Sunday, August 5, 2012

Well here is the newest, and final...FINAL* design

*pending approval of the design board, which they already indicated it was fine.  Will find out next week

Obviously this design looks a little bit different.  But there are reasons behind the design besides just to be different.  Anyone following the previous posts will know energy conservation is a big goal in the shell and design, but this one takes it to a level the previous versions never did, which I have always been uneasy about. 
This design takes major advantage of solar gains to offset winter heating demands.  On a sunny day, it is very possible the furnace may not run at all during the day in the middle of January. To generate heating offsets, several key things needed to be addressed.  This one hits on MOST of them. 

First off, a tight, highly insulated shell.  This house will be insulated in the mid r30s with a air tightness goal of less then 1 ac@ 50 pac.  It will be blower door tested several times during the build to make sure we are on target.  One at the completion of the exterior air barrier and shell, the other after drywall is installed. 
With a tight insulated shell, it will retain as much free heat as possible, and allow the heat to disperse throughout the house with reduced loss through the walls and roof, space to space.

The next item is proper glazing selection and sizing.  Solar rules of thumbs for tempered buildings are from 8-10% of glass to floor area ratio.  Above 10%, you need to start adding additional thermal storage to account for the extra glazing.  Otherwise the risk of overheating increases.  (Yes, you can overheat from the sun in the winter!)  This design sits right around 10%. 

Obviously the window and glass selection is very important.
The window selection will be Inline fiberglass windows, and most likely a dual pane, u .29 and SHGC of .55 for the south to maximize the solar intake.  They are mostly fixed windows, with small awning windows in the dining room and casement windows in the bedrooms.  The north windows will be triple pane, with a u of .22 and a SHGC of around .3 to retain as much heat.  The reason for dual on the south instead of triple is mainly due to the ability to have a higher SHGC number.  Plus they are cheaper, so doing the math they become a net gain positive window.  (they actually take in more heat then they lose).

The next item is properly design overhangs.  You want to keep them short enough to allow full sun during the winter, yet deep enough to block all of the summer sun so you do not increase cooling loads.  Besides the overhangs, window sizes, depths, head heights, etc all play into the design.  A previous post goes into more depth about sun angles and overhangs.

The final item is thermal mass and storage.  This design does not really include any thermal storage, thus its a solar tempered house, instead of a direct solar gain.  Direct gains can absorb the heat into the thermal mass and release it when the sun is not shining to help regulate the home thus reducing the heating requirement even more.  Thermal storage can be in forms of concrete floors, tile floors, added layers of gyp, stone walls, water, etc. 

With that easy explanation, here are some solar study images that shows the importance of overhangs and exactly how they work.

These images shows how sun will hit the south elevation at 9 am, 1 pm, and 4 pm on January 1 for our location.  You can see how, during this time frame, there is nearly full sun on the entire glass surface.

These images show the same times however in mid July.  You can see how the sun only hits just below the windows but full sun is kept off the glass to prevent overheating and adding cooling requirements in the summer. 

For window placement, the large windows beside the garage are in the dining room, which is open to the kitchen and living room.  The large fixed windows on the other side of the door is into the open stairway going into the basement.  This is also open to the foyer and living space.  With it open to the stair and the windows extending below grade slightly, it will also allow some additional light into the basement.
The 2 sets of casement windows on the far left are into 2 bedrooms.  (master is in the back with with west window).
For the clerestory windows, 2 of them are into the living room to allow some south glass and additional light into that space, and the window on the far left is into an inner bathroom which obviously does not have a window to supply some natural lighting to that space.

No comments:

Post a Comment