An experimental study of air flow and temperature distribution in a room with displacement ventilation and a chilled ceiling

Abstract

Displacement ventilation and chilled ceiling panel systems are potentially more energy efficient than conventional air conditioning systems and are characterized by the presence of vertical temperature gradients and significant radiant asymmetry. The characteristics of this type of system have been studied by making temperature and air flow measurements in a test chamber over a range of operating parameters typical of office applications. Results from the displacement ventilation study are consistent with other studies and show that normalized temperature profiles are independent of internal heat gain. Linear temperature gradients in the lower part of the room were found, in all cases, to be driven by convection from the adjacent walls. Significant mixing, indicated by reduced temperature gradients, was evident in the upper part of the room in the chilled ceiling results at higher levels of heat gain. Visualization experiments, velocity measurements and related numerical studies indicated that with greater heat gains the plumes have sufficient momentum to drive flow across the ceiling surface and down the walls. The significance of forced, as opposed to natural convection, is also suggested by relatively low Richardson Number (Ri) values found near the ceiling. Furthermore, in cases with moderately high internal gains, comparison of the temperature gradients indicated that the effect of ceiling surface temperature on the degree of mixing and the magnitude of the temperature gradient were of secondary importance. These findings are in contrast to the view that it is natural convection at the ceiling that causes enhanced mixing.

A validated three-node model for displacement ventilation

“…Results of the model simulation for the cases in the database and comparison with measured data. discrepancies found in some cases were predictable given the simplifications made as well as uncertainties in the experimental boundary conditions (in most experimental studies the boundaries can be best described as "nearly adiabatic" [21]). Fig.…”

Unutarnja okolina renoviranih ureda opremljenih stropnim isijavajućim pločama

“…The system was supported by mechanical ventilation, with inlets and outlets at a level close to the ceiling (Figure 2). These locations were chosen because, in the case of displacement ventilation and chilled ceiling applications, it has been shown that, when internal gains are moderately high, the impact of the ceiling surface temperature on the level of mixing and on the magnitude of temperature gradient is of secondary importance [8]. Table 2) showing radiation ceiling panels, air inlets/outlets of mechanical ventilation system, and vertically positioned air temperature sensors (V1-V5)…”

“…It can be integrated into the floor, wall or ceiling structure as the so-called thermally activated building system (TABS), or installed as a part of a suspended floor or ceiling. The thermal comfort and energy consumption of radiant surfaces have been an important topic of several studies described in the literature [4][5][6][7][8][9][10][11][12][13][14]. These studies are mainly based on small-scale experiments or numerical models, and they focus on rather specific questions about radiant ceiling systems.…”

“…Determination of a proper heat transfer coefficient and the cooling capacity of the system is, however, of crucial importance, especially in connection with solar gains [5][6][7]. Furthermore, apart from the ventilation system, surface temperatures of a room can also have a considerable influence on the efficiency of radiant ceiling systems, so that the latter must be evaluated together with the nearby indoor environment and not as separate HVAC equipment [8,12,15]. Despite good performance, the radiant ceiling panel systems are still not widely used in practice.…”

“…These studies are mainly based on small-scale experiments or numerical models, and they focus on rather specific questions about radiant ceiling systems. Although many of them are limited to cooling or heating only [4][5][6][7][8][9][10], the research is in some cases focused on both aspects [11][12][13][14]. It was shown that radiant ceiling panels can efficiently be used for heating and cooling in buildings with a good thermal insulation and low cooling loads [14].…”