It seems like windows are the weakest link in an efficient house. So we spend large dollars to get efficient windows and try to balance u value with shgc. Just thinking out loud here. Why don't we just go with inexpensive, high shgc windows, and use insulated shutters to keep the heat in when the sun sets? That way you get maximum effiency during day time and at night, at minimum cost. How difficult would it be to build r30 shutters? I do some rough carpentry and it doesn't seem to me like it would be that difficult Or is this crazy talk?

Which side of the windows would you place the insulated shutters. I know it would be more convenient to place the shutters inside, but will frost form on the glass if the shutters are air tight? Maybe you should ask Dana1.

Posted By Alton on 01 Nov 2018 02:17 AM
Which side of the windows would you place the insulated shutters. I know it would be more convenient to place the shutters inside, but will frost form on the glass if the shutters are air tight? Maybe you should ask Dana1.

I was thinking on the inside to keep the shutters out of the elements and make them operable from within the house but you make a good point. I hope Dana and others chime in. Thanks for posting

I tried Styrofoam insulation from inside the home. Moisture in the air from the home frosted on the glass and melted when I removed the insulation and then ran down to the window sill. Obviously, my scheme was not airtight. I may be wrong, but I think the most effective location for the shutters would be outside, just like with storm shutters. That location should keep the glass warmer to avoid frost, provided the shutters are reasonably airtight.

Insulated shutters the inside of a double pane essentially turns the it into a solar thermal collector that stagnates. This will raise the temperature of the insulated glass considerably when in direct summer sun, all too often resulting in blowing the seal on the insulated glass unit (IGU).

Shutters on the exterior keeps the temperature of the IGU close to the indoor temperature, protecting it from high-temperature abuse.

An R30 would be a very thick shutte. Even if using (extremely expensive) aerogel insulation it would be more than 3" thick. R10 shutters can be about 2" thick or a bit less using polyurethane or polyisocyanurate as the insulating core. A code-min window is about R3, so even an R10 shutter would be a substantial improvement in performance. With the additional air-films in the cavity between the shutter and window it ends up at about R14 (U0.07) when the shutters are closed, about an 80% reduction in heat transfer compared to a code-min window.

Double low-E double-panes with a pyrolitic hard coat on surface #4 (the surface in contact with the interior air) and another low-E coating on surface #2 (the interior surface of the exterior pane) come in at about R5 at center glass in an argon-filled IGU. That's about the same performance as a typical triple-pane (though there are some triples that are much higher performance). Depending on the coating type on surface #2 it can be either high SHGC (0.5 or even a hair better), or low SHGC (less than 0.2). With properly designed overhangs to kill direct gains in summer for the south facing glass, putting the high SHGC windows on both the north and south sides, and low-SHGC windows on the east and west sides works pretty well for most houses. In US climate zone 7 or even the cold half of zone 6 the lower temperature of surface #4 in winter (remember, it's reflecting room heat back, not absorbing it and warming up) can lead to surface condensation. Liquid water is VERY emissive, so when there is condensation on surface #4 performance drops to that of a code-min window until it dries out, making it a lousy choice for very-cold climates. But in zones 5 & lower it's a pretty good bang/buck compared to triple-panes.

Several glass vendors make double low-E double panes. I believe both Andersen and Pella use Cardinal glass double-low-E IGUs in both low and high SHGC versions.

I have insulated shutters on the exterior of my workshop covering three 24x36 dual pane double hung low e argon vinyl windows. The difference in comfort and heat load is dramatic at mid January temps (-30c and colder) and darn nice at mid-November tropical temps (-7c highs and -15c lows).
They were relatively easy to build and consist of two layers of glued 2" EPS foam (4" total) in a frame made of 3/8 plywood, the foam is left bare on the side that faces the window, so plywood on 5 sides. They are painted painted white on the exterior but will in the future have faux mullions painted on them to give the appearance of a window from a distance.
They rest on a pair of lower mounts that protrudes from under the window frame about 6 inches (4 1/2" for the shutter plus depth of the vinyl window frame plus enough to to get past the siding), during the summer these mounts serve to hold the window flower boxes. There are two more mounts at the top. These shutters are "pulled" tight against the windows with shims. The upper mounts look like crap and need to be rethought but are effective.
I'm very happy with the shutters BUT they are installed Nov 1 and stay there till April 1st most years.
I am trying to come up with an easier to install and remove, preferably slide, insulated shutter for the house. I'm thinking of reducing the foam to 2" (R8)...this would still be a huge improvement over windows and much easier to move.
I can post a picture is you like.

