Evaluation of integral effect of thermal comfort, air quality and draught risk for desks equipped with personalized ventilation systems

This work evaluates the integral effect of thermal comfort (TC), indoor air quality (IAQ) and Draught Risk (DR) for desks with four personalized ventilation (PV) systems. The numerical study, for winter and summer thermal conditions, considers a virtual chamber, a desk, four different PV systems, four seats and four virtual manikins. Two different PV configurations, two upper and two lower air terminal devices (ATD) with different distance between them are considered. In this study a coupling of numerical methodology, using one differential and two integral models, is used. The heating, ventilating and air conditioning (HVAC) system performance in this work is evaluated using DR and room air removal effectiveness (εDR) that is incorporated in an Air Distribution Index (ADI). This new index, named the Air Distribution Turbulence Index (ADTI), is used to consider simultaneously the TC, the IAQ, the DR and the effectiveness for heat removal (εTC), contaminant removal (εAQ) and room air removal (εDR). The results show that the ADI and ADTI, are generally higher for Case II than for Case I, increase when the inlet air velocity increases, are higher when the exit air is located at a height 1.2 m than when is located at 1.8 m, and are higher for summer conditions than for winter conditions. However, the values are higher for the ADI than ADTI.SAICT-ALG/39586/2018 (CRESC Algarve 2020)info:eu-repo/semantics/publishedVersio

Going native? Flower use by bumblebees in English urban gardens.

BACKGROUND AND AIMS: Although urban gardens provide opportunities for pollinators in an otherwise inhospitable environment, most garden plants are not native to the recipient biogeographical region and their value to local pollinators is disputed. This study tested the hypothesis that bumblebees foraging in English urban gardens preferentially visited sympatric Palaearctic-range plants over species originating outside their native range. METHODS: Twenty-seven surveys of flower availability and bumblebee visitation (Bombus spp.) were conducted over a 3-month summer period. Plants were categorized according to whether they were native British, Palaearctic or non-Palaearctic in origin. A phylogeny of the 119 plant species recorded was constructed and the relationship between floral abundance and the frequency of pollinator visits investigated by means of phylogenetically independent contrasts. Differentiation in utilization of plant species by the five bumblebee species encountered was investigated using niche overlap analyses. KEY RESULTS: There was conflicting evidence for preferential use of native-range Palaearctic plant species by bumblebees depending on which plants were included in the analysis. Evidence was also found for niche partitioning between species based on respective preferences for native and non-native biogeographical range plants. Two bumblebees (Bombus terrestris and B. pratorum) concentrated their foraging activity on non-Palaearctic plants, while two others (B. hortorum and B. pascourum) preferred Palaearctic species. CONCLUSIONS: The long-running debate about the value of native and non-native garden plants to pollinators probably stems from a failure to properly consider biogeographical overlap between plant and pollinator ranges. Gardeners can encourage pollinators without consideration of plant origin or bias towards 'local' biogeographical species. However, dietary specialist bumblebees seem to prefer plants sympatric with their own biogeographical range and, in addition to the cultivation of these species in gardens, provision of native non-horticultural ('weed') species may also be important for pollinator conservation

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

Predicting the air quality, thermal comfort and draught risk for a virtual classroom with desk-type personalized ventilation systems

This paper concerns the prediction of indoor air quality (IAQ), thermal comfort (TC) and draught risk (DR) for a virtual classroom with desk-type personalized ventilation system (PVS). This numerical study considers a coupling of the computational fluid dynamics (CFD), human thermal comfort (HTC) and building thermal behavior (BTB) numerical models. The following indexes are used: the predicted percentage of dissatisfied people (PPD) index is used for the evaluation of the TC level; the carbon dioxide (CO2) concentration in the breathing zone is used for the calculation of IAQ; and the DR level around the occupants is used for the evaluation of the discomfort due to draught. The air distribution index (ADI), based in the TC level, the IAQ level, the effectiveness for heat removal and the effectiveness for contaminant removal, is used for evaluating the performance of the personalized air distribution system. The numerical simulation is made for a virtual classroom with six desks. Each desk is equipped with one PVS with two air terminal devices located overhead and two air terminal devices located below the desktop. In one numerical simulation six occupants are used, while in another simulation twelve occupants are considered. For each numerical simulation an air supply temperature of 20 degrees C and 24 degrees C is applied. The results obtained show that the ADI value is higher for twelve persons than for six persons in the classroom and it is higher for an inlet air temperature of 20 degrees C than for an inlet air temperature of 24 degrees C. In future works, more combinations of upper and lower air terminal devices located around the body area and more combinations of occupants located in the desks will be analyzed.ASHRAE Undergraduate Senior Project Grant Programinfo:eu-repo/semantics/publishedVersio

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

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

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

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

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