Question

How does natural ventilation contribute to passive cooling in buildings?

• A. By circulating cool air throughout the building
• B. By trapping heat inside the building
• C. By increasing solar heat gain
• D. By reducing thermal mass

Hint:

\textbf{Natural Ventilation} uses wind and stack effect for air exchange.
It contributes to \textbf{Passive Cooling} by:
Bringing in cooler outdoor air to replace warmer indoor air (convective cooling).
Increasing air movement across skin (enhancing evaporative cooling and comfort).
Facilitating night flushing to cool thermal mass.
Effective natural ventilation requires careful design of openings, building orientation, and form.

Answer 1

The Correct Option is A

Natural ventilation is the process of supplying and removing air through a building by natural means (i.e., without mechanical fans or systems). It relies on pressure differences created by wind and/or temperature differences (stack effect). Passive cooling refers to design strategies that cool buildings without consuming energy from active mechanical systems (like air conditioners). Natural ventilation is a key passive cooling strategy. How natural ventilation contributes to passive cooling: \begin{enumerate}
Circulating cool air / Heat removal by convection: When outdoor air is cooler than indoor air (e.g., during evenings, nights, or in shaded areas), natural ventilation can bring this cooler air into the building, displacing warmer indoor air and directly cooling the interior spaces and occupants. This process removes accumulated heat from the building's interior surfaces, furnishings, and occupants through convection. (Matches option a).
Enhancing occupant comfort through air movement: Air movement across the skin increases evaporative cooling from the body and can make occupants feel cooler even if the air temperature itself is not significantly lowered. This extends the comfort range to higher temperatures.
Night flushing / Night-time cooling: Ventilating the building extensively with cool night air can cool down the building's thermal mass (walls, floors, ceilings). This cooled mass can then absorb heat from the interior during the following day, reducing daytime indoor temperatures.
Improving indoor air quality: By replacing stale indoor air with fresh outdoor air, reducing pollutants and humidity. Let's evaluate the options:
(a) By circulating cool air throughout the building: This is a primary mechanism. If cooler outdoor air is available, natural ventilation brings it in, flushes out warmer indoor air, and cools the building.
(b) By trapping heat inside the building: This is the opposite effect. Natural ventilation is used to remove trapped heat. Poorly designed or controlled ventilation in hot weather could inadvertently bring in more hot air, but its cooling function relies on bringing in cooler air or promoting air movement for comfort.
(c) By increasing solar heat gain: Natural ventilation itself doesn't increase solar heat gain. Solar heat gain is through windows (glazing) and opaque surfaces. Shading strategies are used to control solar gain. Ventilation is about air exchange.
(d) By reducing thermal mass: Natural ventilation doesn't reduce a building's thermal mass (which is a property of its materials). It can cool down existing thermal mass (night flushing), which then helps in passive cooling the next day. Therefore, the primary way natural ventilation contributes to passive cooling is by circulating cool air and removing heat. \[ \boxed{\text{By circulating cool air throughout the building}} \]