Posted by: @heacol

@derek-m Thanks, I also feel like I am banging my heat against a brick wall. However, If one person listins, they may tell another and maybe the mssage will get out.

Hopefully so. As Mars states later on, a lot of us have systems installed, set up and are left to our own devices. Yes this isn't how it should be but I guess this is the state the ASHP industry is at the moment. 

By learning how systems should be performing from experts (like you) who don't have a vested interest in any particular installation, we can go back to the installers with a better understanding on what to expect.

Without this they could be telling us any old codswallop!

Posted by: @heacol

@editor Weather compensation has no complex logic. It is just a straight line graph that is used by the machine to determine the flow temperature. High ambient temp = low flow temp and low ambient = low flow temp.

I can show you why your COP is low.

Buffer tank - reduces performance by 30-40%

Any TRV's can reduce the performance of the system by another 30%.

Zoning under floor heating can reduce it by another 40%

To control temperature output of an emitter, you have to reduce the temperature, that means you have to start high, and cut it at each stage with each level of control. Fine with a boiler but not a heat pump.

Your heat pump does not stand a chance, it's leg is tied to an anchor and it's arms are tied together between it's legs, and you are expecting it to beat Usain Bolt in the 100 meters. Not a chance.

Remove your buffer tank, remove all the thermostats and actuators on your under floor, remove all TRV's on all the radiators except your bedroom and control the house temperature by altering the weather compensation curve. It will be a little trial and error but when you get it right, you will not have to touch it again.

If you do this, I believe you will be able to remove you oil boiler it will not be necessary. If you do not want to remove your buffer yet (which you do not need) just remove the actuators on the under floor and TRV's, set the flow temp to about 26, leave it for a few days, your house should be toasty and your COP will be drastically improved. (do you have pumps and mixing valves on your manifold?)

Why worry about the running costs, you are getting paid for it on the RHI the more the heat pump works, the more you get paid. You need to improve your performance to reduce you running costs. Currently at a COP of 3, at this ambient temperature, I would be verry embarrassed if I had installed this, it is terrible.

If you do not want to remove your buffer yet (which you do not need)

It does beg the question what are these commonly installed with ASHP systems?

Why worry about the running costs, you are getting paid for it on the RHI the more the heat pump works

I'm pretty sure this isn't how the RHI works. The payments are calculated and pre determined before the system is installed based on expected heating requirements.

Posted by: @heacol

@editor

Actually Mars, it would make more financial sense to get your system fixed, you would not drive your car with flat tyres. There is not much wrong, any good plumber could fix it in a morning.

I agree, certainly as energy prices increase. I imagine you could easily spend a few hundred pounds extra per year running a poorly performing system.

Having an independent expert come in and change things with some level of guaranteed performance improvement would be a simple decision to make.

Perhaps a new area on the website could be created that contains some 'Try these first' tips and include any pertinent information, spreadsheets etc.

So anyone coming to the site with ASHP performance issues can quickly find a useful starting point as to what to do.

@markc 

My understanding is that the buffer tank is installed on systems to provide a little load so that the ASHP is not stopping and starting frequently. It also allows for the water to circulate in case most of the valves (TRV's or motorised control valves) close and the water flow through the system is drastically restricted.

I cannot comment on Brendon's statement of a 30% reduction in efficiency with a buffer tank installed. Provided that most of the possible restrictions due to TRV's and control valves are removed, there should be no reason for a buffer tank to be installed in a system. Without actually carrying out detailed testing, over a period of time, on a system with a buffer tank installed, and then repeating the testing with the buffer tank removed, I cannot state what would be most beneficial.

As an Engineer, I am a firm believer in carrying out investigations and tests to locate the root cause of any problems before engineering a suitable solution. I don't think that most people would find 'ripping everything out and starting again' an acceptable option.

Anyone contemplating installing an ASHP system should closely question the proposed design.

Posted by: @markc

Perhaps a new area on the website could be created that contains some 'Try these first' tips and include any pertinent information, spreadsheets etc.

