Posted by: @heat-pump-newbie

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Hi Derek. I have a further question to this topic if you don’t mind me butting in…

My Daikin (still a mystery to me in many respects) has been running with a low cop around 2 to 2.5 and once it’s reached the target lwt it runs at a low flow rate, 6.5 to 7.1 l/m whereas the manual states the minimum flow rate should be 12l/m.

I can’t set the flow rate, so I have to vary the delta T. Currently the emitter type is set to Radiators which gives a fixed deltaT of 10 degrees.
Almost always the difference between ‘inlet water temp’ and ‘leaving water temp’ is between 3 and 5 degrees, which I assume is deltaT according to the system.
So my question is Why is this not 10 degrees ?

Hi Newbie,

I was beginning to think that you had disappeared in a puff of smoke.

I suspect that your LWT is set too high, which may also be the cause of your low COP. Are you also using thermostats and/or TRV's?

The amount of heat energy being transferred from your heat pump to your heat emitters is set by the water flow rate, and the DT (DeltaT). The amount of heat energy absorbed from the water by the heat emitters, is again dependent upon the flow rate, but also the LWT. The DT is therefore dependent upon how much heat energy has been extracted from the water as it flows around the system. If you have thermostats and/or TRV's restricting the flow rate then the RWT will be higher, producing a lower DT.

To control the DT some heat pump controllers vary the water pump speed, lowering the water flow rate to increase the DT. I suspect that in your system the water pump may be running at its minimum speed, hence the low flow rate, but still cannot achieve the set 10C DT.

What is your LWT and RWT?

I would suggest that you set the required DT to 5C, and turn any thermostats to 2C above the desired temperature. Fully open any TRV's except for those in bedrooms, then set your heat pump controller for WC (Weather Compensation) control if it is not already in this mode. If you are already on WC control then it may need adjustment if the indoor temperatures increase or reduce.

Ah yes, those were the days! I saw the Heat Geeks were also firing up smoke bombs simulating a cold well at hghq, so it’s not just me 😬

I can only adjust the deltaT if I set the emitter type to fancoil or underfloor, i hope that’s not going to have any side effects ?? I am on weather compensation but perhaps it’s too high? I also have modulation on the room sensor which I understand adjusts the lwt accordingly. 
Today at 2deg outside the lwt was 41 and the return was 35 which is the largest difference I’ve recorded. Flow rate 6.5 to 7.1 as ever. Room was 20.6 deg.

Posted by: @heat-pump-newbie

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Ah yes, those were the days! I saw the Heat Geeks were also firing up smoke bombs simulating a cold well at hghq, so it’s not just me 😬

I can only adjust the deltaT if I set the emitter type to fancoil or underfloor, i hope that’s not going to have any side effects ?? I am on weather compensation but perhaps it’s too high? I also have modulation on the room sensor which I understand adjusts the lwt accordingly. 
Today at 2deg outside the lwt was 41 and the return was 35 which is the largest difference I’ve recorded. Flow rate 6.5 to 7.1 as ever. Room was 20.6 deg.

From what I gather, most systems operate with a DT of 5C, so I would say that at present your system is fine. Some systems don't have water pump speed control, so the DT varies as the heat demand changes. It is not that critical.

The main point is to get the heat energy from the heat pump and into your home in the most efficient manner.

How are you calculating your COP values? I can't remember if Daikin are one of the manufacturers who talk about heat energy yield, rather than heat energy output. If that is the case then COP = Heat Energy Yield + Electrical Input Power / Electrical Input Power.

@derek-m I can calculate the COP in two ways:

on the Altherma 3 controller I can look up   Information>Energy data>   and get cumulative consumed electricity and produced energy, for both DHW and heating.

so for heating in February the consumed electricity was 560 kWh and produced energy was 1133 kWh so COP 2.02

I don't think that's very good ! My room temperature is a comfortable 21 deg, I set back 20 at night and it has run on very cold nights but I still think I should be getting better that 2.02 !!

for DHW in February the numbers are 101 kWh consumed and 218 kWh produced so COP of 2.16 

The combined figures from the heat pump of 661 in and 1351 out give a cop of 2.04

The fact that the DHW is marginally better than the heating suggests that the flow rate (which is faster during the hot water cycle) gives better efficiency. Hence my question about the deltaT v flow rate.

