Impact of ventilation design on the precooling effectiveness of horticultural produce-a review

Optimizing the ventilation design of packaging system is of crucial importance for improving the efficiency of the forced-air precooling process to maintain the quality of horticultural produce and extend the shelf life in food cold chain.Many efforts had been devoted to the study about the impact of ventilation design on airflow and temperature distribution inside ventilated packages.This paper reviews relevant research methods,commonly used quantities for the measurement of precooling effectiveness,attractive design parameters,and their impact on precooling effectiveness.These allow us to know exactly the characteristic and deficiency of each research method,identify dominant design parameters,and seek a promising way for the future improvement of the ventilated packaging system.

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

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 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 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 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.

Numerical study on the integrated effects of supplied air velocity and exhaust velocity on particles removal for industrial buildings

Due to production particularity in industrial buildings,high concentrations of particulate matter are always im-portant environmental issues.Long-term exposure to such hazardous environment may lead to respiratory and cardiovascular diseases.Mechanical ventilation plays a vital role in reducing indoor particulate matter concen-trations.However,the current industrial ventilation generally has the disadvantage of low ventilation efficiency and high energy consumption.In this study,we proposed a ventilation design by integrating supply and exhaust ventilation(i.e.,SEV),and further investigated the effects of combined velocities on both indoor particles re-moval and energy efficiency.Computational Fluid Dynamics(CFD)coupled with Discrete Phase Model(DPM)was employed.The RNG k-𝜀model was adopted to simulate airflow field.Lagrangian method was used to trace particles’dispersion processes.A series of cases were conducted under ventilated conditions with combinations of different supplied velocities of 0.75,1.12,1.50 and 1.87 m/s,and exhausted velocities of 0,0.28 and 0.56 m/s.Temperature effects were not considered in this work.The quantification of combined effects of supply velocity and exhaust velocity were investigated in terms of particle removal efficiency as well as energy saving.Results showed that combined effects of supply velocity and exhaust velocity can improve the ventilation efficiency by 20%-40%compared to the conventional supply ventilation without exhaust velocity.Moreover,the reasonable design of integrated velocities will save up to 70%energy while keeping the same ventilation efficiency of SEV.These findings will be of great importance for energy-efficient design for industrial ventilation systems.