So anyone coming to the site with ASHP performance issues can quickly find a useful starting point as to what to do.

Hi Mark,

The problem that I find is that someone will post on the forum a little information pertaining to a particular issue, with basic information about their system. When I ask for further information or simple tests to be carried, they often fail to respond. I don't know if they have resolved the issue or just can't be bothered.

I don't know that 'try these first tips' would actually work, since individual system can be quite different, hence the need to ask questions for clarification.

Well! After reading through these posts and feeling excited at the possibility of increasing the SCOP of my system, I though I'd ring the Mitsubishi Ecodan technical helpline to get their input.

First question: Are compensation curve settings used much on your ASHP systems in the UK.

Answer: They are used but I personally wouldn't use it as I like to come in and turn my heating system on and get heat. (which I thought was a bit strange). He then added, oh but I have a gas boiler. WTF!!! 

I then asked if Mitsubishi had any data/idea on the average SCOP for their 14Kw pumps in the UK as after running throughout October I was only getting an SCOP of 2.7.

Answer: That is quite a good SCOP to be honest. You should be around 3 so you aren't far off.

Not sure where to go with that!

Posted by: @markc

Well! After reading through these posts and feeling excited at the possibility of increasing the SCOP of my system, I though I'd ring the Mitsubishi Ecodan technical helpline to get their input.

First question: Are compensation curve settings used much on your ASHP systems in the UK.

Answer: They are used but I personally wouldn't use it as I like to come in and turn my heating system on and get heat. (which I thought was a bit strange). He then added, oh but I have a gas boiler. WTF!!! 

I then asked if Mitsubishi had any data/idea on the average SCOP for their 14Kw pumps in the UK as after running throughout October I was only getting an SCOP of 2.7.

Answer: That is quite a good SCOP to be honest. You should be around 3 so you aren't far off.

Not sure where to go with that!

Hi Mark,

You were obviously speaking with the head of the technical help department!!!!!

There is a formula for the calculation of SCOP, which involves so many hours at different ambient air temperatures at specified water flow temperatures throughout the year. This time of year your COP should probably be in the 4 to 5 range if everything is functioning correctly.

If you look at the specification section, of the documentation that should have been supplied with your system, you should find a table detailing the expected COP at different air and water temperatures.

I have attached the table for a Midea 14kW ASHP, which is more detailed than the ones I have seen from other manufacturers, but gives you some idea of the values to be expected at this time of year.

I managed to find some data although not as granular as your charts. For the Mitsubishi Ecodan 14Kw R32 PUZ-HWM140VHA model it states that at 7º outside and 45º flow temp should achieve a SCOP of 3.5. Your 12Kw Midea model has 3.89 for the same settings. Approx 10% better.

For my current settings at 10º outside and 50º flow your Midea could achieve 3.46, whereas I'm currently getting 2.7.

All things being equal I should be at an SCOP of around 3.12.

Having read the previous posts it sounds like the 50º flow temp which was set by the installers (interestingly the MCS certificate states this and that is what the RHI has been calculated with) is too high causing the pump to have periods of inactivity.)

@derek-m What are your thoughts on this as a test? At 10º outside and 35º flow temp your Media is at a SCOP of 5.22.

If I set my flow temp to 35º and leave it for a week, assuming outside temp remains at 10º, all thermostats on something unobtainable like 30º and app TVRs fully opened I should see an SCOP around 4.7. 

More granular data for the PUZ-HWM140VHA

@markc 

I am assuming by your comments that your system has not been set up for weather compensation. Whilst I have a read through the Ecodan manual, I think that you should try as you suggest and lower the water flow temperature to 35C.

Sorry, I sent you the Midea data for the 12kW rather than the 14kW unit. I have now attached the correct one.

Could you please provide details of your controller and any other control equipment, so that I can be certain that I giving you the correct information.

I’m seeing lots of comments regarding weather compensation is how you should be setting up the ASHP. 

Currently my heating is all controlled by zoned thermostats.

What is weather compensation, and how do I know if my ashp is capable of it?