Search

The effect of temperature of the heating system elements is a parameter that could affect the airflow in terms of buoyancy and thermal comfort and that should be studied to ensure the quality of ventilation. This study aimed to assess the air change efficiency and thermal comfort with three thermal conditioning systems (radiators, underfloor heating and radiant ceiling) in winter conditions, varying its position in the interior space. This can be used by architects and engineers when planning the position of the heating systems or refurbishing a room. The experimental analysis was developed in the test chamber of the Laboratory of Ventilation of the University of Valladolid, serving as validation of multiple CFD simulations. The results show that, being the thermal comfort achieved, the mean air change efficiency varied only 2.40% among all cases, which makes this factor not significant. Even so, the trajectory of the airflow in the premise would be affected by the thermal action, due to the convective effect, presenting great differences according to the location of the thermal systems. Thus, the air trajectory could falter when it enters the room or rise towards the ceiling creating areas with lower temperature in its centre. [ABSTRACT FROM AUTHOR]

In developed countries, presence at home varies between 60% and 90% of the day, sleeping supposes 30%. Therefore, it is essential to ensure good indoor air quality that enhances health and benefits rest and recovery. In this context, it is necessary to achieve a balance between energy efficiency and air distribution parameters; thus, the influence exerted by the furniture of a bedroom on the air exchange efficiency, in the breathing zone during sleep, is assessed in this study. Computational fluid dynamics techniques, experimentally validated by the tracer gas (SF6) concentration decay method, are used to analyze 52 case studies corresponding to the same space, but varying both the number and the arrangement of the furniture inside. It is concluded that, in order to achieve a significant improvement in the air exchange efficiency, the number of elements included in the bedroom is not relevant, but the position of them. The highest increase in the ventilation efficiency in breathing zone is observed when the furniture is located avoiding the airflow obstruction in the area near the inlet and creating an unfilled volume of air in the area close to the outlet. [ABSTRACT FROM AUTHOR]

People spend most of their time indoors; therefore, maintaining a good indoor air quality and meeting the requirements of comfort and energy efficiency are essential. One of the most widespread strategies to achieve this objective is improving ventilation efficiency; therefore, the main aim of this study was to show an optimization of the ventilation efficiency, in a specific room, considering 47 variations (case studies) in the furniture arrangement. For this purpose, a numerical analysis using computational fluid dynamics techniques, validated by the tracer gas decay technique, was used to assess the distribution of the age of air within the space. The concept of “age of air” was implemented in the computational fluid dynamics code through user-defined functions, using the steady-state method based on the resolution of a transport equation for an additional scalar. Variations up to 5.75% in the ventilation efficiency between the cases studied have been achieved. It is concluded that an improvement up to 1.65% can be obtained when the elements of the study are introduced in a way that facilitates the air movement towards the exhaust; therefore, improvement of the ventilation efficiency through specific furniture distributions is possible, although not significant, according to the outcomes. [ABSTRACT FROM AUTHOR]

Built urban environments modify the air quality of the natural ventilation processes in buildings. The experimental assessment of outdoor air change (OACH) processes is complex due to the air volumes involved. The quality of the OACH can be analysed through the ventilation efficiency concept, which has been extensively studied in order to characterize the ventilation of indoor spaces. Ventilation efficiency through the age-of-the-air concept assesses the air-change capacity of a certain space. A procedure formulation for obtaining an adequate control domain (CD) to evaluate outdoor air change efficiency (OACE) is proposed. A methodology in two phases is presented: first, an evaluation stage, in which the outdoor air behaviour patterns are studied; then, a second phase where an ideal control domain (ICD) is obtained in order to comparatively assess several cases in similar urban environments. The outcomes determine a proposed ICD for evaluating the design of efficiently ventilated buildings in open urban built environments. The methodology of validation proposed simplifies the assessment of the building shape and its impact on the quality of the OACH by the OACE. The suggested ICD has dimensions of L = 5H; D = 3H; and T = 2H. ICD enables the representation of the air behaviour and fulfils the imposed requirements to evaluate efficiency with a mean accuracy lower than 0.6%. [ABSTRACT FROM AUTHOR]

The evaluation of the air quality in light shafts requires a specific study of its air renewal ability due to building shape, dimensions and other external conditions. This research has studied the capacity of light shafts to provide natural ventilation through the air change efficiency concept. A methodology based on the limitation of the computational urban domain is used to adapt the indoor air change efficiency index for outdoor environments. Numerical simulations were performed using CFD and a model that was experimentally validated.The aim is to evaluate the effect of the centreline building width and light shaft dimensions in the air change quality within several wind climates. Results would provide a numerically proven tool for designers, summarised in some design-based strategies in order to select which one improves the air change quality.The results indicate that the light shaft dimension perpendicular to the wind direction has a negligible effect on efficiency. For the range of wind velocities studied (0.75–9.00 m/s), the efficiency decreases at higher velocities, up to −7.41% with respect to the mean. For variations in the wind velocity and the centreline building width, a mean variation of ± 18.77% in the efficiency is obtained.Practical applications: The present methodology defines a proceeding to numerically evaluate the air change efficiency in light shafts inside different dimensional cases of buildings within several urban wind conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Convective strengths prevail with respect to the direction imposed on the air inlet. [•] Changes in age of the air depend on the flow pattern established by the temperatures. [•] The interchange of the energy causes the room average age not to change significantly. [•] CFD tools are very useful for the study of the airflows in rooms. [ABSTRACT FROM AUTHOR]