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timtoos
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September 5, 2022
Solved

Mitsubishi Ecodan Air Source Heat Pump - Low Efficiency

  • September 5, 2022
  • 39 replies
  • 4416 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

    M
    Newcomer
    meldrewreborn
    Newcomer
    September 5, 2022

    Has the efficiency got any better or worse over time.?  Is It A case of the claimed /promised efficiency not being delivered?

    As an aside my 3 bed semi well insulated uses 20,000 kWh of gas a year (17,000 + add back from solar thermal panel) with us two old codgers in it.  Although we cook with gas too  your combined water and heating delivery is still low- presumably because of the very high insulation. is it possible that the delivered values  - however they are measured - are low.  The input i supposed can be squared with your overall energy consumption.

    Eon and EDF customer. Don't think smart meters are worth the expense.
      T
      Rank 2
      timtoosAuthor
      Rank 2
      September 5, 2022

      Hi Meldrewrebron,

      Thanks for your reply.  In our opinion the system has got no better or worse over the 3 years of living with it.  I would say its not lived up to our expectations and is a massive cost to run.  We are looking at £600 through winter if the price rises go ahead and I dont think we have the house like a sauna.

      We were expecting a COP of 3.0 and told 3.2/3.5.  We are well down on these figures if my calcs are correct.

      The values I have given are straight from the heat pump controller.  It has a built in meter - although no idea how accurate this is.

      Thanks

      nealmurphy
      Newcomer
      nealmurphy
      Newcomer
      September 5, 2022

      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. 

        K
        Newcomer
        Koops
        Newcomer
        September 5, 2022

        A couple of things that affect my ASHP efficiency: have the water temperature as low as you can tolerate (usually washing-up?) but might be radiators? Have a buffer tank in the air pump circuit, this reduces the frequency of heat pump operation (if you have conventional radiators and flow through them (not if rad thermostats are off!) then that might be a sufficient volume of water. If you have a large enough domestic water tank to wait, heat the water at the warmest time of day, typically the afternoon in winter (I only have single rate electricity).

          T
          Rank 2
          timtoosAuthor
          Rank 2
          September 5, 2022

          Hi Neal,

          Thanks for your reply.

          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.

            T
            Rank 2
            timtoosAuthor
            Rank 2
            September 5, 2022

            A couple of things that affect my ASHP efficiency: have the water temperature as low as you can tolerate (usually washing-up?) but might be radiators? Have a buffer tank in the air pump circuit, this reduces the frequency of heat pump operation (if you have conventional radiators and flow through then (not if rad thermostats are off!) then that might be a sufficient volume of water. If you have a large enough domestic water tank to wait, heat the water at the warmest time of day, typically the afternoon in winter.

            Hi Koops. 

            The tank is set at 55C and to be honest is too hot.  We need to really cut it with cold water for washing-up and washing.

            We have 2 buffer header tanks installed above the cylinder.  The rads upstairs are on TRVs but the ones in the bathrooms are obviously not, ensuring no dead ends.

              juliamc
              Rank 20
              juliamc
              Rank 20
              September 5, 2022

              Hi @timtoos My hot water is set at 44 degC which is easily hot enough for the two of us. If you lower yours you’ll definitely see an improvement in the COP there. 

              When you say you have thermostats in dining living and utility rooms are these the Heatmisers ? Are they all trying to control the heat pump ? I’ve read that it’s more efficient to do away with thermostats and just use the weather dependant curve to control the heat in the house. If you have a third party controller on a heat pump the two systems are battling with each other and neither wins. Do you have TVRs too ?

                T
                Rank 2
                timtoosAuthor
                Rank 2
                September 6, 2022

                Hi juliamc, thanks for your reply.

                I will look at lowering the cylinder set point.  Am I right this is under the commissioning or set-up pages?

                The thermostats in each room control the zoned area UFH, each area having its own circuit, the one t’stat upstairs controls the the whole of the other 2 floors as these are all radiators with TRvs (except the bathrooms).  Yes, once they call for heat they will switch the heat pump on to heat.  The heat pump has 2 zones, one for the UFH the other for the radiator circuit.  How would the heat pump know how the house, or specific zone, requires heat without a thermostat?  I dont understand how to run the heat pump without something calling for heat?

                Thanks

                  nealmurphy
                  Newcomer
                  nealmurphySolved
                  Newcomer
                  September 6, 2022

                  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. 

                   

                    juliamc
                    Rank 20
                    juliamc
                    Rank 20
                    September 6, 2022

                    Thanks @nealmurphy I knew I’d got that info from somewhere ! Heatgeeks’ explanations are brilliant, if you can ignore the hat and the handwaving !

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