Ref the last point I just don’t have all my emitters/load in so it just can’t give off enough heat yet - we are mod a deep renovation and living here. The house had no serviceable heating system when we moved in so had the heat pump from day one back in July.
I think that’s some good thinking there and as you say it’s better the beast you know.
For supplemental info, I have a 250L cylinder, primary pipework is 28mm and unit is about 10m from cylinder. Setpoint is 45c
Hi Jordan,
Looking at your data I would guess that the heat output has fallen as the flow temperature has.
You are running a WD curve?
The flow temperature has fallen as it gets colder outside, presumably you have played with it or have it set back?
One big difference between the 8 and the 9 is how low the circulation pump will run.
The 8 seems to go to at least 7lpm whereas mine will only go as low as 10lpm.
If mine went to 7lpm I would get the dT of 8c I am looking for in the fixed radiator setting.
I have seen pictures of the circulation pump in the 9kW and it says it can go to a very low level, presumably Daikin have software limited it to 10lpm as that is probably the minimum you would ever need in a house the correct size for this heat pump.
I can’t think of any other reason why my circulation pump won’t run slower to achieve the dT of 8c.
It’s on a very shallow curve and yes I’m always messing with it as you can imagine - I lowered the curve this evening to try and negate some of the issues of having less emitters on my system for the time being.
Would be good to get ESPaltherma on your system - it helped me understand the circulation pump better. It spits out a value which gives you an idea of pump speed rather than just flow rate.
Does the manual say it requires 10l/pm for heating? Mine says it requires minimum 6l/pm for heating so I think that’s why it sits around there.
Hi @matt-drummer & @Rob-G,
For DWH the temperature of the water inside makes a massive difference. I can monitor the tank side of mine very precisely as I have a Mixergy tank (with the main difference than yours is the Plate Heat Exchanger (PHE) + pump stirs the tank up when running a cycle)
I generally only heat mine when the tank is stone cold almost top to bottom, having done testing in my first year even without ESPAltherma I have now.
Poor DWH heating efficiency was more directly linked to the state of the tank pre-heating. Others on here have seen similar.
I stopped doing a mid afternoon DWH cycle and now use the Mixergy top immersion for volumetric (e.g. 5%) top up (which uses their volumetric top up pump) during the evening if we run out as I use less input electricity as only heat what is actually needed, and also the space heating can carry on at hopefully a decent CoP rather than stop/starting.
Sufficiency beats efficiency in this case for me personally.
Back to yours:
A few things people should probably (start?) worth noting for correlation of DWH CoP:
What is the tank temperature?
Estimate of % hot water left which I get is harder on a traditional tank setup, but might be possible to get a good idea (this then will give an idea of how much “cold water” is in the tank to heat
Are you running reheat (great for always having hot water, but I believe quite poor for efficiency), or schedule - and how does the schedule co-inside with usage?
Matt,
I would hire a pro, to (re)do your heatloss, in a proper manner. This step before any major investment.
For the Daikin 9kW, it’s min output should be ~3kW.
You will always get cycling, when outside temp is +7 or above.
Adrian
Hi Adrian,
I think I am way beyond my heat loss now, I know what it is roughly and have no issue with it. A conservatory is always going to cause issues and maybe it should never have been included in the heat loss in the first place as suggested by the first surveyor. But it was because he made a massive mistake and now it can’t be removed.
I can deal with the heat output.
I can get 3kW or less out of it by reducing the flow temperature. The result is a poor COP because of the minimum electrical input.
I can run using the Madoka to limit room temperature and I will get much shorter cycles, it is doable but again results in a poor COP because the heat pump will always be running in the most inefficient phase of the heating cycle. And these Daikin heat pumps seem to take much longer to get into their stride than heat pumps from other manufacturers, it doesn’t make shorter cycles very appealing.
Or I just let it run and control the house temperature using natural heat loss increases, that is opening windows.
When it is warmer outside I can use any method, none of them result in significantly different electricity consumption, I just choose which way I prefer to run and have the house.
The problem is always the same, the range of electrical input is small because the components used are those from a 16kW heat pump.
My 9kW heat pump cannot use any less electricity than the 11, 14 or 16kW versions.
An 8kW Daikin goes down to 400w or less, mine only goes down to 900w whatever I do even though my heat pump is only 12.5% bigger in maximum output.
It’s a stupid design, it’s rubbish, who in there right mind would design something like this? An accountant I assume!
I am happy with the heat pump when it is colder and when it behaves predictably, my only complaint is that I am saddled with the same minimum electrical input as somebody with a 16kW Daikin heat pump in a house three to four times the size of mine.
I can’t see that as being right?
Hi Stephen,
You are quite right about all of that.
Generally I would say our use is similar each day but it does, of course, vary.
I have no problem with the COP or the cost particularly, it is what it is.
But, DHW is a leveler in terms of comparison in similar installations, there are no complications of emitters, heating pipework and house temperatures to consider.
I am having other issues (or think I am) with the ability of my heat pump to maintain a flow temperature and increase flow temperature.
I don’t know whether that is me, my house, my settings or just how the heat pump is.
But I do notice it runs well eventually until the DHW cycle, it very often seems to have trouble resuming heating after the DHW cycle.
But my big clue, I think, that something is amiss is the lack of heat produced during the DHW cycle, it’s just not peaking at what I think, and have been led to believe, it should.
