It is important that ventilation is controllable so that it can maintain a reasonable indoor air quality and avoid waste of energy. These controls can either be manual or automatic. 

AUTOMATICALLY CONTROLLED SYSTEMS: employ a system of sensors that detect the level of water vapour or other pollutants and adjust the ventilation accordingly in order to avoid over ventilation.

This form of ventilation lends itself to larger scale buildings.

Automatic fan
MANUALLY CONTROLLED SYSTEMS: are most commonly seen as trickle ventilators. Theses ventilations systems use natural ventilation as they are located over the window frames, in window frames, just above the glass or directly into the wall. These systems often incorporate a simple flap that can allow users to shut off the ventilation depending on external conditions. 

This form of ventilation is more suited to dwellings.

Trickle vent
Brass slide vent
AIR VENTS: within walls are mostly positioned above the skirting boards at a comfortable height for the user to easily adjust the amount of ventilation.

This type of ventilation appears is general use system found in a variety of buildings.

Humidity controlled extractor
HUMIDITY CONTROLLED DEVICES: regulate the humidity of indoor air and minimise the risk of condensation and growth of mould; these are normally installed as part of an extractor system in rooms such as kitchens and bathrooms.

are manufactured in order to regulate the temperature within a space that is suitable to the size of the air conditioner in question. The majority of ACs on the market are now remote controlled to enable the user simplistic climatic control of their indoor environment.  
Air conditioning unit