Mitsubishi Ecodan Air Source Heat Pump - Low Efficiency

[TimToos]

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.

Edited September 5, 2022 by TimToos

[JohnMo]

There may be a few issues

 

Reducing flow temp to hot water cylinder will increase CoP, store water at a lower temp. Slowly over a couple of days reduce the temperature until the last use of the day starts to go cold, then add a couple of degrees.

 

 

Cold rooms in the house increase the heat loss in warm rooms as they are experiencing heat loss external and internal.  So the heat pump has to run harder to make up the difference.  Also you end up making the heating circuit smaller so the heat pump cannot flow at a high enough rate, so suffers frequent shutdowns or short cycles. Both are no good for the CoP.

 

Go on to heat geek and read up on how to balance your heating system.  You really want the system to have an open system to flow against, but set the flow rates to get the temperature you want.  The thermostat then are set higher than you need and operate as limit stops only, not as temperature controllers.

 

You then need to get your heating flow temperature as low as you can, do the same as the DHW reduce over a period of days, then when it's not heating as you want it bring back a degree or so

 

Can you set up weather compensation?  Again have a read on heat geek site.

[TimToos]

Hi JohnMo, many thanks for your reply.  I will have a look at the site you recommend and see what I can do.  Thanks

[ProDave]

Have a read of this thread

 

 

Some models have an issue with a crankcase heater permanently on that increases the power consumption.

[TimToos]

32 minutes ago, ProDave said:

Have a read of this thread

 

 

Some models have an issue with a crankcase heater permanently on that increases the power consumption.

 

Hi ProDave,

 

This is very interesting and also worrying!

[ReedRichards]

You don't mention whether you use a fixed output water temperature for your heating or if you use Weather Compensation.  The latter should give you a significant improvement in efficiency. 

[TimToos]

Hi, RR, sorry, I have used both settings in the past but have its set to weather compensation.  I have changed to fixed for a short period before realising this wasnt going to help.

[TimToos]

I feel installing a ASHP was rather a lie in terms of what we should except.  Im not sure if GSHP would have provided a better and cheaper long term alternative.  We, as an household, are using much more electric and running the house at lower temperatures, than was forecast.

[joe90]

2 hours ago, TimToos said:

We, as an household, are using much more electric and running the house at lower temperatures, than was forecast.

Forecast by whom? Go back to them with your query?

[ReedRichards]

I cannot measure the COP of my heat pump but comparing running costs with the oil boiler it replaced makes me believe I achieve somewhere like the SCOP value of around 3 that was promised.   I'm running the house at the same temperatures that I used to.  Your 200 litre hot water tank is too small for a household of four people so you have to keep it at 55 C to get enough hot water; my 300 litre cylinder is kept at 50 C.  Your yearly power consumption of hot water is a lot larger than 12 times the two monthly figures (of about 80 kWh) that you gave; any idea why? 

 

The wrong Ecodan model might be costing you in standby power consumption (your summer heating power consumption?).  But even so your COP figures are very poor. You have a big house but if it is well-insulated I'm surprised that you needed a heat pump with an output of 11.5 kW.  I live in a 4 bedroom bungalow, timber frame built in 1980, so not insulated to modern standards but I do fine with a 12 kW heat pump.  I used about 6500 kWh for heating and hot water last year, which is not that much more than your 5400 kWh total (and my house is kept a tad warmer).

 

Is your heat pump smart enough to use a lower output water temperature when the upstairs radiators are not calling for heat?  Could the output from your radiators be too small, forcing the heat pump to use higher output water temperatures?  The most common cause of heat pumps performing badly is when they are retrofitted to an existing heating system without changing the radiators.          

[JamesPa]

2 hours ago, TimToos said:

I feel installing a ASHP was rather a lie in terms of what we should except.  Im not sure if GSHP would have provided a better and cheaper long term alternative.  We, as an household, are using much more electric and running the house at lower temperatures, than was forecast.

Having had 2 ASHP systems installed at work (with spectacular success – albeit that these are air to air not air to water) and wrestled for 9 months with a design for home, I think I am getting the measure of ASHP. 

