On the Ventilation Performance of Low Momentum Confluent Jets Supply Device in a Classroom

Abstract

The performance of three different confluent jets ventilation (CJV) supply devices was evaluated in a classroom environment concerning thermal comfort, indoor air quality (IAQ) and energy efficiency. The CJV supply devices have the acronyms: high-momentum confluent jets (HMCJ), low-momentum confluent jets (LMCJ) and low-momentum confluent jets modified by varying airflow direction (LMCJ-M). A mixing ventilation (MV) slot jet (SJ) supply device was used as a benchmark. Comparisons were made with identical set-up conditions in five cases with different supply temperatures (TS) (16–18 °C), airflow rates (2.2–6.3 ACH) and heat loads (17–47 W/m2). Performances were evaluated based on DR (draft rating), PMV (predicted mean vote), ACE (air change effectiveness) and heat removal effectiveness (HRE). The results show that CJV had higher HRE and IAQ than MV and LMCJ/LMCJ-M had higher ACE than HMCJ. The main effects of lower Ts were higher velocities, DR (HMCJ particularly) and HRE in the occupied zone as well as lower temperatures and PMV-values. HMCJ and LMCJ produce MV conditions at lower airflow rates (<4.2 ACH) and non-uniform conditions at higher airflow rates. LMCJ-M had 7% higher HRE than the other CJV supply devices and produced non-uniform conditions at lower airflow rates (<3.3 ACH). The non-uniform conditions resulted in LMCJ-M having the highest energy efficiency of all devices.

A Numerical and Experimental Investigation of a Confluent Jets Ventilation Supply Device in a Conference Room

“…In the present study, the supply device was a circular duct (0.25 m diameter and 2 m long) mounted 0.05 m below the ceiling level which had 57 nozzles on each side (d = 0.028 m) placed in three rows with 19 nozzles each. The configuration of each side can be seen in Figure 1, the spacing between columns was 3 jet diameters and the spacing between the top and bottom rows was 1 jet diameter, see [33] for more details, shown in Figures 1 and 2. Supply device nozzles can be fitted with caps that block the nozzles.…”

“…The study was performed in a climate chamber (7.2 × 4.2 × 2.7 m 3 ) at the University of Gävle in Sweden, representing a typical conference room environment. The climate chamber is versatile and has previously been used to investigate different indoor environments, e.g., open-plan offices [17,41], classrooms [33][34][35]47], and small offices [15,48].…”

“…The application of CJ for hybrid ventilation strategies has been studied since the early 2000s [20,32]. Numerous experimental and numerical studies have been performed on CJV in classrooms [10,[32][33][34][35][36][37], offices [17,25,31,[38][39][40][41][42][43][44] and assembly halls [45]. The results show a span of ε T from 95% to 131% and an ACE between 99 and 124% depending on the type of room and the configuration of the supply device.…”

“…Since the design parameters for CJV (nozzle spacing, nozzle diameter, jet exit velocity, and jet direction) greatly affect the airflow development and conditions in the occupied zone, it is vital to investigate how these parameters interact under different operational conditions (airflow rate and supply temperature) and how these interactions affect the CJV performance. This study is part of a series of studies [10,33,46] investigating a novel CJ supply device that uses a lower momentum than most other CJ devices and is mounted in the ceiling rather than a wall. The aim of this series of studies is to optimize the configuration of this kind of supply device for energy efficiency, IAQ, and thermal comfort.…”

Sustainable Buildings: Heating, Ventilation, and Air-Conditioning

“…Here, we provide a brief review of the articles [7][8][9][10][11][12][13][14] published in the Special Issue. A graphical summary of the key areas covered in the Special Issue is shown in Figure 2.…”