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Poor COP with an Ecodan

 
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Air Source Heat Pumps (ASHPs)
Last Post by Derek M 2 years ago
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 adam_colwell
(@adam_colwell)
Active Member Member
Joined: 3 years ago
Posts: 21
Topic starter 28/11/2023 11:24 pm  

@gary that makes sense, would that increase my energy use? Because I would rather use less energy and have a lower COP, then use more energy and have a higher cop. Hopefully that makes sense



   
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 guthrie
(@guthrie)
Trusted Member Member
Joined: 2 years ago
Posts: 73
29/11/2023 12:23 am  

Posted by: @adam_colwell
↑

@gary that makes sense, would that increase my energy use? Because I would rather use less energy and have a lower COP, then use more energy and have a higher cop. Hopefully that makes sense

I think that would depend on how quickly your house lost heat and what the hysteresis of the thermostat is, but given the way our one has improved in efficiency when cycling less often, give it a go anyway and see what happens.

 



   
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 HarriUp
(@harriup)
Estimable Member Member
Joined: 4 years ago
Posts: 108
29/11/2023 2:24 am  

I'm not sure you should worry too much. The inaccuracy of the unit's measurement of its consumption builds up, I know my unit thinks it has used 60 kWh more than it actually has, and that all accumulates in the heating figures. If your heating usage is closer to 100 kWh then your COP is around 4 which is probably about right.

Reheating the tank is likely to contribute to poorer COP for HW as it is working in the hotter less efficient end of the cycle. You could probably lower the reheat value quite a lot before you notice you are only getting tepid water out – it depends on your pattern of usage.


Mitsubishi EcoDan 8.5 kW ASHP - radiators on a single loop
210l Mitsubishi solar tank
Solar thermal
3.94kW of PV


   
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 Kev M
(@kev-m)
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Joined: 5 years ago
Posts: 1276
29/11/2023 7:21 am  

Posted by: @adam_colwell
↑

@bontwoody it's a three bed semi detached house. Hopefully it is just reporting it wrong. I'll look at getting the Melcloud app, because by what people are saying, hopefully that is accurate

If it's reporting consumed/delivered energy inaccurately now, that won't change with Melcloud because it uses the same data you see on the FTC screen. You do get a more detailed breakdown though.  What it will also give you is the ability to track flow temperatures, air temperatures, etc. which is really useful if you want to make changes and see what happens. 

The only way for any heat pump to measure COP accurately is to use 'proper' heat and consumption meters but these are quite expensive. 

 

 



   
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 Gary
(@gary)
Reputable Member Member
Joined: 3 years ago
Posts: 350
29/11/2023 7:39 am  

@adam_colwell there are other factors that can impact cycling when your unit is running what is the flow rate, if you go to settings and running information and put in code 540 it will tell you how many litre per min the primary circuit is circulating at.  Also in the settings menu there is a pump speed menu what is that set to? The max is 5.   If you change the pump speed setting do you see a change in the flow rate or hear the pump increasing in speed?  Again under the settings menu there is a thermistor reading screen that will tell you your flow and return temps if these are closer than 3C apart the unit will cycle.  If your dT (difference between flow and return) is closer than 3C you could try reducing the pump speed and this may increase your dT and reduce cycling without having to increase your WC.

 



   
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 Leftbacks
(@leftbacks)
Eminent Member Member
Joined: 3 years ago
Posts: 34
29/11/2023 1:00 pm  

Posted by: @adam_colwell
↑

Hi Guys,

I'm hoping you may be able to help. I'm getting (I think) poor COP. In November so far I'm getting a cop 2.39, with heating being a cop of 2.71 and DWH being 1.65. My heating is weather compensation with a flow rate which doesn't go higher then 30c at -2 outside and the DWH is set at 45c with it heating back up when it drops by 12c. All rads are fully open upstairs and downstairs we have underfloor heating. Thermostats are set at 23c with room temperature of around 21c downstairs and upstairs of around 20-19c. I've attached pics of my readings and the model.

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 Leftbacks
(@leftbacks)
Eminent Member Member
Joined: 3 years ago
Posts: 34
29/11/2023 1:02 pm  

I have a Mitsubishi Ecodan 14kw newly installed into a new build and have had the same issue of it not being to maintain flow temperatures in colder weather which results in my home not being able to be heated.  Do you have this issue? I am in South Wales.



   
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 adam_colwell
(@adam_colwell)
Active Member Member
Joined: 3 years ago
Posts: 21
Topic starter 03/12/2023 4:19 pm  

@gary Hi Gary, sorry in the delay in back to you. I have 14 liters per and pump speed is set at 3. What's the thermostat screen called and where we will say the my DT, sorry I know very little about this stuff and trying to learn. Over this last cold snap I have been using about 16 to 17 Kwh a day (24 hours)  to heat the home. The home has an EPC of 86. Does that sound about right for usage?



   
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Morgan
 Morgan
(@morgan)
Noble Member Member
Joined: 5 years ago
Posts: 698
03/12/2023 4:30 pm  

@adam_colwell 

I might just swap a kidney for that 😲 . I'm at 50KW per day!


Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.


   
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 adam_colwell
(@adam_colwell)
Active Member Member
Joined: 3 years ago
Posts: 21
Topic starter 03/12/2023 4:32 pm  

@morgan depends how big your home is, mine is 94 square metres. 3 bedroom semi detached. 



   
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 Gary
(@gary)
Reputable Member Member
Joined: 3 years ago
Posts: 350
03/12/2023 4:32 pm  

thermistor readings are the page below where you got the pump speed from.  There will be readings for THW1 and THW2 they are your flow and return temps.

Assuming it was below 0 the last few days you are using very low amounts of electricity I used 40kwh to heat my house 



   
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 adam_colwell
(@adam_colwell)
Active Member Member
Joined: 3 years ago
Posts: 21
Topic starter 03/12/2023 4:37 pm  

@gary so my TW1 is at 31c and TW2 is at 32c but I also have TW5 at 34c and TH7 at 4c.



   
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