Site Orientation
Love the sun, love the shade
In the wintertime, we want as much solar heat coming into our building as possible. In the summertime, we want as little solar heat coming into our building as possible. Year round, we want as much daylight coming into our building as possible.
That is quite the wish list!
To do this, we need smart design of our window placement, window sizes, window type and shading devices.
The first step in designing a smart window system for the building is to first understand the site orientation and how to best place the windows. If we have windows facing south, the sun can be used to heat our buildings. We have known this for a long time already. This is one of the original concepts of ‘green building.’ This can be seen in image 1 below.
Image 1: Solar path for winter and summer (Source)
Great, we heat our buildings in the winter with southern windows! Wait, what about the summertime? We cannot forget our second goal of controlling those powerful solar rays during the summertime. Nobody wants to overheat and cook! Good thing for us, the sun’s path is very high in the sky during the summertime. This allows for southern windows to be shaded with the use of large overhangs. This is displayed in image 2 below. Overhangs are extremely important for shading southern windows in the summertime! (Large overhangs are great for water management too! But that’s a story for another day)
Efficient mechanical
In a Passive House, long gone are the days of over-sized mechanical systems used to heat and cool our buildings. We size our mechanical equipment based on the heating and cooling loads of the building. The heating and cooling loads are so small in a Passive House, up to 90% less compared to built-to-code construction! With such tiny loads, we can use very simple and efficient mechanical equipment to achieve superior comfort levels.
Heat pumps are the most efficient way to heat and cool our buildings. Geothermal is a heat pump, but a very expensive heat pump, and often too large for a single Passive House. Instead, an air-to-air heat pump is what most Passive Houses use to heat and cool. No more burning gas in your house!
Image 2: Sun’s angle during winter and summer
Ok, we so have southern windows figured out. What about north, west and east?
East and west orientations represent interesting problems interesting because the sun is very low in the horizon and it cannot be shaded with overhangs. During the summertime, this is a huge problem, especially on the western facing windows where the hottest times of the day are in the late afternoon, and the sun is able to penetrate through unprotected windows.
Exterior shading is the answer, the only answer
Very important to note, exterior shading strategies are the only way to limit the solar energy coming into the building. Interior shading does nothing – nothing but absorb a small about of energy and then release the energy later in the evening. Once the solar energy has penetrated the window, it is inside your building and you will need BTUs of cooling to remove that heat. Again, and this cannot be stressed enough, interior shades will not reduce cooling loads!
We must design our east, and especially our west elevations to have exterior shading devices to limit overheating.
North elevations are a pure loss in terms of heat loss. However, north windows do offer consistent daylight without the risk of overheating the room. In high performance buildings in a cold climate, northern windows are limited to reduce heat loss. However, in hot and mixed climates, northern windows have the potential to be a better option for daylight reasons compared to east or west windows because they are not prone to overheating from solar radiation.
Site orientation is the first step in any high performance design. Southern windows are not a necessity for high performance, but they help. Every project is specific, and the demands of managing heat gains, heat loss, daylighting, views and architectural design will vary. It is possible to achieve greatness in all of these elements, if we are smart about it.
If you are in the southern hemisphere, please interexchange south for north, and north for south. If you are in the southern hemisphere and reading this, that’s pretty awesome!
