Displacement cooling push outside air to the bottom of the equipment room. This forces the warmer air in the room to move up. This is known as displacement cooling, because the hot air inside the room has been displaced by a cushion of cool air. The hot air will push out via a ventilation grill on the highest possible position.
When the outside air is below the required temperature a small part of the hot air well be recirculation to control the lower air temperatures.