Tuning performance of Dakin 8kw Altherma 3

Hardware Heatpump
61

How are you monitoring your heat pump Terry?

What you will find is that if you increase LWT by 1c that will happen pretty quickly and you will see a widening of your dT if it is actually set above what you are seeing.

It will take a little while for the RWT to catch up, but it will in time and then your dT won’t be much different to what it was when you started if the outside temperature is constant.

Nothing happens very quickly, certainly not instantly, and proper monitoring makes it easy to see what is going on.

I find `seeing’ my heat pump very helpful.

Again reducing LWT will happen quite quickly and you will see a reduction in heat but after a little while the RWT will fall and the heat will be pretty much the same.

This is what you will see with a large requested dT and the flow rate stuck on the minimum.

Change the requested dT to something like 4c or 5c and your heat pump will behave differently.

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62

Ok, so if I have a LWT of 30c and a RWT of 30c I haven’t transferred any heat and that is why if it’s LWT 30 and RWT Of 25 then I’ve transferred some heat . [ yes radiator mode and dt of 10c]. So if it’s cold and my LWT goes up to say 40c and my return is 30c , then I’ve taken in a lot of heat and that’s my max because that’s the dt setting ( unless it is altered) . So if I’m running at 30 I could would be taking more heat if my return was at say 20.

Now as I am running in weather comp mode, there is no set temperature. So what is controlling the LWT is the weather comp curve. So the happy place for the Daikin is say LWT of 30c and the max heat I can extract is if my RWT is 20c. Now if my radiators are on 24c, then the max I can extract is 6c, because my RWT will be at ~24c. But if I pump my LWT up to 35 then my radiators could get warmer and so initially I’ll be able to extract more heat, with a dt of 10, RWT of 25, but as the radiators warm up more, then the heat gain will drop, so if the radiators went up to 30, then RWT at 30. So the DT is fixed only in the sense it can’t be exceeded. And if you have a higher set DT then you can extract more heat but it’s relative to the DT. If that’s correct I think I understand that. Then if we factor in the flow rate, so @ebyard upped his flow rate. Now other things being equal ( which they probably aren’t) that means the water goes around more quickly so the radiators will get closer to the LWT and the RWT will be closer to the LWT, so with pumping faster that would be an initial gain in heat and then that would fall off as the radiators warm up. Ultimately the max heat you get is based on the heat of the water in the rads. Or not?

63

Simply by checking the MMI info and calculating the cop, I don’t have any of the monitoring equipment and was told that installing any would invalidate the warranty.

64

I have the 6kW Daikin, its set to Radiators with the default 10C DeltaT. Mine spends the vast majority of its time at 7L/min like yours. When it initially comes on it will run faster until it gets the LWT up to the set point, then it will drop to 7L/min. The only time I see it higher is when its very cold (sub -5C) outside.

65

That’s helpful. And are you running it on pure weather comp?

66

It is pretty difficult to get anywhere with a Daikin if you can’t see what is happening, perhaps with any heat pump.

Anyway.

If you leave the dT at 10c increasing LWT will increase heat produced but 1c of extra LWT will not ultimately increase the dT by 1c, it will be a small fraction of 1c.

All this is assuming the outside and inside temperatures are constant so heat loss is fixed.

All that will ever happen on a dT of 10c is you increase LWT to get more heat, by your wdc in your case.

Eventually you will get to a dT of 10c at a flow rate of 7lpm and then if you increase the LWT even more the pump speed will need to increase to maintain the dT of10c giving even more heat.

If you want a higher flow rate at something around 35c flow temperature then you need to switch to either ufh or fan coils and set something like dT of 5c.

But you will find the flow rate varies wildly and so will the heat output as per my earlier post.

Going on to your next post.

It is important to remember that a wdc is just a varying LWT based on outside temperature, nothing magic.

I control my LWT myself from the app as I find a wdc useless.

I have ruined my system because my radiators are too big. I need a lower flow temperature when cold and a higher one when warm, all because the Daikin cannot run low enough for me and it cannot control the flow rate well enough.

All Daikins go to maximum flow rate at the beginning of a heating cycle for around 20 minutes and then slowly ramp down to get the RWT under control.

They always overshoot the requested RWT and go to minimum flow rate until the RWT is where it is meant to be, and then the fluctuating flow rate starts and never really stops.

67

When I was planning my heat pump install I found it helpful to think about each aspect of the system in isolation.

