Roof Ventilation Research Articles

Transpired solar collectors in building service engineering: Combined system operation and special applications

One of the easiest ways to integrate renewable sources of energy into the heat producing system of a building is the application of transpired solar collectors. They are widespread in North America, where air heating is a common heating alternative, but they are gaining bigger share in the European solar thermal market nowadays. Their simple construction, maintenance-free operation and high working efficiency result in low capital and operating costs. The combination of TSC with other system elements results in additional benefits. Preheating the combustion air of large-scale boilers results in the increase of boiler efficiency and thus the reduction of natural gas consumption and CO2 emission. Whether to choose TSC or heat recovery unit for a certain air conditioning system has to be investigated by examining efficiency-influencing factors of both systems. Besides solar air heating, transpired solar air collectors can reduce the cooling demand on a building. Roof ventilation and nocturnal radiant cooling are two alternatives, which are being presented in the current paper.

Modeling the suitability of the traditional plastic greenhouse for tomato production across Colombian regions

Greenhouse tomato production in Colombia has increased at a rate of 250 t year-1 in the last decade, but yield has remained constant around 106 t ha-1 year-1. The main reasons for this trend is that greenhouses used for tomato cropping are still vulnerable to the high seasonal and intraseasonal climate variability in the Equatorial Zone. To obtain information about the relation between outdoor and indoor environments, we analyzed productive areas with a greenhouse climate model (GCM). The GCM was calibrated, validated and used to simulate the thermal behavior of traditional greenhouses under different climate conditions in Colombia. The input climate variables included global radiation, outside air and soil temperatures, relative humidity and wind velocity recorded at six locations. The locations are situated between 2000 and 3000 m a.s.l. with average temperatures between 10-20°C characterized by unimodal or bimodal rainfall regimes. Automatic weather stations recorded the hourly climate data during tropical wet and dry seasons. The modeled greenhouse was a naturally ventilated plastic one with a floor area of 5670 m2, surface of the cover including side walls of 9610 m2, and maximum roof and side ventilation area of 324 and 370 m2, respectively. The simulations were carried out with the presence of a tomato crop. The simulations showed that traditional structures keep appropriate temperatures for tomato, mainly during the dry season at the six locations. The wind profile for each season explained these results, affecting the efficiency of natural ventilation. The change in the wind profile is due to the meridional migration of the intertropical convergence zone throughout the year. Therefore this atmospheric system is a factor to take into account when designing sidewall and roof ventilation openings. For cold marginal tomato production areas, predictions showed the potential to explore passive heating systems to improve the climate during night hours.

Effects of the spacing of roof ventilation devices on the environment and the yield of oriental melons in single-span plastic greenhouses

The purpose of this study is to provide the standard for the proper installation of roof ventilation devices in single-span plastic greenhouses. The amount of ventilation was 19,140 m3 h-1 in the greenhouse with fans installed at intervals of 15 m, and 15,845 m3 h-1 with fans installed at intervals of 20 m. The amount of ventilation was 14,961 m3 h-1 in the greenhouse with stacks installed at intervals of 6 m, and 13,414 m3 h-1 with stacks installed at intervals of 8 m. As a result of analyzing changes in average day-time temperature during June, a high-temperature period, it was found that the narrower the spacing of ventilation devices, the lower the air temperature; and that air temperature in the greenhouse with fans was lower than that in the greenhouse with stacks. As a result of examining the yield of oriental melons per the span of greenhouse (605 m2), it was found that the yield in the greenhouse with fans installed at intervals of 15 m was 5,075 kg, 8.6% more than that in the greenhouse with fans installed at intervals of 20 m. And the yield in the greenhouse with stacks installed at intervals of 6 m was 4,405 kg, 7.2% more than that in the greenhouse with stacks installed at intervals of 8 m. As a result of analyzing economic efficiency according to roof ventilation device treatments, taking into account the value of oriental melon production, the depreciation of ventilation devices, the electric charges, and the expenses for selection and packaging, it was found that income increased KRW 865,450 in the case of spacing fans 15 m apart, compared with the case of spacing them 20 m apart; and that income increased KRW 660,690 in the case of spacing stacks 6 m apart, compared with the case of spacing them 8 m apart.

