Modelling of room air temperature profile with displacement ventilation

Abstract

Modelling of room air temperature profile with displacement ventilation An accurate temperature gradient calculation is essential for displacement ventilation (DV) system design, since it directly relates to the calculation of supply air flow rate. Several simplified nodal models were developed and implemented in the various building simulation programmes to estimate the temperature stratification in rooms with displacement ventilation. However, the most commonly used models do not take into account the types and locations of the heat loads in rooms with DV. As a result, the calculated air temperature in the occupied zone can defer from the real one by 2-3 °C, which causes poor thermal comfort and inadequate sizing of the ventilation and cooling systems. In the present study, the nodal model was proposed to provide a simplified technique to predict the vertical temperature gradient in rooms with DV. In addition, the effect of the room height and locations of the indoor heat sources were studied for the typical office environment. The measurement data were compared with the existing nodal models and the proposed nodal model in terms of predicting the occupied zone temperatures. The presented nodal model demonstrates an accurate calculation of the temperature gradient for the typical heat loads and combinations of them.

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

“…The multi-nodal DV model (Lastovets et al 2020a) calculates the temperature profile composed by variable slopes between the nodes (Figure 1(b)). This model calculates the height of air temperature stratification (h mx ) with the vertical heat gain breakdown.…”

“…The multi-nodal models introduce a temperature profile composed by variable slopes between the nodes. The models with a different number of nodes, heat gain configuration and mixing height consideration can be found in the literature (Nielsen 2003;Mateus and da Graça 2015;Lastovets et al 2020a). These models calculate mixing height with plume theory depending on types and number of convective heat sources (Hunt and Van den Bremer 2011).…”

“…The multi-nodal DV model implemented in EnergyPlus (Mateus and da Graça 2015), together with the calculation methods of mixing height were validated in dynamic conditions with the measurements in classrooms (Mateus et al 2016) and large rooms (Mateus and da Graça 2017). 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.…”

Influence of installation of displacement ventilation diffusers above occupied zone on the vertical temperature gradient in simulated office rooms

“…Vertical temperature gradients are compared to full-scale tests with installation of displacement diffusers to the occupied zone. The same test setup with installation of displacement diffusers to the occupied zone was used for validation of calculation models [3,4] and CFDsimulation in displacement ventilation cases [5].…”