Passive Solar Heating

Passive solar heating uses the power of the sun to heat your home without the use of mechanical systems. A well designed passive solar heating system will heat your home during winter or morning hours when the sun is lower in the sky, while avoiding overheating of the home during the warmer periods of the day, when the sun tends to be higher in the sky.

Effective passive solar heating system designs aim to reduce heating and cooling loads while providing occupant comfort during both warm and colder seasons. Systems consist of four main components: 

Correct Orientation

 passive solar windows (glazing) must face true south or within 30 degrees of true south and not be shaded by other buildings or trees from 9:00am to 3:00pm during the heating season.

Find true South

Notice that the solar north-south is different from magnetic north-south. The short axis of your home should orient toward solar north-south.

Thermal Mass

tile covered floors, masonry walls, and water filled containers are used to store heat for nighttime heating.

Control Structures

overhangs or controlled openings that block the sunlight and prevent the heated air from entering the house during the summer.

Heat Distribution (optional)

solar heated air is distributed using natural air movement from the passive solar heating systems to actively used rooms. Active mechanical systems such as fans are also commonly used in passive solar designs.                                                                       Image source: www.greenbuildingadvisor.com

 

Passive Solar Heating System Designs

Direct Gain Systems

the most common and the simplest design. These systems use south facing glass windows connected directly to living spaces with thermal mass in the form of concrete or masonry walls or floors to capture and store the sun's energy.                                                                                               Image source: wordpress.com

Passive Solar Sunspaces

these systems utilize rooms independent of the home's heating and cooling system to capture the sun's energy. The sunspaces are comfortable during much of the year, but are not intended to be living spaces for the home.                                                                                                            Image source: wordpress.com

Thermal Storage Walls

also known as Trombe walls, this design requires construction of two exterior walls - one made of south-facing glass, and one made of concrete to act as a thermal storage wall. The wall stores the solar heat gained through the glass, and radiates into the living area.                                      Image source: wordpress.com                                   

Solar Air Collectors

solar air collectors operate on a similar principle as thermal storage walls, though they generally cost less since the thermal mass is reduced. They work by ventilating the warm air in the space connected to the south facing glass into the home through vents in the top and bottom of the wall. 

 

Cost and Payback

Depending on the sizing of the system and the design of the house, passive design can save thousands of dollars throughout the lifetime of the building with little to no added upfront cost for a home. Properly oriented homes with passive solar incorporated in the design have been shown to save 30% – 90% in home operation costs. 

 

Resources

"Affordable Passive Solar Planbook for North Carolina" by Appalachian State College Energy Center

Comprehensive passive solar design overview.

A how-to article examining window to thermal mass area ratios for an effective passive solar heating design.  

Basic overview for passive solar design

A passive design strategy presented by a home owner that implemented an active solar collector approach with natural convective air movement. This website presents a step-by-step assembly of the system.

"Fans" by sustainablesources.com 

Information about how fans can be used​ in passive design

6  Overhang Design Tool (beta) by Sustainable by Design

See how overhangs will affect your window fixtures at home.

Passive Solar Heating by Judy Fosdick, updated by U.S. Department of Energy Federal Energy Management Program (FEMP)

Comprehensive overview of passive solar design, including: Introduction, Description, Types and Costs of Technology, Application, Design Considerations, Operation and Maitenance, and Additional Resoruces.

"Create-a-Sunplan" by Sunplans.com 

Passive solar home planning website that that is well organized, offers consulting services, and offers both customized designs and off the shelf designs.

9 Passive Solar Home Design by U.S. Department of Energy (energy.gov)

Overview of passive solar design.