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conscious living: cool spaces 04 – stack effect

A green space is a space that is built with the local climate in mind. Our country is a tropical climate. And one of the major difficulties of tropical climates is cooling interior spaces.

Cooling a space mechanically generally takes up as much as 50 percent of the electricity bill. By cutting down on your use of the air-con, not only do you save energy and money, but also any greenhouse gases that may have been emitted by the production of electricity. This series looks at the various ways of being comfortable without turning on the energy.

Stack Effect

Hot air rises. Cold air sinks.

In essence (and without getting too technical), this is what stack effect means in tropical climates. It is a scientific fact that air movement in interior spaces follows these directions: up for hot and down for cold.

How does stack effect influence the design of spaces?

Illustration by Arch. Stanley Fernandez

Let’s start with a typical room. Having taller or higher windows allows hot air to escape above. It also implies that a higher ceiling is beneficial in keeping the heat as far away from the living zone.

(This is also the main reason why air-conditioning units should be placed above or near the ceiling, so the cold air could naturally sink and not overwork the motor. Overworking the motor leads to consuming more energy. But we’re advocating natural ventilation here as much as possible.)

If the building or house is multi-story, the ground or lower levels are usually cooler than the floor right under the ceiling. Place the important spaces (or where you spend the most time in) on the cooler levels.

In his own home, National Artist for Architecture Bobby Mañosa located the bedrooms on the ground floor. To him, having a cool, comfortable space to rest and sleep in is more essential. The living room, dining room and kitchen are located above (which are quite open and ventilated too).

Stack effect can also be used to divert the hot air out of the space. Chimneys or flues can act as passages for heat to rise and escape. Since chimneys are quite impractical in this climate, stairwells become the main avenue for the hot air. Ensure the release of hot air by providing egresses above the stairwell. The openings can be operable louvers or clerestory windows.

Previous: proper orientation, maximize openings, cross ventilation 

conscious living: cool spaces 02 – maximize openings

A green space is a space that is built with the local climate in mind. Our country is a tropical climate. And one of the major difficulties of tropical climates is cooling interior spaces

Cooling a space mechanically generally takes up as much as 50 percent of the electricity bill. By cutting down on your use of the air-con, not only do you save energy and money, but also any greenhouse gases that may have been emitted by the production of electricity. This series looks at the various ways of being comfortable without turning on the energy.

Maximize Openings

Natural ventilation is one of the most efficient ways to cool the interior space. It involves creating internal air movement, just strong enough to feel comfortable but weak enough not to blow all the paper around. By circulating the air inside the space, the hot air is pushed outside and the cool air is carried inside.

Last time, we tackled the proper orientation for your desired space. There are two important directions to consider for our country: northeast and southwest. Generally, at any time of the year, prevailing winds travel from these two points. Northeast monsoon (hanging amihan) occurs during the cold months and southwest monsoon (hanging habagat) starts during the summer months. PAG-ASA (Philippine Atmospheric, Geophysical and Astronomical Services Administration) even has localized data on prevailing wind directions specific to cities and municipalities. By having ample windows and openings facing these directions, we can have guaranteed air movement to enter the space.

To maximize ventilation, one also needs to maximize the openings. Having large operable (that you can open) windows is ideal. Increase the size of your windows. Lower the height of the window sill while extend the height of the window up to the ceiling line. Old ancestral houses even have window openings at the top and bottom of regular windows called ventanillas to allow as much air as possible. These can have louvers or screens instead of unobstructed openings to preserve the privacy of the users.

The optimum type of window to specify is the one that maximizes the opening; that means it can be fully opened 100%. Sliding windows for instance can only have a maximum opening of 50%. Awning-type windows have 60-70% openings. Casement types (swing-out like cabinet doors) have 100 percent openings. Jalousie windows or louver types can also have 100% openings, plus having the distinct advantage to adjust the air flow by manipulating the panels.

To screen or not to screen? Common insect screens restrict air flow by as much as 50 percent. There are imported types that impede less, but they are generally more expensive. If the space is not that critical or located atop a high-rise building, I suggest opening up your windows. Use screens only on sensitive areas like bedrooms and nurseries. Besides, there are house plants that deter mosquitoes and other insects.

So maximize natural ventilation for your spaces and minimize your energy costs for cooling.

Previous: proper orientation

Next: cross ventilation, stack effect