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timtoos
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September 5, 2022
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Mitsubishi Ecodan Air Source Heat Pump - Low Efficiency

  • September 5, 2022
  • 39 replies
  • 4408 views

Hi all,

We built a house and it was finished in 2019.  Its to the latest build spec regards to insulation and the likes.  Its over 3 levels, ground, first and second floors.  Its 5 bedroom, two main baths, a downstairs WC and one en-suite.  Downstairs the layout is a kitchen diner, utility with downstairs WC, living room and office.  The two bedrooms and one bathroom on the top floor have their radiators all on frost stat upstairs so never come on.

 

The first floor has radiators and 1 thermostat for the entire floor.  Its set at 17C in the height of winter and I put it in the bathroom - which the temperature barely can reach.  This floor is fully carpeted except the bathrooms which are Amtico vinyl.

 

The ground floor is all UFH, with Amtico vinyl flooring.  Each room with a Heatmiser thermostat.

 

Last year (2021) was a mild year.  I had the thermostats in the rooms we use (dining/kitchen the living room and the utility set at 18C.  The hallway was set at 15C so was the office as we dont use these much or are just pass through areas.

 

We have a Ecodan 11.5kW ASHP with 200L tank.  There are 2 adults and 2 children, one 7 and the other 3.

The DHW is set at 55C.

 

Last year (2021) we used:

 

DHW:

Consumed (kW): 1807

Delivered (kW): 3185

COP: 1.76

 

Heating:

Consumed (kW): 3620

Delivered (kW): 8457

COP: 2.34

2021 was a mild year but in 2020 when we got some real cold weather we used on some days over 75kWs/day, although we had the room temperatures at 21C not 18C.

These COP values seem low.  We expected at least 3.0 as the yearly average.  With bill costs soaring, we are looking at what we can do.

The installer isnt really helping at all.  Does anyone have advice at all?

 

I have just checked July/August usages:

 

July

DHW:

Consumed (kW): 84

Delivered (kW): 173

COP: 2.06

 

Heating: (is this the heater for Legionella)

Consumed (kW): 14

Delivered (kW): 0

 

August

DHW:

Consumed (kW): 80

Delivered (kW): 164

COP: 2.05

 

Heating: (is this the heater for Legionella)

Consumed (kW): 15

Delivered (kW): 4 (The bathroom t'stat battery failed and called for heating)

 

Thanks in advance.

    Best answer by nealmurphy

    I haven't got an Ecodan, hopefully others with this model will be along to assist shortly. But if not I'll send out a pigeon to alert them.

    First thoughts... Have you got weather dependent settings on? Is the hot water set to reheat or on a timed schedule? Do you know what the pressure is in your system? And is the Ecodan able to report the number on/off cycles it's done? Minimising the cycles should improve efficiency. 

     

    Yes, I have the temperature curve enabled.  I have used with and without this enabled.  At the moment its set to on with a offset of -6 (should be 0).  I run this as low as possible to make things cheaper - so I was told.

    I do not know if the unit has a cycle counter.  I havent come across it if it does.

    The system pressure is at 1.5bar, which is what the installer told me to have it set at.  The heating schedule is set to reheat and will do this anytime night or day should the tank temperature drop to its heating setpoint.

    I was toying with the idea of only letting the cylinder top up in the early hours when the electric is cheaper, then wondered if this colder time in the early hours would actually make the unit work harder and cost more in the long run.

     

    That all sounds good.

    I make use of cheaper electricity overnight to heat my cylinder and warm the house ready for the morning. Mine is a high temp heat pump so it’s less of an issue turning it off and on.

    Can you show us your graph of electricity use each 30 minutes to get an idea of any extreme cycling?

    As @juliamc has said it’s generally best to open the circuits up and not have the heat pump fighting with thermostats or radiator valves. This video by Heat Geek may have a few tips in it. If you can run the system low and slow so the thermostats aren’t cutting the heat pump off too often (ideally you want the weather comp. settings to just get to the temperature you want in the room and hold it there. The thermostat can be used as an override to turn it off if it gets too hot. 

