@SarahH , Sarah, thanks, just did my first read through. Very technical for me , will read a few times to get a better feel. But my main takeaway at this stage seems to be, that the overall defrost takes about 5 mins and consumes 500 and some watts. What would your ordinary ( if such a thing exists) average hourly consumption be. And I assume we are talking input watts not output watts.
Hi Terry,
Your situation is quite difficult, you are trying to understand what is going on and optimise your heat pump without the tools to do it.
With no monitoring, it is virtually impossible to replicate what others are doing and find the best set up for your home.
This is how your heat pump works and I would suggest studying the monitored Daikins data to try to make sense of it.
Daikin heat pumps in heat mode do not run at a fixed flow rate and there is no way to directly control the flow rate.
The circulation pump has a range of operation of between around 7lpm and 20lpm.
The amount of heat produced is a function of the amount of water flowing and the difference between the water temperature leaving and returning to the heat pump.
What temperature the water needs to be heated to to get the amount of heat required to keep your house warm enough depends on a few things but mainly the capacity of your emitters and the heat loss of the house at any moment in time.
A Daikin heat pump has two main adjustments, flow temperature and dT (between flow and return).
The heat pump has a maximum heat output and a minimum heat output. We will assume the minimum heat output is one that works efficiently.
For the 8kW the maximum is around 8kW and the minimum is around 2kW.
You can get the maximum output in a number of ways within the limitations of the heat pump.
We already know the water can be pumped between 7lp and 20lpm and this is what limits the minimum and maximum outputs together with the minimum dT between flow and return that the heat pump can operate at.
We can set our dT at anything between 2c and 12c.
At dT of 12c is very high and it will need the water to flow quite slowly in order to achieve this.
If you set a dT of 12c and flow temperature of 30c then you are never likely to see a return temperature of 18c.
The heat pump will still run and it will reduce the flow rate to its minimum in order to achieve this.
If it does not get to a dT of 12c there is nothing it can do about it so the flow rate will be 7lpm and the heat generated will be whatever the radiators can emit at 30c flow and 7lpm.
If you then increase the lwt to 35c the heat pump will be aiming for a return temperature of 23c.
You still probably won’t get that and the flow rate will stick at 7lpm.
But the heat produced will increase as the dT will have increased (bigger dT now and still 7lpm)
If you increase lwt now to 45c you may well see the return get to 33c.
If the return is less than 33c (at dT 12c and 45c flow temperature) the flow rate will increase to keep the return at 33c.
You can keep increasing the lwt and the flow rate will increase, and so will the heat output.
This happens until the maximum heat output is reached, 50c flow at dT 12c and 20lpm is more than 8kW, the heat pump cannot heat that much water from 38c to 50c as it doesn’t have enough power.
Your maximum heat output is not controlled by one factor, it is a result of how much water can be heated by how much temperature.
I have not done the calculations so take this for what it is.
If 50c flow at a dT of 5c and 14lpm gives 8kW of heat, then so does 50c flow at dT of 10c and 7lpm, but so does 40c flow at dT 10c and 7lpm.
It all depends on your house and the emitters, bigger emitters can get the same dT and flow rate at a lower flow temperature, that is why bigger emitters are generally more efficient with a heat pump.
For your house, we don’t know what works best as we can’t see anything.
So, to get a heating system that works automatically in every situation you are likely to encounter you need a dT that will allow you to get the heat you need within the restrictions of the circulation pump speeds, too high and the pump can’t go slow enogh at times, and too low, the pump won’t be able to circulate enough water to generate the heat you need.
A dt of 5c is generally enough to allow you to get the full range of heat from the heat pump within the ability of the heat pump to heat water to a high enough temperature.
Basically the heat pump can be set with a huge dT, a high flow temperature and a high flow rate, or vice versa and anywhere inbetween, but some combinations will fall outside the power capacity of the heat pump, either too high or too low.
There is no one setting that is correct and what works for me may not work for you.
My data is not a good example, I never need more than 4kW of heat and in my set up getting more would be at a higher flow temperature than I could run at. I would need to lower my dT from 10c so that I could encourage the pump to run faster and generate more heat at a lower flow temperature. I operate in a narrow band of the heat pumps range and and is by no means a normal or ideal way to do things.
WDC sounds like something fancy but it is not, it is just automated control of the flow temperature based on the concept that you want more heat when it is colder outside.
Modulation and overshoot also just modify the flow temperature to help keep the house at a set temperature.
These are all just fancy addons.
The main control is the dT, just set it in fan coils at 5c and then find out what flow temperature you need to keep you warm at different outside temperatures, then set up your wdc to suit, and that is it.
Trying to do anything else is a waste of time with no monitoring.