There is a heat loss from the house to outside. This is proportional to the difference in temp between indoors and outside and is a linear relationship. It doesn’t matter whether your house is heated by a heat pump, gas boiler, oil, fan heater, this heat loss is the same.

There is a heat loss from your radiators to the room, this is how the room is heated. This is proportional to the difference in temp between the radiators and the room (this one isn’t a linear relationship, its more complicated). For the purposes of this, this radiator temperature is typically calculated as half way between LWT and RWT, i.e. the average water temperature. Its worth noting this is independent of the outside temperature, it wouldn’t matter if it was 15C outside or -10C the heat flow from the radiators for a given radiator and room temperature is the same.

This heat then needs to be delivered to radiators, this is a function of (LWT - RWT) * Flow Rate * Heat Capacity of Water

Finally the water is heated by the heat pump, again this is Heat Pump output = (LWT - RWT) * Flow Rate * Heat Capacity of Water

If everything is in the steady state, then all four heat losses will be the same. For example the house heat loss is 3kW, the radiators are providing 3kW heat to the rooms, the pipes have water flowing round at 3kW and the heat pump is providing 3kW of heat. If one of these changes, then the system is no longer in equilibrium and the system will alter until they come back into equilibrium (the room temperature changes for example).

The limitation for a lot of people running at a low LWT with radiators is the amount of heat which can be dissipated into the room through the radiators. In my case I can only dissipate at most 1.5kW to 2kW from all the radiators combined when running a LWT of 30C. If 2kW is being lost at LWT 30C and the flow rate is 7L/m then the RWT will be 26C. The heat pump would like to get it to a deltaT of 10C, so a RWT of 20C but it doesn’t have a variable to change to achieve that. The compressor is already at minimum rate, and the flow rate of 7L/min is the minimum the unit will allow, therefore things stay at 7L/m and a delta T of 4C.

If however I increase LWT to 50C then I can dissipate loads of heat into the rooms, if the flow rate continued at 7L/min then the RWT would be 35C, exceeding the 10C deltaT target. To prevent this the heat pump increases the pump speed to 10L/min, this gives a RWT of 40C. But as you can see the heat pump only needs to flow faster than 7L/min at really quite high LWT (at least for my radiators).

FYI a handy rule of thumb is that each 1C of difference between LWT and RWT at 15L/m is equal to 1kW of heat.

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68

Far from it. I use weather comp (50 LWT at -20C, 30 LWT at 10C) and then use Madoka thermostat with modulation (Level 8). I also have TRVs on all main radiators which are used sometimes.

But the weather comp, and Madoka modulation are all just a way to ultimately arrive at a target LWT for the heat pump to try to achieve at any given time.

69

I meant to reply to the flow rate switch question as well. Mine is always showing “off”. The installer manual suggests its a thing that needs to be installed if you have glycol in your system.

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70

To be clear, there is no way to actively control the flow rate with any of these current Daikin heat pumps.

There are no settings to change or adjust.

The only way to fix the flow rate is to run at an unachievably high dT that keeps the flow rate at the minimum.

Once the set dT is reached the flow rate is in the hands of the Daikin software, and it really isn’t very good at controlling it!

71

Thanks . That’s good to know.

72

Jonathan, with all that what sort of cop are you achieving. What internal temperature are you aiming at/achieving? Not sure how the weather comp and the madoka interact, surely they conflict?

73

Interesting one. I only have the Daikin Madoka information, no OEM monitoring. COP for heating is 3.5 with little variation between seasons. My spreadsheet has COP 3.4 or 3.5 for every month from September 24 to January 25. That doesn’t intuitively seem right to me so I do wonder about its accuracy. We typically aim for minimising total energy usage rather than absolute efficiency. Total annual electricity usage is 2,000kWh for heating 3 bed end-terrace in central Scotland.

18C ish living room/kitchen, 20C in studys, freezing cold bedroom.

The don’t conflict.

Firstly the Madoka decides whether to have the heat pump on or not based on the room set point (with a wide hysteresis).

The weather comp then sets a starting point LWT based on outside temperature.

The Madoka modulation then alters this based on how far the actual room temperature is from the set point. For modulation level of 8 it does this:

  • 0.5C or more below set point it adds 2C to the LWT
  • 0.5C or above set point it removes 2C from the LWT
  • 1C or above set point it removes another 2C from the LWT (so 4C total)
    I am not exactly certain about the above, the manual doesn’t detail it specifically and I’m trying to work it out.

Finally any LWT offset you have made (the -10C to +10C change you can make on the APP) is then applied to the LWT temp.