 

Its clear that the underlying technology is mature, but its deployment in and adaption to a domestic situation is still relatively immature.  Houses are complex systems and all different, and we are saddled with legacy installations and legacy practices (particularly sloppy here in the UK as compared to say, Germany) which are going to take time to shift and/or find ways to overcome. 

 

The fact is that it was just too easy to shove in a 28kW gas boiler, turn it up to 70/75C flow temperature (thus undermining the savings from condensing operation), put TRVs on each radiator without accurate balancing, and walk away.  We, the general public, have got used to this way of operation and, from an installers point of view, this approach guarantees that the house is warm (thus avoiding call outs) even if efficiency is 10% less than it could be. 

 

As described elsewhere in this forum, ASHPs require a different way of operating, and crucially more care in design and setting up if they are to work efficiently.  The latter, and quite possibly the former, should eventually be overcome with more intelligent controls and pumps with deeper modulation capabilities, but for the time being the tweaking to get the weather compensation and balancing right appears to be vital to system efficiency.  Furthermore the physical constraints (size, positioning) are more challenging and, if mass adoption is to be achieved, we need a greater variety of form factors to fit more situations and, crucially, to dispense with the need for/obsession with buffer tanks.

 

The ‘commercial’ ASHP industry is well geared up to the typical office installation, generally based on air to air systems, but the ‘domestic’ industry (principally air to water) is still immature, hence the need for government training subsidies - which in reality is what the BUS and its predecessor are.  Hopefully ‘upscale’ initiatives like that being undertaken by Octopus will flesh out some practical ways of overcoming the practical challenges in many common situations.

 

All this is inconvenient but, lets not kid ourselves, we don’t have a choice.  If the hot summer in the UK, the wildfires in mainland Europe and America, the melting Antarctic shelf and the floods in Pakistan aren’t enough to remind us that the threat of global warming is real, then what is?  Currently ASHP (or GSHP) is the only high efficiency low carbon heating technology available in any scale.  Inevitably early adopters/environmental enthusiasts (probably a characteristic of many of those on this forum) will help ‘debug’ the way these are best designed, installed and operated in a real-world domestic environment.  In five or ten years time things will hopefully look a lot different, but only because some people went first!

 

As an aside, last winter I turned my current gas heating flow temperature down to 55C and left it on more or less 24x7, to simulate what an ASHP installation might ‘feel’ like.  The result was a house that was considerably more comfortable, principally because the temperature gradients and temperature variations with time were much less as a result of a reduced radiator temperatures that were more constantly emitting rather than being constantly turned on and off by TRVs.  So I’m pretty convinced that, when I do finally get a design I’m happy with, the result will be a more comfortable house.  That’s something to look forward to, in addition to the feeling that I can feel less guilty about the devastating effect of my carbon footprint on others.

 

As others have said, low flow temperature (swapping radiators is remarkably cheap!), system balancing and weather compensation appear to be the key factors to getting high system efficiency.  Others on this forum report excellent results with the Ecodans, and the high standby power consumption appears to be a feature only of some of the older PUHZ (R410A) models.  Can any of these be improved in your system without too much additional expenditure?  

[JohnMo]

If your heat pump was MSC installed the performance output sheet they gave you with quote is a guarantee of performance.  If you are meeting the figures they gave you, you have recall for them to repair / replace at there cost.

 

As a note You cannot operate weather compensation correctly with zones shut off and thermostats controlling temperature.  Thermostats and trvs are there only to limit overshoot if for example the sun's out heating the room.

[PeterW]

@TimToos what is the DHW set to..? As others have said, 200 litre tank is too small and you’ll also find the internal immersion is heating the tank if you’ve got the temperature higher than about 53°C so that’s causing your low CoP on DHW.

 

Is there any buffer in the system or is this just UFH and rads direct onto the ASHP..?? Any schematic available ..??

[RobLe]

The most important factor determining ashp efficiency, is the flow water temperature from the ashp.  I suggest that a temp sensor be fitted here, if there isn’t one (the heatpump may show this).  Most installs of ashp have a buffer tank, so it may be that this flow temp is a lot higher than necessary for good home heating - the under floor heating can allow very high cop figures, but not if the ashp makes a high temp which is subsequently regulated down.  Generally, ‘Good’ efficiency is expected if this flow is below 45C, poor at over 55C.  My guess is that the flow temp is generally high.

