Our Solar windows are in !

The new solar windows for the house went in last week, just in time for the Green building tour this weekend. It was a tough week to say the least with 4 out of the 5 previous days filled with rain, around 4 inches. On Tuesday morning we finished installing the last of the SIP's roof panels, by Wednesday noon the roof was papered in and weather tight. At the end of the day on Friday, 19 of 21 the solar windows have been installed.

On Saturday they finally got some sun and started to show their stuff, as the windows reached around 110F by 4 in the afternoon. We left one window with the shade down fully to see how much of a difference the exterior solar shades make. The results were pretty impressive as the window with the shade down only reached 70F. Saturday was not exactly a warm day with a morning low of around 40F and a daytime high of only 63F, a slight breeze blew through the house as the other windows have not yet been installed. I can't wait to see how well they work once the house is buttoned up. Here are some IR images of the window at 4PM one with the shades up the other with the shade down all day.  These solar windows are unlike anything you have ever seen. The windows contain 4 layers of glazing, two cavities filled with argon gas, a couple of lowE surfaces and a 1-1/4" layer of clear gel. The gel acts as a thermal mass, storing the thermal energy within the window itself. The combination of glazing gives the window a U-value of .2 nearly 50% better than an energy star rated window for insulation value. Here is were it really differs, these windows have a Solar heat gain coefficient of .72. This means that 72 % of the solar energy is transferred through the outer layers of glass. This energy is then captured right at the point of entry into your home, within the gel. These windows are very heavy, about 250lbs. per unit, (26-1/2"x77-1/2") Each window contains about 170lbs of mass, this means for each degree above room temperature these windows go you have stored 170 Btu's of thermal energy. Raise the temperature to 110F like we did last Saturday and the thermal energy stored is 6,800 Btu's per unit. We have 13 windows that contain thermal mass within the window, this means we stored 88,400 Btu's of thermal energy in the windows of the home, over the course of one day. That is about equal to one gallon of oil burnt in an 80% efficient boiler or about one thermal of gas.       So, that's great right? but what about cooling? Notice the shades in the photo above. These shades are integrated right into the window frame and retract up into itself. The final arrangement of the controls is still being worked out but here is how they are designed to work at this time. The windows all have home run wiring back to the control panel, custom built for this project. The windows are then broken into groups according to location within the house. These groups are then controlled by a thermostat placed within the each zone. If the zone gets to warm the thermostat will send a signal and shut the shades. The really cool part is the remote control that gives the homeowner total control of each individual shade. When these shades are left closed the SHGC drops to .14 making this a energy saving window on the cooling side as well. I will post some more pictures and videos of the windows in action over the next few weeks. Stay tuned Tom Pittsley tom.pittsley@nextsteplivinginc.com