[AIVC, Air infiltration and ventilation glossary, 1992]:a ventilation system in which air is extracted from a space so creating an internal negative pressure. Supply air is drawn through adventitious, or purpose provided openings.[ASHRAE Standard 62.2]:  (reported as exhaust system)one or more fans that remove air from the building, causing outdoor air to enter by ventilation inlets or normal leakage paths through the building envelope.