insulated shutters

[Anonymous]

I'm planning to build some insulated shutters to see if I can make a usable solution, since my arithmetic says they're a very good idea but I haven't had any luck finding any existing products or knowledge (no reply from PHI and no information in the reply from NBT). So I want to see if I can iron out whatever practical or technical issues there are in building internal shutters.

I decided on internal because it means I don't have to deal with weatherproofing but I do have to figure out a vapour seal, stowage arrangements and aesthetics. I figure the basic design is one or more sheets of rigid foam insulation, plus fiddly bits. Foam avoids the need for a strong case, which keeps weight down. Fire risk seems the main concern, which led me to phenolic board – Kooltherm K10 90 mm in particular. But I'd be interested to hear of any alternative suggestions. I've also yet to find anywhere local that has it in stock!

[Anonymous]

You might check with my friend Larry Kinney, there was rumbling about bringing insulated shutters to the marketplace.

http://www.synertechsystemscorp.com/

Doug

[Anonymous]

A standard product in germany is an insulated roller shutter, with foam-filled plastic slats. These are built in, with a webbing strap down one side of the window on the inside, you can have them completely shut for total blackout/massive U value increase, or partially slatted to let some light in. I have never used them in a project, but I imagine a little net research would turn them up.

They arent' particularly pretty, but , and are fairly discreet when they are fully open.

[Anonymous]

@Mervyn, Thanks; I have Shurcliff's book, which is of a similar vintage, and I'd be interested to see Langdon's. I'll send you a PM.

@Doug, Thanks for the link. It looks a little early in their product cycle – there are no product details that I could find – but I'll be sure to watch them.

@Dil, Thanks, I'm aware of insulated roller shutters but I've yet to find one that offers the kind of performance I'm looking for and am somewhat sceptical that they exist. I saw one specific claim but failed to elicit any further information except that the claim originated in Switzerland. But I would be very interested if you have any information about products that offer U-values of 0.3 or so. I have seen claims of 0.7 for some industrial shutter products but I'd like to do better.

[Andy Mitchell]

Dave, there's an interesting presentation to download at http://www.synergisticbt.com/insulatingshutter.html

[Anonymous]

Ah, thanks Chris. I'd looked at that page but hadn't seen the embedded links so your prompt was very useful. The slideshow –
https://secure.goozmo.com/goopages/pages_downloadgallery/download.php?filename=1241_9156577.pdf&orig_name=SBT%20Insulating%20Shutters.pdf – is interesting. They seem to be thinking along sensible lines and I'll keep an eye on them. I hope they do develop something that is useful at our latitudes.

[Mark Siddall]

Dave,
I'm sure that you're on this one but the key problem that you'll have with internal shutters will be the temperature gradient and the risk of condensation, mould (thus impaired IAQ and possible reduced life span) and frost on the inside face of the glazing. Good seals will not help much as you'd be sealing the humid internal air within the void that you'd be creating.

Whilst technically feasible in a PH the cost benefit is limited – at least that's what PHI have said in the past (sadly can't remember where I read this: book, website or other…) From memory PHI did not recommend internal shutters….. If I recall the source I'll let you know.

Cheers,
Mark

[Anonymous]

I think the concept behind insulating shutters is to offer an alternative to the replacement of old, leaky windows. If this could be accomplished with an exterior insulating shutter the return on investment might make good sense. The efficiency of Passive House windows changes the ROI to a considerable degree.

I am with Mark on the reasons not to put the shutters on the inside although the thought of a moveable insulating wall to insulate a bank of south facing glass during sunless periods is intriguing.

Doug

[Anonymous]

@Mark, Yes I'm aware of the condensation risk. I don't think there's a problem with condensation from the air that is sealed in – there's just too little volume for it to be a concern. It's the vapour that is drawn in by the [partial] pressure difference that is created after it has condensed that causes the 'streaming condensation' problem.

I'd be interested to read any analysis that PHI or anybody else has published. I know that Feist tried external shutters and gave up but I haven't been able to find out why. I see the cost quite differently – you could trade the cash spent on shutters for lower spec windows and doors for example, or my goal would be to reduce the cost of making heat demand 0, including DHW.

@Doug, I think you're right about Synertech's price strategy. Instead of replacing your old windows, add some new shutters. But it's easier to make shutters to keep light and heat out than to keep it in and I suspect they may get distracted when they consider the relative market sizes in the US. I think sales in the colder regions might be slow until the product is well-proven unless the price is reduced a lot.

I agree with you both that condensation on internal shutters is a big problem. But I think that engineering reliable weatherproof airtight shutters that will operate without maintenance for a decade or two is a bigger one. I suspect sliding seals will need changing every few years and the track will need cleaning even if nothing rattles or freezes up and the electrics keep working.

[David Olivier]

Feist gave up because of the cost

D

[Anonymous]

I don't understand that. The story as I understood it was that he fitted them and then stopped using them after a year, so I don't understand where the extra cost would come from? That's why I'd like to find a source with the whole story 🙂 And I'd like to see the PHI costings that demonstrate the lack of cost benefit. In particular, what assumptions they made about both the costs and the benefits. Given that the whole of the PH ethos is based on changing a fundamental assumption (you can leave out the heating system at X power loss), I think it's quite important to understand premises in detail.

