From nick@vu-vlsi.ee.vill.eduTue Jan 23 15:06:04 1996 Date: 23 Jan 1996 11:26:04 -0500 From: Nick Pine To: london@sunsite.unc.edu Subject: Birdhouses and solar shelters Over the last couple of months, I've been watching a homeless person who has built himself a small homeless shelter under the 4' concrete overhang of a parking garage on Atlantic Avenue near Court Street in Brooklyn, next door to Saint Vincent's Family and Children's care center. A lot of homeless people in cities are mentally ill, and very suspicious, and not inclined to stay in city shelters, because city shelters are dangerous... Yesterday it was 32 F in Brooklyn and snowing. I wanted to take this man some hot food, but he didn't seem to be home when I stopped by. It's hard to tell when he's home... He lives in a sort of very small cave, like an animal. Will he get frostbite this week? Will he lose some fingers or toes? He and the center have something in common: they are both wasting solar energy. The center has a 60' tall x 40' wide south-facing plain brick wall, upon which the solar heat equivalent of approximately 24 gallons of oil fall every day in December. The south wall of this man's small shelter is a piece of plywood, 6' wide x 4' tall, with various blankets and quilts and sleeping bags stuffed around it to make a dark, concrete-walled cave under the parking garage. Now, there are lots of lean-to shelters on the Appalachian trail, some of them stocked with firewood, put there for the convenience of passing hikers, and we build birdhouses, don't we? Why not extend such charity to humans, and make some sort of urban shelters for people like this homeless man? Outdoor art, if you like, in urban parks... It seems to me that it wouldn't be difficult to put one $500 septic tank on top of another, with some foamboard on the outside, eg Dri-Vit, to make something like this human birdhouse: | 5' | | 12' | pffffffffff --- pppppppppppppppppppppppp p.........f p p p .f p p p .f 6' p p p .f p living space p p .f p p south p.........f --- p p p f.......f p..................... p p f. .f p . p p f. .f p rain . waste p p f.water.f 5' p water . water? p p f. .f p . p p f.......f p . p p fffffffff --- pppppppppppppppppppppppp Being in a city, this would have to be fairly bulletproof. Suppose p above is an 11' x 12' piece of easily-replaced polyethylene greenhouse film, with a few thin pieces of metal sewed into the edges to hold it tight against some magnets embedded in the south edges of the shelter. If the concrete tanks had walls that were 4" thick, the two tanks together would weigh about 4"/12" x (12'x16' + 5'x6'x2) x 150 lb/ft^3 x 2 = 25,200 pounds, with a thermal mass of approximately 0.16 x 25,200 = 4032 Btu/degree F. Filling the bottom tank with water would make the total thermal mass C = 4032 + 1500 gal x 8 lb/gal = 16,032 Btu/F. On an average December day where I live, about 1100 Btu/ft^2 falls on a south wall, so if the poly film has a solar transmission of 0.8, the amount of solar energy that gets into the structure would be about Ein = 11' x 12' x 0.8 = 116,000 Btu/day, And if the average outdoor temperature is 36 F and the average indoor temperature is T, and the poly film has an R-value of 0.8, then the amount of heat that leaves the structure in one day would be about Eout = 24 hours x (T-36) x 12' x 6'/R0.8 = 2,160 x (T-36). If the energy that enters the structure during an average day is equal to the energy that leaves the structure, ie Ein = Eout, then 2,160 x (T-36) = 116,200, so T = 36 + 116,200/2,160 = 86 F. That's a simplified calculation, but at least it seems there would be no danger of frostbite. How would the temperature change over a week without sun? Each day, the structure would lose Ed = 2,160 x (T-36) Btu, which would cool the thermal mass by Ed/C Btu, which would leave the thermal mass with a temperature of T - Ed/C: indoor heat temp Day temp (F) loss (Btu) loss (F) 1 86 108K 6.7 2 79.3 93K 5.8 3. 73.5 81K 5.0 4 68.4 70K 4.4 5 64.0 60K 3.8 6 60.2 52K 3.3 7 56.9 45K 2.8 Nick