In Window Solar Heater: 6 Year Update

Update to the in-window air heater/insulator that I built in the winter of 2015.

This device is installed in a spare bedroom in the house that's used for packing and shipping orders for the business. It faces southwest and gets about 4-5 hours of decent sunlight in the afternoon. However, that means for 19-20 hours per day, it's shaded or dark. Being a single pane of glass, that's a significant heat loss, due to the R1 rating of that window.

This heat panel serves to capture incoming solar heat by moving room air through the panel and blowing that out into the room. That's controlled by a small solar panel outside that turns a relay on and off to control the 2 fans. This double wall polycarbonate panel along with the 2 air gaps between it and the window add up to around an R4 insulating value.

In effect, this device functions like a thermal diode. It passes heat from outside into the room quite readily while slowing heat loss to the outside. On cold winter days, you can feel a cold draft coming down off the uninsulated glass side while the insulated side is at room temperature with no draft. The window sill under the glass side will usually be about half way between the room and outside temperature.

I leave this "heater" in the window year round and simply switch the fans off in the summer months. The panel blocks a majority of the incoming heat due to the labyrinth shape of the air passages behind it. That limits any convective air flow and most of the heat radiates back out through the glass. It works as well as raising and lowering the shades in the room without having to do that. The panel also helps to block the view into my neighbor's bedroom window.

At some point, I'll likely have the old windows in the house replaced with double pane insulated versions. Right now, with running the business out of the house, it's inconvenient to shut down operations for a few days while a window crew works on that job. Also, hoping the local gas utility might come along with a rebate program for window replacement like they've done in the past with blown in wall and attic insulation.

To summarize, this "heater" doesn't capture any more heat than would have come though the window alone. It does, however, significantly reduce the heat loss to the outside compared to the single pane of glass. I've been quite happy with how it works and it's been in place every day since it was installed back in 2015:
https://youtu.be/sO-PAfpgFv8

More to come...
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Intro/Outro:
Louisiana Fairytale by Austin Rogers
https://web.archive.org/web/20170402222425/http://drfiddle.com/show_tune.php?id=94