A friend from the climate change trenches, wrote me about his experience with window reflectors and summer cooling after reading Old Solar: Venetian Vernacular. He adapted the idea of car windshield reflectors to some of his sunniest windows using foamboard, cardboard, and aluminized mylar.
During typical sustained heat waves, when our building retains a lot of heat in its brick mass, my unit can measure as much as ten degrees Farenheit lower than the thermometer reads outside my north window in full shade. We're talking high nineties or above outside.
The original Venetian blinds were installed outside the window to prevent the sun from getting inside the house in the first place but this is still a very good idea because
A South-Facing Window Is Already a Solar Collector
We need to learn how to use it.
...everyone has seen car dashboard and rear window reflectors -- sold in auto accessory shops and depts... lots of us have taped up clear plastic sheeting over drafty windows to conserve heat and money, and kits are sold for this as well. But no one seems to be making a profit (is it possible?) selling good window sun blocks for homes... lots of people use blinds or shades or drapes but many are not that effective, and to some degree they warm up as well... Over the years I've evolved a set of silvered mylar foamboard sheets etc to reflect back the solar gain...
I have south, west and north facing windows and a large skylight in a third top floor condo of a late 1890's brick row house. Solar heat gain is intense from the skylight and northernmost west window especially (a tree blocks the southern west section of that wall).
My wife, cat and I get by without A/C and with a portable window fan and table top fan; but mainly I do some very thorough window and skylight blocking primarily with large sheets of white quarter-inch foam board many of which, but not all, are covered with silvered mylar sheets with an adhesive backing (it comes in rolls about 18" across).
I also use white sheets of oaktag, shirt cardboard, and preferably (but uncommon) white corrugated cardboard from old moving boxes.
At night I remove sunblocks to most windows top and bottom to allow ventilation, and open the skylight some to do some "chimney" venting, use the fans to pull in or exhaust air going with the prevailing breezes of the night, and on the worst days and nights use frequent brief showers for augmented evaporative self-cooling! [During the colder months we keep this place at 60-62 F for the vast majority of the time, so we reacclimate physiologically across the seasons, which makes each season more tolerable, and A/C and too much indoor heat a bother when we visit others or venture into typical HVAC'd venues.]
He also reports that a mutual friend, a solar installer, suggests, that at least in New England, you may be able to be comfortable with a good dehumidifier rather than an air conditioner.
You can get a tax break for installing energy conserving window films too.
I beat the heat with a couple of fans and a total lack of modesty.
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