Ventilation for good indoor air quality and energy efficiency

As a result of new energy efficiency directives and legislations in Europe and elsewhere, the ventilation component of energy usage in buildings has increased relative to the total energy consumption. At the same time, the air quality in some buildings has in recent years deteriorated as building designers and managers have been aiming to design more air-tight buildings and reduce the energy consumption. This article gives a brief overview of the types of mechanical ventilation and air distribution systems that are used for buildings. It briefly describes the performance of traditional and some new types of ventilation systems in terms of indoor air quality (IAQ) provision. A method for evaluating the performance of air distribution systems that uses the ventilation and energy effectiveness is then introduced. This is based on the Air Distribution Index which has two different expressions, depending on the nature of the room environment in which the air distribution system is used. One method is for use in uniform environment and the other for both uniform and non-uniform conditions. The two methods are then applied to different types of room air distribution to compare their performances in terms of IAQ provision for occupants and energy efficiency

Influence of the airflow in a solar passive building on the indoor air quality and thermal comfort levels

The influence of the airflow in a solar passive building on the indoor air quality and thermal comfort levels was investigated. The numerical study for a university library was conducted using a software that simulates the building thermal behavior with complex topology, in transient conditions, for evaluating the indoor air quality and occupants’ thermal comfort levels for typical summer and winter days. Solar radiation was used as a renewable energy source to increase simultaneously the thermal comfort and air quality levels and reduce building energy consumption. Regarding the solar passive building, consideration was given to all of the building structure envelope, shading devices and interior details, while in the solar active building active ventilation was used. To analyze the airflow that simultaneously provides the best indoor air quality and thermal comfort levels, a new integral methodology based on the minimization of the total number of uncomfortable hours was used. The results show that it was possible to determine an air change rate that ensures a good compromise between thermal comfort and indoor air quality. An optimal air change rate of two and three renewals per hour had been determined, respectively, for winter and summer conditions

Computational fluid dynamics modelling of the air movement in an environmental test chamber with a respiring manikin

In recent years, computational fluid dynamics (CFD) has been widely used as a method of simulating airflow and addressing indoor environment problems. The complexity of airflows within the indoor environment would make experimental investigation difficult to undertake and also imposes significant challenges on turbulence modelling for flow prediction. This research examines through CFD visualization how air is distributed within a room. Measurements of air temperature and air velocity have been performed at a number of points in an environmental test chamber with a human occupant. To complement the experimental results, CFD simulations were carried out and the results enabled detailed analysis and visualization of spatial distribution of airflow patterns and the effect of different parameters to be predicted. The results demonstrate the complexity of modelling human exhalation within a ventilated enclosure and shed some light into how to achieve more realistic predictions of the airflow within an occupied enclosure

Energy production of solar DSF for ceiling-mounted localized air distribution systems in a virtual classroom

This paper presents an application of energy production in a solar Double Skin Facade (DSF) used in a Heating, Ventilation and Air-Conditioning (HVAC) system for a ceiling-mounted localized air distribution systems in a virtual classroom. In this numerical work, a virtual classroom, an inlet ceiling-mounted localized air distribution system, an exhaust ventilation system, and a DSF system are considered. The numerical simulations consider an integral building thermal response (BTR) and a coupling of an integral human thermal-physiology response (HTR) and differential computational fluid dynamics (CFD). The BTR numerical model calculates, among other parameters, the DSF indoor air temperature and energy production. The HTR numerical model calculates, among other parameters, the human thermal comfort. The CFD numerical model, among other parameters, calculates the indoor air quality. In this study which is performed for winter conditions, the energy produced in the DSF is used for driving the HVAC system. Six different airflow rates are used. The air temperature and energy production in the DSF are also evaluated. The influence of the airflow rate on the HVAC system performance is evaluated by the Air Distribution Index for mid-morning and mid-afternoon conditions. The results show that energy production reduces when the airflow increases and the operating point can be selected using the acceptable levels of thermal comfort and air quality levels or using the maximum Air Distribution Index value. In this study, the application of the thermal comfort and air quality levels criteria demonstrates that the HVAC system uses an optimum airflow rate.info:eu-repo/semantics/publishedVersio

