Cooling your house through night ventilation

Putting thermal insulation above the ceiling, providing roof vents or outlets and painting the roof a light-colored shade are some of the more common ways to help reduce the heat inside the house.

There is one green strategy, however, that is less known but which is also effective in cooling the house. This strategy is called night ventilation or night flushing. This means allowing the night air to cool down the structure of a house or building by flushing warm air out and cooling the thermal mass for the next day.

Thermal mass is any material of the building that can absorb heat. When a material absorbs heat, its temperature increases.  For example, concrete is a more conductive material than wood.

At night, the cold air must have direct contact with  thermal mass, such as the floor slab since the night air will tend to fall or drop onto the floor. This reduces the daytime temperature rise.

Night ventilation is, technically speaking, suitable for climates with a relatively large temperature range from day to night. This is perhaps the reason it is not as popular here as the other strategies to cool the house—in this country, the difference in temperature between daytime and nighttime is very small.

Night ventilation can still be effective here by utilizing what many homes already have—the permanent fixture in the Asian home—the electric fan.

Fans for cooling the house

Fans can be used to flush the house with cool night air. According to scientists, people feel cooler in rapidly moving air than in still air due to the wind-chill effect. They are a most useful device during nights when there is no breeze at all.

There are now specially-designed fans called whole-house fans that can be installed in the ceiling to blow air into the ceiling or attic which will then exit through the roof ventilation. Window fans can also be used to bring in or to exhaust air.

A simple but effective way to help bring in cool night air is putting a portable fan near an open door and directing the flow of air into the central part of the house, making sure that there is an opening at the end to encourage cross ventilation. Even if the difference in temperature is small, the thermal comfort will be noticeably felt.

A special concern with opening doors to allow night ventilation to cool the house is security. Sliding doors that open into a terrace or lanai are particularly susceptible to intruders, insects, debris, etc.  Wrought iron grilles with insect screen can be installed so that the doors can be left open for night ventilation.

The window near the top landing of a stairway is a good place to install an exhaust fan. Most of the hot air coming from the lower floor will naturally rise and build up in this area.

The unusual rise in temperature has made our houses very hot during the day. At night when the outdoor temperature gets cool enough, you can use the night air to flush out the heat from your house by turning on the fans the whole night.

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