Starting my journey with a Daikin ASHP

I wasn’t happy with the insulation of external pipework from heat pump to house. It was incomplete and too thin. I measured the external dimensions of the insulation and bought new tubular insulation to fit over what is there already. Obviously I had to buy a weatherproof type and got Armaflex. I spent some of yesterday insulating.

I have no way of measuring the heat lost but hopefully next winter it will be much less.

I noticed that a lot of fins at the back of my unit are bent, either reducing airflow or forcing the fan to work harder. I therefore searched for “heat pump comb” on the internet. What a waste of time. “Comb” is the first four letters of combi (as in boilers) and combustion. I got tens of thousands of hits relating to boilers, waste disposal, internal combustion engines and anything else to do with burning stuff. If there was a comb in there I didn’t spot it.

Does anyone know where I can buy a heat pump comb? None of my local plumbers’ merchants even knew what they are, let alone stock them.

Hi Tim,
That’s really interesting to hear, in my experimentation with the ONECTA API, it seems the data points differ depending on the model of HP, but external temperature seems to be a consistent one. Annoying that it’s fallen off your app. The API also reports the ‘power consumption’ but at present the ‘heat generated’ data is only available on the unit itself… We’re only at v1.0 of the API, which seems to be under active development so I’m hopeful more may become available over time.
Give me a shout if you ever want to explore what additional data points are available on your particular system.

Other members may be interested to know that following some DMs I have agreed to allow access to my heat pump for Carbon Co-op research into first viewing settings and statistics and then automated control.

I/we will of course be reporting back to members, probably via a dedicated thread so that the relevant posts don’t get dispersed among other topics of interest.

Don’t get too excited. These things take time.

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Apparently if you want one you need to search for “air conditioner fin comb”. I did that and ended up ordering “Air Conditioning Fin Comb Condenser Clean Refrigeration Tool (Plastic Comb)” from eBay, after first checking for local options.

Edit: I just looked up where this had got too. Apparently it was posted in Guangdong on 11/04/2024 and has now left China. Delivery is estimated to be before 25/04/2024. I’m not concerned about the timing, so long as it’s used before the next heating season, but I am concerned about its carbon footprint.


Apologies for diverting from the main thread of your conversation, but you wrote “small rebate from Tesla for buying an additional Powerwall”.

I have a Powerwall 2 and quite interested in a second as I have just installed an ASHP (not me personally). Anyway in discussions with more than one installer they’ve all said based on experience they’ve not got DNOs to agree with request for second. With no VAT and possible small discount I’m now more interested.

How did you get on with the DNO on this and how did you get the discount?
Thank you, Robin


The rebate was an offer that expired at the end of last year. Unless other offers come up you will need to go without, however with Tesla starting to push the Powerwall 3 you might find Powerwall 2s coming up in “clearance sales”. The two are apparently not compatible, so as you have a PW2 already there is no need to wait for availability of the PW3.

The Gateway 2 is a type approved device for limiting export. My DNO was very quick to grant me a small increase in export allowance, which the Gateway 2 then polices. The gateway can then restrict solar generation if the output is not getting stored, used or exported. It does this by generating a sine wave in your power supply of over 50Hz, the higher the frequency the more your solar inverter(s) hold back.

You might need to buy from a Tesla Energy specialist, who will then handle your request, as they will know what to tell the DNO.

Incidentally, you can now get your Powerwall to export stored energy to the grid if you want. It isn’t relevant for everyone or every tariff. That needs to be activated at installation or Tesla support can activate it remotely. They will want to see your DNO export limit and set it accordingly. You then get an addition to the user interface to allow or deny battery export. As export needs you to switch it on I suggest that even if you have no immediate desire to do so you get it activated, then if circumstances change you just have to select the option. See screenshot below.


PS. My DNO is UK Power Networks.

Hi Tim. This post not immediately relevant to all the above, but anyway… Just had an EPC done (contacted via Carbon Coop people, informally), it came out as a high-C, I was pleasantly surprised. The score was 77 points (out of the 80 for a C), with two recommendations worth a further point each, namely, 1) insulate (further) the flat roof on the kitchen extension, and 2) use any excess from solar-PV for locally-heating some water, instead of dropping it into the grid, as now (for a pittance.) Anyway, quite encouraging! Hope all goes well with the Daikin, tho presumably it’s an easy ride for a few months now…

Your EPC is similar to mine, after I had points deducted for having MVHR. It is also C 77.
Adding insulation to a flat roof that isn’t otherwise in need of maintenance is a costly job. I suggest a generous layer of insulated plasterboard fixed under the (stripped) ceiling if you have adequate headroom. You will also marginally reduce the volume that needs heating, which is beneficial too.

