Due south, or south/east passive solar home orientation?

[rebar]

Ive read some discussions, and seen some passive solar homes that are pointed south east. Fallingwater being one of them. Ive read it can eliminate summer afternoon/sundown rays from reaching the windows, but how do you calculate how many degrees off of due south, and is there a calculator that I’m not aware of? I do remember last summer thinking I should set my new home at a 45 degree angle to east and west for more shade on the east corner balcony in the summer afternoon, but this is essentially the same, but 45 degrees is to much I’m guessing..

Thanks

[J.P.M.]

Solar assisted dwelling design is about equal parts science, art and common sense.
It is also very localized in terms of what's a good design - down to things like landscaping, tree placement and topographical features within 10-20 m of a dwelling.
What works well in New England or most of the cloudier N.E. U.S. regions will most likely not work well in most parts of Arizona or the sunnier parts of the U.S.

To your question, SE exposures tend to provide earlier heating and less afternoon overheating. SW exposure tends to provide more heat to a space in the afternoon, often to the point of overheating and may not be welcome. But, designs ought to be flexible enough with shading, overhangs and other tricks to mitigate either to some extent and also allow for day/day irradiance and ambient temperature variation.

About the only things common to passive solar design in most regions is that a lot of thermal mass tends to make for higher solar fractions and lower HVAC bills. Windows alone without some considerations of what to do with or prevent excess heating will lead to overheating.

Check out Chaps. 14 and 22 of Duffie and Beckman "Solar Engineering of Thermal Processes" or any number of books on passive solar design. You'll find it's a lot more than just about window placement.
Also, Bruce Anderson :"The Solar Home Book". Lots of ideas about passive and active residential solar and reasons why they work in a readable format.
Also, for some historical perspective showing that there's not much new under the sun check out Butti and Perlin: "A Golden Thread: 2,500 Years of Solar Architecture and Technology".

Biggest mistakes a lot of folks make are too much fenestration, not enough attention to reducing the building heat gain/loss transmission and lack of self-education about what's required for interior safety and comfort before they run off and do what seems like a good idea but leads to problems.

Good luck.

[PNPmacnab]

Even "energy efficient" windows are different for northern and southern regions with the amount of light they let in and radiation heating. You could use both types in the same house depending on which way they face.

[J.P.M.]

Even "energy efficient" windows are different for northern and southern regions with the amount of light they let in and radiation heating. You could use both types in the same house depending on which way they face.

Based on my experience and IMO only, exterior, moveable shades are a less expensive and more flexible method to control heat gain/loss. The drawback is they usually take more maintenance and design consideration up front. There ain't no free lunch.