@togfather - I too have an old stone built home, a cottage rather than a barn, though listed. Unless you have done a lot of insulation and leak fixing work, your home is likely to have a relatively high heat loss for its size. The first questions any here is going to ask is (a) what is your calculated heat loss and (b) what is the nominal rating of your heat pump setup (it may be in the model numbers - 11? - but I am not familiar with Daikin model numbering, I have a Midea heat pump). The first thing to be aware of is the nominal output is usually far in excess of the actual output when it is cold outside, something that tends not to be mentioned by manufacturers and installers. But first, let us know the building heat loss, and the pump's nominal output. Others will be along soon to chip in as well, no doubt. 

@cathoderay I have a Daikin EDLA08 monobloc and the number on yours suggests that it is indeed an 11 kW model. As CatodeRay mentioned; more information needed please; did you have a heat loss survey carried out? Is your pump on continuously without pausing at all? As this has only shown signs of underpowering since low temperatures have come about, it rather sounds  though the heat losses exceed the system’s capabilities. How is the heat pump set up - WC on? Have you set up the MMI for the keaving water temperature and the points on the X axis for control of the slope? Question - questions I know but, our house is well insulated, 98 sq. metres, semi of 1930’s build and we are getting a cop of 2.4 when it is 1 - 2 degrees below freesing and this may use 2 kW/h when running in these conditions. We are using Octopus Cosy and charge two Powerwalls at the lowest rate for the two x three hours slots to keep us off the grid when higher rates apply. 

You’ll never beat Oil, it’s the cheapest form of heating out there.

You need to do the following:

1. Turn all room stats right up to 25 so they stay on permanently.

2. Get your weather compensation curve adjusted to 38.5@15, 50@0…. This means that at 15 degrees outside temperature, your radiators will be at 38 ish degrees and feel ‘warm’. At current outdoor temperatures, the radiators will be at 50 degrees and will feel ‘nice and warm’.

Your high energy consumption could easily be caused by a backup heater inside the heatpump running. That needs to be disabled, as there’s no need for that.

Do you have the heat loss and radiator sizing schedule from your installers?

Many thanks to all for your comments.

Here is more information requested.

1) The rating of the Altherma 3 is 11KW ( EBLA 11 DAV 3)

2) It is not set to weather curve, but to static setpoint at 39 degrees, but it is not achieving that.

3) The installer supplied heat loss calculations of Area: 157.72m2, Power(W): 10211, Energy(kWh): 24722. Also supplied Emitter Log showing total output of 12785 (W)

4) Pump is on continuously.

5) All external walls are insulated, except for kitchen and bathroom. Some are insulated internally and some are insulated externally. The loft area that is not used for rooms is insulated, and the two rooms in the loft also have wall/eaves insulation.

6) Pump has automatic defrost system. To avoid freezing it can dump water, after which the radiators need bleeding and the pressure needs topping up to around 1.4bar.

7) Pump often makes loud noise, like a car with choke on.

I hope this information is useful and thank you so much for replying.

Tog 🙂

A few quick calculations suggest your heat pump is effectively running as an electric boiler.

Assuming oil is about 75p per litre and 1 litre of oil produces about 10kW of energy. Your £6.70 a day therefore suggests about 9 litres a day which in turn means about 90kW. Note - I've ignored boiler efficiency which is probably around 85%. 

Similarly your £29.00 a day for electricity is about 100kW  - approx 30p per unit and therefore about 100 units (100kW). 

Adding a heat pump will not change the heat load from your house for the same temperatures. If you added insulation you should need fewer kWs.

If your heat pump was running efficiently and we assume a COP of 3, or 300% efficient it should be using about 30 units a day, say £9.00.

On your Daikin MMI panel go to Information and then sensors - post a photo of what it shows. It should say things like compressor: on, back up heater: off etc.. Also again under Information look at Enenrgy Information - there are two options - energy in and heat out. These will give you a basic idea of the COP.

Lastly under the Information sensors option what's the flow rate - it will be the bottom number in the list and you may have to scroll down to see it.

@chrislay Sorry, the £6.70 a day was not the oil. It was the electricity cost during October, after the ASHP was fitted.

When I had oil, I spent about £1,400 a year on oil, but the ASHP looks as if it will cost at least £2,500 a year.

@togfather as I said before, you won’t beat oil with a heat pump….. Oil really is the cheapest heat source out there.

Anyway, back to the original issue. I expect this is all related to the backup heater that Daikin like to use.

@hughf Thank you. You may well be right, and I regret the decision to move,  but they told me it would save me money, and I foolishly believed them. I will have to wait for a full year to see the actual additional cost, and even then cannot afford legal fees to sue, so i am now stuck with it and need to find the best way to reduce costs and try and keep comfortable.

@chrislay Today the temperature has risen to around 7 degrees outside. The new setpoint of 43 dgrees is being achieved. The room thermostat is set to 17 degrees now, but only acieving 16 degrees, which is more comfortable than the 13 degrees yesterday.

Electricity used in the last 24 hours is down to 67 kWh, which is an improvement.

Maybe the setpoint was too low. Should i increase it again to see what happens?

Attached are imaghes of the sensor menu.

Best wishe.

@hughf Hi Hugh Im curious as to your evidence for saying you wont beat oil with a heat pump. Ive just checked and an average price for heating oil over the last 2 years is about 85p/lt. At 10.35 kW per litre and a typical efficiency of 85% for the boiler, that gives 9.66p/kWh.

Assuming an electricity price of 31p/kWh a heat pump would only have to average a SCOP of 3.2 for equity, thats very easy to do. In fact using TOU tariffs you can get appreciably better rates, Im currently paying about 20p/ kWh which makes the heat pump a massive winner?

You also have the wide variability of oil prices and delivery hassle to deal with. My sister in law couldnt even get a delivery recently and ran out!

@togfather Hi, as mentioned by others, if you really want to get your bill down you need to abandon using a fixed flow temperature and use weather compensation. This makes your heat pump much more efficient.