The Daikin had almost shut itself down for heating but then the external temperature dropped and it restarted. I wake up totally unaware of the outside temperature and can get a shock when I go out in the morning.

Without MVHR the EPC was B 86! The unit is Passivhaus certified and 95% efficient for heat recovery. Trickle vents are 0% efficient.

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I appreciate I am a bit off topic but I wanted to respond to a few points raised.
I had a second Powerwall installed earlier this year after VAT was removed from additional battery capacity. It was substantially cheaper than the first, mostly because it was simply connected to the existing Tesla Powerwall Gateway. I am yet to see how effective it is in terms of powering the home and exporting. I am on Octopus Flux because I also have solar panels and this tariff gives me good export rates. The Powerwalls often have excess energy left after the peak rate which doesn’t seem quite right but I guess that there are various factors at play.
On the EPC the house was rated 74C when I had a gas boiler and no battery. The inspection was flawed and I expect that it would be higher how that I have a heat pump. My assessor has told me that the new EPC methodology isn’t now due to Q4 rather than Q1 when, almost other changes such as rooms in the roof, windows are going to be recorded more accurately.

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Looks like quite a costly installation, Powerwall storage - have you a very large PV set-up? Ours is a modest 2.5kW, so diverting excess to a warm-water (pre-)cylinder might be a better bet for us. (Although I might extend PV sometime to the west-facing roof.) What does Octopus Flex typically pay you per kWhr?

As it happens, I had a large Knaufboard installed a few years back, as an insulating false-ceiling layer - but it couldn’t be included in the EPC assessment as there was no visible evidence, nor documents etc.
So how does the Daikin work as regards the indoor thermostat, and the weather-compensation setting? In warmer weather, does it just ‘go round’ fewer expansion/compression cycles (given that water still needs to be heated)?

The PV setup is rated as 5.11kW and it generates c3,000kW pa.
Diverting can be a very good solution and certainly less costly.
Octopus Flux has three tariff periods. Octopus pay 25p per kWh at peak rate (4-7pm) for exports. The batteries also get charged at Flux rate (2-5am) costing 14.8p per kWh.

It’s a shame you have no evidence about the insulated ceiling.

I have set the (3rd party) internal thermostat to 30°C, so that it continually calls for heat. All the balancing is done with the weather compensation. The weather compensation “curve” calls for water at 21°C if the outside temperature is 21°C or more, effectively switching the system off. Until then the system modulates down as far as it is capable, effectively reducing compression. Between times the system switches off.
As you mention, there is also demand for hot water. The water is on a schedule so adds demand to the system twice a day, mainly overnight and with 90 minutes starting 15:00, to top up the hot water ready for the children to get home and shower after school. The higher temperature demanded for hot water means that modulation is unlikely and therefore COP is also lower.

I have had solar thermal since 2006, so the heat pump hasn’t come on every occasion that hot water was needed and will not come on at all over the summer.

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I also have PV, which has gradually built up to 5kWp. I have battery too. I run the heat pump in the six hour off peak at a slight increase in temperature so although COP is reduced the overall cost is less. The heat stored in the house carries through to mid to late morning, depending on the weather, and the battery powers the heat pump for the rest of the day, also on off peak (plus about 15% to allow for losses in charging and discharging the battery).

It occurred to me that people might be interested in my energy use before and after heat pump. There are other variables of course but you will get the general picture.
Until I replaced the boiler my only gas usage was heating and occasional hot water. As a matter of principle I had already stopped using gas to heat the water under normal circumstances. I used the immersion at off peak rates.

Winter 2022-23 we used 14.5 MW of electricity and gas combined.

Winter 2023-24 we used 9.6 MW of electricity and no gas or gas standing charge.

In both cases that included charging the car.
Weather conditions varied between the two winters.
In neither case is export factored in. The figures are for import only.
The April 2024 figure and to a lesser extent the March one are increased by other factors, so are not like for like.

