Our recent posts on how historic homes stayed cool without air conditioning generated a ton of great feedback.
Now, a cutting-edge design approach is focused on the same goal in modern homes.
It’s called “passive solar design.” It was pioneered in the U.S. in the 1980s, refined in Europe in the 1990s, then reintroduced stateside in the early 2000s.
With passive solar, the home is designed to be comfortable with little or no use of an air conditioner or furnace. Instead, the home relies on the science of climate, thermodynamics and fluid mechanics, along with high-tech home features, to keep occupants cool or cozy.
Passive solar energy follows a set of basic design principles:
Orientation to the sun
The home is carefully positioned based on its latitude and the known path of the sun across the sky. The passive solar design incorporates a large, usually south-facing, bank of windows. The windows are placed to allow as much sunlight as possible to enter the home in the winter, and as little as possible in the summer. The latter is usually aided by various control features (see below).
The home’s interior includes some form of thermal mass—a feature that absorbs heat. A typical thermal mass is a concrete slab or stone floor. Insulated masonry walls can serve the function, too. In the winter, the thermal mass absorbs heat from the sun, and releases it as air in the home cools. In the summer, the thermal mass “scrubs” heat from the air during the day, and releases it only when the home cools at night.
Solar heat is distributed throughout the home via the principles of conduction, convection and radiation. Circulation is key for both cooling and heating. A passive solar home is also well insulated and nearly airtight. It allows for controlled ventilation outside only through a small, powered heat exchanger. In very hot climates, where the focus is on keeping cool much of the year, the home may incorporate additional ventilation features.
The home has mechanical and non-mechanical features that help regulate sunlight and circulation. These might include roof overhangs, shutters or awnings, blinds, vents and dampers.
Ideally, a passive solar home provides comfort without any mechanical air conditioning or heating. In practice, many have small, auxiliary systems, especially in very hot or cold climates. Still, even where these systems are needed, a passive solar home stays comfortable at a fraction of the usual energy cost.
Applicable to big and small, new and old
Passive solar energy can be applied to buildings of all sizes—from small homes to large buildings. The features are most easily integrated into new construction. But, some or all can be retrofitted into many existing homes.
According to Passive House Institute US (PHIUS), a passive building currently costs five to 10 percent more than a conventional building. It expects those costs to drop in the future, as technologies like triple-pane windows—which are frequently incorporated into passive solar design—become more common.
Passive solar certification
PHIUS has developed certification standards for those interested in passive solar construction. The standards vary by geographic region, owing to differences in climate.
As of 2015, PHIUS estimates more than 200 homes in the U.S. will meet the standard. While a small number, certifications are growing exponentially year-to-year. The PHIUS website offers resources for homeowners, including links to energy consultants who are versed in the principles.
A powerful combination
All this seems to beg the question: What if you combined passive solar design with active solar technology—electricity from solar panels? Working together, they would make for undoubtedly the greenest home on the block.
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