Being green by only paying to heat a room once

[williaty]

This is a big read, but hopefully you guys will slog through it until the pictures show up :lol:

As we’ve slowly been trying to improve the energy loss out of this house, one of the things we’ve had to tackle is the 300 square feet of glass on the end of our Great Room. The lower 3 panels are actually a sliding door and glazed with low-end double-pane glass without any coatings for an assembly value of about R2. Sadly, the upper two windows are single pane uncoated glass for an assembly of about R1! Our first winter here, once outside temps dropped into the 50s, the Great Room became basically unusable because it was so cold. There’s two reasons for this. First, the room as running 1-2 degrees colder than the rest of the house due to heat loss out the glass. More important is something called mean radiant temperature. MRT has a HUGE impact on how comfortable you are!

So you guys probably learned in high school that heat moves in 3 ways: Conduction (stuff touching each other), Convection (thing heats up air, air moves to other object, warms other object up), and Radiation (stuff emits infrared photons). Radiation is the thing that doesn’t get enough attention. Your body can’t sense temperature. What it senses is how rapidly heat energy is moving in our out of your skin. When heat is moving into you, you perceive higher temperatures. When heat is moving out of you, you perceive lower temperatures. How fast the heat is moving is how you actually judge what temperature you think something is. This is why a book at 70F will feel warmer than a block of metal at 70F: They’re both colder than you, so you perceive heat flow out of you and into them but the heat moves MUCH faster into the metal, so you mistakenly perceive it as colder. While that example uses conduction, it sets us up to talk about mean radiant temperature. You emit infrared photons at whatever temperature your skin happens to be. These exiting photons represent a loss of heat. However, everything in your environment is also emitting infrared photons and some those hit you and you absorb them (which represents heat moving into you). When the stuff around you is about the same temperature as you, the photons you emit are balanced but the photons you absorb, so you don’t lose or gain any heat this way. The Mean Radiant Temperature is a measure of what temperature your surroundings feel like to you in terms of radiant energy. When the things around you are colder than you, the MRT is low and you lose significant heat energy by radiating it off towards your environment without getting an equal amount back from them.

There’s some practical implications to this. First, this is how those space/survival blankets work: shiny metal surfaces reflect infrared photons, rather than absorbing them, so your environment turns out to be reflections of you. So you get most of your emitted photons back because they bounce off the blanket and smack back into you. This is also why you can hang one of these blankets behind you while you sit in front of a fire and the infrared photons will come out of the fire, bounce off the blanket, and run into you, warming you. It’s like having a fire on multiple sides of you. Second, if you have a lot of uncoated glass that just transmits IR photons beside you in a room, that whole glazed area feels like it’s the same temperature as outside. So sitting in our Great Room, one whole end of the house felt like it was 50F outside, or -20F, depending on the day. Very uncomfortable.

Step one in fixing this room was to take the glass we could get to easily and make opaque insulating shutters for it. Basically, we leave the glass uncovered in the day so the sun comes in and then put the shutters in the windows (from the inside) at sunset. The shutters are made from sheets of Owens Corning Super TUFF-R. This is a polyisocyanurate insulation board with a reflective metal foil on one side. Dow Thermax would be better if you can get it because it’s safer. The important thing about this product is that it’s light, rigid, and has thermal properties we like. They’re easy to handle even though each shutter is almost 4x8 feet. If you drop one or one falls over, nothing gets hurt. They also move that part of the wall from R2 to R10, which is a BIG savings in energy! More importantly, we place them with the shiny metal side facing in to the room. What this means is that the shutters reflect the IR photons from the rest of the house, and us, back into the room, raising the MRT massively. Instead of feeling like the entire end of the room is at whatever the outside temperature is, it feels like it’s about 70F, since that’s what’s being reflected back. Suddenly, the room was comfortable, even in winter. Interior skin temperature improved dramatically. With the bare glass, the inside skin of the glass was about 40F when the outside temp was 20F. With the shutters in place, the interior skin of the shutter is at about 67-68F when the outside temp is 20F.

Step two in fixing the room was to do something about the single-pane glass windows up near the ceiling. The problem is that they’re 18 feet off the ground so we can’t put shutters in them and take them back out each day. However, at 150 square feet, we can’t really just ignore them either. We needed something we could put up there and just leave through the whole winter. For this, we decided to use the corrugated polycarbonate panels often used to build small greenhouses. The specific product we went with is Lexan Thermoclear triple-wall 19mm thick panels. The panels are a little better than R3.5, so combining that with the existing single-pane glass plus the air-gap between them ought to produce around an R5.5 assembly. In other words these should stop 80% of the heat that was previously falling out the crappy windows. Our plan was to make panels what would just fit within the jamb of the window and press forwards against the wood frame of the glazing in order to provide an air seal. The picture below shows most of the relevant details. The Thermoclear is divided up into cells with two cells being between the inside and outside world. We used polyethlyne tape to seal the ends of the cells and then normal weatherstripping to provide an air seal against the frame of the glazing.


Same stuff, just a little more context:


This is an inside view. You can see how they do distort the outside world enough you can’t really use it as a picture window anymore, but that’s a decent tradoff for what we’re getting. They still let light and solar heat into the house all day but slow the rate of heat loss at night. You can see we secured the shutter by pressing it into the window using cleats I made from PVC that are screwed into the window jamb. The vertical stripe about 2/3rds of the way to the left is the seam we made because we had to join two panels due to the width of our windows.


