging.

@rickk54

Posted by: @rickk54

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I know the efficiency of ASHPs can fall off a cliff the more load it is under. 

While I am new to heat pumps (just installed 16kW Samsung Gen6) - what I have learnt is that the carnot equation only has 2 parameters (Temp outside ambient, and Temp flow).  Efficiency cannot directly be about anything else. (of course it is more complicated than this .... but bear with me)

So efficiency is about flow temp (which you may be able to control depending on your situation) and ambient temperature (the bit you likely can't control with  an ASHP).  There is a lot of experience and knowledge needed to design/tweak a system to operate with as low a flow temperature as possible and that is the journey I am on, learning from others on this site and elsewhere.  This journey made more difficult by the fact the plumbing components you need to have an optimal system are not easy to source, it seems.

Below is the expected COP for flow and ambient of a good modern heat pump, taken from site below.

Link to Heat Pump Model

@kev-m thanks very much for this - I'll try to get the information.

@william1066 thanks for your feedback. I don't have enough knowledge about ASHPs to fully take this in - at this stage - but I can see that incorrect settings may be part of our problem. thanks again, John

@allyfish got it, makes sense, thank you.

@rickk54 Hi rick, much appreciated, that's really helpful, thank you.