Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO7730 versus adaptive debate

Loveday, Dennis L.; Parsons, Ken; Taki, A. H.; Hodder, Simon

doi:10.1016/s0378-7788(02)00007-5

Cited by 53 publications

(42 citation statements)

References 4 publications

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“…The first supply devices (A) were installed in the lower section of the corners. The height location of these devices was similar to those used by many other researchers [4,8,14,17,49,50]. These devices represent DV.…”

Section: Experimental Set-upsupporting

confidence: 71%

Experimental Investigation of the Ventilation Performance of Different Air Distribution Systems in an Office Environment—Cooling Mode

et al. 2019

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The performance of a newly designed corner impinging jet air distribution method with an equilateral triangle cross section was evaluated experimentally and compared to that of two more traditional methods (mixing and displacement ventilation). At nine evenly chosen positions with four standard vertical points, air velocity, turbulence intensity, temperature, and tracer gas decay measurements were conducted for all systems. The results show that the new method behaves as a displacement ventilation system, with high air change effectiveness and stratified flow pattern and temperature field. Both local air change effectiveness and air exchange effectiveness of the corner impinging jet showed high quality and promising results, which is a good indicator of ventilation effectiveness. The results also indicate that there is a possibility to slightly lower the airflow rates for the new air distribution system, while still meeting the requirements for thermal comfort and indoor air quality, thereby reducing fan energy usage. The draught rate was also lower for corner impinging jet compared to the other tested air distribution methods. The findings of this research show that the corner impinging jet method can be used for office ventilation.Energies 2019, 12, 1354 2 of 15 the average IAQ in the occupied zone, and the results showed that there was a 35-50% improvement in the breathing zone due to the buoyancy effect around the mannequin body [4]. In a more recent publication, four different ventilation systems were compared in terms of ventilation efficiency, thermal comfort and energy-saving potential by using numerical simulations. The four systems compared were DV, mixing ventilation (MV), wall confluent jets ventilation (WCJ), and impinging jet ventilation (IJV). The comparison was done for an office environment. The results showed that DV was better than the other air delivery systems in all areas except when evaluating the vertical temperature gradient between ankle and neck levels for a standing person [5]. Other research groups have also concluded that DV is more suitable for cooling by exhibiting higher ventilation and energy effectiveness. It also creates a temperature stratification which facilitates the concentration of pollutants in the lower strata of the occupied space [6][7][8].Another type of air distribution system is IJV, which has been the subject of much research [9-13]. However, very few studies have examined multiple inlet devices based on IJV. In an early study, Karimipanah and Awbi [14] compared IJV to wall displacement ventilation in a laboratory classroom. They tested several key parameters such as ventilation efficiency, local mean age of air, and other characteristic parameters both experimentally and by numerical simulations. One of the conclusions of their research was that the IJV system showed a slight improvement in mean age of air and velocity distributions due to a better balance between buoyancy and momentum forces. Similarly, Koufi et al. [15] also reached the conclusion that IJV ha...

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Section: Experimental Set-upsupporting

confidence: 71%

Experimental Investigation of the Ventilation Performance of Different Air Distribution Systems in an Office Environment—Cooling Mode

et al. 2019

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“…Head height would be similar to the top of the heat sources used here. Although occupant simulators were not available, the same test chamber and table arrangement was used for a related comfort study with human test subjects [38]. The temperature profiles were found to be very similar in nature to those reported here using artificial heat sources.…”

Section: 2mmentioning

confidence: 54%

“…These experiments, in addition to providing the necessary data for model development, have also allowed the study of the operating characteristics of displacement ventilation systems used with and without chilled ceilings. The same test chamber has been used for thermal comfort studies reported elsewhere [37,38].…”

Section: Introductionmentioning

confidence: 99%

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

Rees

Haves

2013

Building and Environment

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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.

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“…Regarding users’ comfort, critical body parts for local discomfort are the head and feet. Several authors have investigated the effect of thermal comfort in vertical temperature gradients: Eriksson and Domier, Olesen et al, Tanaka et al, Bohgaki et al, Wyon and Sandberg, Palonen et al, Ilmarinen et al, Mayer, Hori et al, Loveday et al, Hodder et al, Kawahara et al, Yu et al, Cheong et al, Melikov et al, Matsuo et al, Hashiguchi et al, Liu et al, and Schiavon et al . In the following chapters, we present a literature review on recent research on thermal comfort and the effect of vertical temperature gradients.…”

Section: Introductionmentioning

confidence: 99%

Thermal comfort in environments with different vertical air temperature gradients

et al. 2018

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The use of displacement ventilation for cooling environments is limited by the vertical temperature gradient. Current standards recommend a temperature difference of up to 3 K/m between the head and the feet. This paper reviews the scientific literature on the effect of vertical temperature gradients on thermal comfort and compares this to the results of our own experiments. Early experiments have demonstrated a high sensitivity of dissatisfied test subjects to changes in the temperature gradient between head and foot level. Recent studies have indicated that temperature gradients of 4‐5 K/m are likely to be acceptable, and the mean room temperature may have a greater sensitivity on the percentage of dissatisfied (PD). In new experiments, test subjects have evaluated the thermal comfort of different vertical air temperature gradients in a modular test chamber, the Aachen comfort cube (ACCu), where they have assessed vertical temperature gradients of ΔT/Δy = 1, 4.5, 6, 8, and 12 K/m at a constant mean room temperature of 23°C. The results of the different temperature gradients are in contrast to ANSI/ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy, Atlanta GA, American Society of Heating, Refrigerating and Air Conditioning Engineers, 2013) as the PD increases almost constantly with higher vertical air temperature gradients. The PD for the overall sensation increases by approximately 7% between gradients of 1 and 8 K/m. The evaluation of our own tests has revealed that vertical temperature gradients of up to 8 K/m or higher are likely to be acceptable for test subjects.

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Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO7730 versus adaptive debate

Cited by 53 publications

References 4 publications

Experimental Investigation of the Ventilation Performance of Different Air Distribution Systems in an Office Environment—Cooling Mode

Experimental Investigation of the Ventilation Performance of Different Air Distribution Systems in an Office Environment—Cooling Mode

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

Thermal comfort in environments with different vertical air temperature gradients

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