From outside, you can see that stuff near the shutters is somewhat visible, but you can’t make out any of the outside loft just a few feet into the room.



There’s one final benefit: these are impact rated and effectively air and water proof. So if the glass is every broken (say during a hailstorm), I can unscrew these from the inside, screw them to the outside, run a bead of caulk around the edges, and I’ll be able to wait out however long it takes to order custom windows in this stupid size without having water leaks, air leaks, having to use tarps, etc.

 

[lml999]

Very interesting approach, thanks!

 

[woodgeek]

All seems pretty reasonable....two questions:

1) Have you had condensation problems between the lexan material and the single glazing? I would guess that the glazing would need to be alittle leakier than the seals around the lexan....or you would get some. If the frames are Aluminum, I suppose you are still aok, though.

2) What fraction of winter days do you really take down the polyiso in the morning and put it up in the evening....how long does it take to do both? When you are away....do you leave it in or take it out? Have you thought about taping the edges of the foam sheets with Aluminum tape to make for fewer foam crumbs and reduce the fire hazard? Any concerns about fire safety/spread or impact to insurability? I would think the foil side would be less ignitable than the plastic side...prob another good reason to have it face inward.

 

[Circus]

Ruins your view. Polycarbonate is good stuff, it's in my collectors, but I wouldn't build storm windows out of it. What's wrong with plexiglass?
Note: Polycarbonate has an inside and outside. The outside has a UV coating that protects the polycarbonate from the sun.

 

[williaty]

1) Have you had condensation problems between the lexan material and the single glazing? I would guess that the glazing would need to be alittle leakier than the seals around the lexan....or you would get some. If the frames are Aluminum, I suppose you are still aok, though.

Single glazing, wood frame, pretty good air seal. Yes, we get a little fog. This was something we watched closely this year to see what it did. Most of the time, we get no visible condensation whatsoever. On cold nights (below 10F) we get a light fog that doesn't even bead up into visible droplets (it just looks like frosted glass). On VERY cold nights (below -5F), we get visible droplets but they've never gotten big enough to run down the glazing. I'm fairly sure this is minimal enough never to cause water damage to do the wood frames but we intend to take the panels out through the warmer 6 months of the year in order to let everything dry out just in case. I'll be measuring the wood frame with my moisture meter right after I take panels down but I don't expect any problems

2) What fraction of winter days do you really take down the polyiso in the morning and put it up in the evening....how long does it take to do both?

The polyiso in the lower windows comes in and out every day. On sunny days, we want to let the sun in. On heavily cloudy days, we need to let the condensation dry out. Because the polyiso panels can't be sealed to the windows as well as the polycarb in the upper windows, we do get condensation with them.

It takes about 15 seconds to get all three polyiso panels out and about 35 seconds to put all 3 pack in.

When you are away....do you leave it in or take it out?

We haven't taken a vacation since we bought the place. I think we'd have to leave the polyiso in the lower windows out with the blinds down if we were going to go on a vacation.

Have you thought about taping the edges of the foam sheets with Aluminum tape to make for fewer foam crumbs and reduce the fire hazard?

Taping the edges with the aluminum makes the edges of the panel really stiff and that causes problems pushing them into place. I switched to the red polycrylic tape used to seal housewrap to itself and it is a good balance between providing structural support to the edge of the panel and still letting it squish a tiny bit to fit into the opening.

Any concerns about fire safety/spread or impact to insurability? I would think the foil side would be less ignitable than the plastic side...prob another good reason to have it face inward.

Yes, I definitely have concerns about fire. Then again, what can you use for a window covering that isn't more flammable than glass? Curtains and blinds go up like tissue paper as well. Not to mention we're living in a house made of plywood that's at about 8-9% moisture content bonded to 5.5 inches of styrofoam. We're only going to have seconds to get out regardless. DOW Thermax is rated for use without an ignition barrier by code, so that's the polyiso to use for code compliance.

 

[williaty]

Ruins your view.

Gee, I never would have noticed that what with talking about that issue in the first post and all.

Polycarbonate is good stuff, it's in my collectors, but I wouldn't build storm windows out of it.

These aren't storm windows.

What's wrong with plexiglass?

1) Low maximum working temp. Low enough to realistically be a problem in this application
2) Absorbs water through its edges which is a problem in this application
3) Considerably easier to break
4) Not available in multiwall configurations which are required for this application

Note: Polycarbonate has an inside and outside. The outside has a UV coating that protects the polycarbonate from the sun.

Cheap polycarb has an inside and an outside. The Lexan Thermoclear-branded multiwall panels we're using are coated on both sides and rated for 15 years direct exposure to UV. These only see direct sun for less than half the day and are behind a sheet of glass which will block at least some UV so I expect I'll drop one and ruin it long before it yellows from UV.

 

[Dobish]

i use small bubble wrap sheets, and a spray bottle for water. makes a huge difference and says up all winter.... no adhesives needed, just surface tension!

 

[jaybarr]

Interesting, would have to try it out

 

[semipro]

i use small bubble wrap sheets, and a spray bottle for water. makes a huge difference and says up all winter.... no adhesives needed, just surface tension!

I've been collecting bubble wrap. I think I'll try this this winter.