Cross Ventilation
Introduction
Cross ventilation is a concept used by bioclimatic architecture to define a ventilation mode for buildings.
For this and depending on each site and the time of day, there are characteristic winds that generate areas of high pressure to the leeward "Sotavento (sea)") and low pressure to the windward. This implies promoting ventilation that, if the interior windows and doors of the premises are open, sweeps all the premises of a building or home as homogeneously as possible.
In the reference literature, specialists such as Givoni, Izard and Guyot") or Olgyay recommend it for humid warm temperate to humid tropical climate zones as a strategy for passive cooling") of buildings.
This strategy should be used with the combination of shaded environments and an envelope (walls and ceilings) whose surface temperature is similar to the ambient temperature. Otherwise and due to insufficient thermal insulation, they may be several degrees above the ambient temperature, implying an emission of heat in the infrared that reduces hygrothermal comfort.
Thus, the possibility of ventilating the premises throughout the day will work as long as the outside temperature does not exceed 30 to 34 °C with a relative humidity of 70 to 90%. Outside these ranges the cross ventilation strategy loses effectiveness.
Comfort zone
According to the Givoni climogram, the comfort zone with cross ventilation is defined as a shaded environment, a wind speed close to 1.5 m/s, dry bulb temperature between 20 and 32 °C and relative humidity between 20 and 95%. This with a restriction in the triangle formed by temp: 32 °C, RH: 50%; temp: 32 °C, RH: 95% and temp: 27 °C, RH: 95%.
The effect of thermal mass
In general, the literature associates this strategy with lightweight construction systems with low thermal mass, which is achieved with walls and ceilings weighing between 15 and 100 kg/m². Recent studies show that better performance can be achieved in hot and humid climates with outdoor temperatures not exceeding 35°C; with a combination of interior thermal mass and exterior lightweight thermal insulation. The thermal mass with walls or roofs weighing between 200 to 400 kg/m² and thermal transmittance "K" or "U" (depending on countries) between 0.5 to 0.7 W/m².K.
In these cases, the strategy works best by taking advantage of the minimum enthalpy difference between day and night, preferably ventilating when the sun goes down and accompanied by a solar chimney to promote convective ventilation due to temperature difference.