Numerical simulation of Double Skin Facade used to produce energy in buildings

This article introduces a numerical model to project and construct a Double Skin Facade (DSF) in windows facing south, in order to be used on thermal energy generation in winter conditions. The DSF system is applied to a virtual chamber similar to a real experimental chamber and it is connected to a mixing ventilation system. The thermal energy generated by this DSF system is used to further indoor air quality and thermal comfort for occupants. The numerical simulation is done by a software that simulates the virtual chamber and the DSF thermal response. This software uses energy and mass balance integral equations for the opaque surfaces, transparent surfaces and internal air. It also considers the solar radiation simulator, the glass radiative properties and the assessment of radiative and convective coefficients. The results show that the proposed DSF system, using solar radiation, contributes to having acceptable conditions of thermal comfort, during most of the occupation cycle, and indoor air quality.publishedVersio

Development and Application of a Ventilation System Based on Vertical Descendent Confluent Jets

This paper presents the development and application of a ventilation system based on vertical confluent jets. The thermal comfort and indoor air quality levels, Air Distribution Index and energy consumption are evaluated and discussed. The numerical study is carried out in a virtual chamber with dimensions of 4.502.552.50 m3. This chamber is equipped with six tables, twelve chairs, one outlet system and one confluents jets system, and is occupied with twelve virtual occupants. The inlet system has two horizontal 0.15 m diameter ducts, installed at a height of 1.8 m from the floor, which have consecutive holes in order to promote downward jets close to the side walls. The outlet system has six air ducts, located above the head of the occupants, connected to the ceiling area. The study was developed for three different airflow rates, considering winter conditions. When the airflow rate increases, indoor air quality improves, thermal comfort remains within an acceptable level and ADI improves slightly.publishedVersio

Energy production in solar collectors in a university building used to improve the internal thermal conditions in winter conditions

In this numerical study the energy production in solar collectors in a University building used to improve the internal thermal conditions is made. Passive and active solutions, using external solar collector and internal thermo-convectors, are used. The numerical simulation, in transient conditions, is done for a winter typical day with clean sky. This numerical study was carried out using a software that simulates the Building Dynamic Response with complex topology in transient conditions. The software evaluates the human thermal comfort and indoor air quality levels that the occupants are subjected, Heated Ventilation and Air Conditioned energy consumption, indoor thermal variables and other parameters. The university building has 107 compartments and is located in a Mediterranean-type environment. External solar water collectors, placed above the building’s roof, and internal thermo-convectors of water/air type, using mixing ventilation, are used as passive and active strategies, respectively. The thermal comfort level, using the Predicted Mean Vote index, and the indoor air quality, using the carbon dioxide concentration, are evaluated. The results show that in winter conditions the solar collectors improve the thermal comfort conditions of the occupants. The indoor air quality, in all ventilated spaces, is also guaranteed.SAICT-ALG/39586/2018info:eu-repo/semantics/publishedVersio

Production of thermal energy in university building greenhouses in cold climate conditions

The present work focuses on the production of thermal energy in University building greenhouses in cold climate conditions. The building model uses a system of energy and mass balance integral equations, which are solved by the Runge–Kutta–Felberg method with error control. This numerical study is about the thermal behaviour of a university building with complex topology, in winter and transient conditions. The thermal comfort of the occupants, using the Predicted Mean Vote index, and the indoor air quality, using the carbon dioxide concentration, are evaluated. This building has 319 compartments distributed by four floors and it is equipped with one internal greenhouse in the third floor. This greenhouse is located on the south facing facade and the heated air in this space will be transported to compartments located on the north facing façade. The spaces subject to the influence of the heated air coming from the greenhouse improve the level of thermal comfort of its occupants. The level of indoor air quality in occupied spaces is acceptable according to international standards.SAICT-ALG/39586/2018; (CRESC Algarve 2020)info:eu-repo/semantics/publishedVersio

