Ecodan 8.5KW not reaching set water temp

[Gary68]

Hi all,

 

As we reach the start of the heating season, my fading memory reminded me of an issue I've had with my Ecodan since it was installed.  Its not a massive inconvenience, more an annoyance to myself personally as I don't understand why its not doing what it should, the house maintained 20°C last year in the coldest months.

 

The flow temperature will not reach target temperature when its really cold outside and the both the UFH (downstairs) and the radiators (upstairs) are calling for heat.

 

The Ecodan has no issue getting DHW to 50°C in the depths of winter even when its run in the middle of the night during off peak prices so I know the flow temps can get that high.

 

Its run in weather comp mode and when its subzero outside the flow temp should be 45°C.

 

When its only the UFH calling for heat then it will reach 45°C but if the thermostat upstairs calls for heat the flow temp will drop and try to recover but never makes it back to 45°C until the upstairs thermostat turns off.

 

Is this just the limit of the heat pump and it can't output enough heat at -5C with respect to the volume of water its trying to heat when both circuits are on?

 

There are a lot of pumps in my airing cupboard attached to the hot water tank with the ecodan controller and I have no idea what they should be set to. 

 

There is one that relates to the HP itself that I can change the flow rate on through the ecodan controller it was set at 5 when the installer left and that was far too noisy so now set at 3, maybe I have caused the issue by reducing the flow rate too much?

 

There is a pump for the upstairs rads a Grundfos UPM3 auto and another for the UFH circuit but then another pump that supplies the UFH manifold downstairs in a separate cupboard. 

 

These all have settings for proportional and constant curves and I have no idea what they should be set to.

 

Any thoughts suggestions on what could be the cause or what to change to test appreciated.

 

thanks in advance.

 

 

[Marvin]

Hi @Gary68

 

The fact that the flow temperature drops and won't recover suggests that the amount of heat coming out of the system is more than the ASHP puts in. 

 

If there was something with the pumps or valves, the flow temperature would reach temp but the house would be cold.

 

I would insulate to death any external pipes from the ASHP to the building thermal envelope.

 

Otherwise home looses more heat than expected / calculated.

 

In the winter airtightness is a BIG heat loss factor. Without knowing your building design etc one can only guess..

 

Good luck

 

M

 

[sharpener]

49 minutes ago, Gary68 said:

Is this just the limit of the heat pump and it can't output enough heat at -5C with respect to the volume of water its trying to heat when both circuits are on?

 

Sounds like it! If the house is warm enough in the coldest weather though I would not worry. If it bothers you maybe you can shift the zone timings so that everything is not calling for heat simultaneously?

 

50 minutes ago, Gary68 said:

There is one that relates to the HP itself that I can change the flow rate on through the ecodan controller it was set at 5 when the installer left and that was far too noisy so now set at 3, maybe I have caused the issue by reducing the flow rate too much?

 

You could try changing it back but you will have to wait until it is really cold to see the result.

[Gary68]

53 minutes ago, sharpener said:

 

Sounds like it! If the house is warm enough in the coldest weather though I would not worry. If it bothers you maybe you can shift the zone timings so that everything is not calling for heat simultaneously?

 

 

You could try changing it back but you will have to wait until it is really cold to see the result.

Yes - that's where I was, its not a performance issue as such as the house is warm enough, I think its just on the limit of the capacity of the heat pump I will monitor more this winter. thanks for the response

[sharpener]

41 minutes ago, Gary68 said:

Yes - that's where I was, its not a performance issue as such as the house is warm enough, I think its just on the limit of the capacity of the heat pump I will monitor more this winter. thanks for the response

 

From what you say you are lucky enough to have an HP that is exactly the right size for your property. So you will benefit from the best possible turndown ratio, the least cycling, the highest efficiency and the lowest capital cost!

[JohnMo]

Are you just trying to do things too quickly? Low and slow compared to quick and high.

 

45 degree flow temp to UFH, says you are trying to heat it up quickly.

 

The result is the heat pump is too small to keep up. Run everything at a lowered temp for longer is likely to fix this.

[Gary68]

1 hour ago, JohnMo said:

Are you just trying to do things too quickly? Low and slow compared to quick and high.

 

45 degree flow temp to UFH, says you are trying to heat it up quickly.

 

The result is the heat pump is too small to keep up. Run everything at a lowered temp for longer is likely to fix this.

Hi John,

 

When its sub zero outside, the HP never really turns off its on 24 hours a day, I learnt that at low temps, set back overnight wasn't really an option as the HP wouldn't be able to catch back up it could only maintain, so it runs 45°C constantly between defrost cycles which were occurring every hour reducing flow temp further, it would just get back up to temp then back to another defrost cycle.  If then the upstairs circuit came on then it couldn't get back to 45°C hovered around 40°C if I recall correctly.  I have a better handle on the weather comp curve this year and have maxed it out at 40°C to see if it can maintain temp and maybe defrost less.

Edited September 20, 2023 by Gary68

[AliG]

It sounds like what is happening is that the house gets up to temperature and the heat pump switches off before the flow has got back to 45C. This is not an issue. the heat pump is not going to keep heating the water once it is not needed. Even a gas boiler will show a lower flow temp than you might expect whilst heat is being extracted from the flowing water. The heat pump just cannot generate enough instantaneous heat to get the water up to 45C whilst energy is being removed from the water into the house.

 

21 minutes ago, Gary68 said:

I have a better handle on the weather comp curve this year and have maxed it out at 40°C to see if it can maintain temp and maybe defrost less.

 

There is a decent chance doing this that the house will be too cold. It sounds like the flow probably has been running at between 40 and 45C when the temp is below zero. Reducing the maximum flow temp to 40C will just reduce the maximum heat input into the house. If the flow never gets above 40C it might not make a difference.

