Heat loss and shutters

[dedee]

Reading Rogers' thread on heat loss calculations has got me thinking again about external shutters and what, if any, contribution they make in reducing heat loss. I've had a trawl around the web on this subject before but have only ever found info regarding internal shutters.

Has anyone got any info?

The shutters in question can be seen here.

The gap between window and shutter is about 12"

Andy

 

[Jenx]

An absolutely negligable effect Andy ...
Unless they had an airtight fit around the building, their contribution to the U-Value of the wall on which they're sited... virtually zero effect.

Look nice though ! :wink: 8)

 

[dedee]

Jenx, thanks. As I suspected.

I have noticed though that we seem to get a lot less condensation on the windows with the shutters closed.


Andy

 

[Paul Chapman]

I would have thought the effect would be more significant, but more as a result of reducing the amount of cold air getting in. In much the same way as a porch and double front door deflects the wind, reduces draughts and has a significant effect in keeping a house warm, window shutters should help to keep the house warmer. Probably quite difficult the measure the effect though.

Cheers :wink:

Paul

PS The fact that you get less condensation with the shutters closed surely demonstrates that the external surfaces of the windows are less cold with the shutters closed. QED :wink:

 

[CHJ]

I would have thought the effect would be more significant, but more as a result of reducing the amount of cold air getting in.

I think it is more a case of slowing down the heat loss out Paul, by reducing exposure to direct wind/cold elements contact, the heat loss through the glass/casement is reduced.

I know on my sons property in Bavaria, although fitted with external plastic sliding shutters not wooden 'doors' they make quite a significant difference to the internal window area chill factor even when adjusted to let small proportions of light thorough, in fact the fitting of fine mosquito screens to the outside of the casements has an effect on winter chilling of the glass during daylight hours when the shutters are open. It's a job to quantify but you can feel the difference if you stand by the windows. It has resulted in the screens being left in place all year now.

Bizarre really as I would not have thought either shutter or screen would be significant compared with the double glazing.

 

[Jenx]

See the "heat loss calculations" thread -
have posted up a bit of detail there that may help hopefully

 

[CHJ]

See the "heat loss calculations" thread -
have posted up a bit of detail there that may help hopefully

Don't want to clutter up the thermal debate in the other thread Jenx but it's good to see someone 'down to basics' , way back in the 60's (that's 1960's you lot I'm not that old) I was involved with a lot of 'central heating' installations as a side job to pay the mortgage.

It amazed me how pedantic some of the calculations were regarding radiator sizes etc. in given 'proffesional' quotes.

The figures we used as rule of thumb, no double glazing at that time, were 7btu's per cu ft groundfloor and 4 btu's per cu ft upstairs due to natural heat rise. (uninsulated upper floors) never had a customer complain about a cold room, often had feedback that they had to turn some of the rads down a tad though.

Often used the next physical rad size up as it was only a matter of a few hundred BTU's and little cost difference and the difference in individual pipe restrictions fell well within this margin. (talking with clients we also often referred them to 1-2-3 bar electric fire equivalents which they could relate to and indeed try out.) (1kw=3,400btu's)

 

[Jenx]

Spot-on. Chas ... thats the crux of the whole thing ....
its so variable, and diverse, that the installer has to try and cover all bases for all people

28 years in the trade (aged 43 next birthday ) with a good few of them on the Gas & oil burner servicing field, and I've yet to find someone who'll tell me they're cold ! Mind you.. nothin' like tempting fate !

It's gone the way of so many other trades though... very few proper apprentices nowadays... the older skills like lead-burning and sheet-copper work may very well disappear in the not too distant future... its a shame really, I guess most older 'hands' feel the same way...
Last bathroom I did for a pal, he brought a 'joiner' in to frame up the pressed-steel bath and the guy had done one of these 'one-year courses' at the college, and after about 2 hours and no progress, the poor fella had to admit defeat and confess he didn't know what to do - cant have been easy for him to admit it.. he wasn't a young guy or anything, and had previously been a baker ! Framed it myself after that - my pal thought he was doing me a favour by bringing the lad in to do it, and he didn't like to 'assume' I'd just do it myself. :roll:
You worry on behalf of the people who'll end up with the lad in their property, carrying out all manner of 'jobs'.. the potential disasters don't bear thinking about !