Optical properties of traditional clay tiles for ventilated roofs and implication on roof thermal performance

A remarkable advantage of clay tiles roof coverings in hot climates is the realization of a ventilated air layer between them and the roofing underlay that allows a natural and forced convection through the tiles joints and the channel from eaves to ridge, thus cooling the roof materials. However recently, in many countries, regulatory developments on buildings energy efficiency or buildings sustainability certification protocols are increasingly encouraging the use of alternative strategies, with the aim of reducing the urban heat island (UHI) effect and the buildings’ cooling consumptions. Among them, the use of ‘cool’ materials for roof covering. These mandatory or voluntary measures de facto push the construction products market towards specific directions, risking penalizing traditional components such as clay tiles. This article reports the results of experimental and numerical activities carried out in order to extensively characterize the optical properties of clay tile materials and investigate their impact, also coupled with above sheathing ventilation, on the thermal performance of a ventilated roof under warm-temperate climate. In the first phase of the research, the main optical properties of over 30 different clay products have been experimentally characterized in order to get a clear and extensive picture of such properties for the materials spread in the market. In a second phase, starting from the thermal data collected on an experimental real-scale building, a dynamic energy analysis tool was calibrated and used to perform simulations by varying the optical properties of the roof covering thus assessing the impact on the roof temperatures, also in comparison to a clay tiles roof. The results underline that the use of the above sheathing ventilation obtained through clay tiles is an effective strategy to reduce roof temperatures, even if covering materials are not qualified as ‘cool’, thus impacting on both UHI and indoor comfort.

Network modelling of dry-type transformer cooling systems

PurposeThe application of dry-type transformers is growing in the market because the technology is non-flammable, safer and environmentally friendly. However, the unit dimensions are normally larger and material costs become higher, as no oil is present for dielectric insulation or cooling. At designing stage, a transformer thermal model used for predicting temperature rise is fundamental and the modelling of cooling system is particularly important. This paper aims to describe a thermal model used to compute dry transformers with different cooling system configurations.Design/methodology/approachThe paper introduces a fast-calculating thermal and pressure network model for dry-transformer cooling systems, preliminarily verified by analytical methods and advanced CFD simulations, and finally validated with experimental results.FindingsThis paper provides an overview of the network model of dry-transformer cooling system, describing its topology and its main variants including natural or forced ventilation, with or without cooling duct in the core, enclosure with roof and floor ventilation openings and air barriers. Finally, it presents a formulation for the new heat exchanger element.Originality/valueThe network approach presented in this paper allows to model efficiently the cooling system of dry-type transformers. This model is based on physical principles rather than empirical assessments that are valid only for specific transformer technologies. In comparison with CFD simulation approach, the network model runs much faster and the accuracies still fall in acceptable range; therefore, one is able to utilize this method in optimization procedures included in transformer design systems.

Evolución tipológica de cubiertas ventiladas ‘a la catalana’ en la obra de Antonio Bonet

En este trabajo analizamos la evolución de una serie de edificios diseñados por Antonio Bonet que comparten una tipología constructiva de origen vernáculo: la cubierta ventilada ‘a la catalana’. Trataremos de demostrar el método investigador de Bonet quien no concibe la forma en sus proyectos como una pura invención personal. El patrón puede mutar o transgredirse por diferentes motivos, ya sea para adaptarse al avance tecnológico de un sistema constructivo, ya sea por adaptaciones topográficas, climáticas o programáticas. 
 
 A partir de la información del archivo del arquitecto, elaboramos y presentamos nueva documentación gráfica, a través del redibujado de las obras, con el objetivo de ordenar un material de archivo de difícil acceso por diferentes motivos: dispersión, diferencia de escalas, diferentes soportes gráficos. Con este trabajo, cualquier interesado puede obtener los datos básicos de cada edificio.

