Optimization of Sampling Positions for Measuring Ventilation Rates in Naturally Ventilated Buildings Using Tracer Gas

Abstract

Finding out the optimal sampling positions for measurement of ventilation rates in a naturally ventilated building using tracer gas is a challenge. Affected by the wind and the opening status, the representative positions inside the building may change dynamically at any time. An optimization procedure using the Response Surface Methodology (RSM) was conducted. In this method, the concentration field inside the building was estimated by a three-order RSM polynomial model. The experimental sampling positions to develop the model were chosen from the cross-section area of a pitched-roof building. The Optimal Design method which can decrease the bias of the model was adopted to select these sampling positions. Experiments with a scale model building were conducted in a wind tunnel to achieve observed values of those positions. Finally, the models in different cases of opening states and wind conditions were established and the optimum sampling position was obtained with a desirability level up to 92% inside the model building. The optimization was further confirmed by another round of experiments.

Comparison of CO2- and SF6- based tracer gas methods for the estimation of ventilation rates in a naturally ventilated dairy barn

“…This lower variability of ratios in the ridge indicates that measuring at this location could result in more precise estimated values for ventilation rate. This result is not consistent with the optimal position for concentration measurements defined by Shen et al (2012) using response surface methodology. The major difference between their study and ours is that the ridge did not act as an outlet in the study of Shen et al (2012).…”

“…This result is not consistent with the optimal position for concentration measurements defined by Shen et al (2012) using response surface methodology. The major difference between their study and ours is that the ridge did not act as an outlet in the study of Shen et al (2012). When the ridge functions as a permanent outlet, it may yield more precise estimates of the VR ratios because concentrations of both CO 2 and SF 6 are more stable and are similar to the conditions that occur near the outlets of mechanically ventilated livestock barns.…”

“…However, in naturally ventilated barns, outlets can also act as inlets depending on wind direction, leading to large errors in the calculation of ventilation rates (Bjerg et al, 2012;Van Buggenhout et al, 2009;Wu et al, 2012). Using an optimisation procedure with different simulated barn sidewalls opening situations, Shen et al (2012) determined that the universal optimal sampling position was close to the centre of the barn (i.e. near the central axis, at 27% of the barn height).…”

“…However, the location of exhaust air can be difficult to determine in naturally ventilated buildings as it may be subject to cross ventilation from variable directions. From an experimental study conducted by Shen, Zong, and Zhang (2012), it appeared that the optimal sampling position for indoor gas concentration measurement was found to lie close to the centre of the building, at approximately 30% of the barn height. Similarly, using one sampling point situated in the middle of the barn was shown to be equivalent to using the mean of 5 sampling points throughout the house (Bjerg et al, 2012).…”

Investigation of discharge coefficient of louvre openings in naturally ventilated buildings

“…In addition, NV can provide adequate ventilation [3,4]. However, accurately determining the ventilation rate of a naturally ventilated building remains a challenge [5,6]. It is crucial in building design to control ventilation openings and monitoring gas and dust emissions from NV housing [7].…”