Development of a double Skin Facade system applied in a virtual occupied chamber

In this study a system constituted by seven double skin facades (DSF), three equipped with venetian blinds and four not equipped with venetian blinds, applied in a virtual chamber, is developed. The project will be carried out in winter conditions, using a numerical model, in transient conditions, and based on energy and mass balance linear integral equations. The energy balance linear integral equations are used to calculate the air temperature inside the DSF and the virtual chamber, the temperature on the venetian blind, the temperature on the inner and outer glass, and the temperature distribution in the surrounding structure of the DSF and virtual chamber. These equations consider the convection, conduction, and radiation phenomena. The heat transfer by convection is calculated by natural, forced, and mixed convection, with dimensionless coefficients. In the radiative exchanges, the incident solar radiation, the absorbed solar radiation, and the transmitted solar radiation are considered. The mass balance linear integral equations are used to calculate the water mass concentration and the contaminants mass concentration. These equations consider the convection and the diffusion phenomena. In this numerical work seven cases studies and three occupation levels are simulated. In each case the influence of the ventilation airflow and the occupation level is analyzed. The total number of thermal and indoor air quality uncomfortable hours are used to evaluate the DSF performance. In accordance with the obtained results, in general, the indoor air quality is acceptable; however, when the number of occupants in the virtual chamber increases, the Predicted Mean Vote index value increases. When the airflow rate increases the total of Uncomfortable Hours decreases and, after a certain value of the airflow rate, it increases. The airflow rate associated with the minimum value of total Uncomfortable Hours increases when the number of occupants increases. The energy production decreases when the airflow increases and the production of energy is higher in DSF with venetian blinds system than in DSF without venetian blinds system.SAICT-ALG/39586/2018, CRESC Algarve 2020info:eu-repo/semantics/publishedVersio

Application of semi-circular double-skin facades in auditoriums in winter conditions

The DSF (double-skin facade) system is an important element in building design and is used in adjacent spaces to control the inlet solar radiation, heat the air, reduce energy consumption, decrease the acoustics levels, and produce photovoltaic energy, among other improvements. The DSF system can, for example, be used in winter conditions to heat the air, which is then transported to non-adjacent spaces to improve the thermal comfort level and the indoor air quality that the occupants are subjected to. Smooth DSF systems, which are a focus in the literature, are subjected to higher solar radiation levels at a specific hour of the day. The semi-circular DSF system used in this work, which was built from a group of smooth DSF systems with different orientations, guarantees the reception of the highest incident solar radiation throughout the entire day. This work presents a numerical study of a new DSF system, called the semi-circular DSF. The DSF system consists of a set of 25 smooth DSFs with different orientations, each one consisting of an outer glazed surface and an inner surface provided by the outer facade of the auditorium, both separated by an air channel. In this work, the influence of the radius of the semi-circular DSF system and the opening angle of the DSF system on the thermal response of the auditorium was analysed. Thus, six auditoriums were considered: two sets of three auditoriums with radii of 5 m and 15 m, with each of the auditoriums having a different DSF opening angle (45°, 90°, and 180°). It was found that the greater the radius of the semi-circular DSF and the opening angle of the DSF system, the greater the area of its glazed surface and, consequently, the greater the availability of solar heating power. Therefore, during the occupation period, only the set of auditoriums with the largest semi-circular DSF radius managed to present acceptable levels of thermal comfort, which were verified from mid-morning until late afternoon. As for the opening angle of the DSF system, the influence was not very significant, although slight improvements in thermal comfort were noted when the value of this angle was reduced (see Case F as an example) due to the corresponding decrease in the volume of indoor air to be heated. In all auditoriums (see Case A to Case F), it was verified that the indoor air quality was acceptable for the occupants, so the airflow rate was adequately promoted by the ventilation system.info:eu-repo/semantics/publishedVersio