Numerical investigation of an inclined rectangular cavity for ventilated roofs applications

The present paper illustrates a numerical investigation on natural convection within an inclined rectangular cavity, which can be considered as a prototypal ventilated roof for residential use. Three different two dimensional cases are considered, namely a symmetric geometry where half of the domain is considered, a symmetric geometry taking into account the complete ridge and a complete geometry. The length of the roof is 6.0 m, inclined with respect to the horizontal plane of 30° and the ventilated channel has a height of 10 cm. The investigation is performed in order to evaluate the thermal and fluid dynamic behaviors of the ventilated roof as a function of the following parameters: 1) exit section of the channel; 2) heat flux on the top wall of the cavity; 3) boundary condition on the bottom wall of the cavity.The problem is solved numerically by using of the commercial code Ansys-Fluent by considering a two-dimensional steady model in turbulent conditions. Results are determined for a uniform heat flux on the top wall and the turbulence is taken into account by using the k-ε model.Different cases are proposed in terms of variation of the outlet section, boundary conditions on the lower surface of the roof and heat flux on the top wall according to the sun position. Results are given in terms of wall temperature distributions, air velocity and temperature profiles in different cross section of the roof, so that the differences among the various configurations can be appreciated.

Wind pressure coefficients for roof ventilation purposes

Wind pressure coefficients (cp) are important inputs for analytical calculations of wind load. The aim of this research is to investigate wind pressure coefficients on a test house located in Norway in order to pave the way for improved analysis of wind-driven roofing ventilation. The large-scale test measurements show that the wind pressure coefficient along the eaves of the house varies with different wind approach angles. Assuming wind-driven air flow through the air cavity beneath the roofing, an average Δcp¯ value of 0.7 is derived for practical engineering purposes. The results from the study are applicable for single or two-storey houses with pitched roofs at different roof angles.

Passive cooling of the green roofs combined with night-time ventilation and walls insulation in hot and humid regions

Green roof and night-time ventilation are promising passive cooling strategies. These two strategies and walls insulation have been researched separately in many studies. In this paper, a new strategy combining the three techniques together is discussed. Based on the analyses of a field experiment of a single-story building with green roof in Shanghai, a model was established using DesignBuilder software and validated with the experimental building. And then, the model with green roof was simulated in three cases: no ventilation, night-time ventilation and night-time ventilation combined with walls insulation. Results show that when the night ventilation operated, the indoor temperature under green roof decreased while the air change rate increased. With the improvement of external walls insulation, the cooling effect of the night ventilation becomes more obvious for the extensive green roofs. Additionally, a simplified multiple regression model is proposed to assess the passive cooling of green roof which combined with night ventilation and walls insulation in hot and humid regions. According to the model, for a building with green roof, the indoor average temperature can be reduced by up to 2.3 °C compared with the building combined with night ventilation and walls insulation together.

Modeling of Natural Ventilation Using a Hierarchical Fuzzy Control System for a New Energy-Saving Solar Greenhouse

Abstract. Natural ventilation as part of a greenhouse environment control system can save energy, reduce pollution, and cut the costs of production. Many studies have used the energy balance method to model greenhouse environments and calculate the rates of ventilation needed to control them. However, the efficacy of this method is influenced by many factors. There are often many parameters in the energy balance model, related to the greenhouse structure, crop growth, and climate. Thus, the effectiveness and applicability of greenhouse ventilation systems based on energy balance can be compromised. Here, we study a hierarchical fuzzy control method and use simple fuzzy logic controllers to control the coordination and opening angles of a new energy-saving solar greenhouse roof and sidewall ventilation. This design reduces the complexity of the fuzzy rule base and the fuzzy subsystem related to the physical model, therefore making it easy to design and build. The system uses the fuzzy tool in the Matlab environment, enabling a quick design, and the fuzzy inference engine fis.c file (Fuzzy Inference System) to load the design results into the fuzzy control system, thus making the modification and maintenance of the system easier. The experimental data showed that the new hierarchical fuzzy control reduced temperature fluctuations and maintained temperature closer to desired temperature than a non-fuzzy control method. Moreover, this method can also be easily used to control other equipment in the greenhouse. Keywords: Hierarchical fuzzy model, Natural ventilation, Matlab, Solar greenhouse.

Energy Saving Potential with a Double-Skin Roof Ventilated by Natural Convection in Djibouti

In the Sub-Saharan African countries like Djibouti, the energy situation, the high rate of urban areas growth and the inadequate techniques of construction offer an exciting potential for the bioclimatic approach and sustainable construction. However, this poorly explored potential requires an investigation of different construction types in Djibouti and a good knowledge of the behavior of buildings components. Further a low energy building can be obtained because of the good realization of all its components. In fact, roofs call for attention as they represent a large part of a building’s total surface area and amount of absorbed solar radiation. The goal of this paper is to investigate the benefit of using double skin-ventilated roofs for reducing cooling load under the Djiboutian climate. It is a first step towards ideas that will transform local construction practices to make them effective in energy, economic and functional dimensions. During investigation, we compared a ventilated roof assembly with traditional configuration after that the consistency of our model was validated with experiment of the literature findings. The computational fluid dynamics (CFD) model has been used for the characterization of the airflow and heat transfer phenomena in the ventilation cavity and provide fundamental information about the thermal performance of the roof. The results show the amount of the energy saving obtainable by the double-skin ventilated roof.