Measuring the kWh of delivered heat is difficult to do accurately, so it’s also possible that figure is poor quality, and more heat is delivered than you think.

[PeterW]

3 minutes ago, JamesPa said:

Its clear that the underlying technology is mature, but its deployment in and adaption to a domestic situation is still relatively immature.

want to tell the Nordic countries that have been doing it for 30 years that ..?? 
 

8 minutes ago, JamesPa said:

ASHPs require a different way of operating, and crucially more care in design and setting up if they are to work efficiently.  The latter, and quite possibly the former, should eventually be overcome with more intelligent controls and pumps with deeper modulation capabilities, but for the time being the tweaking to get the weather compensation and balancing right appears to be vital to system efficiency. 

no more than a normal gas or oil system. The issue is that most aren’t designed to meet the building requirements, they are carbon copies of the last one the plumber / heating engineer installed and they don’t go through the basics and stuff is installed that is inappropriate for the house or it’s occupants.
 

On an occasion recently I saw radiators removed for an ASHP retrofit where  some of the existing rads were absolutely fine and perfectly sized to the lower delta for ASHP flow, and the installers argument was “they always install 50% larger”…  so that’s £2k added to an install for something not required. 
 

4 minutes ago, RobLe said:

Most installs of ashp have a buffer tank, so it may be that this flow temp is a lot higher than necessary for good home heating

sadly not - there are still the installers who are piping direct to UFH with no blender and no manifold pumps and mixers, buffer tanks are the exception unless properly specified  

[ReedRichards]

54 minutes ago, JohnMo said:

IAs a note You cannot operate weather compensation correctly with zones shut off and thermostats controlling temperature.

 

There are some fundamentalists who advocate that you rely entirely on weather compensation to keep your house warm and don't use zones or thermostats.  This means that you have to keep your house at the same temperature 24/7 (or you have some pretty sophisticated control) and it might not work with a mix of UFH and radiators unless set-up to work this way from the outset.  I have a two zones and I have thermostats and weather compensation gives me significantly greater efficiency than using a fixed output flow temperature, as I did initially.  And the right weather compensation curve gives me significantly greater efficiency than the over-conservative one I inherited from the installer.      

[TimToos]

Ive just looked, the tank is 250L.  Is this still too small?

[ReedRichards]

Try setting the tank temperature to 50 C and see if that produces adverse effects (i.e. you run out of hot water when too many people take baths or showers in quick succession). If there are no adverse effects then your 250 l tank is not too small and you can improve efficiency by setting the temperature lower.  

[TimToos]

1 minute ago, ReedRichards said:

Try setting the tank temperature to 50 C and see if that produces adverse effects (i.e. you run out of hot water when too many people take baths or showers in quick succession). If there are no adverse effects then your 250 l tank is not too small and you can improve efficiency by setting the temperature lower.  

You have got me worried now about the tank size.  I did want a 250L cylinder when the installer came round and he said it would be a waste of energy as that volume of hot water would not be required.  Now I am thinking that once the kids grow up will the 250L be too small?

[JohnMo]

59 minutes ago, ReedRichards said:

 

There are some fundamentalists who advocate that you rely entirely on weather compensation to keep your house warm and don't use zones or thermostats.  This means that you have to keep your house at the same temperature 24/7 (or you have some pretty sophisticated control) and it might not work with a mix of UFH and radiators unless set-up to work this way from the outset.  I have a two zones and I have thermostats and weather compensation gives me significantly greater efficiency than using a fixed output flow temperature, as I did initially.  And the right weather compensation curve gives me significantly greater efficiency than the over-conservative one I inherited from the installer.      

It doesn't mean having the temperature the same 24/7, that's why all system have a set back.  The set back reduces the flow temp and by default the room temperature, still doesn't need a thermostat.

