@editor

From LG. I haven't rang MCS as I've been told by Omnie: " They weren't commissioned to do one" so there isn't one, and I know the fitter won't be registered. I could phone them to double check though. 

Hi Sam,

Another route that you could explore is the National House Builders Council (NHBC), who set standards that should be followed.

Regards,

Derek.

Hi Sam,

Based on the figures you were provided by I am assuming LG, they have sized your property at 246m2.

From the calculated heat loss of 0.035kW/m2 x 246m2 = 8.61kW/h. Your system is rated at 9kW full output, when working at optimum efficiency.

I think, though someone can correct me if I am wrong, that the above figures are based on an outside air temp of 2C.

As I think everyone knows by now, the efficiency of a ASHP starts to reduce at low outside temps and falls off a cliff below 0C.

It is therefore abundantly clear that your ASHP system is 'not fit for purpose' and requires a much larger unit, at least 12kW, probably 14kW.

Regards,

Derek.

Has the ASHP been checked to see if its repeatedly going into antifreeze/frost protection mode?

I had a period of time with our Mitsubishi ecodan when it was really cold at night where it would repeatedly go into antifreeze mode every 15 minutes for hours and hours switching off the central heating for most of the night. I was able to change the frost protection mode and it fixed it. Now it will go into antifreeze mode once or twice a day on the cold days.

For me even if its at its limits if the 9kw unit is running 24/7 with a flow temp of at least 40 it should keep your house warmer than 16.5 so I believe something is going on with the pump at low temps that shouldn't be.

Derek,

Our MCS calculations to sized the ASHP and rads assumed an outside temperature of -3.2 deg C.  Not sure if you can calculate Sam's requirement based on that?

Our heat loss is about 8kW for 165 m2 and we're getting a 14kW ASHP.  Our house is smaller, but older, draftier and has chimneys.

Sam, you could complete (or get someone else to do it) an MCS spreadsheet for your house.  That, along with your evidence from LG would be a good start to approach the developer.  If you don't get anywhere with the developer then you could try Money Claims On Line (aka small claims court).  The developer will have had to comply with Building Regulations and Planning for the fabric of the building so it would seem a reasonable argument that they should comply with the OFGEM guidance for ASHPs. MCOL is designed for lay people to use without solicitors.  Like any legal action it should be seen as a last resort.

I used MCOL successfuly to recover money from a tradesman for a botched job so it does work and it's not as daunting as it might sound. If it comes to this and you want some tips let me know.  Hopefully it won't come to that. 

Kev

Hi Kev,

Thanks for the info, I knew there was a 2 in there somewhere.

If they have calculated the heat loss, at an outside air temp of -3.2C, as being 8.61kW/h, and sized the ASHP at 9kW, they obviously think that there is no problem.

But unfortunately the output from the ASHP at -3.2C will be nothing like the 9kW specified, you would be lucky if it is 7kW.

I also used the small claims court to get money back from a trader. It takes a while, but if successful it is possible to get a full refund plus expenses etc.

Regards,

Derek.

@derek-m

I'm even more confused now. So are you now saying 9kw will be considered big enough? There doesn't seem to be a definitive answer, which is what concerns me; the system designer will simply come back with the argument it's under 9kw heat loss, therefore 9kw is ok.

@kev-m

Thank you Kev, I pray it won't come to that and that the builder will comply with his obligations.

Hi Sam,

Sorry, maybe I should have made it clearer what I was saying.

They have probably sized your ASHP on ideal conditions and even at that it is on the brink of meeting requirements.

What I was saying is that at an outside air temp of -3.2C, which is probably what was used for the heat loss calculation, a rated 9kW ASHP would not be able to produce 9kW of heat energy, it would probably only produce 6kW or 7kW of heat energy when running at full output. It would therefore never be able to meet the predicted heat loss of 8.61kW/h. As the outside air temp falls below -3.2C the heat loss increases and the output from the ASHP reduces. Not what you would call a 'win -win' situation.

Hope this make it clear.

Did you ever carryout any of the tests that I suggested?

Regards,

Derek.

@derek-m

Ok, thanks Derek. Now it's even more understandable why we suffered during the cold winter as badly as we did.

I did get a thermometer and now I have a couple of weeks off work, should have time to do the test. All of this has been so time consuming when all I wanted to do was buy a house and get on with my life. I suspect the battle yet to come will be even more stressful...

Hi Sam,

There is no need for you to get stressed, don't forget we are all here to support you. One of my favorite pastimes is getting companies to do what they are being paid to do.

From what I can see you have a strong case that the system supplied is not fit for purpose.

I suggest that you request a copy of the calculations made by omnie when they designed your system and who decided that a 9kW ASHP would be adequate. Was it omnie or the builder? I would do so via e-mail, so that you have a written copy of your request and hopefully their reply. Did trading standards, consumer protect or NHBC provide any help?

Regards,

Derek.

Sorry, this is a long post. Take a deep breath. You will understand why I think an ASHP is not just for heating but a way of life.

Our house is a restored Cotswold cottage of about 1,500 sq.ft, massively insulated, with new floor slab and underfloor heating. It is all electric.

Our ASHP (Grant Aerona 9.1kW with a COP rating of 2.66) was installed 4 years ago. For the last 3 years I have taken periodic electricity meter readings. These are for the whole house as the ASHP control system doesn't produce any figures (unless I have just not found them) for the pump alone.

I recorded these numbers in a notebook and did nothing with them other than keep a casual eye on our electricity consumption. In October 2020 the PCB had to be replaced (another story) due to mains power surges blowing the old one. From then onwards I noticed higher electricity consumption but dismissed it as due to lots of pre-Christmas cooking and laundering of curtains and loose covers (one of my wife's rituals). In January we had the coldest weather in the last 4 years and the electricity consumption went off the scale. It peaked one day at 105kWh. That is more power than needed to heat the house without an ASHP!

Got an engineer around asap.  I also started to record daily electricity consumption. I went back through the notebook and compiled (now all in a spreadsheet - yawn) a monthly record of average kWh per day. This shows the January peak and the seasonal variation in power consumption which is to be expected. But it also shows that consumption has been rising steadily over the last 3 years (I have no explanation for this). In another set of figures (not shown here) I computed the 12 month rolling average total electricity consumption. In the 12 months to March 2019 this was 11,800 kWh. In the 12 months to March 2021 it was 15,400 kWh (it peaked at 15,970 in January). A one third increase.

I have no idea if even the earliest 2019 figures are reasonable - they are just what they are and I have no benchmark against which to judge them. But at that time our RHI payments mostly covered the entire electricity bill. The current figures are outrageous although, as you will see in the attached chart, we appear to be getting them back under control. February and March have been good.

I can't explain whether or not the improvement since January is because the engineer's visit made a difference or perhaps the weather has been warmer than average since then. For the daily chart I'm also recording (using a MaxMin thermometer since mid-January) the daily external temperature range. This is clearly the most important single factor affecting power usage.

At times like this I pine for the inefficient gas central heating system we had in our old house. You turned it on and it worked, no problems.!