Dynamic performance of displacement ventilation in a lecture hall

Abstract

An accurate temperature gradient calculation is essential for displacement ventilation (DV) system design, since it directly relates to the calculation of the required supply air flow rate. Inaccurate temperature prediction can cause the poor thermal comfort and w sizing of the ventilation and cooling systems. Several simplified nodal models were developed and implemented in the various building simulation software to estimate the temperature stratification in rooms with DV. Recent studies reveal that the multi-nodal models provide the most accurate temperature gradient prediction. However, the most building simulation software uses the air models with only one air node. The present study introduces the dynamic temperature gradient model for DV and investigates the effect of thermal mass on the temperature stratification. The model was validated with the experimental results of the lecture room with displacement ventilation. The room air temperature measurements were conducted during three weeks at 20 different heights. The supply air temperature and occupancy rate were recorded during each scheduled lecture. The developed dynamic nodal model is able to accurately calculate the air temperatures in occupied zone. The effect of the thermal mass and varied heat loads on the indoor air temperature stratification is analysed for the lecture room with DV.

The comparison of design airflow rates with dynamic and steady-state displacement models in varied dynamic conditions

“…The dynamic DV model (Lastovets et al 2020b) represents a hybrid of the room air multi-nodal DV model (Lastovets et al 2020a) and 2-capacity model of building structures (Sirén 2016). The model calculates dynamic energy balance where the thermal mass of building structures and air capacities are taken into account.…”

“…The capacities C a and C m and the conductances H m-out and H a-m were calibrated, so that room air temperature calculated with the two-capacity model matches the results of the detailed building simulation model (IDA ICE) (Shalin 1996) in the fully-mixed air conditions. The calibration methodology was presented in detail in the paper related to the dynamic DV model development (Lastovets et al 2020b). While the ventilation and window conductances H a-out and H a-s are defined before the calibration (Eqs.…”

“…The measurements for two typical applications of DV in the lecture hall (Lastovets et al 2020b) and orchestra rehearsal room (Mateus and da Graça 2017) are selected for the validation of dynamic DV model. These spaces differ from each other in different ceiling height, thermal mass, heat load breakdowns and time schedules.…”

“…The principle of heat gain breakdown applied in the Mateus model (Mateus et al 2016) was later developed in the multi-nodal DV model and validated for different heat gain types and combinations of them (Lastovets et al 2020a). While the assumption of unified air temperature over the mixing hight has been applied in the previously developed multi-nodal models, the model used in the current study (Lastovets et al 2020b) allows accounting for both type and vertical position of the indoor heat gains.…”

“…The present study applies a simplified dynamic DV model to calculate the vertical temperature gradient (Lastovets et al 2020b) that integrates the multi-nodal DV model (Lastovets et al 2020a) and two-capacity building energy model (UNI EN 2008;Sirén 2016). The heat capacities and conductances of the dynamic multi-nodal model are calibrated against the results taken from the dynamic building simulation model IDA ICE (Shalin 1996) and validated in a lecture room and an orchestra rehearsal room.…”