Should a fan be sucking or blowing air?

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Should a fan be sucking or blowing air?

Forever a controversial subject that occupies the minds of those who purchase cars with ventilated seating, computer geeks but also wheelchair manufacturers and their end users.

Think of the computer problem for example: every computer has multiple fans placed inside to cool down the elements such as graphics card and CPU that are prone to overheating. Should the fans be sucking environment air in and blow it onto the hot elements? Or should it be sucking the hot air away? Opinions vary!

Why is it so important for wheelchair users?

Ventilation reduces the risks of skin infection and irritation associated with humidity and temperature. Additionally, it reduces exhaustion, pain and discomfort caused by over-heating or over-sweating.

WheelAir's Answer to sucking or blowing air:

Heat Exchange

When looking at the human body in comparison to a computer, more elements come into play. Throughout the day, the body uses four mechanisms of heat exchange to maintain homeostasis: conduction, convection, radiation and evaporation. Each rely on the property of heat to flow from a higher concentration to a lower concentration and vary depending on the conditions of the environment. WheelAir’s technology influences all four heat exchange mechanisms.

The key types of heat exchange we will focus on for this topic are convection, conduction and evaporation heat loss.

Let’s say that we were to suck air from the body to the environment. Heat and moisture would be sucked away, which should leave you feeling cooler. Simple convective heat loss.

Now let’s assume the fans were blowing air – like WheelAir does.

The isothermal stream of air taken from the environment passes through the blower fans, taking the heat away from the body by flowing past it, creating convection heat loss and wicking away heat and moisture. By pushing the air through the blades of the fans before touching the body, greater turbulence is created which improves efficiency.

Clinical Indications also showed that over time the temperature of the back stabilises with the ambient temperature of the environment, thus avoiding any heat and moisture build-up in the first place.

Second, the flow of air will speed up the natural evaporation heat loss process more commonly known as sweat. The rate at which evaporation occurs depends on relative humidity. The isothermal WheelAir airflow lowers the humidity level, increasing the evaporation heat exchange rate.

Lastly, the constant flow of isothermal air in contact with a 3D spacer fabric, such as the Spacetec® used in the WheelAir product will cool down the full spacer surface, which in turn cools down the user’s back through conduction heat loss when both surfaces touch.

A key take-away from WheelAir’s ventilation is prevention. Rather than sucking away heat and moisture that builds up, we prevent it from building up in the first place.

User Design

Now let’s look at some design challenges. When extracting heat, a big fan as well as power source are needed to reach sufficient cooling levels. Blower fans on the other hand have a much smaller profile and higher output. Because who wouldn’t want a smaller, lighter and more silent fan cooling them down?

The debate won’t be over any time soon, but at WheelAir our decision is clear: we blow!