Super Solar Collector

An interesting thing happened on the way to insulating the windows. On Friday we put the housewrap around the tiny cottage, turning it from a pink house to slate grey. Yesterday and today we had planned to work on sealing the housewrap around the windows and putting up outer plastic. We haven’t gotten to do this work yet because of farm chores that needed doing and the cold wind making it less than pleasant to work outdoors, especially standing up on a ladder.

What is interest in that since adding the house wrap the windows of the tiny cottage have not had any ice crystals on the inner surface for two days despite very cold night time temperatures. Not only was there no ice but there was barely any condensation and then only on the east and west windows near the bottom. The inside of the glass was warm. The dew point had moved outside the glass so that water vapor within the cottage didn’t condense on its inner surface. Just the single layer of housewrap, open at the bottom, was enough to create a buffer zone that warmed the window glass. On top of that the house temperature went up a bit despite light not being able to get in through the windows as easily. That I really had not expected at all.

I’ve figured out what happened. The housewrap is a dark grey which absorbs solar energy quite nicely. The outer surface feels cool but behind it feels warm. By wrapping the housewrap around the tiny cottage we created a huge solar collector. It is sealed at the top trapping the rising warm air even though it is open at the bottom. The wrap is actually billowing out from the house under a little pressure to to the warmed air between it and the house. This creates an air gap all around the house further insulating the walls and windows.

One other thing to notice is the icicles along the side. These formed during the cold of the last two days. Icicles are often a sign of heat loss through the roof and thus inadequate insulation. These icicles aren’t particularly large but they are more than we had before. The rising heat under the typar solar collector is leaking up under the cap warming the roof which is melting a small amount of the snow on top causing it to drip down and refreeze at the eves as icicles. Better insulation on the roof would be good but it isn’t in the cards for this winter. All that is there right now is the cap of Reflectix.

I had expected some improvement due to the house wrap keeping the wind off the insulation but I had not foreseen this much effect. It gives me all sorts of ideas for making inexpensive solar collectors. It will be interesting to see what happens after we replace the typar over the windows with the clear plastic shrink film. Will it perform as well as the typar? Will it be better due to the increased solar gain within the cottage? Questions, questions, questions…

In other news, today I plowed up a snowboarding jump in the south field. It is a start.

Outdoors: 9°F/-10°F 2″ Snow, Windy
Farm House: 64°F/45°F nine logs
Tiny Cottage: 50°F/44°F Cleanup & prep

About Walter Jeffries

Tinker, Tailor...
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3 Responses to Super Solar Collector

  1. Urban Agrarian says:

    I love following the progress of the new house. From looking at the temperatures, I’m impressed with how cold it isn’t inside. I’ve always wondered if it would be possible to design a house in a cold climate that could be left alone and not have the pipes freeze if the heat went out, or even just forget about heating it when you were away. I don’t think I’ve seen the temperature in your new house dip below 32 degrees yet when closed up. Has it?
    Also you got me thinking. I thought lots of snow on a roof is a good insulator, but if the roof is black would it be better to leave the snow on or brush it off? I guess it might depend on how well the roof is insulated, but I don’t really know. Any thoughts??

  2. LJB says:

    There are some passive solar air heaters that sound similar to what you’ve created accidentally, where the dark surface heat the air that moves by convection, or something like that. I’m not savvy on the details but maybe you are, or could read up on it?

  3. pablo says:

    I wonder what kind of condensation you’ll have when the five of your (and uncounted hordes of dogs?) are living in there. The good thing is, however, that you will give us a full account.

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