I had the Daikin software upgrade recently. Since then the power usage has reduced and the COP has greatly improved. However, my modulation is poor, as shown in attached screen shot. It is about half an hour between drops. Suggestions on way to improve without having effect on COP/Power.
Current WDC is 45 @ 15 and 30 @ -3
Also noticing the DeltaT is not great, lower than 5.
Do you have a representative screenshot of what it looked like before the update?
That modulation looks normal to me. It’s quite warm outside at the moment (15C), cycling is expected and unavoidable. A couple of cycles per hour is nothing to worry about. When the outdoor temperature gets lower, the cycles will get longer.
That’s normal, most heat pumps operate less than DT5 most of the time, this is nothing to worry about. Often you’ll only see DT5 when it’s cold outside and the heat pump is running close to maximum output.
Is this system on HeatPumpMonitor, if so you could use the Heat Demand Tool to see if the heat pump is oversized.
Afraid not.
Thanks for that. Will put system on HeatPumpMonitor.
I agree, that looks normal. Good cycling is tens of minutes between compressor operating periods. Bad cycling is a couple of minutes between, or if the compressor never stops cycling however cold it gets outside.
Thanks for your comment.
The only way to get lower power consumption is to ask for a lower flow temperature. That may or may not suit your setup. I’ve seen less than the 825W shown, but only in mild ambient (e.g. 14C this morning, drawing around 600to 750W for a flow temp around 25 to 30C). We have a lot of radiators and a high system volume, which probably helps.
Have entered details on HeatPumpMonitor.
Unsure if what is being shown is what I should be ok with. The blue dots all appear well below the ‘Heat Pump Badge’ (HPB)and ‘Heat Loss Value on Form’ (HLVF).
The HPB appears to show the capacity of the HP (9kW) - should the blue dots be up at this level and if not does this indicate that the HP is not working to capacity? Also what about the HPB how does this fit into the picture?
Checking other individuals version of this I appear not to have inputted all the data required. Some of the required data not too sure how to work it out.
Minimum continuous heat output on a 9kW Daikin is ~3-3.5kW, I don’t think there’s anything you can do to reduce the cycling from where it already sits.
If the heat demand data is from across a whole heating season then it looks like you could have had an 8kW unit without any issue - you’d see less cycling with one but you’d still get it when it’s 15C outside.
The heat loss value when you filled in the HPM form was incorrectly entered as 50kW! I’ve now reduced this to 7kW.
However, you can see from the Heat Demand Tool, your actual heat loss at -3C based on extrapolated heat delivered is about 4kW
I have been discussing with Octopus about this point but they insist that I need a 9kW unit.
@glyn.hudson Thank you for entering the correct data. I was confused as to what data needed to be entered in the lower part of the form.
Hi Derek, I’ve been running an 11kw Daikin for over 2 years now and thought you might find the comparison illuminating. The 11, 9, 14 and even 16kw units certainly used to be identical but for the badge and very little else. Thanks for flagging the software upgrade, I had not checked mine since that was done earlier this year but I now see that the minimum power input has dropped by about 10% to around 810w with a good COP increase at higher outdoor ambient.
My unit (hopefully visible in the link above) is just about big enough to heat my house in freezing conditions (the max output of this 9-16kw range of units is 9kw under rapid defrosting conditions, they all have the same evaporator which creates this limit). Yesterday Nov 6th it used 7.2kwh to produce 37.2kwh of heat, this includes 1.4 kwh input for 3.9kwh of DHW. By contrast you used 6.4kwh to produce 25.8kwh of heat - I could not see DHW in your charts. So with the same outdoor conditions I’m getting 5.1 COP with DHW and you are getting 4 COP.
You’ll see that I am running with a minimum flow temp of 35c whereas you are much lower at 31c. I have a very large radiator capacity. Your (probably smaller) radiators at this lower temp are severely limited in their output and you would see much better performance at a higher flow temperature, pervious work with other Daikin users suggests that they are optimum above 35c. Incidentally, there is no way they can lose 5c of heat with such a low input temp. The zig zag pattern of your flow temp is a big tell-tale of this issue.
I presume all your TRVs are fully open, if not they should be, so I would suggest increasing the flow temp until you get a stable flow temp. This should then use all the heat the HP is trying to produce at minimum input power. Your house will then cycle on the room temp control (a Madoka?) and not on the flow temp overshoot. If this cycling is still quite fast (an hour or less) then it is a strong indication that the HP is oversized.
