The comparison of design airflow rates with dynamic and steady-state displacement models in varied dynamic conditions
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The comparison of design airflow rates with dynamic and steady-state displacement models in varied dynamic conditions Research Article
Natalia Lastovets1 (), Risto Kosonen1,2, Juha Jokisalo1 1. Aalto University, Department of Mechanical Engineering, Espoo, Finland 2. College of Urban Construction, Nanjing Tech University, Nanjing, China
Abstract
Keywords
A temperature-based method is usually applied in displacement ventilation (DV) design when overheating is the primary indoor climate concern. Different steady-state models have been developed and implemented to calculate airflow rate in rooms with DV. However, in practical
displacement ventilation design,
applications, the performance of DV depends on potentially dynamic parameters, such as strength, type and location of heat gains and changing heat gain schedule. In addition, thermal mass affects
dynamic model,
dynamically changing room air temperature. The selected steady-state and dynamic models were validated with the experimental results of a lecture room and an orchestra rehearsal room. Among the presented models, dynamic DV model demonstrated a capability to take into account the combination of dynamic parameters in typical applications of DV. The design airflow rate is calculated for the case studies of dynamic DV design in the modelled lecture room in both dynamic and steady-state conditions. In dynamic conditions of heavy construction in 2–4 hours
airflow rate, temperature gradient, simplified building energy models
Article History Received: 24 May 2020 Revised: 26 August 2020 Accepted: 16 September 2020 © The Author(s) 2020
occupancy periods, the actual airflow rate required could be 50% lower than the airflow rate calculated with the steady-state models. The difference between steady-state and dynamic multi-nodal model is most significant with heavyweight construction and short occupancy period (17%–28%). In cases with light construction, the dynamic DV model provides roughly the same airflow rates for four-hour occupancy period than the Mund’s model calculates. The dynamic model can significantly decrease the design airflow rate of DV, which can result in a reduction of investment costs and electrical consumption of fans.
1
Introduction
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Indoor/Outdoor Airflow and Air Quality
Displacement ventilation (DV) has been first applied in industrial buildings and since the 1980s in non-industrial applications. The basic principle of displacement ventilation is that the cool air is supplied into the occupied zone of the room at low velocity and then rises upwards from the heat sources by the vertical convection currents. As a result, room air with DV has both stratified and mixed zone with different temperature profiles. The design of displacement ventilation is usually based on controlling the desired air temperature in the occupied zone. Thus, the estimation of the vertical temperature gradient is essential in displacement ventilation design. Design DV models with different level of complexity
have been intr
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