The result is:
Target LWT = WeatherComp(external temp) + Modulation + Offset

So the idea is that the Weather Comp gets roughly the right LWT to keep the house at a constant temperature. But if its below target then the LWT gets bumped up a couple of degrees, and if its above target then the LWT gets dropped down a couple of degrees. Ultimately that should be a preferable result to having the heating click on and off based on a thermostat.

The TRVs are then used to either allow us to “turn off” a room entirely, which we do quite a lot and only heat the parts of the house we want to use. Or they prevent rooms from overheating, the south facing half of the house gets hot very easily mid-morning to mid-afternoon while the north facing side stays cold.

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74

Couple of observations based on nothing but ignorance and what I’ve worked through over the last few months. My pump was installed in June 2024. I’m currently getting a cop of 4.2. Everyone I’ve spoken to and the heat geek website amongst others says an open system works best. Ie let the water flow through the whole system, don’t adjust it down. That’s what I do. And it does suit me because I have had some damp in the bedrooms, which now seems to be addressed. Apparently it takes no more energy and the system is more efficient that way. I run with a target temp for downstairs around 18 , although the system was specced because of MCs with a 21 target downstairs and upstairs runs a couple of degrees behind. I also benefit from solar gain, but I just leave the system to run in the belief that if the radiator is too warm then it won’t be taking any of the heat. Also because I run at the 18c/15c any additional heat feels like an occasional bonus and it’s free!

Now I’m in the south west, so your temperatures are going to be lower than mine I would imagine. At the moment we’ve been bumping along between 3 to 6, with occasional dips below. I don’t know how much at all the much lower temps may, if at all impact the efficiency of the pump. But if you are keeping rooms cold for preference that’s good, but if you are aiming to reduce costs my guess is it may actually be costing more because it impacts system efficiency. I have kept my system as simple as possible, so I’ve set the weather comp curve to be give me the sort of indoor temp I want, then I have used the offset to tweak that a little if necessary.

Even so cop isn’t everything, because you can have a great cop and be spending a fortune. Actually I think I am. The question is really how is it in comparative terms. So in January I used 482kwh, for the heating, I don’t use a lot of hot water so that was only 6kw. That was 7/24 and keeping a reasonably constant temp.

So broadly I am happy, but I get these queries pop up from time to time, like this whole question about flow rates and whether higher flow rates improve efficiency. Have to say I need to re read a few times all the input from everyone today, it fair makes my head spin.

Thanks for all your input.

75

The Daikin rounds the electricity and heat energy values to the nearest whole kWh and this introduces massive inaccuracy. Comparing my system’s COP reported by OEM versus Madoka it has been ±1 variance, especially over longer periods like an entire month or year.

76

I was very concerned about the reporting from the MMI. But as long as you take the total numbers from instal you iron out the issue. If I compare usage reported by the MMI to my smart meter it’s pretty much in line. So I put a tiny spread sheet together, which takes the total figures and then will calculate overall cop heating and DHW and then do the same for the interval period, ie the period between the readings. I find this gives reasonably good results. In terms of the cop itself, I can only say that the produced electricity does seem to link to the kind of temperatures I’m getting in the house compared to the calculated heat loss for the house.

77

Yeah and I think what’s actually important is:

  1. Is your house at the temperature your household wants
  2. Do you have enough hot water
  3. Are your energy bills reasonable

COP really is just a way of comparing your system to itself, did the setting I change make the system more efficient whilst maintaining the above list. The whole “Top of the SCOPs” stuff is almost pointless.

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78

The biggest COP improver I’ve tried so far was to switch from Comfort to ECO hot water generation.
Only problem is that the heat pump won’t even put 45°C in the tank as it should!
It gets to 40°C and goes all super green and stops🙄
Perhaps not surprising the hot water COP improved a lot🙂

We could live with a tank of 45° water everyday, but not 40.

On Comfort it powers all the way to 48°C no problem.

Am I doing something wrong or missed a trick?

79

Surely that’s a typo - I used 823 kWh for heating in January alone (according to the Onecta app!).

I’m getting a lot of data together before I post again, from the pre-install survey to yesterday’s running data, have been around the house with a thermal camera getting the flow & return temps recorded. Interestingly, 4 radiators appear to have the F&R back to front! Back soon with a ton of data…

80

No typo, figure is correct (and validated as reasonably accurate from a CT clamp).

January usage this year was 308kWh, with a sustained cold period below -5C followed by a warm end to the month.