windows and u values.

[kalathedog]

Hi everyone, this is my first post so treat me gently.
Hopefully someone can help me get my head around this. I lived in Spain for a few years and practically all the homes are fitted with roller shutters. Since my return to the UK I've been thinking that it would be a good idea to fit them to a UK home. Now comes the problem, finding u values. Internet trawling and putting bits and pieces together has given me an overall u value of about 0,5 W/m2k when using an insulated roller shutter over a double glazed window unit. This seems to be a very low u value, which leaves me thinking that my calculations are wrong (it wouldn't be the first time)
Hopefully this link will work, it might need to be opened by clicking in the downloads box....
http://dl.dropbox.com/u/32255831/shutter u value.ods
Which shows my, rudimentary, calculations.
Is anyone able to help and show me where I've gone wrong?
Thanks.

 

[freddiemercurystwin]

Why is the overall U value so important? Also your link does not work.

 

[kalathedog]

U value from an insulation point of view.
Sorry about the link, I thought Dropbox was supposed to allow this sort of thing...
It did work for me though.

 

[freddiemercurystwin]

I understand what U Values are thanks, I am trying t grasp why working out the U Values for such a set up would be useful other than for curosity.

I would also be interested in the proposed manner in which the shutters are sealed within the reveal to maintain air tightness/insulation and how the fact that there will be a massive cold bridge caused by the fitment of the shutters in the outer skin will be overcome. Unless your calculations take these factors into account I think working out the U Values would be of no use to calculate possible thermal transmission from inside to outside if that is your goal, any heat loss calculations being highly inacurate.

 

[kalathedog]

I understand what U Values are thanks, I am trying t grasp why working out the U Values for such a set up would be useful other than for curosity.

Clearly I didn't understand your question, sorry. The point being that an insulated roller shutter will offer an insulated barrier. It did seem quite straightforward to me.
Regarding cold bridging, I'm not 100% sure of what or where you're talking about. I assume that any perceived cold bridging issues would be resolved by using a specifically designed lintel, or have I made another mistake?
I'm not sure what you mean about fitting in the reveal is either.
This fits with my initial thought that I'd made mistakes in the calculations.
You clearly have experience in this area, you also sound negative towards the idea, is there any reason why? My experience of them in Spain was very positive and I thought it might be a good idea to do some investigation over here.

 

[freddiemercurystwin]

I can appreciate that having some kind of insulated shutter on the inside that could fit within the reveal as long as an airtight seal could be achieved would be of benefit, although having to physically store during the day and fit a shutter on the inside is easier said than done.

I am not aware of how this could be easily achieved on the outside and in a cost effective manner.

Insulated roller shutters that are insulated do not tend to roll up very tight and consequently they sit on the outer face of the wall rolling up into a box at the head (lets not forget that they look hideous too). When in the closed position this will leave a big chunk of masonry between the insulated shutter and the window enabling any heat that was retained by the shutter to escape via conduction through the masonry at the sides, cill and head.

Assuming all of these practicalities could be overcome it would cost an arm and a leg to fit insulated shutters on every window, surely they would need to be powered too costing even more. The pay back period would be ludicrous. Cheaper and easier just to fit higher performing windows, hang some heavy curtains and improve the rest of the property.

 

[kalathedog]

Thanks, it's becoming a bit clearer now. My understanding is that internal shutters are not good because they can provoke condensation and even break the glass in extreme cases. Not something I'd be too happy about.
How airtight does airtight have to be to be beneficial, all the shutters I've seen have an insert to help seal and, of course, due to the flexibility it is a compromise (same as glass, no?).
The shutters I'm looking at would have an internal box and according to the literature a u value of 1,9 W/m2ºC when open and 1,4 W/m2ºC when closed. But the problem you mention of conduction would exist with or without the shutter, or am I missing something again?
I have to agree with you on the ugly aspect when the shutter box is on the exterior, but I can't agree with the boxes I'm looking at as they'd be mounted internally and hidden, in fact I'd go as far as to say that I find British home lacking something because they don't have roller shutters.
Payback periods are dependant on many factors, I think that a 10-11 year payback period isn't unrealistic. I'm not sure how that would stack up, I know shutters are cheaper, against improving the double glazing or indeed triple glazing and as a way of reducing energy bills a viable option.
Adding to the insulating effect I think the roller shutter can offer me more peace of mind over curtains in the security dept too, something that is a bit more difficult to throw into the payback equation.
Thanks for the info, you've given me some food for thought.

 

[masona]

What if they don't open in the event of fire?

 

[kalathedog]

Masona, I'm not really sure I see that as being a problem, or any more or less of a problem than we have now. Why would they not open? If a house complies with current building regs there should be adequate escape provisions built into the design, if not simply open them and jump out.
Again in all my time abroad I don't think I saw one single fatality attributed to shutters.
Also neither the local council planning dept or insurance company have raised similar concerns in conversations with them.

 

[freddiemercurystwin]

If your shutters are shut and powered by the mains there is a chance the power may be lost during a fire, without a battery back-up feature that opens them in the event of power loss they would remain shut. If ever there is a fire, a window will become a very attractive escape route. Planning would not know about the fire implications if you shoved them in a room full of smoke! Your insurance phone operator will have a limited grasp of the implications either. The latest building regs would prevent they're fitment without said battery back-up. The fire brigade will also be hindered in their response as they will have to smash through the shutters to get to access a fire.

