Control systems which are not well-understood or
simple to use are subject to misuse by occupants or
building service personnel. For example the controls on
a unit ventilator include a room temperature thermostat
which controls the valve on the heating or cooling coil,
a damper control which adjusts the proportion of fresh
air mixed with recirculated room air, and a low-limit
thermostat which prevents the temperature of outside
air from dropping below a preset temperature (usually
55 to 60°F; 13 to 16°C).