Understanding Passive Solar Heating and Cooling

Learn what it takes to create a comfortable building environment with less reliance on fossil fuels (and lower energy bills).

  • Passive solar home
    Passive solar design has come a long way since the ’70s. Modern solar houses are attractive as well as energy efficient.
  • Passive solar house
    Sun spaces are a great way to take advantage of solar heat. Open the doors between the house and the sun space during the day to add heat to the house. Close the doors at night to prevent warm air from escaping.

  • Passive solar home
  • Passive solar house

Being passive isn’t always a bad thing, especially when it’s passive solar heating and cooling. The idea behind passive solar is to design buildings that take advantage of natural heat from the sun in winter; and shade and wind and in the summer. Although the concept has been used in many cultures for centuries, passive solar design principles recently have been refined a great deal, even since the 1970s.

Passive solar, on it’s most basic level, works like this: Rays from the sun enter a building through windows, heat the air and are absorbed by floors, walls, furniture, etc. Some materials, such as stone, brick and plaster, more effectively absorb the heat. As the air cools at night, the absorbed heat releases into the building and maintains a comfortable temperature.

How Passive Solar Works

Kelly Lerner, architect and author of Natural Remodeling for the Not-So-Green House, says there are four things to consider when designing or remodeling a building to most effectively utilize solar energy: south-facing glass (glazing), shading, insulation and thermal mass.

“In most North American climates, the right amount of south-facing glass is 7 to 12 percent of the floor area of the building — a lot less than you might think if you’ve seen solar home designs from the ’70s,” she says. “In the ’70s, we really used too much glass with too little thermal mass, so instead of passive solar heat, we had something more like ‘passive-aggressive’ solar heat, creating buildings that were too hot during the day and too cool at night. Too much glazing can be a detriment on cold winter nights, allowing heat to escape.”

Longtime passive solar expert Ron Judkoff, director of the Buildings and Thermal Systems Center at the National Renewable Energy Lab, says, “It’s the thermal storage part that’s kept passive solar from becoming more widespread. It’s also the biggest additional expense: adding brick or another internal thermal mass instead of drywall.”

Judkoff points out that production builders are accustomed to using lightweight materials not suited to storing (and releasing) heat gathered through south-facing glass. “But you need adequate thermal storage mass for a passive solar thermal building to work as it’s supposed to,” he says.

6/15/2019 1:45:56 PM

Hi Anachronism, I see your post is several years old, but hope you see this message. Have you written a book or complete articles on how, steps, and pictures to do what you have done on passive heating and cooling? I would definitely buy a book regarding seasoned and proven methods for heating and cooling! Seems with your know how, knowledge and existing examples, there would be many people interested in it, and you could make extra for retirement sharing your expertise. Yes, hundreds of thousands of articles have been written in the past 40 years, but there are younger generations wanting and doing tangible things to make a difference for themselves and their families. Millions of people have learned that starting today, their life can be different by choices made. :) (If you do write a book, please use a seasoned editor. ;) Best Regards

6/14/2019 12:47:28 PM

Dan Jacobs, if you already have the South Bay window if the shades are open then you are using Passive Solar to heat that room. Question: Is the room getting too warm? If not, then adding mass is a bit pointless. If it does get too warm where you close the drapes or open a window, then mass can help moderate the temperature swings, BUT, mass is heavy and your house may not be designed to hold the amount of mass bricks/water etc. to effectively store excess heat. Study passive solar mass storage requirements carefully.

Dan Jacobs
2/10/2009 8:16:52 PM

Dear Mother Earth, I have a large bay and picture window facing south in my home. My couch currently sits in front of it, but I would be interested in a suggestion of decorative thermal mass that may provide passive heating. Is there some brick/lego type structure that can go on a foot wide window sill? Also have you any suggestions if I wanted to go all out and use focused mirrors to intensify the solar heat through a window? Thanks for all the years of trying to keep our planet green! Dan Jacobs

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