Solar chimney? What is it? and some really important steps to insulating a foundation

We are using a passive solar cooling technique in this home that is referred to as a solar chimney. A solar chimney is a little hard to explain but I will do my best. To fully understand how a solar chimney works you need to know a little bit about building science and the term commonly referred to as the " stack effect". The stack effect is what happens within a home when warm air is allowed to escape from your roof or through your attic. Something we try hard to stop in most homes by air sealing the attic space. The pressure created from the stack effect causes air to be drawn in from other places in your home, commonly your basement or a leaky envelope and windows within the home. Not something you want to do on a normal basis. The higher the point in which the air escapes the higher the pressure gets.

   This home uses the stack effect to our advantage. We are building a box located on the roof of the home. This box will not only contain the wood stove pipe but a whole house fan system as well. This box ( chimney) will be uninsulated and covered with a dark siding material. The heat created within the chimney will want to rise and escape from the vent pipes located on top. When the insulated (R-38) doors to the whole house fan system are opened, this will create negative pressure within house. In this home we are able to control where the air entering the home is able to come from. We have placed windows low to the ground on the north side of the house that need to be opened to allow the chimney to work. This will draw cooler air in from the north, fully shaded side of the house. If the system does not provide enough natural ventilation the whole house fan can be turned on to really move the air through the house. While not enough research has been done on solar chimneys to fully calculate how much cooling effect this will have on the house. It will be interesting to see how well it works next summer. What I did feel was the effect it will have on the building when constructing it. The last piece of the chimney was the top and when I was placing it I had to hold it down and could feel the air trying to escape, it wasn't even a warm day.

Foundation insulation, important steps!



  Foundations in most homes have little or no insulation at all and it has a negative effect on the whole house. Most basements here in the northeast contain the mechanical systems of our homes.( heating, domestic hot water and cooling) When these spaces are not conditioned we loose a percentage of our energy to this location. Conditioning this space for most homes means running a de-humidifier to control the moisture and consuming a large amount of electricity in the process. In this home we are using a better approach that includes insulating the foundation on the exterior from the footing all the way up to the sill of the home. We are using a product called Geofoam that is made of high density EPS, 2" thick with an R-11 insulation value. While building codes here in MA require you to insulate your foundation most builders stop this insulation at ground level, leaving a large hole in the homes thermal envelope. It does create additional work ( insulation, stucco and flashing) to do this but the result is a much better home in the end.

The other area of the foundation that needs attention in the basement floor or slab.

In this home we also insulated under the entire floor of the slab and up the side of it as well. This is commonly referred to as a thermal break, we have stopped or slowed the movement of thermal energy from moving through the basement floor. Along with this we place a 6-Mil vapor barrier under the concrete to stop the movement of water through the slab also. This eliminates the need for an energy hogging de-humdifier.

      When attempting to reach the standards for passive solar homes, all energy uses need to be considered. From the top to the bottom, no details is to small to overlook and in the case of the foundation,

it is no small detail.

 To finish off the foundation insulation, we simple cover it with a stucco and flash to top of it. Once again a little more work but in my opinion well worth the efforts.

Stay tuned

Tom Pittsley

tom.pittsley@nextsteplivinginc.com

Solar windows are really heating up

I did a little video of the windows in action over the coarse of a day. It was pretty impressive to see just how well they work. They video gives a better explanation of how the windows work as a system to not only capture and store the suns energy, but also how to control it as well.




I can't wait to see how well they work once the doors are installed.

Some other things that have been going on on the site is the interior framing, that was completed earlier this week. Along with installing the vapor barrier and insulation under the basement floor. Yes we not only insulate the exterior of the foundation but we also insulated under the basement floor and up along the sides of the concrete, eliminating a thermal break in the envelope of the building. Combining a highly insulated thermal envelope with air tight construction is what make a passive solar how possible. The higher the insulation level the lower the energy costs needed to control your indoor environment.

  This coming week we will be installing the solar chimney. What is a solar chimney? Stay tuned and find out.

Tom Pittsley
tom.pittsley@nextsteplivinginc.com

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