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u-values

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u-values

Postby RogerS » 17 Feb 2017, 18:34

Having been in the new place for a fortnight, we've decided that it needs a lot more work doing. First up is to rip off the plasterboard on all the external walls, insert Kingspan between the studs, replace the plasterboard and skim.

We also want to replace the radiators with a more modern style and so need to do heat loss calculations. Most online systems only give a few types of outside wall - brick cavity, brick cavity with insulation, solid brick, timber frame - but none of these fit our type of wall which is probably 200mm stone, maybe a cavity then thermalite blocks. If you look at this picture, you'll see that they paid lip-service to any extra insulation and so our plan is to put Kingspan in between those studs - 100mm thick or thicker if I can squeeze it in.

So my question is does the u-value of this proposal match or come close to any of the u-values used in the online calculators (brick cavity etc) ? I tried Googling but couldn't find any sensible answer. Or at least one that I could understand !

Also not sure but does one need to use foil-backed plasterboard ?

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As an aside, the reason why I opened up these panels was to see if there was an original fireplace behind. Up in the loft space there are four original Georgian bedroom fireplaces and it would have been great to find a ground floor one.

Image

My surveyor was round the other day and we investigated a bit more and delighted to find that there is a flue behind those thermalite blocks and so he's planning to come along with a borescope.
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Re: u-values

Postby RogerS » 17 Feb 2017, 18:41

I forgot to add that the roof construction is, I think, sublimely elegant and uses a double-fink construction which means that those timbers can be as slender as they are in these photos.

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Re: u-values

Postby Tusses » 17 Feb 2017, 18:44

Have you considered insulating on the outside, and letting the walls become a thermal mass ?
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Re: u-values

Postby TrimTheKing » 17 Feb 2017, 18:47

Mike will know I have no doubt!

That roof is lovely, unless you want usable loft space!

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Re: u-values

Postby RogerS » 17 Feb 2017, 19:32

Tusses wrote:Have you considered insulating on the outside, and letting the walls become a thermal mass ?


Yes. For a nano-second. I think it would be a bit of a shame :D

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Re: u-values

Postby Tusses » 17 Feb 2017, 20:23

:lol: haha .. ok .. I see :-)
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Re: u-values

Postby Andyp » 17 Feb 2017, 20:33

RogerS wrote:
Tusses wrote:Have you considered insulating on the outside, and letting the walls become a thermal mass ?


Yes. For a nano-second. I think it would be a bit of a shame :D

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I thought you had moved up north? What's that blue stuff behind the chimney pots? :D
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Re: u-values

Postby RogerS » 17 Feb 2017, 22:23

Andyp wrote:
RogerS wrote:
Tusses wrote:Have you considered insulating on the outside, and letting the walls become a thermal mass ?


Yes. For a nano-second. I think it would be a bit of a shame :D

Image


I thought you had moved up north? What's that blue stuff behind the chimney pots? :D


I think it's called 'Sky' ...mind you, not seen it for a bit.
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Re: u-values

Postby Doug » 18 Feb 2017, 09:19

Mears recommends a 10% increase in calculations for exposed dwellings, so I'd personally base my calculations on 9" solid & not allow the increase.
Also whilst getting the smallest rads which take up the least space to heat up each room is preferable, as long as you use the same criteria for each room ( obviously making adjustments for upstairs & downstairs rooms & room temperatures) the rooms should all heat up at the same rate so when the room stat is satisfied all rooms are up to temperature. This is also presuming you are slightly over compensating which is always preferable due to the base level calculators work from.
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Re: u-values

Postby RogerS » 18 Feb 2017, 10:00

Thanks, Doug.

I found a useful calculator on the Celotex site and played around with the values of various types of wall construction. Brick cavity with insulation comes out pretty close, I think, and so I'll run with that.
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Re: u-values

Postby 9fingers » 18 Feb 2017, 11:34

I would suggest you do your radiator calcs based on a low flow temperature say around 50 C
This will maximise the time the boiler is in condensing mode and so at its most efficient.

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Re: u-values

Postby Doug » 18 Feb 2017, 11:38

RogerS wrote:Thanks, Doug.

I found a useful calculator on the Celotex site and played around with the values of various types of wall construction. Brick cavity with insulation comes out pretty close, I think, and so I'll run with that.



Makes sense if you are lining with ridged insulation.
Out of interest does the online calculator deduct a % for upstairs rooms? I still use my old dad's rotating disc type calculator which is probably 40+ years old but other than working in imperial & btu's ive always found it accurate.
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Re: u-values

Postby Doug » 18 Feb 2017, 11:40

9fingers wrote:I would suggest you do your radiator calcs based on a low flow temperature say around 50 C
This will maximise the time the boiler is in condensing mode and so at its most efficient.

Bob



Wouldn't that mean increasing the radiator size by 30% though?
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Re: u-values

Postby 9fingers » 18 Feb 2017, 11:46

Doug wrote:
9fingers wrote:I would suggest you do your radiator calcs based on a low flow temperature say around 50 C
This will maximise the time the boiler is in condensing mode and so at its most efficient.

Bob



Wouldn't that mean increasing the radiator size by 30% though?



Yes this is needed to get published efficiencies from modern boilers. I think they specify the performance at return temps around 40C.
Most installations retrofitting a modern boiler on existing systems can't get anywhere hear that.

In the first post Roger is talking of replacing all the radiators which is why I suggested it.