Thanks for the info Dana.

Wow kenora, you did what I was thinking except I thought of making it even thicker.
I would LOVE to see a picture

I was browsing some Dept of Energy house plans from 1982 and found one that included shutters which were 1" polyiso? surrounded with wood for r-value of 7.

I wont be content with R7 though. so I will be looking to design a shutter that can achieve r15 at least.

https://www.builditsolar.com/Projects/SolarHomes/91HomesBook/South/S03WythevilleVA.pdf

You can get the use of simple window.

Remember with shutters they would need to be operable from both sides in case of an emergency such as a fire. This is required by code for bedroom windows.

Okay, average R-value of a decent window will be around R-5.
A simple wood shutter, closed over it, will bump the R-value 2-3 points.
Insulated shutters will (like blackout cellular shades) net you about 4-6 points.
Not sure going nuts on shutters or windows to net an R15 is a worthwhile objective unless you're looking at especially heavy glazing (high "glass-to-wall-area" ratio).

When it comes down to a choice between "okay" wall assembly and "great" windows or "great" wall assembly and "okay" windows, you generally see better performance out of "great" wall assembly and "okay" windows.

Posted By TWhite on 21 Dec 2018 02:37 PM
Remember with shutters they would need to be operable from both sides in case of an emergency such as a fire. This is required by code for bedroom windows.

great info. thanks! I did not know that and that is important for safety and code compliance. thanks.

Posted By Dilettante on 22 Dec 2018 03:30 AM
Okay, average R-value of a decent window will be around R-5.
A simple wood shutter, closed over it, will bump the R-value 2-3 points.
Insulated shutters will (like blackout cellular shades) net you about 4-6 points.
Not sure going nuts on shutters or windows to net an R15 is a worthwhile objective unless you're looking at especially heavy glazing (high "glass-to-wall-area" ratio).

When it comes down to a choice between "okay" wall assembly and "great" windows or "great" wall assembly and "okay" windows, you generally see better performance out of "great" wall assembly and "okay" windows.

that's the thing though is to get r15 covering a window should not be that difficult. are cellular shades really r4 to r6?

Think about what it takes to get R15.
3 inches of XPS (which gradually degrades)
3.5 inches of EPS

I honestly think you're overthinking this.
Just build your wall assembly right.
Use decent windows and you really shouldn't have to worry much about losses to glazing.

I was thinking something like this

https://www.youtube.com/watch?v=mvwywKd5FLs

but you are right. 3.5" depth is quite a lot

Something like that looks good up front.
However. You're cutting off air circulation around the window. So you can get condensation in the air that DOES reach the window surface.
So be careful with something like this.

Most of you won't experience the cold temps we get around here..consequently the rather extreme measures I've taken are probably more than needed (for you)... however it gets cold for a long time here (climate zone 7) and heating costs are very high so it was well worth the effort to build the insulated doors i/f/o the insulated overhead doors and the removable insulated shutters for the three windows. I have since finished the barn style doors (and improved the hanging system for the insulated shutters). Here is an early picture when the work was in progress. I am now able to keep the shop at 70f with a pellet stove running on low (output 8500 btus/hr) at -30c. I KNOW my next project and priority is to insulate around the slab edge..the shop is currently losing most of the heat through the slab edge.... I have the EPS for that...just gotta do it :) this picture was taken couple years ago

yup...tyvek is considered a siding material out here in the hinterland :) edit... hummmmmm no picture!

Kenora, I would love to see a pic. if you want to email it to me I can post it on imgur for you.