I don't really understand your comment about how a shutter on the inside would be attractive, how can having a dirty great box above the head be considered attractive?

 

[kalathedog]

I see where you're coming from on the fire stuff now, I'm looking at manual mechanism, I can't see any advantage in having motors. They're not heavy and not a problem. Are you saying that planning are incompetent??

I was speaking to someone a bit further up the food chain at the insurance co too.

We seem to be crossing ideas regarding what I'm talking about here, so here's a photo.

The shutter is external but the box is built into the wall (right photo) and hidden as is the shutter in the up position, there are specially designed lintels which avoid any problems of cold bridging (so I've been told), and that's pretty much it apart from finding info on the improved insulation u value.
I couldn't agree more that the external boxes are fugly (left photo).



I'm not interested in going for triple glazing as the u values aren't worth the expense and am looking for something that will also allow me to close out the solar heat gain in the summer yet take advantage of it in the winter then prevent losing all that winter heat gain through the night.
As I said I see glass as a compromise and the shutters will allow me to use the flexibility of shutters to my advantage.
Does that make sense to you?
And thanks again for oyur time and knowledge.

 

[freddiemercurystwin]

Yes I understand what you are saying about having the shutter integrated with the lintel, systems are readily available here eg: http://www.rslbristol.co.uk/downloads/DETAIL LINTEL TYPE A1 INS 100-50-100.pdf however I am not aware of a manufacturer who makes an insulated shutter, AFAIK they are all designed with security in mind. If it wasn't insulated I really cannot see much advantage, yes you will reduce solar gain during the summer but only whilst the shutters are down. They are so thin they will not provide any meaningful insulation during cold weather. They would no doubt do something but as mentioned much more of a gain could be achieved by other far cheaper methods than replacing all the lintels.

In a new build for security I can see the attraction and would agree solar gain can be reduced, as a retrofit to reduce heat transmission through the windows I think its barmy.

 

[JohnD]

but surely they will give a pocket of still air against the window, in the same way that a curtain does, and will also block radiated heat loss and draughts (noise, too).

I have used roll-down external blinds, operated by an indoor strap, in Switzerland, and they make a very noticable reduction in heat loss at night.

 

[freddiemercurystwin]

There is no doubt that eliminating the wind driven cold air on the outer face will reduce heat transmission I have conceded they would have an effect but would still argue that there are much better (cheaper) ways to minimise the overall heat loss out of a dwelling. This proposal replaces all of the window lintels, add up the cost of the lintels/shutters/labour/making good ...............

 

[kalathedog]

That brings us back full circle to the question that experience tell me that the polyeurethane foam filled aluminium lats do have an insulating property, the question being how much, and the level of accuracy of my calculations (apparently not very).


.............................................width........k value.........r value
glass (thickness m)..................0,005....... 0,9........... 0,0055555556
air gap m.................................0,02...........0,025........0,8
Glass (thickness m)..................0,006........0,9...........0,0066666667
shutter....................................0,004..........0,02.........0,2
air gap m (window/shutter).......0,02..........0,025.......0,8
...............................................................r value.........1,8122222222
...............................................................u value.........0,5518087063

The weakness is that the shutter front is not going to be airtight therefore elevating the final u value for the overall unit.
Regarding costs, again I have to agree with you regarding installation and unit costs, but if we set this against the cost of changing frames and glass from double to triple and a supply of blinds that is considerably cheaper than UK prices, the whole idea now comes into a 10-11 year payback period, which I think you'll agree isn't too bad. We're also looking at it from another point of view and that being that glass is a pretty poor material for windows, ok you can see through it, but that's about it.
In the summer the solar heat gain can can be sufficient that A/c becomes the norm for cooling, I never used A/c when I lived abroad, and also it'll fade fabrics over time (replacing furniture and carpet has a negative cost impact). If you fit a glass that reduces solar heat gain you're going to lose any gains you need in the winter and of course vice versa, anything you choose has pros and cons. Cost factors against for using just glass, I think a combination of materials will improve the situation dramatically.
This is without looking at the security aspects, if we ever see a long hot summer again they will allow me to leave the windows open all night and the shutters down (outward opening windows need not apply) allowing fresh air to enter but not the burglar.
The way we're looking at it is as a supplement to double glazing, and not a replacement, to move things closer to triple but with extra benefits that triple can't offer. As I said earlier I'm comfortable with the look of buildings with shutters and a hidden box gets rid of the idea of ugliness. And I think the correct choice of colour can actually add to the building's look.
I think you'll agree that if I'm looking at having a chunk of the work done anyway as an upgrade from double to triple, then the extra added cost for replacing the lintels and the reduced cost (I'd say i'm looking at 30-40% less) of the shutters combined with what I see as extra benefits kind of adds up. So in my opinion it's far from being barmy, and possibly you'll agree, as I'm writing this it actually seems to be making bloody good sense....
I understand what you're saying about replacing windows and lintels in and existing property is going to increase the payback period and new build would be better, but as said above if some of the work is going to be done anyway and the shutter cost is low.
The key being the u value, I'm British I need facts and figures.
@ JohnD, it's nice to see a real life, positive experience in mid/northern Europe, they appear to be very popular in Germany, Holland and Poland. There must be a reason for this, no?