In mid-summer and with high temperatures, the moment you get in the car loses charm. With the steering wheel, grips or trimmings burning and suffocating heat, it seems necessary to cool the cabin as quickly as possible , but what is the best way to do this?
Before entering the subject, it is important to remember roughly the three ways in which heat is transferred and that explain why the car heats up and how it is possible that we cool it even without waiting for the air conditioning to do their work. function.
How heat transfer works
There are three ways of heat propagation:
Radiation : Thermal radiation or heat radiation is the radiation emitted by a body due to its temperature, and is generated by the thermal movement of charged particles in matter.
Contact : it is a process of heat transmission based on direct contact between bodies, without exchange of matter. When we place our hand on a hot object, heat transfer from the object to our hand occurs by contact.
Convection : this form of heat transfer can be an application of contact transfer, in this case by contact between moving molecules (natural convection), or by pressure difference (forced convection), and also the combination of both . When we open a window, fresh air cools the environment by natural convection.
Why does the car heat up?
A car parked in the hot sun is heated by radiation. The sun’s energy warms the roof, and the heat that this huge metal surface captures is distributed to the rest of the car by contact. Hence we try to park in the shade in summer . Actually, what we want is to avoid thermal radiation.
In other words, when the sun hits the car, the wheels, the sheet metal, the glass, etc., get hot and consequently raise the air temperature inside the car.
Therefore, the solution is evident. If we manage to park in the shade or in a garage, the temperature will not rise as much inside the car and, therefore, we will facilitate the process of cooling the car even without air conditioning , something that is achieved by convection.
How does the car cool?
This process of heat transfer, convection, is accomplished through the movement of molecules. Opening the windows creates an air stream from the outside of the vehicle that cools the interior.
Even if, when we get into the car, the first thing we do is to lower the windows in addition to turning on the climate control or the air conditioning to blow cold air, an air current is generated from the outside to the inside that helps to lower the temperature of the cabin.
In this way we manage to ventilate the vehicle and a temperature exchange between the car, which can reach a temperature in the passenger compartment of up to 70ºC according to the DGT , and the outside air.
And starting from this point, the classic trick of fanning the car by moving the driver’s door vigorously with the window down, also makes sense , as we thus accentuate convection.
The procedure is simple: simply lower the passenger window and then open and close the driver’s door vehemently, in order to accelerate the movement of the air and thus lower the interior temperature by several degrees .
Once we start the route, driving with the windows down for a few minutes will also promote this process and help the car’s air conditioning or cooling system to cool the interior, since the interior temperature will decrease more quickly.
However, it should not be forgotten that from 80 to 90 km / h, carrying the windows down consumes more energy than if we circulate with the air conditioning activated.
This means that by city we could save the climate control and open the windows, whenever the temperature allows it, but not so on fast roads: driving at 120 km / h we will always consume less energy with the air conditioning running and running the closed windows.
No, the sunshade will not make the car colder, but it will not burn you
On the other hand, it is common to use a parasol that covers the windows in an attempt to mitigate the temperature rise inside the vehicle, or even cover the seats with heat-absorbing fabrics to remove them just before getting into the car, chasing the same end.
The parasol is a very useful element, and sometimes indispensable, to avoid being able to start the journey without burning your hands from contact with the steering wheel after having been in the car for a few hours in the sun.
However, this element cannot prevent heat from being transferred by contact from the ceiling to the rest of the cabin, and even by convection into the interior air.
Ultimately, the best way to cool a car is to keep it from heating up in the sun. And if this is not possible, we can speed up the convection process so that the air from outside quickly lowers the temperature inside.