Image courtesy of The Handyman
I have previously discussed the application of passive solar design through the use of the interior materials of the house, as well as external landscape and shading devices.
However, I have yet to specify how best to achieve passive solar design through the house’s physical orientation. It is certain that a key principle of passive solar design is proper orientation in relation to the sun.
The following guidelines should be heeded when constructing a passive solar home:
Orient the house on an east/west axis, with the longest side facing South:
Due to the sun rising in the east and setting in the west, orienting the longer axis of the house (or the ridge line) to east/west allows the longer side of the house to face South, where the largest portion of the house is optimally placed to receive solar benefits.
It is important to note that the south-facing side of the house must have large windows (or other forms of solar glazing) in order to best absorb sunlight.
The particular east/west orientation means that a typical passive solar building will have a rectangular shape, with the long side facing south.
The following diagram from Green Passive Solar Magazine illustrates how a house can be best placed for maximum mass to absorb sunlight from its southern position:
Orient the house within approximately 30 degrees of true south:
While the ideal placement of the long side of the house is facing precise true south, there are discrepancies regarding how much allowance one has when building in relation to true south.
From the California Energy Commission site, Consumer Energy Center, the orientatin can be varied within 20 degrees of true south without significant detriment.
GreenBuilding.com says there is an allowance of 30 degrees from true south in order to retain about 90% of solar gain. Less than 30 degrees can make shading difficult and may lead to overheating.
Builditsolar.com provides methods for determining where true south is located.
Place areas or rooms of the house most frequently used on the longer, south-facing portion of the building:
This allows optimal sunlight to enter and be absorbed through south-facing windows. Less-inhabited rooms such as the garage, laundry room and storage space can be placed on the shorter, east/west-facing sides of the house, thereby acting as an additional thermal buffer.
Understand that windows and glass must be appropriately angled and/or shaded to accommodate the different seasons:
Within the northern hemisphere, a house that has its long, south-facing side dominated by windows can accommodate passive heating and cooling needs in both winter and summer—assuming the windows are appropriately angled and proper overhangs are in place.
Solar homes are often built with large, upward-tilted and, of course, south-facing windows and/or glazing (southern-facing glass that has the ability to absorb and transfer sunlight).
The upward tilt of these windows can best receive the sunlight year round.
However, in order to prevent overheating during the summer months, when the sun is higher in the sky, appropriate overhang devices can be used.
When properly employed, an overhang will reduce the amount of sun that enters the windows when the sun is at a higher point, without preventing the sunlight from entering when the sun is at a lower point in winter.
Green Passive Solar Magazine provides a handy diagram to illustrate this point:
It is also important to note that windows should be well-insulated (double or triple-glazed), in order to prevent sunlight from quickly escaping the home during the cold winter months.
Alternative shading devices include landscaping, which can also help regulate heating and cooling throughout the year. Southern-planted deciduous trees, for example, which lose their leaves in the winter, can shade the windows in summer to reduce heat gain, and let sun in when the leaves are winter bare.
By adhering to these orientation guidelines for passive solar design, natural heating and cooling can best be achieved, and mechanical systems can be reduced or even eliminated.