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Re: u-values

Postby Phil » 18 Feb 2017, 13:55

Roger, nice looking house. All stone and no painting.

Did they really paint the walls that colour? :lol:
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Re: u-values

Postby RogerS » 22 Feb 2017, 17:29

Yes, I'm afraid that they did, Phil

This u-value nonsense has me in a right kerfuffle.

I've worked out that sticking 100mm Kingsoan in between the existing wall studs is pretty much equivalent in u-value to a brick filled cavity with insulation. So far, so good.

Sticking in the same room dimensions into four or five online calculators for radiator sizes gives me four or five widely differing BTU requirements. From 4800 to 8400 BTU. So much so that I have absolutely NO idea which one to trust.

What makes it even more bizarre is that some of them seem to be using the same calculator engine.

If anyone knows of a definitive calculator then please let me know.

If anyone fancies trying their favourite calculator then I'd be interested to see the results. Parameters are:

length 4.95 m
width 5.56
height 2.8

purpose living room

no. outside walls 2

window area 2.7 sq m wood double glazed

floor - concrete

room above - heated room
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Re: u-values

Postby old » 22 Feb 2017, 18:01

Have a look at Stelrad Stars on google then get the app you should find lots of info and be able to design your rad. sizes . it takes time but result is good.
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Re: u-values

Postby RogerS » 22 Feb 2017, 18:42

Many thanks, Old. :eusa-clap:

Certainly very detailed !

I put in the parameters for one of the rooms and it came up with a value pretty close to that from one of the other sites which means that I can use that site for the rest as it's a little bit more straightforward.
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Re: u-values

Postby 9fingers » 22 Feb 2017, 19:05

Making some guesses for parameters not stated, the Myson calculator seems to be coming out at the upper end of your range - about 8000 BThU/hr

http://www.myson.co.uk/useful_services/ ... anager.asp

To be accurate you need air and water temperatures - as suggested in my earlier post to optimise boiler condensation performance.

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Re: u-values

Postby RogerS » 22 Feb 2017, 19:23

9fingers wrote:.....
To be accurate you need air and water temperatures - as suggested in my earlier post to optimise boiler condensation performance.

hth
Bob


That's a very good point as I recall you mentioning a temperature of 50 degrees to keep a condensing boiler at its optimum working conditions IIRC. Many of these calculators assume, I think, 80 degrees. Therefore presumably one needs a larger radiator for 50 degrees.

Trust SWMBO to choose bloody expensive radiators :evil:

Which reminds me.....time to feed The Beast.
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Re: u-values

Postby 9fingers » 22 Feb 2017, 19:46

RogerS wrote:
9fingers wrote:.....
To be accurate you need air and water temperatures - as suggested in my earlier post to optimise boiler condensation performance.

hth
Bob


That's a very good point as I recall you mentioning a temperature of 50 degrees to keep a condensing boiler at its optimum working conditions IIRC. Many of these calculators assume, I think, 80 degrees. Therefore presumably one needs a larger radiator for 50 degrees.

Trust SWMBO to choose bloody expensive radiators :evil:

Which reminds me.....time to feed The Beast.


The Myson calculator allows you to change the mean water temperature. A mean of 55 (flow 60 and return 50) should allow good levels of condensation but the lower temp the better within reason.

Running the boiler at these sort of temperatures is useless for DHW therefore there are a couple of needs of the boiler and its control system.

1) the control system should permit two different settings for the flow temperature.
one should be set low for the radiators and the other set higher at 65-70 for DHW.

2) Ideally the CH should be shut off when heating water for best economy. This not always practical but it is not unreasonable to shut off the CH for say 15mins to heat water (if there is demand) in each hour and you are unlikely to notice any loss of heating comfort.

A further highly desirable feature is to use a weather compensating controller which will estimate/learn the rate of heat loss of the building with differing external temperatures and modulate the boiler power accordingly during CH sessions.

When choosing radiators, it there is not one that is spot on pick the higher output one.

When choosing the boiler avoid the temptation to get one that is too high rated. Whilst having a margin of power in hand might seem desirable, the efficiency will suffer. The efficiency is highest when the boiler is working at or near full output.

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Re: u-values

Postby RogerS » 22 Feb 2017, 22:51

Thanks for the extra info, Bob.

I had a :idea: moment tonight. Sod the calculations. Just get a few electric heaters in a room and turn them on until the temperature is what you want. Stick them on thermostat and wait to see how it develops. Repeat a few times when it's colder outside. Bingo.
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Re: u-values

Postby Tusses » 22 Feb 2017, 23:33

if you like sperimenting with stuff like that, then these are fun ....

https://energenie4u.co.uk/catalogue/product/ENER007
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Re: u-values

Postby Mike G » 23 Feb 2017, 00:37

RogerS wrote:..........I found a useful calculator on the Celotex site......


That's exactly where I would have sent you. If you have a wall that varies from the typical, just ring them up and they'll email you a print out of the U value and give you a dew-point calculation/ graph. The good thing about the Celotex site is that they will calculate U values for other types of insulation, not just Celotex.
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Re: u-values

Postby Jimmy Mack » 25 Feb 2017, 10:30

I got in a right kerfuffle over u values and clacs. It wasn't until I gave in and just called up kingspan (as Mike suggests) and got them to do the calcs for me.


BTW, that's a beautiful looking house.

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