When I look at other heat pumps from Daikin, the heat output during the DHW is much higher than mine. My flow rate looks good and consistent, I just don’t see the 9 to 10kW of heat output I am expecting.
Coupled with my other (perceived?) issues I feel that my heat pump is not capable of producing hot water, and therefore heat, like it should.
Hi,
Thanks for the feedback.
My biggest worry with regards running costs is if I decide to sell my house.
The weird thing with my install is that it does not seem to be using a scary amount of energy.
For the last 12 months about 739kWh for hot water 2025kWh for heating so for the year will probably be about.
With being on Octopus intelligent, battery storage, and solar it’s easily cheaper than running the gas boiler.
When the outdoor temp gets below 10 degrees the cycling reduces but as it’s cold the COP stays low.
The time of year that is supposed to boost your sCOP the shoulder heating months the heat pump is cycling all the time so never has a chance to boost my averages.
Just to confirm my room thermostat is set to 22c all day and 21c overnight.
Regards,
Rob.
That’s more or less what the Octopus engineer said.
At first he thought that it could be an issue with the diverter valve being misaligned and letting water in to the heating circuit while heating hot water but he checked that.
The feedback so far from Octopus seems to be to trash the Daikin MMI figures.
I remain unconvinced.
I did read a post from one owner who found the factory had not put enough refrigerant in their heat pump which apparently is a know issue on some Daikin units.
Robert,
Three issues,
I learnt something at my second heat loss survey, the radiator schedule is not the heat loss.
The rooms are not included twice in the actual heat loss but any unheated areas are not shown in the radiator schedule but are included in the heat loss.
You can’t determine the heat loss they used from their radiator schedule.
What does stand out is the limited radiator capacity, it is smaller than mine was and I really struggled.
I had about 9,000w at those design temperatures and my house is smaller than Rob’s.
Hi @Rob-G
Sounds like you have a very similar setup to me.
I have a converted 1960’s bungalow, now 150m2. I have solar PV, 18kwh battery and an EV. We are 
intelligent go. I have an 11kw Daikin but the slightly older r410a model, not an Octopus install.
You can read the background to the heat pump journey here, and my different heat loss assessments here. https://forum.ovoenergy.com/my-smart-home-138/correctly-sizing-air-source-heat-pumps-ashp-bigger-is-not-always-better-14428
My actual heat loss is around 6kw, not the 9kw estimated. To deal with my system, after nearly 3 years, I now run with a fixed LWT at 38C for central heating with the Daikin controller applying a little modulation and then acting as a thermostat, and heat the hot water on reheat with a hysteresis of 10C. The system is much more settled and the average COP for the last month 3.4, not great but an improvement on the 2.9 before.
Hi,
Thanks I will have a look.
Has anyone tried the pure weather compensation mode in the control menu(Leaving Water rather than Room thermostat) that is supposed to be the most efficient?
In theory this should stop the problem I was having with the room stat shutting the heating off before the north facing rooms get up to temp.
Yes I do.
The other parameter you need to configure is Overshoot
4C overshoot mitigates cycling, and will inform your weather curve is tight/shallow enough if you keep going into the overshoot temp.
Minimum output of your unit compared to your emitters and heat loss will also play a part here.
I think as I may have said in another post I did hear that some Daikin heat pumps left the factory with an incorrect refrigerant charge whether this is my problem or not who knows.
The only way to check is for a qualified tech to come out drain the refrigerant and weigh it.
Thx for the info.
So if I understand the overshoot correctly if the WD curve is calling for 45c it will heat the leaving water to 49c and then only reheat when the leaving water temp drops to 41c?
I went and checked this setting on my HP and it’s already set to 4.
Rgds Rob.
The overshoot allows the heat pump to increase flow temperature within the set range to allow it to keep running. If it didn’t increase flow temperature it would have to shut down.
This mitigates short cycling as Stephen says when the heat produced can’t be delivered to the home, generally because the emitters are at their limit at the requested flow temperature.
What flow temperature are you running when it is something like 7c outside?
I am running straight LWT at the moment, no WD curve or Madoka influence. I am at 36c (in theory) as going any lower uses no less electricity. Plus these heat pumps don’t seem very happy at really low flow temperatures.
I find the heat pump takes so long to get into its stride that it is better to just leave it running.
I use no more electricity this way than turning it on and off.
I turn off the heat pump if we are out for a few hours, the house doesn’t lose much heat and it warms up quickly in any case.
I am controlling the house temperature with windows, sad, but it is what I am doing.
Based on my experience with this heat pump, the knowledge gained here and the size of your house I am certain your radiators are way too small to run efficiently at low flow temperatures.
It may well be that you can make it work in terms of overall energy consumption but the COP can never be good.
Your heat loss is probably the same or more than mine judging by what you have said, your house is bigger than mine and I doubt it is any better insulated than my house. Your downstairs is as big as my whole house.
I think Stephen’s house is about the same size as yours and he was getting a 9kW but ended up with an 11kW, not that it makes any difference and he’s actually better off with the 11kW, they should just give everybody the 16kW, you lose nothing.
It should work, there are just not enough/big enough radiators for this heat pump.
I would try and find out what they say your heat loss actually is and try and verify it, either yourself or with another heat loss survey from somebody other than Octopus, somebody reputable.
Then you will know how to proceed.