     

    39 replies

    Show previous replies
    juliamc
    Rank 20
    juliamc
    Rank 20
    September 6, 2022

    @James_N  has an Ecodan so will be able to assist with the DHW temp.

      T
      Rank 2
      timtoosAuthor
      Rank 2
      September 6, 2022

      @James_N  has an Ecodan so will be able to assist with the DHW temp.

      Fantastic.

      Thanks

      J
      Rank 6
      James_N
      Rank 6
      September 6, 2022

      Hi there,

       

      My DHW is set to 50C. I would say 55 is too much. I can tell you in the summer (because the heating isn’t on) I’m getting a DHW COP of about 2.4. On a really hot day maybe 2.8

      Obviously in the winter it will be much lower.

      Overall I have a total SCOP of 3.02. My house is a semi which no doubt helps, but its using the original radiators, and I have no cavity wall insulation upstairs due to hung tile outside. Its worth using the melcloud app in the winter to see the actual minute by minute temps that the system is running at. The lower the better, as long as its keeping the house warm. My thermostat is set at 21C

       

      Any other questions fire away :)

       

      J

      11.2k Ecodan ASHP. 4 Bed semi.
        T
        Rank 2
        timtoosAuthor
        Rank 2
        September 6, 2022

        I have changed these setting:

        Set all the downstairs room t'stats to 1C temperature higher than what I require.

        Changed the upstairs temperature to a temperature I require.

        Changed the ASHP to run with a fixed temperature.  Zone 1 (upstairs) is set at 18C and zone 2 (downstairs) is set at 20C.

        Changed the HW tank setpoint to 49C.  Left the 10C drop as it was.

        Thoughts?

          juliamc
          Rank 20
          juliamc
          Rank 20
          September 6, 2022

          Are you still using the weather dependant curve ? Does that mean target temperatures of 18 and 20 degC. My controls are different so maybe I should not interfere !!

          T
          Rank 2
          timtoosAuthor
          Rank 2
          September 6, 2022

          Hi juliamc,

          I have the system to use the internal temperature of the room as people say to do.  I presume this still uses the outside temperature to do this!   Am I correct?

          Yes, those are the targets at the heat pump end, not the thermostat setpoints.

          juliamc
          Rank 20
          juliamc
          Rank 20
          September 6, 2022

          Not sure exactly what you mean but yes, the weather dependant business uses a sensor outside and adjusts the leaving water temperature accordingly, to balance the heat loss from your house and keep the rooms at the target temperature. It takes a bit of trial and error to get it right and of course it needs to be cold outside !

            T
            Newcomer
            Topbuilder
            Newcomer
            November 17, 2022

            Does anyone know how to turn off the setting for the pump to run water round the system when external temperature is below 5 deg?.

            Very annoying can here it running all night and no risk of the pipes freezing.

            BPLightlog
            Super User
            BPLightlogSuper User
            Super User
            November 30, 2022

            Does anyone know how to turn off the setting for the pump to run water round the system when external temperature is below 5 deg?.

            Very annoying can here it running all night and no risk of the pipes freezing.

            I don’t have the same system and each interface is a little different but there should be a section for weather dependant control (wdc) which should have that if enabled 

             

            Bring me Sunshine ~ E&E {Solar PV, Battery Storage, Hybrid EV, ASHP and Home Assistant automation}
            nealmurphy
            Newcomer
            nealmurphy
            Newcomer
            November 30, 2022

            Does anyone know how to turn off the setting for the pump to run water round the system when external temperature is below 5 deg?.

            Very annoying can here it running all night and no risk of the pipes freezing.

            Again, don’t have that make of ASHP. But I think you are looking for something called “Freeze Stat Mode” on the Ecodan.

             

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            OVO Energy Ltd, Floor 5, Crescent, Temple Back, Redcliffe, BS1 6EZ, (Company no. 06890795) registered in England and Wales.

            OVO (S) Gas Limited is registered in England and Wales (Company No. 02716495) at Floor 5, Crescent, Temple Back, Redcliffe, BS1 6EZ.

            OVO (S) Gas Limited is part of OVO Group Ltd