Very high 75,000kw per annum gas consumption

[HRP123]

now you enter a different aspect of delta t. The method of heat transfer now depends upon the barrier to air (the top layer of flooring) and the heat loss you have downward. What is the total volume of liquid of liquid in the coil, what temperature is that, what are the loses....all this need collating to reach an answer. You also need to consider that the room has an even heat source which is rising (not falling as per wall rads) so you will feel more comfortable at a lower temperature. My daytime temp across the entire property of 5 levels (using oversized wall rads) is 16 degrees centigrade with 48% humidity, which is a comfortable "doing things" environment. This is achieved with flow temp of 35 degrees and I achieve a delta T of 10...yes 10
To lift the temp on an evening I up the flow to 45 to achieve 17 degrees and running at 50 degree for an hour lifts to a sweltering 18 degrees.

With such a huge ground floor and with underfloor heating, my approach would be to heat this space using a dedicated boiler to run low temp flow. The Japanese know all about this and have a range of combis that are perfect for your needs. They can even be fitted outside without the traditional flue and only need a cover if the temp is likely to drop to -20.
A 24kw multi function boiler with integrated IoT controller (as standard) is around £900 delivered.
Search Rinnai zen

Wow, I am surprised at how low you can set your temperatures and be comfortable inside the house. My family are shivering with temps below 20 degrees but I suspect this is because we grew up near the equator!

 

[HRP123]

Hmm. Do you have any pics of the JG blending valve fitted (it sounds like) at the LLH?
And was this valve part of the original install or a retrofit? If it was a retrofit, what was in place originally to regulate the water temperature in the UFH setup?
The 'usual' setup with UFH (as I'm sure you've discovered) is for the supply pipes to be at system temperature (55 upwards), at the UFH manifold there'd be a separate pump (circulating within the UFH pipework only) and a blending valve which keeps the UFH tubes at temperature by bleeding in heat as needed from the main loop.

EDIT I'm starting to think you might be onto something with your theory. If the blending valve is at the LLH there'll be a comparatively large (20-30 litres maybe) of low temperature water heading to the UFH and returning to the LLH and thus the boiler. If the blending valve is at the manifold, that 20-30 litres in the pipes of hot system water becomes part of your thermal buffer which will keep the UFH warm without firing the boiler incessantly.

I've attached a picture, you can see the little white valve above the black underfloor pump below the boiler in the middle. It has the flow and return connected to the valve.

This valve was connected as part of the boiler installation (retrofit) about 10 years ago now. I think originally the Geminox boiler would regulate the output to the heating circuits - and both the radiators and underfloor were getting the same output temperature. There are no blending valves on the underfloor manifolds.

Yes, this is not the usual setup as we had to install a separate underfloor pump from the LLH when we installed the new boiler.

Thanks for your help!

 

[HRP123]

I've put some sensors on my flow pipes and have noticed the hot water cylinder calls for heat almost every hour - just for a short time about 15 to 30 mins - I'm guessing this is because of the secondary hot water circulation pump (on all day).

With the 2012 WB 40 CDI which operates at a min flow of 9kwh from the technical information - does this mean that at a minimum you would be using 4.5kw over 30 mins and at a maximum lets say around 20kw? And that consumption depends on how the boiler modulates to the heat demand from the cylinder... which is only driven by the return temperature to the boiler?

 

[Harry Bloomfield]

With the 2012 WB 40 CDI which operates at a min flow of 9kwh from the technical information - does this mean that at a minimum you would be using 4.5kw over 30 mins and at a maximum lets say around 20kw? And that consumption depends on how the boiler modulates to the heat demand from the cylinder... which is only driven by the return temperature to the boiler?

Best way, is - with CH off, read the gas meter before and after the boiler runs to top up the HW, when no HW is actually used. Carry out the same test a few times, and it will improve the accuracy.

 

[roguetrader]

Without rereading the whole thread, have you run it for a few days without the secondary pump running.

 

[HRP123]

Basically I think one major problem having observed the boiler for a few days now is that throughout the day it is turning on an off for different circuits. With a 9kw minimum output, even just to heat for example a slight drawdown in hot water (because of secondary recirculation) or to heat up one underfloor room by a degree, it is like in my head starting up a big V8 when you only need a small 3 cylinder most of these times.

It will only be the peak loads in the morning and evening (all circuits on) where the full capacity of the boiler is used.

 

[old duffer]

Wow, I am surprised at how low you can set your temperatures and be comfortable inside the house. My family are shivering with temps below 20 degrees but I suspect this is because we grew up near the equator!

and humidity and building fabric temperatures (radiation heat) and draughts etc etc).