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Sorry, @Terry247, I was trying to address a wide range of technical backgrounds. Don’t worry about the finer details as these may not apply to Daikins. The Samsungs seem to particularly effective at dealing with defrosts - looking at the defrosts on @dmajwool’s output above it looks like more like 10-15 minutes duration, which probably means twice the heat removal from the house too - I could easily believe 1kWh per defrost, maybe a tad more.
I can’t really quote an energy consumption for my 8 kW Samsung, because I operate with a big setback, so just after startup each morning it quickly gobbles up about 4-5kWh for space heating (house re-heating) on a cold day (say 0degC) then another 15kWh or so over the rest of the day, i.e. around 20kWh total/day for space heating at 0degC outside. (Total household power consumption averaged about 25kWh/day this January - which was a little colder than average - but this figure also includes DHW, cooking, appliances, lighting etc.)
Defrosting is just part of life with an air source heat pump, they all do it.
My 9kW Daikin used to get a visible thick layer of white ice on it and would defrost twice an hour at times from anything around +3c and below.
My 8kW Daikin doesn’t get any thick layer of ice, it is barely visible but defrosts around -2c if it needs to.
This generally only happens when it is particularly damp.
Today was -4c and thick fog, it was defrosting every 45 minutes for a few hours.
There’s very little you can do to stop it.
I have frost protection enabled so my heat pump runs below 5c whatever.
In any case, it’s cold, why would I want to turn the heating off?
Surely that’s when I want it most and what I installed heating for in the first place!
The only way to minimise defrosting is to run as low power as possible, but with a correctly sized hear pump that is difficult.
This is a time when an oversized heat pump is a benefit, it is not working so hard in defrost conditions.
But, defrosting is not a problem, in isolation, an `expensive’ annoyance, nothing else.
Matt, thanks. As the heat pump is off at the moment apropos the panic, I ‘m going to have a look and see what my settings are, I’m not going to change anything just look. But I’m still not clear about modulation and overshoot. I thought modulation was simply a term to describe the ability of the heat pump to use more or less power, within whatever limitations it has. However people are talking about a setting, which seems to be something other than I thought. Similarly the overshoot. I use offset, have usually got that set at -3, but I believe overshoot is also something else and is one of the settings. Generally I have taken the principal of low and slow and that has largely worked. I think almost by accident I have got the house comfortable with minimum changes. A change to the WDC and then the offset. That I think is the extent of my changes. Since install I’ve got an overall cop of 4.25, not stellar, but it equates to gas costs! Obviously getting the changes done to sort out the conflicts has I think smoothed things, that’s getting rid of the hive, second pump and converting buffer to volumiser. But I’m still looking to tweak things to improve that COP. So maybe narrowing the WDC, along the lines you have done. Though if you’ve done that outside of a WDC I’m still not clear how you’ve done that. I think the delta T standard for rads works pretty well for me and based on other posts you’ve made I’m surprised you are suggesting a dT of 5. I feel anyway that the pump has a little more flexibility with the dT10 and I don’t want to constrain it in that way. In any event it usually is in that territory anyway. But I do admire, envy even , your very consistent numbers, a thing of beauty.
Matt, you set me on this path when previously you told me it was all in the dT, which puzzled me. So I have done the maths, which was where I came up with the anomaly I have since been trying to resolve. Maybe you can help. But first, at 50c dT5, you need a flow rate of 22l/m to get the almost 8kw, 7.67kw to be exact. Similarly, at 40 , but at a DT of 10 you therefore need 11l/m, to get the full 7.67kw. So running in weather dependent mode, with a Target dT of 10 ( which as you said previously is the primary determinant of output, along with the flow rate, LWT doesn’t come into it, but that has a different role to play) you’ll get 4.88kw at 7L/m. And this is where the anomaly appears to arise. Because based on what I have seen on my system, and confirmed by others including yourself, the pumps algorithms prioritise LWT, then they focus on reducing dT to Target, then they are content and bring flow rate down to resting rate, which in my system seems to be 7.1l/m. Now it’s stable and there is nothing to say it needs to do more. EXCEPT if it’s cold you want the full 8kw (7.67kw). However you cannot have it because the flow rate is at 7 and I can’t discover any parameter that is going to shift that. And whilst I may be wrong, if that is so why won’t Daikin answer my question, which I’ve put to them multiple times. Because, I feel, though I don’t know if it’s true, that the only way to get the max out of the Daikin, when it’s cold is to switch over to thermostat control. Because that may trigger the system to up the flow rate. What do you think? Unless of course the formula is wrong!
Maybe @Andre_K’s excellent treatise Optimizing flow rate for ideal COP might resolve your obvious inner conflict, @Terry247…
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Thanks, I’ll definitely read it.
Set your dT to 4c and the flow temperature to say 40c and see what the flow rate is, it won’t be 7lpm.
