Home Up
Hybrid Truck
Video
New Troop 51 web page
| |
Here is my attempt to show how a solar
home works. I am calculating only the heat gain due to the
sun. I am not taking into account heat losses or gains due to the
outside temperatures. My experience is based on building in
North East Tennessee (36 degrees North Latitude) where we have frequent cloudy winter days and
somewhat humid summers. The numbers would be far more dramatic in
areas of the country which receive more direct sunlight as in high desert
areas as in Colorado and New Mexico.
While facing directly south you have maximum solar gain, you still
receive 85% of the sun's energy 30 degrees off of due south.
Personally I prefer to orient the home about 15 degrees east of
south. While I loose about 5% of the sun's potential heat, this
brings in more morning light and heat, when you need it most, and it gives
additional summer evening shading.
One way to think of solar gain is every 2' of glass on the south side
will give as much heat in December as a 1500W heater running for an hour.
So a 5' by 4' window is the same as running a space heater 10 hours each
and every winter day. If you have 3 sqft of glass on an east/west
wall that is the same as running that same space heater for an hour every
June evening. So 20 sqft of glass is like running a space
heater for 7 hours in the summer time. That is just extra time your air
conditioning will have to work.
|
Window
Orientation |
Window
Area |
Summer
BTU's |
Winter
BTU's |
Standard
Home |
|
|
Good
Orientation |
|
|
South |
95 |
27,577 |
79,515 |
North |
50 |
11,859 |
3,672 |
East |
15 |
9,177 |
4,277 |
West |
10 |
6,118 |
2,851 |
total |
|
54,731 |
90,315 |
Hours
for 2 ton HP |
1.5 |
|
Hours
for a 1500W heater |
17.6 |
|
|
|
|
Poor
Orientation |
|
|
South |
10 |
2,903 |
8,370 |
North |
15 |
3,558 |
1,102 |
East |
50 |
30,592 |
14,256 |
West |
95 |
58,124 |
27,086 |
total |
|
95,176 |
50,814 |
Hours
for 2 ton HP |
2.6 |
|
Hours
for a 1500W heater |
9.9 |
|
|
|
|
Solar
Home with proper overhangs |
South |
145 |
29,463 |
121,365 |
North |
15 |
3,558 |
1,102 |
East |
5 |
3,059 |
1,426 |
West |
5 |
3,059 |
1,426 |
total |
|
39,139 |
125,318 |
Hours
for 2 ton HP |
1.1 |
|
Hours
for a 1500W heater |
24.5 |
|
Most homes by design have the majority of their windows on one side, usually
the front or the back. Then they have relatively few windows on the
sides. So here I simulate a rather typical US home of 1700 sqft with
10% window area. If that home is oriented with the side
with the most windows to the south It would gain 95,000 BTU's or about 25%
of a typical heating load. This would be the same as running a 1500W
heater for 17 hours each day at no cost. Then in the summer it would gain
about 57,000 BTU's. That is enough to cause a 2 ton heat pump to run
about 1.6 hours in a day.
If that same house was built facing west the summer heat gain nearly
doubles while the winter gain in nearly half. So you need to run your
air conditioning at least an hour more each day during the summer just to
overcome the sun. This will also cause one to place heavy blinds on
the windows to keep the penetrating rising or setting sun out of the house
when it is needed least. Likewise the house will be darker in
the winter when most people prefer a bright home to offset the shorter
days.
A solar house simply uses the orientation of the sun to it's advantage
adding a few more windows to the south while minimizing windows on the the
other walls. A well designed solar home can in our area can get 30%
- 70% of it's heating needs met by the sun. 30% for a standard
insulated house and 70% in a very well insulated home. It is like having a
1500w heater run 24 hours a day at no cost. In the summer air
conditioning would be
cut in half compared to a poorly oriented home. In all
cases insulation and construction costs are identical. |
|
A proper overhang is critical to proper shading on southern
windows. The following is a chart I use from the recommend book Modern
Carpentry. |
|