Effect of Pre-Cooling on Natural Ventilation of Buildings with Multiple Stacks

Chenvidyakarn et al (2004a) investigated the natural ventilation of an occupied open-plan space, which was connected to an exterior through two stacks and a low-level vent. Occupants located at an intermediate level between the stacks and the low-level vent acted as a uniform source of heat, providing buoyancy to drive the ventilation. Their work showed that these conditions could produce up to three steady state ventilation regimes. In the first regime, the bottom opening and the shorter stack acted as inflow vents, while the taller stack acted as an outflow vent. In the second regime, the bottom opening acted as an inflow vent, while both stacks acted as outflow vents. In the third regime, the bottom opening and the taller stack acted as inflow vents, while the shorter stack acted as an outflow vent. The present work considers the situation in which a passive cooling system, such as thermal mass, is connected to the low-level vent to pre-cool supply air, as may be required in low-energy buildings operating in summer or warm climates. Using a combination of laboratory experiments and a theoretical model, the paper explores how the pre-cooling affects the ventilation and steady state temperature in the space under the three ventilation regimes. The study shows that sufficiently large pre-cooling can stall the inflow through the bottom vent in the first and third regimes, or the outflow through the shorter stack in the second regime. Depending on the ventilation regime and resultant flow rate, an increase in the pre-cooling can lead to either a decrease or an increase in the temperature in the occupied zone. To achieve desired ranges of temperatures and ventilation rates while minimising energy use, an appropriate range of pre-cooling is required. The paper shows how to determine such an appropriate range of pre-cooling for a given ventilation regime.