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Passive Solar Heating

Use the Sun's natural energy to heat your home

Passive solar design strategies use the sun’s “free” renewable energy to reduce your home heating costs. In a passive solar home, windows, walls, and floors are specially designed to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This approach is called “passive” because it can require no special technological or mechanical devices, just smart design and quality home construction. Note, however, that varying degrees of energy-efficient mechanical systems can be integrated with passive heating and cooling strategies to enhance the effects. Please check out our “Sun Smart” Radiant Heating and Renewable & Efficient Energy Systems pages to learn more about these methods.

Greenovision new home clients report that they do not run the heat on any sunny, cold day in the fall, winter, and spring. The energy-efficient, back-up radiant floor heating may kick on late in the night to maintain an even interior temperature. Even on sunny days with temperatures as low as negative 20 F, Greenovision-designed homes are heated entirely through passive solar energy and the back-up heating systems do not turn on! In Montana and other northern states, 49% of home energy usage is used for the heating of home spaces. Passive solar design reduces this usage by more than half.

Design

Correct and thorough design is the most important aspect in the creation of a comfortable and efficient passive solar home. There are many variables to be put together as well as past experience in knowing what works and what does not work.

Energy Source

A passive solar home’s heating energy source is source is pretty obvious- the sun. But, what is not as easy to understand are the many changes in sun angles that effect the solar radiation on your home throughout the day and year. It is through close study of those changes in sun angles throughout the year that we can determine how best to harvest solar energy or prevent its harvest.

Site Situation

Every building sits has it’s assets and obstacles that need to be evaluated in order to best design and situate your home for passive solar energy harvest. Sites that are sunny and fairly free of tall coniferous trees, especially to the southern aspect, have great passive solar potential. Deciduous trees on the south side of the home can help screen the sun to reduce excessive solar gain during the summer. During the colder months, deciduous trees drop their leaves, allowing the lower angled sun rays into your home.

Collection

Windows allow for the collection of solar radiation. Window location, height from floor, and typology all must be specifically designed and chosen to either allow solar radiation to enter or home or shut it down. The tuning of window sizes and types, U Values (insulative values), and high emissivity or low emissivity values is crucial for keeping your home comfortable, yet also protecting valuable interior furnishings from powerful UV radiation.

Storage

Solar energy in the form of heat is stored in a mass source with your home. We mostly focus on using concrete surfaces and slab floors to capture and store this “free energy.” An important aspect of storage is its containment inside of a well sealed and insulated advanced building envelope. Without such measures applied to your home design, the home will bleed more heat than it gains, also known as conductive losses. The insulated mass source is a thermal ballast that also helps prevent radical temperature swings within your home.

Open Floor Plans

It is important that the energy-storing mass source is in the correct location in regards to solar aspect and that a certain portion of this this area is not blocked by furniture or throw tugs. Passive solar homes favor open floor plans in order to collect and store the solar heat as well as to promote convective air cycles as part of the passive cooling strategies. Concrete or tiled flooring is typically used the mass source along the south-facing solar collecting areas of your home.

Control

There are many methods to effectively control solar heat gain. Roof overhang design, window design, peripheral awnings, and proper window blinds all can be designed and utilized to allow the suns’ energy in when wanted and to shut it down when unwanted. A high-performance building envelope also helps prevent heat loss during the colder months and heat gain during the warmer months, promoting energy-efficiency within your home during all seasons.

Cooling

Cooling strategies must be designed into passive solar homes in order to exhaust possible excess heat. Window design, height from floor ratio, size, and operability are all critical in setting up passive convective cycles inside the home that help exhaust unwanted heat. By understanding of your building site’s wind patterns, we can create exterior and interior air pressure differences, which can help your home naturally ventilate unwanted heat.

Multi-functional Benefits

Passive solar design creates a perfect setup for other design strategies which can improve the energy efficiency of your home as well as the comfort, beauty, and living experience. With thoughtful design, the same windows utilized for passive solar heating strategies during the colder months can used to promote passive ventilation and cooling during the hotter months. And the same roof overhangs that allow solar energy to enter your home when desired in the winter also help keep your home cooler in the summer by blocking unwanted solar radiation.

Natural Lighting

Another multi-functional benefit of passive solar design is the ample natural sunlight entering through windows. This light is shared throughout your interior spaces, creating a bright and comfortable experience while eliminating the need to run energy-consumptive electric lights during the day. According to data we found, “electric lighting accounts for 35% to 50% of the total electrical energy consumption” in some buildings, so eliminating this electric usage can drastically reduce your total home electric usage.

What is passive solar design?

Watch our videos to learn how passive solar heating and passive cooling strategies keep your home efficiently warm in winter, cool in the summer, and bright during day.

Tools of the Trade

While passive solar principles are simple in theory, correct implementation is a complex process and incorrect design may result in a poorly functioning home. This is why it’s important to work with a trained home designer, like Greenovision, who is experienced in passive solar design and incorporates these strategies into your new home while it is still in the initial design phases.

During the design phases, we use computer modeling in conjunction to solar system light modeling to tune the solar performance of your home. The following videos are examples of how we evaluate a home design to set it up for optimal shading in the summer and fall, while maximizing natural light and solar radiant gain in the winter.

December Solar trials

Here we are running the solar system on December 21st on exterior, interior, and plan view models to see the sunlight exposure throughout the day. This type of study is used to best orient windows and calculate roof overhangs depths in order to maximize total solar radiant gain of mass surfaces. This is free heat during those sunny winter days.

June Solar Trials

Running the solar system on June 21st on exterior, interior, and plan view models to see sunlight exposure throughout the day. This type of study is used to best orient windows and calculate roof overhangs depths to totally cut off solar radiation on the interior mass surfaces to reduce heat gain. A shaded floor mass stays cool throughout the day.

September Solar Trials

Running the solar system on September 21st on exterior, interior, and plan view models to see sunlight exposure throughout the day. This type of study is used to best orient windows and calculate roof overhangs depths to reduce the amount of solar radiation on the interior mass surfaces to reduce heat gain. Passive cooling strategies, window blinds, and light filtering awnings help to prevent overheating during the fall and spring when the daytime temperatures can possibly be warm, but the sun angles are penetrating under roof overhangs.

Using Google Earth for assessing a site's solar potential

People interested in having an active/passive solar home designed can benefit by starting out with choosing an appropriate building site. This video might help narrow that choice down.