 

But as you say you need to work at to get it set to run correctly.  UFH and rads is not an issue, as you balance the room flows to get the temp you want.  Thermostats just get set a degree or so higher than the target room temperature.

[Stones]

We have an 8.5kW Mitsubishi Ecodan, FTC5 controller and 300l pre-plumb cylinder package. It has been running 5 years, and consistently returning CoP of 2.5 - 2.6 for DHW, and 3.6 - 3.7 for Heating.

 

The DHW temp is set to 50C.  With a 300 litre tank we do not run out of hot water. Tank size was a specific requirement and not the normal match for the heat pump size. I knew from experience that a 200 litre tank was too small. As has been suggested, reduce the temperature the DHW is being heated to, 1 C at a time. You should also (if you have not already) select the Eco DHW function - this heats the DHW more slowly but improves your CoP by around 10%.

 

On heating, our system is set to auto weather compensation. I have had to do nothing more that. We run our house (155sq m floor / UFH) as a single zone (albeit we do have thermostats in the bedrooms should we wish to isolate them) using the master controller / thermostat as the control mechanism - i.e. temperature set at the master controller. I strongly suspect from what you have described is that there is insufficient volume of water in the heating circuit when you have differentials set in the house, and consequently the heat pump is short cycling and never getting to its most efficient.  The easy way to test this theory is to open everything up, set the heating to 21, and see what happens. If as I suspect, you see a big improvement in your CoP, you then have a choice. Operate as a single zone, or install a buffer to provide additional system volume so you can operate multiple temperature zones.

 

A quick example - a friend of mine has the same heat pump and control, yet his heating CoP was only a little over 1.  He has a small area of UFH and the rest large radiators. He had all the radiators throttled back and consequently the heat pump was constantly trying to maintain the set temp through a limited area (and volume) of UFH.  By simply opening up the radiators to full, we doubled the CoP to over 2. Not great but vastly improved. In his case it will get better again as he has another 40 sq m of UFH to add to the system in his final phase of renovations.   The point of the example really is to stress the need for the system volume to meet or exceed the minimum requirements of the heat pump. If you go below that, you will get significant short cycling and poor performance.

[PeterW]

35 minutes ago, TimToos said:

You have got me worried now about the tank size.  I did want a 250L cylinder when the installer came round and he said it would be a waste of energy as that volume of hot water would not be required.  Now I am thinking that once the kids grow up will the 250L be too small?

250 has about 190 litres usable and depending on the time of year that will blend out to around 25 mins of shower time in total without recharge. That’s not that much hot water with teenagers and a low recovery heat source such as ASHP.

 

Who designed the rest of it, and who did all the calculations for heat loss etc..?

 

 

[JamesPa]

2 hours ago, PeterW said:

want to tell the Nordic countries that have been doing it for 30 years that ..?? 

Different starting conditions, different climate (wetter!), different public and installer mentality.  Perhaps I should have said 'Its clear that the underlying technology is mature, but its deployment in and adaption to a domestic situation in the UK is still relatively immature.

[TimToos]

29 minutes ago, PeterW said:

250 has about 190 litres usable and depending on the time of year that will blend out to around 25 mins of shower time in total without recharge. That’s not that much hot water with teenagers and a low recovery heat source such as ASHP.

 

Who designed the rest of it, and who did all the calculations for heat loss etc..?

29 minutes ago, PeterW said:

 

Hi, we used a company in Harrogate.  They did the system design and sized everything accordingly.  I did question the how water tank saying I wanted a 300L (I like overkill) and he said that would be a waste of money, both for the tank and to run the system.

 

He sized up the radiators for upstairs and the ones in the bathroom are too small, we now need to install a second one in the large bathroom.

 

The more I live with this system the more I feel very cheated.  We paid him on the dot and as far as I can tell hes walked away from our issues.  I have emailed lots, even to talk about investing in solar PV, and still he has never got back.  I think theres a lesson here...

 

I wish there was some comeback as Im so annoyed.

Edited September 6, 2022 by TimToos

[JohnMo]

I am sure MSC has a complains process, you have a look in to it.

 

Read up on heat geek, lots of free info on how set things up, well worth an hour of your time.