Airflow Fluctuation from Linear Diffusers in an Office Building: The Thermal Comfort Analysis

In buildings, the HVAC systems are responsible for a major part of the energy consumption. Incorrect design or selection of the system and improper installation, operation, and maintenance of the systems’ elements may result in increased energy consumption. It is worth remembering that the main aim of the appropriate system is to maintain the high quality of the indoor environment. Appropriate selection of the HVAC solution ensures both thermal and quality parameters of the air, independently of the internal and external heat loads. The microclimate of a room is affected not only by air temperature, humidity, and purity, but also by air velocity in the occupied zone. The proper air velocity distribution prevents discomfort, particularly at workstations. Based on the measurements in the office building, an analysis of velocity profiles of air supplying two different types of linear diffusers was carried out. The analysis was made based on the results of measurements performed with thermoanemometers in the actual facility. During the study, temperature of the supply air was lower that the air in the room. Analysis was focused on the airflow fluctuation and its impact on the users’ comfort. This is an obvious topic but extremely rarely mentioned in publications related to air diffusers. The results show the importance of air fluctuation and its influence on the users’ comfort. During the measurements, the instantaneous air velocity for one of the analyzed types of the diffuser was up to 0.34 m/s, while the average value from the period of 240 s for the same measuring point was relatively low: it was 0.19 m/s. Only including the airflow variability over time allowed for choosing the type of diffuser, which ensures the comfort of users. The measurements carried out for two linear diffusers showed differences in the operation of these diffusers. The velocity in the occupied zone was much higher for one type (0.36 m/s, 3.00 m from diffusers) than for another one (0.22 m/s, 5.00 m from diffusers). The improper selection of the diffuser’s type and its location may increase the risk of the draft in the occupied zone.

FEATURES OF VENTILATION SYSTEMS IN AUDITORIUM

The choice of air distribution scheme is the most important task which determines indoor air quality, comfort thermal mode of the room and effectiveness of ventilation systems. The article presents comparative analysis of displacement and mixing ventilation systems for large premises. The methodology of the study is based on existing theoretical provisions and standard calculation approach of supply air jets. Multivariate calculations of mixing air distribution in cinema hall are presented. Horizontal jets along room surfaces can not provide required air velocity. In the case of vertical air distribution relative jet area beyond the recommended values. This factor had thus determined the possible formation of circulation contours with high concentrations of harmful emissions. The results of the calculation shows that the speed of the fan jet at the entrance of occupied zone lower than maximum permissible air mobility. The required temperature is achieved by using all air-distributing units considered.

Modelling indoor pollutant distribution via passive scalar and virtual box approach

The distribution of PM2.5 around a thermal manikin with realistic female body shape in a naturally ventilated room has been modelled. The health risk (HR) due to inhalation of the PM2.5 has been quantified by integrating the pollutants mass flux over the boundaries of a virtual box around the mannequin’s head (the breathing zone). By the same approach HR is evaluated over the boundaries of another virtual box that surrounds the manikins body and defines the occupied zone. The paper focuses on the peculiarities of creating and meshing a virtual geometry, as well as on the application of user-defined functions (UDF) for defining a pollutant source within the room using Ansys Fluent modelling package.

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

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.

In Hiding, 1942–44

This chapter describes the continuous imposition of anti-Semitic measures on all parts of everyday life for Jews in the Occupied Zone by the summer of 1942. It recounts Raymond Sarraute's return from Drancy after being cleared of any suspicion of Jewishness and the practical measures he came up with to keep his wife, Nathalie Sarraute, out of harm's way. It talks about Nathalie and her family's stay at a gardener's cottage in the village of Janvry, which Raymond visits on the weekend after he resumed his legal practice. The chapter details how Nathalie resumed her writing in the café two doors along from the cottage, where completed what she later described as a sequel to “tropisms.” It mentions Raymond's participation in various Resistance groups, including one supported by the lawyers at the Paris Bar.