Comparison of Three Ventilation Rate Measurement Methods under Different Window Apertures in Winter and Spring

Abstract

The ventilation rate is an essential parameter for the continuous monitoring of the photosynthetic rate for greenhousecultivated plants via the CO₂ balance method. Diurnal changes in the ventilation rate (G) according to window aperture (W) and solar radiation level were therefore measured using the heat balance (HB) and water vapor balance (WVB) methods during winter and spring in a naturally ventilated greenhouse cultivating tomatoes. The results were indirectly compared with those of the tracer gas (TG) method. The G obtained through both methods increased with increasing W. However, when W increased rapidly, the increase in G was delayed when using the HB method compared to the WVB method. The G obtained via the WVB method performed similarly to the TG method at small values of W, and similarly to the HB method at moderate values of W. Furthermore, when measured using the HB method, the value in G was sensitive to the change in solar radiation level. Meanwhile, the G measured using the WVB method exhibited a stable response to the changes in W and could permit continuous real-time monitoring of greenhouse ventilation rates, which is necessary to estimate the photosynthetic rate for the plants in a greenhouse.