News / Science News

    Wind more effective than cold air at cooling rooms naturally

    The researchers 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.



    Wind more effective than cold air at cooling rooms naturally. Photo: Annie Spratt/Unsplash


    The results could be used to help designers and urban planners incorporate natural ventilation principles into their designs so that buildings can be kept at a comfortable temperature while using less energy.

    Heating and cooling account for a significant proportion of energy use in buildings. In addition, as global temperatures continue to rise, demand for air conditioning – which emits greenhouse gases – rises as well, creating a damaging feedback loop.

    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.

    “We’ve all gotten used to having a well-controlled, narrow temperature range in our homes and offices,” said Dr Megan Davies Wykes from Cambridge’s Department of Engineering. “Controlling natural ventilation methods is much more challenging than switching on the heat or the air conditioning, as you need to account for all the variables in a room, like the number of people, the number of computers or other heat-generating equipment, or the strength of the wind.”

    In the current study, the 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.

    Using the results from lab-based experiments, Davies Wykes and her colleagues built mathematical models to predict how temperature difference between inside and outside affects how well a room is ventilated.

    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.

    “It was surprising that although temperature differences do not have a strong effect on the flow of air through a window, even small temperature differences can matter when trying to ventilate a room,” said Davies Wykes. “If there are no openings near the ceiling of a room, warm indoor air can become trapped near the ceiling and wind is not effective at removing the trapped air.” (University of Cambridge)

    NOVEMBER 21, 2019



    YOU MAY ALSO LIKE

    On some of the Galapagos Islands where human-introduced predators of Darwin’s finches were eradicated over a decade ago, the finches are still acting as though they are in danger.
    Pregnant women exposed to persistent organic pollutants, or POPs, had slightly smaller fetuses than women who haven’t been exposed to these chemicals, according to an analysis of ultrasound scans by researchers at the National Institutes of Health and other institutions.
    NASA’s Fermi Gamma-ray Space Telescope has discovered a faint but sprawling glow of high-energy light around a nearby pulsar. If visible to the human eye, this gamma-ray “halo” would appear about 40 times bigger in the sky than a full Moon.
    Australian scientists have successfully blocked the deadliest malaria parasite —- Plasmodium falciparum — in its transmission stage, paving the way for developing preventative therapies to stop the spread of the disease.
    An international joint research team led by NIMS succeeded in fabricating a neuromorphic network composed of numerous metallic nanowires.

    © 1991-2023 The Titi Tudorancea Bulletin | Titi Tudorancea® is a Registered Trademark | Terms of use and privacy policy
    Contact