Each reader can calculate the cost to them based on their own tariff but in fact a change of supplier/tariff can be an important factor in getting the books to balance. I didn’t need to change tariff as I was already on one with a very cheap overnight rate, which I utilise to the full.

PS. Getting rid of the gas standing charge can be a real headache. I was “lucky” that it only took a few months.

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Summer is practically here and I have made changes.

As we will not be requiring heating between now and some time in the autumn I have set my first attempt at summer settings.

I have left the heating as it was. The weather compensation should deal with that.

I have increased the hours for water heating and raised the temperature to 53°C. Now the air is warmer the loss of COP in doing so should be minimal. In high summer the system won’t come on at all, as my solar thermal will kick in. In fact today it hit 67.8°C, so that is already well underway. The solar thermal is sensitive to cloudy days (•), so the heat pump is a backup.

The winter backup is the immersion heater. That is now off at the isolator switch, but not locked off. Just in case.

(*) if you have solar thermal you should have the biggest hot water cylinder/tank you can get, to buffer against dull days. Since fitting our system in 2006 the family has grown in numbers and size, and we no longer have an inter-day buffer.

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There is already an amendment to my above post.

Last night we were sweltering in bed, covers off. The situation was made worse by the presence of a hot object in bed with us. We had been joined by our youngest, who wasn’t feeling well.

The experience got me thinking.

Overnight we had the flow temperature a couple of degrees above the weather compensation curve, which uses cheap overnight electricity to preheat the house for the next day.

Even in good weather the external temperature drops overnight, so the house was being heated well beyond the overnight comfort level. Although the bedrooms have thermostats to reduce the risk of overheating, heat still rises from downstairs and is also distributed by the MVHR.

Today I cancelled the nighttime boost. I left the schedule entry in place ready for next winter but set the night flow temperature to the same as the day time one. I’ll try that for a while and may reduce it further.

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I found that my third party thermostat was directly controlling the heating circulation pump (not the pump for the heat pump flow). Even when the heat pump had shut down the circulation pump was running. First I disconnected the pump but then by trial and error I found how to block the signal to the thermostat’s controller (not the heat pump’s controller). The pump is now plugged in again ready for next winter.

Unfortunately this means the heating won’t become functional without manual intervention up in the loft. This isn’t acceptable for a normal family heating system but something I can do. It is an added incentive to get a Daikin thermostat and possibly to convert to a bufferless system.

Unfortunately there are hard wired settings in the heat pump casing to specify whether the thermostat is Daikin’s own or a third party, so it isn’t just a matter of swapping over thermostats.

Ideally, if I’m only using flow temperature then I shouldn’t even need a house thermostat.

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  • In your experience so far, is it feasible/practicable to use the flow temp setting to ‘set’ the end-result house temp?
  • Is this flow temp determined/controlled via the weather compensation setting, or do you directly input it somewhere?
  • What are the manual interventions you’d have to make, up in the loft? - is that basically as you have described, or is there more?
  • Not directly related, but in winter 2022 I set our gas-boiler’s flow temp downwards to 53deg; however manually-attached thermometers consistently show flow= 24deg, return= 22deg, even at the pipes directly below the boiler. Is this likely to mean the gas boiler never actually gets anywhere near 53deg??

Yes, you can set a target temperature but the target is in your mind not in a device on the wall.

The weather compensation adjusts flow temperature. I put the thermostat to 30°C to prevent interference and adjusted the warm ish weather setting and guessed at the cold. Then when it was cold I adjusted the cold weather flow temperature. I repeated this a few times.

My third party thermostat (Heatmiser) has a link to a controller which is in my loft. Others might be elsewhere. I can link and decouple the thermostat.

I have solar thermal and when the sun shines the water can get very hot. Rather than have a low safety limit on solar I allow the temperature to get dangerously high and then mix down the temperature with a thermostatic mixer adjacent to the top of the cylinder. The temperature of that is set to 50°C. The cylinder thus operates as a thermal battery and sterilizer but water emerging from the hot tap is pretty safe.
I wasn’t sure that it was working properly so I bought a pack of 3 clip on pipe thermometers, one for hot, one for cold and finally one for mixed. The temperatures displayed on the thermometers have never diverted more than 5°C from room temperature! From this I conclude that clip on thermometers are a waste of money.

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