Calculating Solar Gain from Skylights


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Old 02-27-11, 09:16 AM
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Calculating Solar Gain from Skylights

I'm trying to decide whether its worth installing a couple of skylights in our greatroom. I'd like to try and estimate if I can expect some solar heat gain.

Are there any online resources I might use? What kinds of data would I need to know up front?

If it helps, the greatroom has vaulted ceilings and they'd be facing south.
 
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Old 02-27-11, 10:56 AM
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Hi doc, I think some of the more advanced energy programs can add in for solar gain, but I don't have a simple equation. Unfortunately, skylights are noted for being more of a loss than a gain so yes there will be some solar gain, but the energy escaping will be larger. IMO, the benefits of a skylight have to be the daylight as opposed to energy.

If you decide to go ahead, be sure to specify a glass that will allow the light in. I'm in north country and trying to find a high efficiency window with a high solar heat gain coefficient (SHGC) is difficult. I haven't looked at this in awhile, but there are also low-e coatings on the inside glass or outside glass. Down south they want it on the inside of the outside pane of glass and up north we want it on the inside of the inside pane of glass. Try asking your sales person that question.

There are some window pros here, so let's see if they jump in.

Bud
 
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Old 02-27-11, 12:11 PM
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All I can say is.... go with VELUX (I hear Andersons aren't bad either). VELUX basically invented skylights as we now know them. No plastic, acrylic or off brands. If its just for natural daylight in a room, the sun tunnel type can be a good option.

VELUX has tons of options for blinds and shades (for their OE stuff) if you need to be able to darken the room. They even have solar shades that go outside.

I replaced the existing double paned acrylic dome types with VELUX FCCMs with LoE and a grey tint. Those rooms were hot and since the old domes had yellowed, the light was junk. Now I get more heat gain and loss from the framed tunnels themselves than I do from the skylights. Different region and construction of course. Eventually I need to get up there and re-insulate the tunnels.

Skylights (like doors and windows) are nowhere near as efficient as a solid wall...but in some case are worth it. I'd think twice about having them in a bedroom or living area if you ever need it quiet or dark. Mine are in the guest bath and laundry and are great.
 
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Old 02-27-11, 12:35 PM
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Hey, Bud and Gunguy -

I was hoping this was a question with a simple answer - silly me....

I understand what both of you are saying. I had already figured I'd need lo-e and shades, maybe even vented with electric controls.

We basically live in the greatroom, so adding light would be nice so as to cut down on electricity. Not a big fan of the idea of heat loss since we already lose heat at the floor level because of the vaulted ceiling. Huhm....

I'll do more research. Hell, I have lots of time - I haven't even mentioned this to my wife! That'll take years.....

If anyone else has info and/or opinions, I'd love to hear them.
 
 

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