Orientation

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.