Distinctly Montana Magazine

Distinctly Montana Summer 2018

Distinctly Montana Magazine

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D I ST I N C T LY M O N TA N A • S U M M E R 2 0 1 8 96 SMART NATURAL VENTILATION STRATEGIES Natural ventilation is achieved through three strategies: cross ventilation, convection through stack effect, and Venturi effect. By utilizing a combination of these different passive strategies, a home can be cooled on both breezy and non-breezy days. In order to set up these effects within a home, win- dows are positioned low to the floor on the cool side of the building and high windows are positioned on the high-wall side of the building. Stack effect helps to cool the home on a non-breezy day. In this design, a natural vacuum is generated throughout the home when hot air rises and exits through the high windows, while fresh, cool air enters through the low windows. e air pressure differences due to hot and cold variations inside the building and outside the home create a natural cross breeze. is subtle air movement encourages evaporation of moisture on our skin and gives the sense of cooling—aka, natural air conditioning. Prevailing wind directions are also taken into effect to further pres- surize the home, promoting a jet-like Venturi effect, which increas- es air flow rate within the home. is works when wind blows through or across a restricted area such as a small window. We typically design homes with lower and higher walls, often achieved through singled-sloped shed roofs. e width of the building, an open floor plan (fewer inner walls), and proper window heights/types are critical aspects to consider when designing a home to be ventilated passively. Most conventional homes have wide footprints, flat 8 foot high ceilings without any height difference, and inner partitioned walls. ese features trap heat within the house and inhibit cross ventilation, making the interior hot and stuffy in the summer. In addition, the windows are typically all at the same height, which doesn't allow for stack effect to set up convective air flow. Heat trying to escape the home through open windows prevents cool breezes from entering. Even a gable-ended home with vaulted ceilings inhibits ventilation because the building shape does not allow for enough space for high operable windows on the gable ends. Hot air usually gets stuck in the ceiling peak. W ITH THESE HOT, SUMMER DAYS UPON US, MON- TANANS USE EVERY OPPORTUNITY TO SEEK REFUGE IN OUR STATE'S COOLEST NATURAL ENVIRONMENTS—RIVERS AND LAKES, CANYON BOT- TOMS, AND HIGHER MOUNTAIN ELEVATIONS WHERE THE AIR IS CRISP. Even standing in the shady canopy of a tree can feel significantly cooler than being directly in the sun's intense rays. Returning to our homes, however, we often find ourselves swelter- ing until the cool night air finally finds its way indoors. Either that or we run energy-consumptive fans and air conditioners around the clock to improve the interior comfort. It doesn't have to be that way though. In a house designed for passive cooling, you can return on hot summer days to an inte- rior that naturally feels fresh, cool, and comfortable (reminding you of your favorite cooler outdoor escapes), but with little to no energy use. Passive cooling is a home design strategy that works by removing heat from a home through natural ventilation, and also preventing heat from entering the home in the first place through heat-gain prevention. is 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 cooling strategies to enhance the effects. by MARK PELLETIER AND EMILY VARMECKY PASSIVE COOLING DESIGN: THE NATURAL WAY TO AIR CONDITION YOUR HOME

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