@nigel42 

Hi Nigel,

Thanks for the improved photo's.

I have discovered this document which explains in more detail how to use the unit shown in your photo's. Unfortunately the forum still will not allow me to attach a copy so please follow the link below. Once again this document does not give details of how to modify the weather compensation parameters, which it would appear that Vaillant seem reluctant to reveal. Maybe you could search for the required document or someone on the forum could provide a copy.

@nigel42 

Looking at the information shown on the screen in the photo, I think that your system may be performing quite reasonably, but without further information I cannot be certain of the fact.

I would suggest that you record your daily electricity consumption, along with the value shown on the blue screen.

Also try to get status data from both Vaillant units, and record it on a daily basis along with ambient air temperatures and weather conditions, that way you should be able to assess how your system is performing.

It may also be useful if you could compare data with other Vaillant owners to see if there are any vast differences.

sorry if it's repeating what's been posted but is this any different? not quite the same model but may help

Posted by: @kev-m

sorry if it's repeating what's been posted but is this any different? not quite the same model but may help

VAILLANT.CO.UK "https://www.vaillant.co.uk/downloads/product-manuals/vrc-700/vrc-700f-installation-instructions-1968308.pdf"

 

Hi Kev,

Thanks for searching. This is the other unit, the VRC720 that is part of Nigel's system. Although it claims to operate under weather compensation control, it does not contain any details of how to set the parameters of the compensation curve. It would appear that Vaillant deem this to be a closely guarded secret. There will probably be an installers manual that provides the details, but the location of that also appears to be a closely guarded secret.

@derek-m Hi Derek, For my own setup it's done on the VRC 720 (Sensocomfort) where you can set the Heat Curve options. 

@colin 

Hi Colin,

Thanks for looking. Unfortunately Nigel's system does not appear to have a SensoComfort controller, and although the documentation mentions weather compensation, it does not appear to show how the parameters can be adjusted.

From what I can see, his system may not be working too badly, so he may not need to make any further adjustments.

This is the compensation curve settings I have settled on for the moment. This is giving me a constant 22ºC downstairs (using UFH) and 19/20ºC upstairs (using rads) 24/7.

FTC controller is set to 0º curve adjustment.

Red line was the initial curve settings which I was running with a -6º curve adjustment on the FTC.

@markc makes me wish I had underfloor. The lower flow temperatures make your COP enviable. For the near term I am stuck with rads...

Posted by: @batalto

@markc makes me wish I had underfloor. The lower flow temperatures make your COP enviable. For the near term I am stuck with rads...

It does make a difference yes. Although it did cost around £10k to install (part of a wider refurbishment) when you factor in everything. So at the end of the day we'll both probably be paying a similar amount for keeping the house warm!

@markc my wife wants a new kitchen in a few years - we'll do the floor then... for an extra expensive install

Hi Everyone,

If anyone is seeking help or advice to try to improve the operation and efficiency of their ASHP, to save time and effort it would be highly useful if you could provide as much of the following information as possible.

Type of home and floor area in square metres.

Heat loss calculations.

Type and size of ASHP. Please try to indicate the year it was installed and the related instruction manual details.

Size and type of heat emitters.

A comprehensive list of all the associated equipment, pumps, valves, TRV's, thermostats, controllers etc.

Any further information that you think may be relevant.

I recently had the first annual service on my ASHP system and the engineer asked why I had the system set up using the compensation curve. Having chatted through the reasons he, without prompt, confirmed our thoughts that the installers liked to set the system up to run with a 50º flow because it was simpler for the customers to understand, as it worked more like a gas boiler.

'Weather compensation curves take time to get right and you can imagine installing a system which has luke warm radiators would get a lot of complaints about how the system isn't working properly.'

He commented, 'You can imagine the sales person saying to the potential customer, Ah yes Mrs Miggins, we will install your new heating system, it will run 24 hours a day and the radiators will only be luke warm to the touch.'

Thinking back before I had gone through a year of living with the ASHP, I think I would have been put off by someone saying the system would be running 24/7 and only have luke warm rads.

I had noticed the previous 2 days had been around 5ºC outside and the next 2 days were forecast to be similar. Because I can't help myself tinkering I decided to do another quick experiment, and at 12 midnight I set the ASHP back to a 50º flow temp.

All 4 days the internal temp was maintained 24/7 at 21-22ºC downstairs and 19-20ºC upstairs.

THE DIFFERENCE IN ENERGY USAGE WAS SCARY!!!

8/12 and 9/12 the system had been running on the compensation curve and used 51.6kWh on heating.

10/12 and 11/12 the system was run with a 50º flow temp and used 90.1kWh on heating.

ALMOST DOUBLE.

We have to assume these findings will not literally transfer to all properties/ASHP systems. I'm sure my 100sqm 60mm concrete screeded floor adds quite a good thermal mass to my property, so compared to a property which has all radiators, figures might be different.

But what it does show is that if your energy usage seems high, you really should be experimenting with the settings.

At some point in the future there needs to be some sort of database created so the optimum setup can be derived for any particular property/system without the need to meter usage and experiment with different settings.