The pump speed varies to keep the requested dT.
Forget my heat pump, I have double the radiator output you have and I never want more than 4kW of heat.
I’ve taken the tour through my settings now. Some are as expected some, one in particular is not. The anti frost in 4c, is set to off. That doesn’t sound right. Advice?
4.7 My pump limitation is set to 80%,
4.5. pump mode is set to Sample. Only 2 options sample and continuous.
4.3 Operation range. Space heating off at 22c. Anyone know what temp that is, is it outside temp, as measured by the Daikin sensor, internal temp which it gets from the Madoka, or third party thermostat. Does it apply across the board regardless of what control setting you have, ie leaving water, etc.
2.B1 the Delta T was set to 10 and can’t be changed. Presumably that frees up if you choose an option other than Radiator.
2C Modulation, greyed out, no access.
4.9 Pump outside range - set to RESTRICTED.
4.A increase around zero, was set to NO. I saw a number of mentions about this in various posts, presumably that lifts LWT?
4B Overshoot was set to 4. Does that allow system to overshoot the target LWT by 4 degrees, presumably upwards only as it’s an overshoot?
9. Installer Settings, I only looked at the list.
I have to say I don’t like the way the settings, set. It seems to work on the rather odd principal of whatever is lit blue. Doesn’t feel very robust.
Any observations, the no anti frost is a little concerning. Why would there even be a choice?
My anti frost is on, below 5c and my heat pump starts heating if it is not switched on with a flow temperature of 26cm, I have never changed this.
My pump is limited to 60% by choice, there shouldn’t be any limitation unless you have a reason for doing it. I do it to allow me to get the heat pump running at low flow temperatures when it is warmer outside. I wouldn’t do it for any other reason and not if I needed the full heat output of the heat pump.
My pump is set to sample, I don’t want it running continuously between heating cycles.
22c is the outside temperature from the external temperature sensor, the heat pump won’t run in heating when it reaches 22c outside, you can change this if you need to.
A dT of 10c is a minimum in radiators, you can increase it. If you want less then you need to be in fan coils or ufh.
Modulation only operates when you have Madoka room temperature control. It allows the heat pump to vary its heat output in response to changes in room temperature.
Pump outside range is off for me and should be off.
Increase around zero just boosts the flow temperature when it’s really cold. Mine is off.
Overshoot is upwards only and allows the heat pump to run in warmer weather without cycling when it would otherwise stop. It is also necessary to get the heat pump running at low flow temperatures when it is warm outside, mine is 4c, as is most people’s I believe.
Installer settings is where you make fundamental changes to the configuration, such as radiators or fan coils, Madoka or not, fixed lwt or wdc etc etc
Matt, that’s an interesting suggestion. My belief is that it would work for a short time, but because of the flow rate, very high to get the dT down to 4, it probably wouldn’t take it that long to get to dT 4 , call it an hour? At which point it would drop back to 7L/m and because the dT is 4 the output would drop massively. But it may work. However Daikin say the rad dT should be 10 and they recommend the weather dependent mode, so really it ought to have a mechanism for delivering the max heat without the workaround. I guess if lots of folk have very overstated heat losses then the 4.88kw max , that I seem to see , is maybe sufficient. But I dislike anomalies , I want to know Daikin’s answer. Or to find the error in my model. As a by the way, should my anti freeze mode be ON or OFF, because it’s set to off at the moment?
And another thought, on the 9kw, what was its resting flow rate?
No it wouldn’t.
It would continue to pump enough water to keep the dT at 4c.
The trouble is, you can’t see that on your MMI.
These Daikin heat pumps do not keep a steady flow rate (other than rock bottom with an unachievably high dT), the flow rate changes all the time lurching between high and low, it rarely settles.
These heat pump’s main goal in life is to maintain the set return temperature and they do it with flow rate.
So, if you set a flow temperature of 35c and a dT of 5c the aim of the heat pump is to keep the return temperature at 30c. That is how it works.
Daikin make suggestions but there’s nothing special about the radiator setting, the heat pump has no idea what it is connected to.
We don’t know what the differences are between the settings other than variable dT’s. My best guess is slightly different responses in the way water is heated as that can be all it is.
If you want to run as radiators and get the maximum output from the heat pump then you just need to turn up the flow temperature.
Eventually you will get to a dT of 10c and then the flow rate will increase giving more heat.
If you get to the maximum flow temperature and your flow rate is still 7lpm with a dT of 10 or less, then you need bigger radiators,
Matt, thanks for that, very helpful. I think I shall go and put the anti frost on. Maybe I should turn the heat pump heating back on too.
