As with all forms of solar power – solar thermal, PV panels, solar chimneys and others – the amount and quality of sunlight to which a home is exposed is extremely important in holistic home design. Thankfully, again in common with many other forms of solar power, even areas that might appear at first sight to be far too gloomy can, in fact, provide enough energy to reduce heating bills by 50% or more.
When you read about solar systems, especially solar thermal and passive systems, you may come across the "10-Degree Rule". The rule states that, wherever possible, a building should be constructed with the long axis facing within 10 degrees of true south (not magnetic south).
The reason for this rule is very simple: south-facing walls get the most sun (in the northern hemisphere). You want as much of a building as possible facing that way to gather as much heat and energy as possible.
Thankfully, the days of cookie-cutter houses built quickly to exactly the same design are on their way out. Even in places where the homes are all based on the same floor plan, individual home owners add and change things to suit themselves. One of the easiest things to change in any home is the color of the exterior walls.
In most cases, we talk about thermal mass as something that absorbs and stores useful heat from the sun's light, releasing it when your home gets colder to maintain a comfortable indoor temperature. However, it is possible to use thermal mass as an effective cooling mechanism.
If you're designing a direct gain passive solar home, you will need to maintain a careful balance between two vital parts: the amount of glazing on each side of the house and the amount of thermal mass available inside to store and later release heat. Getting the glass-to-mass ratio wrong will result in too much or too little heating.
One of the most infuriating aspects of passive solar design is that one size never fits all. A design that works perfectly on your site may be ineffective two miles away on the other side of a hill, on higher ground, or in a rural area.
With that in mind, regional adjustments are not too difficult. The basic design can stay much the same in areas with similar climate, but you will have to adjust four factors:
Direct gain passive solar homes have many advantages and disadvantages compared to other approaches. Historically, the first direct gain homes were often a complete mess, because the designers had little understanding of the need to balance things like solar glazing and thermal mass. Modern designs are much better, especially since analysis software is now available to help make the tough decisions.
Thermal walls, or Trombe walls, are the single most flexible passive solar option: they work in any climate and on any home, providing extra heat throughout the night after gathering heat during the day.
As with all passive solar design options, Trombe walls are a great addition to your home design: they retain a lot of heat, helping to reduce your nighttime heating costs throughout the cool period of the year. However, again like all other options, they need to be used correctly or they won't do you any good.
