What science says about the “trick” of two crossed fans to cool the house: it works, but with limits

With heat waves hitting the thermometers, the desperation to cool the house without increasing the electricity bill leads us to look for any shortcut. And although the new air conditioners have shown that they have a low daily costthe reality is that many people prefer to opt for the classic fan and there are ways to optimize its operation.

An idea. Something that has become popular in recent days is the possibility of using two fanshaving each in opposite windows. Under this premise, the idea is that one of them brings in air from the street and the other manages to get it out to ensure that the house in the end is as cold as possible within their possibilities.

It has support. What is proposed here is to take to the extreme a concept that has been used for a long time in the architectural world to ensure that homes, passively, can acclimatize. And, according to the design standards and manuals of entities such as the IDAE, uwell-designed cross ventilation can reduce the interior temperature by up to 5°C.

The two-fan technique falls into the category of hybrid or assisted ventilation. As detailed by platforms specialized in architecture such as ArchDaily or the technical area of ​​Tinsa, it is not enough to open windows at random. For there to be flow, a pressure difference must exist.

The idea. By placing one fan pointing inward on the coldest façade, which is normally the north one or the one facing a shady patio, and another pointing outward on the opposite façade, we are mechanically forcing that pressure differential. The goal here is for the cool air to push the stagnant hot air mass out the opposite window.

Although yes, for this flow to accelerate and be more efficient, the opening through which the air leaves should be more open than the one through which it enters.

It’s proven. A thesis from the Piloto University of Colombia wanted analyze the effectiveness of this ventilation methodand it was seen that this system showed a significant reduction in thermal load in a hot-humid climate. Although here it is important to highlight that the thermal insulation of the home or building is very important, logically, to maintain an adequate temperature.

It has small print. Logically, these two fans cannot work miracles, and if the outside temperature exceeds 30 degrees and especially if the relative humidity is high, cross ventilation loses all its effectiveness. Far from cooling, here there would be thermal energy in the home and forcing the entry of air at 35 °C with a fan is the equivalent of turning on a giant hair dryer.

The best hour. Here the official recommendations point out that cross, forced or natural ventilation is a strategy that should be left for the first thing in the morning or at night. when the temperature is considerably lower.

For the “two fans trick” to work and achieve that promised 5°C drop in the structure of the house, you must apply it only when the outside temperature drops below the inside temperature. This is called “selective ventilation” since during those hours, the mechanical technique of the two fans will sweep away the heat accumulated on the walls and ceilings during the day.

Images | Delaney Van

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