Experimental analysis of an innovative tile covering for ventilated pitched roofs

This study investigates the thermal and fluid-dynamic behaviour of two ventilated roofs equipped with a new tile shape in comparison with a standard Portuguese tile. The novel tile shape was designed to improve the air permeability of coverings, thus producing a further above sheathing ventilation (ASV) enhancement as proposed in the ongoing LIFE HEROTILE European project, in which original roof tiles with innovative sidelock and headlock patterns have been designed, produced and are now under testing with real operating conditions. The heat transfer in the different roof layers and the ASV fluid flow have been experimentally analysed by means of a dedicated real scale mock-up. The results of the preliminary testing period are presented in this paper, they are referred to a first period with open eaves and to a second one in which eaves were closed to observe the only effect of tile air permeability. The data analysis shows that the ASV is strictly linked to the external wind conditions and grants better performances in HEROTILE roof. Moreover, the new tile design produces a significant increase of the ASV, so that better thermal performances are achievable in reducing solar heat gain during hot periods. As a consequence, the mock-up with HEROTILE ventilated roofs need less energy for air conditioning and allows high energy saving when compared with the standard one.

Effects of an Improved Side Vent on Yield of Oriental Melon and Temperature in Single-span Plastic Greenhouse with Roof Ventilation Fans

Effects of an Improved Side Vent on Yield of Oriental Melon and Temperature in Single-span Plastic Greenhouse with Roof Ventilation Fans

Thermal analysis of extensive green roofs combined with night ventilation for space cooling

Green roofs and night ventilation are well-known passive techniques for energy saving during cooling period. This study refers to the analysis of thermal properties and energy performance of the combination of green roof and night ventilation. Firstly, a field experiment was conducted to compare the thermal performance of green roof and bare roof when combining with night ventilation. Three series experiments were carried out to analyze cooling effect of green roof with and without night ventilation on summer sunny day and another experiment with natural ventilation all day long on summer rainy day was also monitored. Then, data from the field study were used to validate the green roof and night ventilation model incorporated within a building energy simulation program. This model was then used to estimate the energy saving for an office building in three typical climates. Results show that combining green roofs and night ventilation can significantly reduce the indoor air temperature and heat gains on sunny day but have no appreciable effect on rainy day. Because the cooling potential of green roof and night ventilation strongly depends on the climate and thermal mass, a simple equation to assess the air flow rate of night ventilation when combined with green roof was proposed. Furthermore, the correlation analysis between weather factors and cooling effect of green roofs as well as the air organization mode for night ventilation is also discussed.

Thermal behavior evaluation of ventilated roof under summer and winter conditions

Thermal behavior evaluation of ventilated roof under summer and winter conditions

Energy saving effect of air circulation heat storage system using natural energy

A central air circulation system that uses a roof ventilation layer and a phase change material (PCM) unit is proposed as a possible means of controlling thermal load and peak load. The central air-conditioning air-circulation-type system enables reduction of sensible heat load and facilitates radiative cooling/forced heat exchange in summer, and solar heat collection in winter, via the roof ventilation layer; thereby improving efficiency. The PCM unit is incorporated into the air circulation route to store the cold energy of the cooled air by radiative cooling and the heat energy of the heated air by solar heat collection. The actual measurement results of an experimental house were analyzed and numerical simulations were performed to evaluate the effective sensible heat and peak load reductions. The quantitative simulation and experimental results indicate that significant sensible heat reduction can be achieved by employing the proposed system, which uses natural energy to reduce the energy consumption of indoor temperature control.

