How relevant are the so-called active grilles in a hot and humid country like Singapore? I would imagine that car engines here need all the cooling they can get. And how much aerodynamic efficiency is there in closing the grille?
Air flow through a car's engine compartment, while necessary for cooling, creates resistance to motion. The active grilles found on some cars were developed specifically to cut off air flow into the engine compartment to reduce aerodynamic drag.
The active grille is controlled by its own electronic unit, which takes into account a number of factors before deciding whether the grille should be open or closed.
Here in Singapore, where ambient temperatures are consistently well above 25 deg C, and most commutes are in urban traffic, an active grille will likely spend most of its time in the open position.
However, this does not mean that its function is not relevant in the country. When moving off on a "cold" engine, the grille will indeed remain closed so that the warm-up period is minimised.
Engine performance and efficiency are optimal only at "normal" operating temperature, so it is important that this is attained as quickly as possible.
As for the aerodynamic efficiency, at most highway speeds even as low as 70kmh, there is sufficient air flow for engine cooling, around and through auxilliary apertures on the front of the car that permits the main grille to be closed.
This effectively reduces drag. A closed grille is claimed to reduce aerodynamic drag by up to 10 per cent.