Sorry, I got interrupted halfway, and had to come back later...
Well, the roof is out of the question, since it's straw covered... Not going to work at all, as you can't mount anything too it, and sealing around the potential holes is insanely expensive... The space I have to work with is the door, period, the house is listed as a historical building, so I'm limited in what I can do...
I know it's not going to be enough to keep temps too high, I'm just hoping to keep it from freezing... While not exactly insulated per see, as the walls are naked stone, once heated, they stay that temp forever, so all I need to do is maintain enough warmth...
My thoughts are to build a solar air heater, by making a timber frame in place of the old door frame, placing a pane of thinwall polycarbonate glasing, (10 mm channels) and using black corrugated metal sheets behind that as the absorber, and a "door" behind it of insulation and planks...
My thoughts are to increase the efficiency of that solar airheater as much as possible without making it hugely expensive...
I already have a 10W PV panel scavenged from an RV, to run two 120mm computer fans from, which are supposed to have a combined airflow of 160 cfm at full speed, and the plan is to make an intake at the bottom where I can select outside air, or inside air... The SO says she won't accept the PV panel sitting on the wall "looking unsightly" so it has to sit inside the SAH, meaning I need airflow over it, and can't use a backpass construction...
I was thinking that if I used two sheets of corrugated metal, I could place them so that they meet at the highpoints, making standing channels between them... By then allowing air in at the bottom, up and over one sheet, and down between the two sheets, I'm hoping it's a efficent enough design to heat the air... Then either a flat sheet, or another corrugated one to direct the air up to the top and out again... The fans will go on the bottom, as pusher fans, to prolong lifetime...
How do you all think the idea with the "channels" works? Will it be to restrictive? I'm hoping that the sun will be able to at least partially heat the second sheet of metal...