REDESAIN PASAR CEPOGO DENGAN PENDEKATAN ARSITEKTUR KONTEKSTUAL DI BOYOLALI

<p><strong><em>Abstract:</em></strong><em> </em><em>Pasar Cepogo is a public commercial centre in Cepogo. This traditional market is the preferred place to shop daily needs by the residents of Cepogo and people living in its surrounding area since it offers array of affordable prices.</em><em> </em><em>There are </em><em>social aspects of the tradition manifested in the way bargains are settled</em><em>. Yet, this market still has </em><em>problem</em><em>s</em><em> such as inconvenient environment, cluttered floor plan, unc</em><em>harte</em><em>d activities, and decaying infrastructures</em><em>. Based on these conditions</em><em>, the design</em><em> problem consists of creating a space to cater all activities in Pasar Cepogo and taking form fitting to its surrounding in order to maintain its existence as a traditional market. </em><em>Redesign project of Pasar Cepogo aims to improve the condition of the market in order to provide convenient commercial space suiting present-day demand without leaving its traditional roots</em><em>.</em><em> </em><em>Hence, contextual architecture ap</em><em>p</em><em>roach is considered fit the notion. Contextual theme aspires to appropriate the redesigned building for its site, which concerns physical features, climate, culture, and local architecture aspects of the surrounding area</em><em>. Physical features approach influence the site management adapted to the site conditions. Climate aspects approach is implemented into design response to the local climate, such as the use of a high and sloping roof, tritisan, and cross ventilation. The cultural approach is actualized into the space management adapted to the context of activities in Pasar Cepogo. Local architecture approach is implemented into the form and appearance of the building, adjusting Java architecture and Hindu architecture that once evolved in Cepogo.</em><em></em></p><p> </p><p><strong><em>Keywords</em></strong><em>: </em><em>C</em><em>ontextual </em><em>A</em><em>rchitecture, </em><em>M</em><em>arket </em><em>R</em><em>edesign, </em><em>T</em><em>raditional </em><em>M</em><em>arke</em><em>t.</em></p>

Life-cycle cost analysis of roofing technologies in tropical areas

Various technologies have been applied on roofs to reduce the air-conditioning load in buildings during summer or in tropical areas, including cool paint, roof ventilation, mass and reflective insulation. These technologies help to reduce roof temperatures or heat transmission effectively in summer at different economic costs. It is desirable to evaluate the cost effectiveness of different roofing technologies, especially in the tropical climate.This work analyzes the heat gains of concrete-based roofs combined with different roofing technologies, as well as the cost effectiveness of these technologies in the tropical climate of Singapore. The transient roof temperatures and heat transmissions are predicted using Complex Fast Fourier Transform (CFFT) method, and the impacts of roof ventilation on heat gain are predicted using correlations proposed for convective resistance prediction via computational fluid dynamics (CFD) simulation. The daily heat gains of different roof components are hence predicted, and Life-cycle Cost Analysis (LCCA) is performed to evaluate the payback periods of different roofing technologies, including cool paint, expanded polystyrene foam (EPS), radiant barrier (RB), and roof (natural and forced) ventilation. It is concluded that the application of cool paint on unventilated roof shows the shortest payback period, and the combined use of RB and natural ventilation yields the largest energy savings in the long run. Compared with forced ventilated roofs, those passive roof technologies (cool paint, RB, air gap and EPS foam) without electricity requirement are more recommended, due to their cost effectiveness.

A ventilation system in the Portuguese mining company Almina

In order to work in a mine, two main requirements have to be met - roof and ground support and ventilation support. Roof and ground support is important because in case of an accident, workers can, without problems, evacuate the mine. However, besides roof and ground support, in order to fulfill normal working conditions inside the mine, a ventilation system is a valuable and key part of the working process. This paper represents the ventilation system in the Portuguese mining company Almina. It encompasses a ventilation system in the underground and on the surface. The main problems of a ventilation system are discussed, as well as a short scheme of fresh air inhalation and stale air exhalation outside the mine. The result of the paper was to figure out how the ventilation system operates in practice. The aim of the paper was to present a real ventilation system by taking into consideration the fact that there are no mining companies in the Republic of Croatia where people could learn facts of mining companies and ventilation systems, which is very important in case of dangerous situations.

Effects of Modified Installation Methods of Roof Ventilation Devices in the Single-span Plastic Greenhouses on Yield and Fruit Quality of Oriental Melon

Effects of Modified Installation Methods of Roof Ventilation Devices in the Single-span Plastic Greenhouses on Yield and Fruit Quality of Oriental Melon