I cant speak for the majority of the UK, but certainly here, we're over-run with east-European workers in the "trades" now - and whilst this may not be the 'ideal' situation - as a country, we seem to have allowed this to happen through our gradual erosion of our home-grown skills base. It really is a great pity to see this happening. Once these skills go.. they'll be so difficult to ever replace. Thats probably a can of worms that could be debated ad-infinitum

 

[CHJ]

I still get the odd comment from people about having a cold spot somewhere but they can't do anything about it without changing the boiler because their system will only cope with 7 rads or similar, having seen the glossy brochure guide with its generalization of available btu's output.

My immediate reply is, 'are all your radiators full on on the coldest day?'

Nine times out of ten the answer is no, or just one or two days a year, or we only leave the back bedrooms on low when not in use etc.

I say go fit another rad there then and put the heat where you need it most of the time, worry about the odd day when and if it happens and switch on a fan heater for a few minutes, much cheaper than fitting a new boiler just to get an extra 10k btu's that won't be needed most of the year.

28 years in the trade (aged 43 next birthday )

Still a youngster then :lol:

 

[Jenx]

heh heh... yes indeed.. still just a tiddler !
( an 18 1/2 stone Tiddler its fair to say.. but a tiddler all the same ! :wink: )

I must say, its been a while since I was referred to as a nipper, but Chas, thats made my entire week ! Brilliant !

 

[CHJ]

By the way dedee, anybody forgotten and tried to run down those missing steps yet. :lol:

 

[dedee]

Chas,
No not yet:lol:. Although for the life of me I cannot understand why they were ever taken out. Am seriously thinking of putting them back.

Going back to the shutters if I can find two thermometers that give the same reading I'll put one each outside a shuttered window and a non shuttered window (I have 3 windows all facing south in one room so they should not be affected too much by external variations in wind etc.). I'll then see what affect the shutters have.

BTW I'll have to start another thread soon on how to light a fire
This particular city boy is struggling to understand how to control an insert type wood burning stove.
I've also got to make room in the garden for 10 stères of wood. I know in theory that should equal 10 cubic metres but I am sure by the time I attempt to make a wood pile it will be a wee bit larger than that.

Andy


Andy

 

[CHJ]

BTW I'll have to start another thread soon on how to light a fire
This particular city boy is struggling to understand how to control an insert type wood burning stove.
Andy

Not knowing what type or draught system the fire uses it's a bit like how long's a piece of string.

One thing most people not used to burning wood do wrong is to clear all the ashes and partially burnt (charcoal) wood out of the grate when removing the bulk of the waste from the ashpan. A good wood fire thrives on a bed of charcoal embers to maintain the heat source, especially in an open grate.
Even with forced draught boilers they need the bulk of the gas producing charring wood to maintain a steady combustion.

Mind you the ones I see in Bavaria look more like raging infernos when you lift the charging doors to throw another couple of logs in.

Took me nearly 2 days to get an easily maintained wood burner going well in the holiday cottage we had this year, It gets a thorough cleaning by an over zealous cleaner it would seem and the first evening was taken up just trying to fill the grate with a charred wood bed.

 

[Taffy Turner]

Andy,

Calculating the thermal performance of windows is what I do for a living (sad eh??). :-({|=

If you can gaive me a few more details regarding the windows viz: -

Frame material (timber, ali, pvc)
Glass Spec (single, double, argon fill?, low-e coating)
Inter-pane gap (e.g. 20 mm)
Shutter material (hardwood, softwood)
Glass to shutter distance

I will happily run a few simulations for you and give you a definative answer - I am quite curious myslef, as I suspect that it makes considerable difference. Although I have done thousands of calculations, I have never done one for shutters.