Are there any academic papers at all that analyse shutters in heating climates?
(I confess I hadn't thought to do that specific search, I'll try tomorrow)

[Mark Siddall]

I think that the Feist concept for shutters was to achieve zero heating. It was successful briefly – then a cold overcast winter set in. In terms of costs I think that it was the life cycle cost that put the damper on things – the cost per kWh saved was not deemed realistic. (Again from memory – if only I could remember where I read this stuff! – probably a website or somewhere in “Sustainable Solar Housing”)

Mark

[Anonymous]

Because I'm thinking about internal shutters, I'm thinking about seals around the edges. I haven't found a good description of how tight such seals need to be, so I've been doing some back of the envelope calculations. I'm currently looking for an explanation of how seals work – in a specific sense to answer a particular question.

Normally the pressure on both sides of a seal is going to be pretty much the same, and the standards for rating such seals and for airtightness testing describe what to expect in general. But while the pressure on both sides of a seal may be roughly equal, there may be considerable differences in the partial pressure of water vapour (serveral hundred Pascals). In many ways the gases in the atmosphere behave independently, but do they here? Will water vapour pass through a seal according to its partial pressure difference or just as part of the total pressure difference?

PS The Langdon book is excellent! I don't think it answers this question, though.

[David Olivier]

Feist gave up because the cost in mass production would clearly be high. He wanted to give correct signals to others re. what to invest in.

D

[Anonymous]

Thanks Mark, thanks David. That information clarifies things a bit. I guess it's the old problem about the publication of negative results that makes it difficult to find details!

[Robert Rickey]

This is something I'm interested in, too. Back in New Hampshire, my wife made insulated roman shades for our draughty windows. These feature a sheet of aluminised mylar and some polyester insulation (think multi-foil), with strips of magnets along the edge to snap them to the architrave. They helped, but I didn't know how to measure the success. Second idea is the supply air window, which works with a flow of air (rather than trying to eliminate it). Secondary double glazing plus stack ventilation. Less of a moisture problem, and when the sun is shining you get negative u-values, but the overall case has not been proved as far as I know. Anyone with info?

[Anonymous]

I think the notion of supply-air windows is enticing, as is dynamic insulation (or is that active insulation, I can never remember?). But I've never seen a convincing explanation of how flow is controlled when the wind varies, nor of how the heat is recovered from the air that is expelled somewhere else. Then again, I've no experience of the technique! There are a lot of ideas that work well in some circumstances but are questionable at Passivhaus levels.

With regard to draughty windows, I think the standard advice is to cure the draughts before adding the shutters/blinds. But oddly, I had a suggestion today from somebody I respect to make a hole in the wall behind an internal shutter, to let the water vapour escape outside instead of condensing. Which still seems to make a lot of sense a few hours later.

[Anonymous]

Sorry, Chris, I should have been more explicit. The idea was to make a hole in the wall that is normally filled by a plug of insulation. The plug to be removed when the shutter is in place, ideally being displaced automatically by the act of closing the shutter.

[Mark Siddall]

Dave,
Was thinking – have you considered the pane temp of the glass resulting from the insulated shutter? One concern would be that the internal glass temp could rise to a point whereby thermal stress causes the glazing to crack, esp with triple glazed low-e. This kind of thing is known to happen when low-e is on mid pane – my concern is that you could induce the same result by using internal insulated shutters. My suspicion is that this fracture damage to the glazing may be more likely to happen in the mid morning when the occupant has not opened the shutters. Any thoughts?

Mark

[Anonymous]

No, I haven't considered that Mark. I think experiment would be the simplest way to determine if there is a problem and if so, it would be another factor tending towards use of external shutters (or no shutters!). I am planning to have a reflective foil surface on the outside face of the shutter, which should help to reduce heat buildup if the sun shines. Opening the shutter on time is another way to avoid problems, of course!

[Mark Siddall]

Dave,
Placing a foil on the outer face of the internal shutter could make the problem worse (more energy bounces back towards the glass).

Mark

[Anonymous]

I don't think so, Mark. The reflected photons still have the same frequency that enabled them to pass through the glass on the way in,so they can go out too. The ones that cause heating are those that are absorbed and re-emitted at lower frequencies/energies at which the glass is opaque and/or are emitted in other directions. Or at least, that's what I suppose.

But experiment is the best way to determine the facts. It's beginning to be cold enough to do some now.

[Anonymous]

A long time ago in a topic far far away I wrote:

Normally the pressure on both sides of a seal is going to be pretty much the same, and the standards for rating such seals and for airtightness testing describe what to expect in general. But while the pressure on both sides of a seal may be roughly equal, there may be considerable differences in the partial pressure of water vapour (serveral hundred Pascals). In many ways the gases in the atmosphere behave independently, but do they here? Will water vapour pass through a seal according to its partial pressure difference or just as part of the total pressure difference?

I recently came across a new paper that addresses this subject. It's “Revised Model for Molecular Diffusion and Advection” by Corey et al in Vadose Zone Journal 9:85-94 (2010) http://vzj.scijournals.org/cgi/content/abstract/9/1/85

The one sentence summary as I understand it is that the answer to my question is not either/or, it's both at the same time.

[Author]

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