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

  • September 5, 2022
  • 39 replies
  • 4412 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
    L
    Newcomer
    lycandroid
    Newcomer
    November 30, 2022

    Yes, it’s the freeze stat function.  You need to go through the Service menu to get to it.

    It is mentioned in http://www.mitsubishitech.co.uk/Data/Ecodan/Controls/PAC-IF041B-E_FTC3/PAC-IF041B-E_IM1.pdf which probably has the same menu.  Go to Page 4 and it shows the full menu structure, and how to get to the Freeze stat function setting.

    This video roughly shows how to get to the Service menu https://www.youtube.com/watch?v=Pl7w7Zwq7zI.

    E
    Newcomer
    epolyzois
    Newcomer
    December 5, 2022

    Hi

    recently installed an ECODAN SW160YKA, along with a buffer tank of 100lit(4 way connection), 3 third party thermostats controlling 3 different areas.I have 14 radiators and the house is very well insulated.The water temperature is set ot 45 degrees and sanitary water to 50 degrees.The thermostats are not connected to the hydrobox.The hydrobox is checking the water temperature of the buffer tank through activation of the indoor unit circulation pump.So even when the thermostats are closed the system is checking and supplying if needed with hot water the buffer tank.

    The COP of heating is 2.4 which i find it very low compared to the performance data of the manual.

    Could you suggest any ideas of getting the best of the system?

    Thank you in advance

    juliamc
    Rank 20
    juliamc
    Rank 20
    December 5, 2022

    There are a fair few heat pump owners here, I have a Daikin so not much help on specifics. However from what I’ve read third party thermostats will not help your COP on a heat pump, also some argue a buffer tank will drag the COP down too. Do you mean you have a fixed leaving water temp of 45 deg ? If you switch to Weather Compensation mode (may be called something else by Ecodan) then the leaving water temp adjusts with the outside temp which improves the COP.

     

    Also looking at HeatGeek.com is time well spent - for anyone with a heating system !!! 

      M.isterW
      Rank 6
      M.isterW
      Rank 6
      December 6, 2022

      I'll echo the comment from @juliamc to read some of Heat Geek's website and watch their YouTube videos. This will help you understand what should make your heat pump more efficient.

       

      A few questions…

      Did you have a heat loss assessment done and are your radiators all correctly sized?

      Are you running a fixed flow temp for your heating (your post suggests you are) or are you using the weather compensation mode?

      If the thermostats aren't connected to the heat pump controls what are they doing?

      1992 4 bed detached house. Solar PV + battery, Zappi EV charger, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.... No gas 😊
      E
      Newcomer
      epolyzois
      Newcomer
      December 6, 2022

      Thank you Juliamc for your comments. Just for the info i have a fixed leaving water temp of 45 deg.

       

      Thank you M.isterW for your comments also.I am not using the weather compensation and i do not know whether it would make difference considered that i have radiators not underfloor heating.The size of the radiators are pretty ok for low water temperatures.

      The 3 thermostats are just opening and closing the specific 3 circuits in order the heated water to enter the radiators of the assigned areas of the house.

      Many times when the thermostats are closed, the unit is running in order to check and maintain the buffer at 45deg.temperature.

      I suppose if i connect the thermostats to the unit then i would have many on/offs.Would that though be efficient?

      M.isterW
      Rank 6
      M.isterW
      Rank 6
      December 6, 2022

      Having multiple heating zones isn't straightforward with a heat pump. Have a look at this video to understand why https://youtu.be/zpTVIeUh04E.  

       

      I think you've got two options. The first is to tweak your existing setup. You could reduce your heating flow temp as that should improve efficiency.

       

      The second option is to turn on weather compensation. Set the thermostats to high and use the weather compensation controls to get the house temperature as you want it. This will only work if your rads are correctly sized for each room.

       

       

      1992 4 bed detached house. Solar PV + battery, Zappi EV charger, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.... No gas 😊
        juliamc
        Rank 20
        juliamc
        Rank 20
        December 6, 2022

        You should try setting weather compensation which would mean you’re running at a much lower temperature (eg my leaving water temp is 35 deg at 6 deg outside). Open up all rad valves and turn up thermostats so they no longer control your three areas. Let the system balance out for a day, then turn down any radiator in a room that’s too hot eg bedroom. That way your heat pump is running continuously low and slow. 

          E
          Newcomer
          epolyzois
          Newcomer
          December 6, 2022

          Thank you both for the feedback.I really appreciate your time.Do you know if it’s possible to set a command to the hydrobox to supply hot water of i.e 42deg to the buffer tank when the buffer tank’s water temperature falls below let’s say 35deg?

          Thank you in advance

          juliamc
          Rank 20
          juliamc
          Rank 20
          December 6, 2022

          Sorry not me, I don’t have a buffer tank.

          E
          Newcomer
          epolyzois
          Newcomer
          December 7, 2022

          Juliamc, the three thermostats should give info of the internal temperature to the hydrobox?

          Should they be linked to the hydrobox in order to activate the weather compensation?

          And how i will control the temperature of the 3 areas?

          Show more replies
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