Tim Watts wrote:

On 12/11/17 13:18, Roger Hayter wrote:
Tim Watts wrote:

On an aside:

Very pleased that my calculations seem to have borne out.

This is my spreadsheet:


https://drive.google.com/open?id=1fW...qxguvxZKXpMbXX
-PTdk

I tried to design the biggest radiators in that I could, without taking
up excessive space. It was nice to have a clean sheet... PS the rad
prices were less via the plumber's discount and over half of the costs
were labour, so in the grand scheme of things not too bad.

Today, Heat Genius showed the kitchen/dining room (a difficult room to
heat - large, 2 big bay windows, no door to side lobby) went from

18.4C at 6am to
20.5C at 7am

with a *flow* temperature (external to boiler) of around 55C - that
would be the green column H on the sheet, delta-T=30K

Sadly the WB boilers do not have a simple weather compensation option
(they want you to use their smart programmer to get that and that
doesn't work with an external programmer) - so we're pretty much in the
land of twiddling the knob each month.

However, I'm hoping to reduce that to a simple guide on the boiler -
Novemeber - position 4, January - 5 or 6, or something like that...

My WB Greenstar oil boiler has two ways to do weather compensation.
Either via a fancy controller or via a separate sensor (plastic case,
choc block connector, one thermistor, not even a PCB, 26GBP!) with it's
own dedicated terminals on the boiler. Are you sure yours can't do it
that way?



No - I read the installer's manual and rang WB tech. They also confirmed
that the CDi fancy "Wave" IIRC programmer could not accept an external
control input - so not very fancy.

That's a shame, I thought that it was one of the big selling points of
condensing boilers that you could do this. Not that there appears to be
any choice about getting a condensing boiler! I suppose an alternative
would be to adjust the flow temperature according to the return
temperature, but it probably varies too rapidly for this to work. How
does the fancy controller do it without any external informaion? One
thing I don't think is common in oil boilers is modulation of heat
ouput, It would I think be dfficult to achieve without multiple burners.
I don't know how modulation in gas boilers is controlled without
external temperature - speed of temperature rise or something?





--

Roger Hayter