The other way I can calculate COP is using the Sontex heat monitor which I have alongside the indoor unit, and the electricity meter for the heat pump. Those figures for Feb give 1463.52 kWh heat produced and 620.34 kWh consumed. This gives a COP of 2.35 (I have no idea why these figures are different to the heat pump ones btw!!! I haven't used the immersion at all over that month)

Posted by: @heat-pump-newbie

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@derek-m I can calculate the COP in two ways:

on the Altherma 3 controller I can look up   Information>Energy data>   and get cumulative consumed electricity and produced energy, for both DHW and heating.

so for heating in February the consumed electricity was 560 kWh and produced energy was 1133 kWh so COP 2.02

I don't think that's very good ! My room temperature is a comfortable 21 deg, I set back 20 at night and it has run on very cold nights but I still think I should be getting better that 2.02 !!

for DHW in February the numbers are 101 kWh consumed and 218 kWh produced so COP of 2.16 

The combined figures from the heat pump of 661 in and 1351 out give a cop of 2.04

The fact that the DHW is marginally better than the heating suggests that the flow rate (which is faster during the hot water cycle) gives better efficiency. Hence my question about the deltaT v flow rate.

The other way I can calculate COP is using the Sontex heat monitor which I have alongside the indoor unit, and the electricity meter for the heat pump. Those figures for Feb give 1463.52 kWh heat produced and 620.34 kWh consumed. This gives a COP of 2.35 (I have no idea why these figures are different to the heat pump ones btw!!! I haven't used the immersion at all over that month)

I would expect the Sontex readings to be more accurate, assuming that the equipment was correctly installed.

For a correctly operating system, the CH COP should normally be higher than that achieved producing DHW, so I suspect that there may be a problem with your system. Do you have a buffer tank or similar device present within your system? If you are not certain what one looks like then Google buffer tank. Some photo's of your equipment may be useful.

No buffer tank - it's quite a simple setup with 7 radiators.

Just out of interest Derek, why do you say the Sontex heat meter would be more accurate than the internal Daikin meter ? I’ve always wondered why they are different, I assumed it was because the Sontex is set a short distance from the Daikin unit so there is a temperature difference.

Posted by: @heat-pump-newbie

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Just out of interest Derek, why do you say the Sontex heat meter would be more accurate than the internal Daikin meter ? I’ve always wondered why they are different, I assumed it was because the Sontex is set a short distance from the Daikin unit so there is a temperature difference.

The main reason would be that the Sontex is designed and built to measure heat energy, it is a heat meter, that is its primary function. The device has a specified accuracy, which it should achieve if installed correctly. It should have been calibrated to confirm that it meets the specified accuracy.

The primary function of the heat pump is to heat water, but it does also contain equipment to measure temperatures and flow rates. Whilst the controller produces a heat energy produced figure, I do not remember reading where any manufacturer specifies the accuracy of this value.

For best overall accuracy, equipment has to be correctly installed, in the correct location, and calibrated against known standards that are at least three times more accurate than the device under test. The standard equipment being used must also have been calibrated against even more accurate equipment, so on and so forth.

You could try writing to the manufacturer and ask how accurate the readings on the controller will be.

You could try writing to the manufacturer and ask how accurate the readings on the controller will be. 

Well I probably won't as that's the least of my worries 🙄 

Thanks for your explanation though. The COP figures aren't massively different: low and lower !

@derek-m I have checked the Sontex version of my COP, having separately recorded the values for DHW and heating cycles. (The benefit of the heat pump version is that I can read off values for these separately, but only as whole numbers so meaningless for these short periods)

DHW ran for 50 mins outdoor temp 13 deg, COP = 2.74 not too bad.

Heating ran for 5 hours outdoor 13 deg falling to 10 deg, COP 2.94 LWT was 33 deg not very good, flow rate v slow.

The SCOP figure for a flow temp of 35 deg is given in my documents as 4.37 - wouldn't that be nice ?

All part of the learning process 🤓 

Posted by: @heat-pump-newbie

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@derek-m I have checked the Sontex version of my COP, having separately recorded the values for DHW and heating cycles. (The benefit of the heat pump version is that I can read off values for these separately, but only as whole numbers so meaningless for these short periods)

DHW ran for 50 mins outdoor temp 13 deg, COP = 2.74 not too bad.

Heating ran for 5 hours outdoor 13 deg falling to 10 deg, COP 2.94 LWT was 33 deg not very good, flow rate v slow.

The SCOP figure for a flow temp of 35 deg is given in my documents as 4.37 - wouldn't that be nice ?

All part of the learning process 🤓 

@heat-pump-newbie,

your ASHP is probably running at very low output in the conditions above; 33 deg LWT is barely lukewarm and outside temps are quite high.  I know my ASHP is less efficient in these conditions (and the manufacturer data confirms this).  The energy overheads of just running the ASHP are still there but the energy output is low so the COP tends to be lower.  When heating DHW the ASHP is probably working a bit harder and delivering more energy. so the overheads are spread out more. 

The SCOP of 4.37 will be measured when the ASHP is working at its rated output - 7kW or whatever.  Yours will be delivering a fraction of that in these conditions.  

Just a thought anyway.    

@derek-m in the same way as the hp heat meter would be less accurate than the sontex, would the hp pressure reading be less accurate than this dial ? They always read about 0.4 bar different