Are There Two-Story Passive Solar Homes?

Are there two-story passive solar homes? Heat chimneys make two-story passive solar homes possible. The Northern California Solar Energy Association, in its glossary, defines natural convection as "A method...

The Northern California Solar Energy Association, in its glossary, defines natural convection as "A method of heat transfer where a fluid (liquid, gas or molten metal) picks up heat from one object and carries it to another by currents that result from the rising of lighter, warm fluid and the sinking of heavier, cool fluid. The two objects exchanging energy don't have to physically touch. Convection is the source of the 'wind chill factor' and the 'cooling breeze' we experience outdoors and the 'draft' we feel often feel while indoors." In a two-story passive solar house with open spaces, warm air will rise to the top. The house can be designed to take advantage of this form of natural convection in order to cool the house using passive methods.

Frederick Bernard, the owner of Acorn Builders, a custom home designer, builder, and remodeler, says, "In a lot of these types of homes, you see what's called a heat chimney. It's like a cupola with vents in it. It can be made with operable windows so that you can open them at night and the heat will leave the house and draw in the cooler outdoor air. That's a passive way to cool a house."

The website, a project of Portland's Office of Sustainable Development, says, "When warm air rises and leaks out at the top of a building, cooler air is drawn in at the bottom. Openings and spaces, such as atriums, can be designed to encourage this type of flow. A heat chimney is a device that uses the sun to heat air to create convection. An example of such a device is a cupola on top of a house."

The Office of Sustainable Development cites the People's Food Co-op in Portland as an example of a building that successfully uses a heat chimney. The Co-op "installed a chimney stack to help cool their building using natural ventilation. The stack was installed as one component of an well-integrated heating and cooling system that eliminated the need for mechanical cooling." Another Portland example is Ode to Roses, where the designer constructed the building "to take advantage of heat rising and consequently avoided the need to mechanically cool the building. The owner strategically installed a multi-purpose clerestory (or monitor) on the second floor that drastically increases daylight penetration and serves as a hot air outlet when perimeter outlets are opened."

You can also use active methods, such as traditional air-conditioning, to help equalize the temperature differences between the first and second stories of a two-story passive solar house. Bernard says, "It's all in the design of the system. You can design your two-story house with an air-conditioning system so that it distributes more cool air to the upper floors or draws the heat from the top floors and cools it, then distributes it back to the lower floors or draws heat from your upper floors and sends it back into your lower floors so that your upper floors aren't hotter than your lower floors. These are ways to make sure your top floors aren't always hotter than your bottom floors. You need to rely on your heating and cooling contractor for that."

Bernard adds, "Some cities, like Austin, have rebate programs for sealing and insulating your home to hold a more constant temperature and make it more energy efficient."

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