Study examines effectiveness of wind over cold air at cooling rooms


Scientists have looked at effectiveness of wind over cold air at cooling rooms and found that non-mechanical, low-energy methods for moderating temperature and humidity.

The study found that a temperature difference between inside and outside has a remarkably small effect on how well a room is ventilated when ventilation is primarily driven by wind. In contrast, wind can increase ventilation rates by as much as 40% above that which is driven by a temperature difference between a room and the outdoors. The exact rate of ventilation will depend on the geometry of the room.

Natural ventilation, which controls indoor temperature without using any mechanical systems, is an alternative to traditional heating and cooling methods, which reduces energy use and greenhouse gas emissions.

There are two main types of natural cross-ventilation: wind-driven and buoyancy-driven. Cross-ventilation occurs in rooms that have windows on opposite sides of a room. Wind blowing on a building can result in a high pressure on the windward side and a low pressure at the leeward side, which drives flow across a room, bringing fresh air in from outside and ventilating a room. Ventilation can also be driven by temperature differences between the inside and outside of a room, as incoming air is heated by people or equipment, resulting in a buoyancy-driven flow at a window.

Researchers used a miniature model room placed inside a flume to recreate the movements of air inside a room when windows are opened in different temperature and wind conditions. The researchers found that the rate of ventilation depends less on temperature and more on wind. Anyone who has tried to cool down on a hot night by opening the window will no doubt be familiar with how ineffective this is when there is no wind.

This is because in many rooms, windows are positioned halfway up the wall, and when they are opened, the warm air near the ceiling can’t easily escape. Without the ‘mixing’ effect provided by the wind, the warm air will stay at the ceiling, unless there is another way for it to escape at the top of the room.