After 12 years of living in our passive solar home we have finally built some insulating window shutters for the large south-facing windows that really work well at reducing heat loss in cold weather and preventing heat gain in hot, sunny weather. You can see them above in their closed position and below in their open position. The big windows are simple double-glazed units that have no reflective coatings or argon gas between glass layers to boost their insulating value, as the windows above them and on the east and west sides do. We chose them to maximize solar gain during cold, sunny, winter days. But this means lots of heat lost on winter nights and loads of added heat on sunny summer days. We also hung the shutters below the upper windows because the upper ones are open-able, allowing us to vent warm indoor air outward during the summer.
In previous years we had tried several variations of both thin, fabric-covered insulating panels that required twice-daily installation and removal and semi-clear twin-wall polycarbonate panels that were left in place continually during the winter. While both worked to some extent they either blocked the view during daytime or were difficult to take down and put up, especially on windy days. And both suffered from a fair amount of air leakage at the edges that compromised their insulating efficiency. We even tried interior insulating roll-up curtains and Venetian-style slatted metal shades but both have additional issues. The curtains have to seal very tightly at the edges or room humidity seeps around to the cold glass and condenses on the windows; when its cold enough it actually forms ice. The slatted blinds reflect a bit of radiant heat back inward overnight during winter nights and reflect some solar radiation back outward on sunny summer days, but they don’t do either very well.
After years of proposals and discussions about pros and cons we settled on permanently attached sliding panels with double layers of Reflectix insulation (a brand-name, dual layer, aluminized bubble-wrap). Now we simply slide them open or closed as needed. We still have to add the locking hardware that will hold them in place during extreme winds, but we will soon have a link to a detailed PDF on our website’s Strawbale home page that will show exactly how they were constructed and how they lock down(or you can link to the PDF here).
In other fall fix-ups, we finally have a defrostable windshield in the electric Porsche. Years ago we purchased a 600-watt heater coil to replace the original fluid-filled heater core in the car’s air ducts. Now it is wired to the fan switch on the dash. When the fan is switched on the blower sends air out the windshield vents and a 12-volt, 10-amp relay switches 144 volts from the propulsion battery to the heater coil, warming and drying the windshield to prevent cold-weather condensation. I had always worried that this would significantly reduce the car’s range, but its power draw is pretty low compared to the demands of the drive motor. And really, on days when we need to use it, the cold weather’s effect on the car’s range is a lot more significant than some minor accessory load. Batteries are just not as useful when the temperatures dip below freezing, so we will soon be retiring the Porsche for the winter, switching back to the 40 mpg (yearly average mileage, not just warm weather highway mileage!) 1996 Geo Metro as our weekly winter commuter.