The control of pre-cooled natural ventilation

Abstract

This paper investigates the control of the natural ventilation of an auditorium or other occupied open-plan space, which vents into a cold exterior through its upper opening, and into which fresh pre-cooled air is drawn through its lower opening. The occupants located at an intermediate level between the upper and lower openings act as an internal source of heat, providing upward buoyancy which drives the ventilation and draws fresh air through the pre-cooling system. These conditions produce a steady state displacement ventilation regime in which the room becomes stratified into two layers, with the transition zone dividing the upper layer of warm air from the lower layer of pre-cooled air across the occupied level. A quantitative model is developed to describe this ventilation process and to investigate the sensitivity of the system. The model is successfully tested with laboratory experiments and shows that with pre-cooled natural ventilation, both ventilation rate and the temperature in the region above and below the heat source may be controlled by the pre-cooling. The paper discusses how such pre-cooling may be manipulated to bring about ventilation and thermal comfort in the ventilated space with a view to maximizing the seasonal range for which natural ventilation is possible.