Posted by: @batalto

@peterr your house size is about the same as mine. Given you've got UFH you should be using less power. Have you done a heat loss assessment? How well are you insulated?

Insulation is as installed when the house was built 15 years ago.  Cavity walls are well insulated, double glazed all round. House was built as 3 storeys without an attic, and the roof area is one that I think may need looking at for insulation.

@peterr 

Hi Peter,

As I have often told young Engineers over the years, "if all else fails, read the instructions". 😊

Based upon the data you have supplied, I suspect that the indicated values could possibly be correct, in which case your system has a number of problems that need to be corrected.

First of all I would suggest that you record the electricity consumption at the main electricity meter and also on your controller and MELCloud. Keep a record of the readings and compare them. Obviously, the main electricity meter will read slightly higher than the ASHP meters. Try to take the readings at approximately the same time each day, along with weather data if possible. Don't worry, you won't have to do it for life.

It is possible that the present design and operation of your system is not particularly suited to an ASHP, and that changing to weather compensation may have had a detrimental affect. For the moment I would suggest returning your thermostats to their original settings, and switching your FTC controller back to water flow temperature control, but with a setting of 35C, rather than 50C. If the system cannot maintain the indoor temperature, then increase the water flow temperature by 1C at a time until temperatures are maintained.

Please collect data for a few days and post on the forum so that it can analysed.

If the installer provided you with a schematic diagram of how your system is designed and its component parts then please post. If not, then drawing upon your artistic skills, please provide a 'fag packet' sketch of the system with a list of component parts.

Have a read through the manual for the FTC controller and familiarise yourself with the controls, what data is available and how to extract it. Anything that you are not certain about then just post a question.

@derek-m 

Thanks for the advice Derek.  I would like to leave the system in weather compensation mode for a day or so longer, so I can get realistic data for how the system has performed now that the UFH slab has heated up.

Once I have done that I will do as you suggest.  A couple of questions though:

1. According to the compensation curve that I have set, the current flow temperature should be 28 to 30C (outside temperature has varied between 10 and 12C for the last 24 hours), and the house is maintaining a temperature of about 21C, should I perhaps set the flow temperature to 30 rather than 35?

2. When using flow temperature control does the setting of the thermostats affect when the system runs?  If the rooms with UFH get up to temperature and then switch off the flow, won't it take a lot more energy to get the UFH back up to temperature if the slab is allowed to cool?  Once the rooms are up to temperature it can be 12 hours (or more if the sun has been shining) before they have cooled enough to kick the ASHP in to heating mode again.

Thanks,

Peter.

@peterr 

I suggested 35C because I don't know the calculated heat demand for your home, and also that they are predicting colder weather next week. You should be able to find data on the FTC controller which shows the actual flow and return temperatures, though there is also a hysteresis setting, so once the water flow is up to the desired temperature, it will have to fall by the hysteresis value before the heat pump starts again.  

 If you look at some of the graphs posted by Kev, you will see that during mild weather, his ASHP fired up until the water flow temperature reached the calculated value, and then shutdown for a period of time until the water cooled. You should be able to obtain similar graphs from MELCloud which would be highly useful in analysing your system.

Because I don't know exactly how your system has been wired and configured, I am having to make assumptions of how it is operating until you can clarify from observations. On water flow temperature control, the ASHP should operate to raise the water to the set temperature and then stop. As any of the thermostats call for heating, the indoor water pump should start and probably also the ASHP, any associated zone valves would also be opened. When the room is up to temperature the indoor water pump would stop and any zone valves closed. I am assuming that you have a buffer tank or low loss header, so your ASHP may continue running for a short period of time then stop when the flow water reaches the desired setting.

With weather compensation control I would expect any zone valves to be controlled by the relevant thermostat, but the indoor water pump and the ASHP should be controlled by the FTC controller. When you changed your system to weather compensation the other day, did you change any DIP Switch setting within the main control panel? If not, control of your indoor water pump would have remained with the thermostats, rather than the FTC controller.

From my limited knowledge of UFH control, I understand that there are temperature sensors on the actual pipework, to ensure that the water does not get too hot or too cold, so may work in conjunction with the room thermostat to help maintain the desired room temperature.

Have a look at the manuals provided by your installer, any points about which you are not certain I will try to clarify.

@derek-m 

Hi Derek,

This is a quick sketch of our system that I knocked up this morning, not sure if it gives you all that you need:

Also, here are some metering figures that I've obtained over the last few days. All taken at about 8AM on the relevant day, with weather shown for the preceding 24 hours:

According to these figures, the ASHP is consuming more than is being supplied & generated!

Yesterday morning I changed from weather compensation back to flow temperature control, with the thermostats adjusted to 20C on the UFH zones and 19C on the wireless stat, and the flow set to 35C.  It was a bright sunny day yesterday, so we had quite a bit of solar heating through the windows, this meant that the rooms warmed up without the UFH being on.  When the temperature dropped overnight, the ASHP didn't kick in until the rooms had dropped to 20C.  Because the UFH had been off for quite a time (probably about 14 hours) the slab had cooled and it took a long time before the rooms started to heat up again, and the temperature had dropped to ~18.5C. I suspect they only warmed up as quickly as they did this morning because it's a nice sunny day again.  Our UFH controller is not particularly sophisticated, it only uses the zone stats to tell it when to switch on and off.  If we want it to work in harmony with the ASHP I suspect we will have to upgrade the controller, which I don't have the funds for at the moment.  In the meantime we will have to find a way to deal with the considerable latency in the system, which is why I think weather compensation may be the way to go.

I need to work out how to get information from MelCloud about when the ASHP is actually running.  Over the weekend I noticed that at times the main circulating pump was running, but the ASHP was not, and at times the circulating pump switched off, but seemingly not under control of any of the stats.  This would seem to suggest that it is being controlled by the FTC.