On the above that I’ve quoted, I have a little glitch. I don’t have an external sensor only the sensor that is in the outside unit. Because the pump is sitting in a sunny position, apparently not recommended I now discover, the sensor gets very warm. I have a little thermometer that I attached to the back of the unit, which gives a true reading, but that’s just to tell me, it doesn’t do anything. So today for example the MMI was showing an outdoor temp of 23c, I don’t know if it would have shut down, but as it was off for heating it didn’t arise. Actual outside temp was 10c. But I get really good solar gain when the sun is out in the rooms on the front of the house and also the temp in those rooms can get very high. So I’m thinking does it matter if it switches off, because I’m getting the heat and in those rooms the rads are probably not going to be able to diffuse much heat. The back rooms however do suffer. But not enough to worry about, and I guess I notice it more simply because the front rooms are so warm. The biggest concern though arises from a weird form of cycling. Because it is the sun, as soon as it pops behind a cloud the temp drops again very quickly, and so the heat pump could start again etc. You get the drift. A bit of a conundrum. Another one!
Matt, maybe my huge radiators are too small. Although the modelling doesn’t show that. Because my system gets to dT 10 very quickly and then drops to 5. And it tends to run between 5 and worst case 3. So if I read your comments correctly you’d say my rads are too small?
I have my heating on when I want heat and turn it off when I don’t.
I really cannot understand why anybody would do anything different?
I left the anti frost alone, if it is 5c outside I want heat, so if if I had turned the heating off as it was warm, if it got cold at night, I am happy for the heating to come on.
There’s no perfect answer for heating in my opinion. If the sun is out, it gets warmer, as you would expect. I don’t turn my heating off just because the sun is shining and a couple of rooms are a bit warm.
Your heat pump does not get to a dT of 10c very quickly.
You are misreading what you are seeing.
The dT always starts off quite large at the beginning of a heating cycle because the water in the system is cold. It takes time to warm it all up. Mine takes about an hour. You are not getting a dT of 10c, you are getting between 5c and 3c.
You still don’t seem to have grasped that because you have set a dT of 10c the circulation pump cannot go any slower to get to that at your chosen flow temperature. That is why your flow rate is stuck at minimum after the first 30 minutes of the heating cycle.
I didn’t say your radiators are too small.
Although 27kW of radiators is more than enough you are quoting huge to the wrong person as I have double that.
I said they would be too small if you couldn’t get 8kW out of your 8kW heat pump.
Turn it up to 50c flow temperature and you will get 8kW of heat even at a dT of 10c.
The point is that you will be able to get 8kW at a lower flow temperature with a lower dT as the flow rate will be higher.
You are trying to micro manage your heat pump with limited data.
What you see on the MMI is just a snapshot, you cannot do anything particularly meaningful with that information, it isn’t enough.
You just have to make changes and see what happens over a long period, you have nothing to look at.
Those of us with real time monitoring can see exactly what our heat pumps are doing and the instant results of any changes we make.
You do not have that luxury and so it is very difficult to go into the level of detail you are with little useful data to work from
Matt, perhaps I am misreading it, I don’t think so , so correct me. I started the heat pump up at 7pm,
At start up the LWT was reading 18c, RWT 18c and flow rate 24.9l/m, 10 minutes in the LWT was at 28c, RWT was at 20c and the flow rate was 15l/m. 20 minutes in The LWT was at 32c, one degree over Target, RWT was 24c and flow rate still 15l/m. 30 minutes in the LWT was at 34c , RWT 26c and flow rate 8.9l/m. At 33 minutes the LWT 34c, RWT 26c and flow rate settled at its usual 7.1l/m.
Now I may be mistaken but I thought delta T, for the heating system, not the radiators, was the difference between the LWT and the RWT. You will notice that during the whole period the dT was within target, never outside. 33 minutes. The dT of 10 is not a target the system is trying to achieve, or at least it never has with my system, it is a target not to be breached. Once under dT, the system doesn’t care. Or again, that’s how it appears with my system. I will say though that we seem to have a different concept of numbers. A large dT or a high one, to me would be 20, a low one 1 , 2,3 or 4, but anything below 10 in my book is low, mathematically low, and below target. So when it started up today, it had to make no effort to keep it within Target. In fact we know that when you have a large dT, say 20, then the flow rate speeds up to bring it down to target. But when it’s already in Target it doesn’t have to do anything. As was the case this evening. Are we on the same page now?
No.
I don’t know why you think our heat pumps are different, they are not.
In radiators, the dT is 10c as standard and is large in heat pump world.
You have never got to a dT of 10c, it got to a maximum of 8, and it never got to 10c because the circulation pump cannot go slow enough to get there.
The target is a dT of 10c.
But if you are happy that you know how it works, then that is good enough.
I’ll leave you to it now you’ve worked out how your system works.
I can’t help you seeing as you have a different Daikin control system to the rest of us.