It might seem obvious that for bus saloon heating and ventilation control, we could simply give
the driver on/off switches for, say, the saloon heater fans and water valve. However, if the
driver switches on the fans right at the start of a cold day, the passengers will actually be blasted by an
icy chill until the engine warms up. In the afternoon, as the sun warms things up, the late shift may not switch the
water valve off, turning the bus into an oven!
Another
example might be where a vehicle has separate heating and ventilation systems. On a warm day, the driver might turn the ventilation
on - but will he remember to turn the heating off?
Consequently,
it's almost impossible for the driver to maintain accurate saloon temperature control as well as drive
the bus, so some form of automation is usually required.
An automatic system can be as simple as thermostatic control of the heater fans. Full automation, however, should
monitor and react to such things as the exterior air temperature, the saloon air temperature, the engine water temperature,
the engine rpm and any other manual inputs or settings, and use in-built logic to control fans (e.g. on/slow/fast),
water valves, pumps, and vents. An automatic system can be set up to ensure that passengers always get just the right level
of heating or ventilation, and free the driver to concentrate on driving.
In practice, semi-automatic operation, with the driver simply selecting heating or ventilation, with the
additional option of switching off completely if, say, a fan is noisy, is the most popular and common-sense approach.