This is a screen grab of the flow and return temperatures over an hour this morning, which would seem to indicate that the ASHP is cycling to try and keep the temperature to ~35C:

Thanks for your help and suggestions.

Peter.

@peterr 

Hi Peter,

I will have a closer look at the information and get back to you.

@peterr

The electric meter readings.

Are these from a smart meter or an older type manual electric meter? If it is a smart meter do you have an online account to see the electricity used? 

I assume you only have a single phase supply and a single meter with a single reading and nothing special like some legacy economy 7 or something setup that may be confusing things with dual meter readings? 

Do you know how much electricity you used prior to the ashp on average? Be interesting to know how much the meter reading has gone up.

Finally are you sure the delta in the meter reading is actually the electricity used and there isn't a multiply conversion factor? An old bill may help you confirm this.

Basically be good to rule out any potential confusion with the meter readings. 

@jeff 

Meter readings are from a smart meter.  Nothing available online, because the meter hasn't been able to connect to the metering network since it was installed almost 12 months ago.  We live in an area with crap mobile coverage!

Single phase only and only one meter, no multiplication factor involved.  I'm charged on the basis of the meter reading.

I do have historical meter readings, but not easily to hand at the moment.  When I get a moment I'll dig them out and do a comparison with current versus previous usage.

If, as it seems, the ASHP is over estimating my consumption, it might explain the rubbish CoP that I'm seeing at the moment!

Cheers,

Peter.

Posted by: @peterr

@jeff 

Meter readings are from a smart meter.  Nothing available online, because the meter hasn't been able to connect to the metering network since it was installed almost 12 months ago.  We live in an area with crap mobile coverage!

Single phase only and only one meter, no multiplication factor involved.  I'm charged on the basis of the meter reading.

I do have historical meter readings, but not easily to hand at the moment.  When I get a moment I'll dig them out and do a comparison with current versus previous usage.

If, as it seems, the ASHP is over estimating my consumption, it might explain the rubbish CoP that I'm seeing at the moment!

Cheers,

Peter.

It is definitely not normal but does happen sometimes that the electric meter, even smart meters are wrongly calibrated. It is usually people complaining about a meter over estimating rather than under estimating usage for obvious reasons. Also not normal but sometimes single meters are setup with a dual tariff in error and people unwittingly submit the wrong readings. 

A creep test can help when meters look like they may be overestimating by turning everything off at the consumer unit. But in your case that won't help. 

You could try a simple test yourself turning appliances on and off as a sanity check and seeing the impact. . Your supplier can do a meter accuracy test but these are not free so am not sure i would do that under the circumstances. 

I am no expert you may be right about the ashp. Perhaps it is something that happens with ashps sometimes. 

It does seem strange. 

@peterr 

At first glance I would say that the problem appears to be with the energy used and produced readings, which I assume that you are obtaining from your FTC controller or MELCloud? Please confirm.

Looking at the data, on the 20th to the 21st, your home consumed 37kWh of electrical energy, your solar PV supplied 0kWh, but your ASHP used 54kWh and produced 67kkWh of heat energy.

On the 21st to the 22nd, your home consumed 30kWh of electrical energy, your solar PV supplied 18kWh, but your ASHP used 62kWh and produced 49kkWh of heat energy.

The maths don't even add up, and I am more likely to believe your electricity meter and solar PV system data than that provided by the FTC controller or MELCloud.

Based on the manufacturers data for an 11.2kW ASHP, when operating at 35C, the anticipated COP should be in the range 4.8 to 6.25, so the output energy should be in the order of 5 times the input energy.

Looking at the temperatures graph, my earlier concern that your heating system itself may have some problem areas may be incorrect, in that at the ambient air temperatures you stated, and the fact that your ASHP is still cycling with a water flow temperature of 35C, would indicate that there are no major problems, and your system is working reasonably well.

Do you have any heat loss calculations for you home?

Did your installer fill out and provide a copy of the Engineers Forms as detailed under section 7 of the FTC controller manual? If so could you please post a copy.

Do you have any electrical meters installed in addition to your main electrical meter?

If you could please answer the above while I have a look through the manual to see if there are any settings that may need to be adjusted.

@derek-m 

Hi Derek,

Energy used and produced readings were taken from the FTC controller.

No, I'm afraid we don't have any heat loss calculations, nor did we get anything from the installers after they had finished.

No meters other than the main one.

Thanks,

Peter.

Posted by: @peterr

@derek-m 

Hi Derek,

Energy used and produced readings were taken from the FTC controller.

No, I'm afraid we don't have any heat loss calculations, nor did we get anything from the installers after they had finished.

No meters other than the main one.

Thanks,

Peter.

Hi Peter,

I find it rather annoying that installers do not fully check and test the operation of the system, before disappearing rapidly into the sunset. I would be more inclined to believe the temperature readings rather than the energy readings, but just for confirmation, measure the temperature of one of the radiators to see how it compares with the indicated water flow temperature. If possible, measure the temperature of the radiator over a period of time because it will heat up and cool down as the system operates.

I would suggest that you contact your installer and inform them that the energy consumed and energy produced data appears to be incorrect and that you would like it to be corrected. Explain that according to the FTC controller, the ASHP is consuming more energy than is being supplied from the grid. You could also ask your installer to complete the Engineers Form so that you have a record of all the system settings, in case the FTC controller needs to be replaced at some point in the future.

You could also contact Mitsubishi and ask them for reasons why the energy values on your FTC controller may be incorrect.

If your installer seems reluctant to help, then refer the matter to MCS, it would be interesting to see if MCS are actually of any use.