Passive solar design can save you money on heating and cooling. It’s a style of home design that takes advantage of free solar heating and lighting, making it less reliant on conventional home heating systems to maintain a comfortable temperature. You don't need to pay for any expensive solar energy harnessing equipment like you do with a solar electricity or solar hot water heating system (though we still think those are great investments!)
Passive solar design alone cannot keep a house warm, but it can save you up to 65% on your heating bill according to EcoHome Magazine. In this article, we’ll talk about how you can use passive solar design to plan the initial construction of a home or remodel an existing home to take advantage of solar energy.
Passive Solar Design in New Construction
Home designs that stretch from east to west provide more wall area for southern windows, capturing more solar heat. Passive solar design prioritizes southern windows because they bring in the most heat from the sun. A home facing within 20° of true south is ideal, but 40° will still give you the advantages of passive solar design.
Having a sealed home envelope is key to passive solar design because your home must trap warm air instead of letting it draft out through the walls. Insulate your home envelope so that you are in control of where and when your home ventilates. Seal gaps in windows and trim with caulking.
Windows in Passive Solar Design
The type of glass we need for a home utilizing passive solar design is called high solar-gain-glazing. Window glass has something called a solar heat-gain coefficient (SHGC) that identifies how effective the glass is at capturing solar heat. This coefficient is expressed in either “glazing-only” or “whole-window”. In passive solar design on south-facing windows, we’re looking for a high whole window SGHC of ideally 0.56 according to GreenBuildingAdvisor.com.
Increase large fixed windows in a home utilizing passive solar design. These windows cost less than operable windows and will assist in your efforts to provide a sealed home envelope.
Other Factors in Passive Solar Design
Overhangs in a home utilizing passive solar design should be sized to completely shade south-facing windows during the summer solstice and allow maximum sunlight to enter on the winter solstice. Overhangs protect siding from the weather and help influence the temperature of the home on especially hot days when homeowners are using the air conditioner.
Thermal mass is equivalent to heat capacity, i.e. the ability of a body to store thermal energy. The idea is that a home with more thermal mass will absorb and store heat energy and release it when the house cools down to even out the temperature. Uncarpeted concrete is a common example of an effort to increase thermal mass in passive solar design.
Landscape factors into passive thermal design as well, but is controversial in effectiveness. Typically a home designer will remove trees that shade the south side of the house as a best practice, but passive solar design can still perform well even in the shade of trees.