Analysis of the influence of the return position in the vertical temperature gradient in displacement ventilation systems for large halls

Abstract

a b s t r a c t Displacement ventilation systems are widely used in spaces of small and medium heights (up to 7.5 m), taking advantage of their high efficiency in removing contaminants by means of the air stratification. This outcome usually hides major drawbacks compared to admixture systems, such as inadequate temperature gradient in the occupied zone and low cooling capacity. On the contrary, its use in large spaces with high ceilings displays the best features of the system, provided the return is placed near the ceiling. When, due to architectural reasons, this option is not feasible, alternatives for the return position are assessed using simulation tools that result in excessive time consumption during the design stage. In this article a simple Mundt's equation based iterative process is proposed to quickly evaluate the influence of the return height in the vertical temperature gradient and the additional cooling load due to overheated ceiling. It has been applied to the case of Madrid airport new terminal, and their results have been comparedtoa CFD simulation, with areasonable degree ofaccuracy foraninitial stage ofa design process. The results show that the higher the return is placed, the lesser airflow rate is needed to match the additional cooling load due to radiation from the ceiling. The calculation process also shows that Mundt's radiant heat exchange coefficient is far from being constant, for it is affected by the height of the return point, and takes values much greater than the usually accepted.

Air temperature gradient in large industrial hall

“…Four metres above floor level the air temperature stabilises and temperature increase is minor. Such dependence was previously described [2,3,[7][8][9]. The higher was the temperature in the operating zone, the higher was the temperature in the highest hall point, however technological sensible heat load at that time had the lowest value during the whole year.…”

“…There are numerous publications related to temperature stratification in the operating zone [1,2,5,7,8]. Research results of the operating zone are available to provide best possible conditions for the people and technology used in the room.…”

Indoor thermal stratification and its statistical distribution

“…In buoyancy-driven ventilated spaces including displacement [5][6][7] and/or underfloor ventilation systems, [8][9][10][11][12] and natural ventilation in large spaces 13,14 during cooling seasons; and 3). In buoyancy-driven ventilated spaces including displacement [5][6][7] and/or underfloor ventilation systems, [8][9][10][11][12] and natural ventilation in large spaces 13,14 during cooling seasons; and 3).…”

“…20 Various measures of reducing or removing thermal stratification have been developed, so-called thermal destratification, for example, using air mixing devices and/or ventilation systems. In the past decades, many studies have been conducted to understand thermal stratification and its impact on thermal comfort, 27 air quality, 5,6 energy saving, 28 and design and operation of these systems. In recent years, the study of thermal stratification and destratification in warehouses attracts more attentions.…”

“…In large industrial warehouses and storage facilities especially in winter seasons 2-4 ;(ii). In buoyancy-driven ventilated spaces including displacement [5][6][7] and/or underfloor ventilation systems, [8][9][10][11][12] and natural ventilation in large spaces 13,14 during cooling seasons; and 3). In a more extreme stratification case, such as during enclosure fire, buoyancy-driven hot smoke rises to form an upper smoke layer on the top of a cold lower air layer.…”