 

[Gary68]

18 hours ago, AliG said:

It sounds like what is happening is that the house gets up to temperature and the heat pump switches off before the flow has got back to 45C.

 

Hi thanks for the response, the house doesn't get up to temperature the HP is on 24/7 in the depths of winter, the thermostats are set to a level that means they are always calling for heat.  I will have to review this winter but what maybe happening is the unit has to defrost before getting back to 45°C and if it didn't have to defrost then it may be able to get there its just not powerful enough to get there between defrost cycles. 

[AliG]

On 20/09/2023 at 09:24, Gary68 said:

When its only the UFH calling for heat then it will reach 45°C but if the thermostat upstairs calls for heat the flow temp will drop and try to recover but never makes it back to 45°C until the upstairs thermostat turns off.

I think I misread this. I didn't realise it was just the upstairs thermostat. So it's just the upstairs thermostat that goes off then the flow gets to 45C whilst it is still heating the UFH loops.

 

I think it is very clear that simply when the UFH and radiators are both on and it is cold then they can extract more energy from the water than the ASHP can provide at its maximum output so the flow remains below 45. Thus the heat pump is arguably slightly too small, you have no overhead for extremely cold days by the sound of things. Probably not a big problem, though, just put on a jumper if it is very cold and the heat pump doesn't quite cope.

 

I very much would not turn the flow temperature down as this will probably make things worse. I see what you're saying that maybe it would defrost less, but I have to believe that the designers took this into consideration and the heat pump cannot put out more energy in total with the flow temp set lower. That would make no sense at all.

[sharpener]

 

4 hours ago, Gary68 said:

the house doesn't get up to temperature the HP is on 24/7 in the depths of winter

But this is what you said in yr original post, is the HP output just sufficient or not?

 

On 20/09/2023 at 09:24, Gary68 said:

the house maintained 20°C last year in the coldest months.

 

Perhaps we can reconcile the two statements if you don't consider 20C warm enough, in which case I would endorse the suggeston to put on another jumper.

 

A former colleague of mine heated his house so he could wear shirt sleeves in the depths of winter. He now lives on the isle of Skye(!?!). I wonder what his fuel bills are like.

 

[Gary68]

2 hours ago, sharpener said:

 

But this is what you said in yr original post, is the HP output just sufficient or not?

 

 

Perhaps we can reconcile the two statements if you don't consider 20C warm enough, in which case I would endorse the suggeston to put on another jumper.

 

A former colleague of mine heated his house so he could wear shirt sleeves in the depths of winter. He now lives on the isle of Skye(!?!). I wonder what his fuel bills are like.

 

It would be more correct to say the HP doesn't turn off as the thermostat isn't satisfied- it kept the house at 20°C but the thermostat was set at 21°C and it couldn't reach that internal temp - I agree with everything else that has been said the HP is probably a little undersized for the worst case days but better that way than too big for the remaining 360 days of the year

Edited September 21, 2023 by Gary68

[JohnMo]

Put an electric heater upstairs on the landing with the bedroom doors slightly open on the coldest days. Get one with a timer and thermostat, that should back fill the heating on the coldest days.

[JoeBano]

I’ve just put an electric towel radiator in my bathroom. It’s 500w just for drying towels so I don’t have to put ashp on. It’s smart Wi-Fi one, it’s got a nice feature when’s its -2c outside it will turn on. That could be an option for you. 

[Gary68]

Thanks Joe, do you have a link, we do need to renovate the bathroom at some point and the towel rads are pretty poor emitters at low temps.

[JoeBano]

https://www.toolstation.com/tcp-white-smart-wifi-fixed-pre-filled-towel-radiator/p78466?utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=_dm&pcrid=&pkw=&pmt=&gbraid=0AAAAAD-vLcXV65VFZMjbXGhYzP1GQnEMv&gclid=Cj0KCQjw06-oBhC6ARIsAGuzdw1opv17VkQTOCcva4CCfeb1jAXa7m9G7ip81vgcQb007fQ_vCFH6QYaAqmaEALw_wcB&gclsrc=aw.ds that’s one I fitted very happy with it 

[Onoff]

On 21/09/2023 at 11:03, AliG said:

just put on a jumper

 

[joth]

On 20/09/2023 at 10:20, sharpener said:

On 20/09/2023 at 09:24, Gary68 said:

There is one that relates to the HP itself that I can change the flow rate on through the ecodan controller it was set at 5 when the installer left and that was far too noisy so now set at 3, maybe I have caused the issue by reducing the flow rate too much?

Expand  

 

You could try changing it back but you will have to wait until it is really cold to see the result

 

It turns out the ecodan has an undocumented "feature" that it can PWM control the speed of the primary pump, so if this turns out to be an issue one option would be to use pwm speed control on that pump and in theory it will only run at full tilt (full noise) when it really needs it. 

[Gary68]

I did a bit of a test last week when the temperature dropped overnight, in the depths of winter is was very difficult to determine what was going on as defrosts and recovery of the flow temp from defrosts was masking the issue.

 

This isn't the case at the moment as its not cold enough, but what it did show is that with both circuits opened the flow temp had a dt of 8 where as its usually around 4 with only one circuit open.

 

After I increased the pump speed to 4, with both circuits open the dt has returned to 4 so it would seem I had aggravated the issue with too low a flow rate which meant the HP just could raise the flow temp high enough.

 

So will see how this works when winter hits.

 

Changing the pump speed back to 4 has also highlighted another issue I had forgotten about.  When set at a speed of 4 of 5 the pump speed seems to oscillate up and down slightly which is highly annoying as it more noticeable due to the varying frequency rather than it just being a constant frequency in the background.