I hope this helps
Colin
Having written this I have just realised that the answer is written clearly in your own data;
With a constant power input notice how your radiator output and hence COP and hence DT increases as the flow temp goes up from 30 to 35c? Even at this top temp your rads are still the limiting factor as you should be able to get up to 5.3kw. Try a flow temp of 38c to see if the flow temp stabilises. (theory suggests 38.3c for standard convectors). Your COP will still be lower than mine but then you would have to increase radiator sizes to improve further.
Hello Colin
Thanks for your feed back. I do not use the heat pump for DHW, I use the Boost procedure on my SolariBoost to heat the hot water tank at night during the cheap period.
You are getting quite an excellent COP, I thought I was doing not bad by getting mine up around 4. I have nine radiators working, during installation they added one and enlarged three.
This is my system currently running:
The temperature in my hall is 22.9 degrees. As shown above the flow temperature is still down at 33 degrees and deltaT on 2.2, both seem low to me.
I leave the TRV’s open all the time.
My WDC is set at 45 @ -3 and 30 @ 15 When you say increase flow temperature, do you mean increase the WDC from 45 to 50 and 30 to 35? Or do you mean something else.
I have had the heat pump for 3 years and have had an ongoing disagreement about the size of the pump for a long time but they will not budge.
I would suggest 38 @10c and 45@-3 to start with. It is a pretty flat weather compensation line I know but I think it would be best for you. You might trim the 38 to 37 later if the flow temp is flat and does not saw tooth.
Most people think that the only thing that matters for HP efficiency is a low flow temp. This is because Carnot efficiency defines the maximum that can be achieved and that max is related to flow temp. In truth though anyone’s system efficiency is really Carnot efficiency X % of Carnot your system achieves.
The best systems can achieve maybe 70% of Carnot, on Nov 6th you achieved about 42%;
Whereas my system was above 60%;- hence the COP difference we saw’.
So your question is not ‘how do I improve my carnot efficiency’ ( answer = lower flow temp and that would give a small improvement in the max output) but instead how do I improve my % of Carnot from 40 to 60% - a massive improvement. To do this you have to match your radiator output with the minimum heat pump energy production and to do this you have to raise the flow temp and not lower it. For our heat pumps the minimum HP output is just over 5kw - at any outdoor temp over 5c. So you have to make sure your rads can release 5kw. As rad output for a free convector rad is proportional to (Mean rad temp - Room Temp)^1.4. Then you can see that raising the flow temp has a big impact.
I suspect this a very common issue so I hope you will excuse the ‘lecture’.
Colin
I should also add that if your house heat loss at -3c really is just 4kw then there will be no need to raise the flow temp at that lower temp as your rads and heat pump will deliver this easily.
So If 38c gives a flat flow temp (ie rad output matches minimum HP heat output of around 5kw ) then 38c will also be sufficient to heat your house at -3c.
So I would go for 38c@ 10 and 38c @-3 … which is the same as turning off weather comp. This will save a lot of energy when you are using the most.
Thanks for the information, do not worry about the ‘lecturing’ when you get into your 80’s and are not too technically minded it is always good to get help.
I shall try your suggestion to see if there is an improvement. Will 38°c provide sufficient heat to keep property warm at -3?
I am always open to any advice that makes my HP work at its best.
Have I filled in this section of the form correctly? if not where do I find information.
I’m just a youth of 70, a retired physicist…and have benefitted from a lot of help from @TrystanLea and @glyn.hudson . They are best placed to advise on filling out the form.
I see that this morning since 4am your system has achieved a good equilibrium, producing 4kw at minimum power at a shade over 6c outside. To me it looks optimal although you could cut back the target DT to 5c. Did your house warm up much during the 4 to 7am period? It has obviously cycled off now so I presume it reached the room temp set point.
As a quick rule of thumb you don’t need heating when the outside is 16c or above so if your design minimum temp is -3 then its a fair approximation that you will need 50% of your heat capacity at the half way point between 16 and -3. Which is 6.5c outside - conveniently close to this morning. So if your indoor temp at 4 am and 10am today is the same and you have put in 4kw for half than time then we can surmise that 4kw for all of that time should be enough when it is -3c
You might need to tweak it to say 40c at -3 but it should be easy enough to fine tune your system when you get below freezing. At the moment I would stick at 38c.
I am a bit puzzled by the kinks and bumps in your flow and return temp curves - the cool down sections should be neat curves. Perhaps you have some other heat sources influencing the pipe temps?
Stayed warm during that period.
Adjusting to settings recommended, will keep an eye on situation.