Regards

Gary

 

[dedee]

OK Gary, thanks, here goes

Frame material........ Hardwood
Glass Spec...... double, I've no idea if they are argon fill. They were put in when the house was built 15 years ago. There are none of those glass bubbles inside.
Inter-pane gap.... How do I measure? I would guess about 15mm
Shutter material.........softwood, 20mm thick
Glass to shutter distance.........300mm

Will you show us how you calculate as this may prove useful when I replace the shutters, 1 or 2 are in need of repair already.

cheers

Andy

 

[Taffy Turner]

Andy,

Ok - I have enough information there.

If the units were put in 15 years ago, then they almost certainly don't have low e coatings or argon fill.

The inter-pane gap is most probably 16mm - 16mm and 20 mm are the most common ones.

As for showing you how to calculate it - it is a bit complicated as I have to build a numerical model of the window in a specialist piece of software called Therm. It is all too involved to into here - suffice to say I normally charge £800 to do this sort of calculation, so you are getting a bargain!!

I am a bit tied up with a door simulation at the moment, but should have something for you tomorrow afternoon with a bit of luck.

Regards

Gary

 

[dedee]

Gary,
what can I say? But thanks. I would like to think the information would be useful for others too so I will buy you a few collective pints.

I've had a look around all he shutters and reckon that there is never more than a 1/2" gap between the shutters (hinge side) and the walls, top and bottom are pretty snug fit too. A lot of the gaps are less than 5mm.

Thanks again.

Andy

 

[Taffy Turner]

Andy,

I have some results for you now, and they make interesting reading (from my point of view also). Using the information that you gave me, together with a few assumptions regarding frame hight and thickness etc (which as we are interested in the difference, won't cause too much of an inaccuracy) I got the following results: -

With shutters in the open position Uwindow = 2.4 W/m2K

With shutters closed Uwindow = 1.5 W/m2K

If you were able to make the shutters a better fit, so that the gap all around was <= 2mm, then Uwindow = 1.2 W/m2K

The U value is a heat loss in Watts per square meter of window per Kelvin (degree C - it's the same thing).

Assuming your house has a window area of 12 square meters (measure the area of the reveal, not just the glass), and an internal temp of 20 deg C and an outside temp of 0 deg C (reasonable for your part of the world during the winter), we get the following heat loss figures: -

No shutters - Heat Loss = 2.4 x 12 x 20 = 576 W

Loose fitting shutters - Heat Loss = 1.5 x 12 x 20 = 360 W

Tight fitting shutters - Heat Loss = 1.2 x 12 x 20 = 288 W

There is also a significant effect on the sight-line temperature. This is where the glass meets the frame, and is always the coldest spot on a window assembly - hence the point were condensation starts to form.

No shutters - SLT = 8.2 deg C

Loose Shutters - SLT = 12.5 deg C

Airtight shutters - SLT = 13.7 deg C

All of which tells me that it is worth closing the shutters at night during the winter! I suppose this is hardly surprising - as if the shutters didn't make much difference, why do most houses in mainland Europe have them fitted?

As an aside - this is the reason that windows in the UK open outwards, and windows in Continental Europe open inwards - it is to allow teh shutters to be closed from inside the room. As the UK traditionally doesn't have shutters, hence the windows open outwards.

Hope that this helps.

Regards

Gary

 

[dedee]

Gary,
that is brilliant, I owe you one, or two.

From now on all the shutters will be closed at night. When I come to repair or replace I will make sure the gaps are reduced as much as possible.

Incidentally inward opening windows are a PITA as they never seem to have any stays or other method of holding then in a fixed open position.

Cheers


Andy

 

[RogerS]

Gary

That is fascinating. Out of curiosity, would you expect to see a better relative performance if the windows were only single glazed? Or would the improvement be only marginal?

Guess what I'm saying is that with your calcs there is a 50% improvement with tight fitting shutters and double glazing. If one gets the same (or better) with single glazing then it's definitely worth me thinking about this.

Just hope SWMBO doesn't read this as she's always liked the idea of shutters!