As summer ramps up, many of us will be looking for ways to cool off. If you’re one of the lucky ones with a swimming pool, we’d love an invite! In the meantime, the rest of us will be exploring ways to stay comfortable through some passive cooling techniques.
Preventive vs. Modulation Techniques
These are the two main categories of passive cooling. Preventive techniques are the steps you can take to keep heat from building up in the first place. Modulation is a technique used to transfer the heat via thermal mass or natural cooling, dispersing it at a later time or when needed. It's easiest to set these systems up when designing a new build, but they can also be incorporated in your existing space.
This technique takes into account the distribution of interior spaces with respect to the activities they'll be used for. Use temperature stratification to your advantage. Lower places in the home are naturally cooler, so use higher areas for spaces like bathrooms, where warmth will be appreciated.
Local climate should also be considered in order to find the proper ratio between volume and surface (aka form factor.) Because of this ratio, forms that are more compact have the tendency to hold more heat than less compact forms. This means smaller homes in hot temps will heat up quickly.
The microclimate of the landscape surrounding the home refers to the combined effects of sun and wind on the way the building is sited, as well as any other structures on the property. Microclimates can vary significantly, causing noticeable temperature differences between protected areas behind buildings and exposed spaces.
That’s fancy speak for shading. Window films provide shade for transparent and opaque surfaces which helps to keep accumulation of solar radiation within the inner spaces to a minimum.
Providing shade for the exterior of the home itself reduces the amount of heat gain through windows. This can be accomplished by planting trees in key spots. Unfortunately, it can take years to feel the effects, so take a look at some fast growing trees that might be good options.
Windows and doors, attics and basements, and everything in between will affect the way your home handles the heat (and the cold!). You’ve heard it before, but we’ll say it anyway—proper insulation works wonders to keep heat and cold at bay for maximum comfort.
Modulation/Heat Dissipation Techniques
This technique uses the building’s thermal mass to absorb heat during the day, and releases it to the space when needed. Thermal mass refers to the ability of the material to store heat. Concrete and bricks have a higher thermal mass than materials like wood. Think of the higher thermal mass of the building as a barrier against the heat since it makes it "harder" to heat up the internal temperature than a building of lighter thermal mass.
Examples of natural cooling include ventilation, night flushing, radiative cooling, evaporative cooling, and earth coupling.
Ventilation uses air to remove heat via cross ventilation or stack ventilation. Cross ventilation is created when openings on two sides of the space uses the wind to cool the interior. Stack ventilation relies on warm air rising and exiting the space through openings at ceiling height, while cool air enters through openings near the floor.
Night Flushing is another type of natural cooling that keeps heat built up during the day to "flush" out of the house at night. Windows are kept closed during the day, then opened at night to bring in the cool air. This type of cooling is very effective in locales with significant temperature swings between day and night.
This refers to the process in which heat is lost through thermal radiation. It involves designing a roof to act as a "radiator". The radiation emitted from the building is greater than long-wave radiation from a clear sky aka your building cools off when the sun goes down.
Evaporative cooling systems use the natural process of evaporation to lower air temperature while increasing surrounding humidity. This can be accomplished through exterior systems placed outside the building to avoid an increase in interior humidity. Cooling is accomplished through roof ponds and water spraying.
This method uses the soil to cool the space. It works best in hot climates where the temperature of the earth is cooler than the air temperature. This can be through either direct or indirect coupling. Direct or earth sheltering reduces heat loss and heat gains by using the consistently cooler temps of the surrounding soil to limit heat infiltration. Indirect coupling uses earth ducts that are buried in the ground that connect to the building. The air is cooled via surrounding soil before entering the building, then drawn in by a fan.
Passive cooling techniques are both efficient and environmentally sound ways to deal with increasingly extreme heat due to the climate crisis.