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Mitsubishi Ecodan Air Source Heat Pump - Low Efficiency

  • 5 September 2022
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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.

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Best answer by nealmurphy 6 September 2022, 10:15

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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.
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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
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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. 

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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).

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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.

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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
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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 ?

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

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

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

Fantastic.

Thanks

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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.
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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
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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 !!

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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
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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 !

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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
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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 

 

Independent volunteer - Sitting in a Faraday cage, waiting for a signal
nealmurphy
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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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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.

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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
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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
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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 😊
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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?

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