A new type of double-skin façade configuration for the hot and humid climate

The performance of the double-skin façade depends closely on the chosen ventilation means within its intermediate space. The modes of ventilation could be natural (buoyancy driven), forced (mechanically driven) or mixed (both natural and forced). Oesterle et al. has attempted to classify the double-skin constructions into four different types, namely box window façade, shaft-box façade, corridor façade and multi-story façade. A number of interesting investigations and findings are reported in the literature pertaining to passive ventilation in buildings and the thermal performance of double-skin facades. The researches have revealed close link between natural ventilation design and the function of double-skin façade. Most of them are using the idea of stack effect or the solar chimney concept and found that passive ventilation in summer is possible even for multi-storey buildings. It was found that significant energy saving is possible if natural ventilation could be exploited through the use of double-skin façade. In this research, CFD was used to analyse various thermal comfort parameters with different double façade configurations to determine a new type of double-skin façade configurations which will provide a better indoor thermal comfort in the hot and humid climate through natural ventilation strategies for the high-rise buildings.     

Reduction of energy consumption using passive architecture in hot and humid climates

Energy shortages, pollution, global warming, and the impacts of urban heat islands are among the pressing issues in this century all over the world. Historically, local architecture was based on people’s experience and knowledge. It was sympathetic to the climate and environment. After a period of building design that ignored the local climate, more passive buildings, low energy buildings, and zero buildings have come into focus because of the environmental pollution caused by an excessive use of fossil fuels. The historic architectural style in Dezful includes underground shelters, 5–12 m deep, to improve the indoor climate conditions in this hot and semi humid city. This type of underground shelter, known as a Shavadoon, is regarded as one of the passive energy strategies to seek temperature comfort using the earth annual temperature stability and natural ventilation. The present study was conducted in a house owned by Mohammad Reza Ghamsari. The house was used to test the accuracy of numerical simulation of the temperature and air flow within the Shavadoon spaces. Temperature contours, streamlines, and other related findings are reported. The results show that space conditioning costs could be cut and adequate comfort could be derived using such passive heating and cooling systems.     

Impact,absorption and evaporation of raindrops on building facades

In this paper, the impact, absorption and evaporation of raindrops on building facades is investigated by experimental and numerical means. Laboratory experiments were carried out to study the impact of water drops with different diameters, impact speeds and impact angles on a porous building material surface (ceramic brick). The measurements showed that large drops with high impact speeds splash, and that drops with high impact speeds and small impact angles bounce. The measurements, furthermore, allowed measuring the maximum spreading length and width of the drops as a function of drop diameter, impact speed and impact angle. Then, a numerical analysis was performed to study the distribution of impact speed and angle for raindrops hitting the facade of a 4×4×10 m³ tower building. The results demonstrated typical and important tendencies of impact angle and speed across the facade. Finally, the experimental and numerical data were used in a more precise three-dimensional simulation of impact, absorption and evaporation of random and discrete wind-driven raindrops. This was compared with the common one-dimensional simulation of absorption and evaporation at the facade considering a continuous uniform rain load as boundary condition, and significant differences between the two approaches were observed.     

Energy analysis of the personalized ventilation system in hot and humid climates

Personalized ventilation (PV) is an individually controlled air distribution system aimed at improving the quality of inhaled air and the thermal comfort of each occupant. Numerous studies have shown that PV in comparison with traditional mechanical ventilation systems may improve occupants’ health, inhaled air quality, thermal comfort, and self-estimated productivity. Little is known about its energy performance.In this study, the energy consumption of a personalized ventilation system introduced in an office building located in a hot and humid climate (Singapore) has been investigated by means of simulations with the empirically tested IDA-ICE software. The results reveal that the use of PV may reduce the energy consumption substantially (up to 51%) compared to mixing ventilation when the following control strategies are applied: (a) reducing the airflow rate due to the higher ventilation effectiveness of PV; (b) increasing the maximum allowed room air temperature due to PV capacity to control the microclimate; (c) supplying the outdoor air only when the occupant is at the desk. The strategy to control the supply air temperature does not affect the energy consumption in a hot and humid climate.     

Effect of building interface form on thermal comfort in gymnasiums in hot and humid climates

The thermal environment and thermal comfort of a building are greatly affected by the design of the building interface form. Most contemporary architectural designs consider only the relations between architectural form and architectural beauty. Few studies on the correlation of architectural form and thermal comfort address the influence of architectural form on thermal comfort and thermal environment. These studies are particularly important for gymnasium architectures located in hot and humid areas, which have high requirements for thermal comfort. This paper presents an experimental investigation and an analysis of the effect of the building interface form of gymnasiums on thermal comfort in hot and humid subtropical regions durings ummer. Results showed that the influence of the top interface forms on thermal comfort is mainly dominated by the mean radiant temperature, which could be controlled to improve thermal comfort. The influence of side interface forms on thermal comfort is mainly dominated by air velocity, and thermal comfort could be improved by promoting natural ventilation on the side interface form design to reduce indoor heat. This research enhanced our understanding of the relation between the interface form and the thermal comfort of gymnasiums. In addition, this paper provides a theoretical reference for the sustainable design of gymnasiums in hot and humid climates.     

Empirical validation and modelling of a naturally ventilated rainscreen façade building

In this paper the thermal behaviour of a rainscreen ventilated façade has been investigated both experimentally and numerically. Field measurements were performed during the 2009/10 winter season in a test building located in San Mauro Pascoli (Italy) having a squared base of internal dimension of 2.89 m and a total internal height of 7.75 m. The external walls of this tower are rainscreen ventilated façades with a 24 cm air cavity and an external side composed of stoneware with open joints. Ventilation grills are located at the top and at the bottom of the tower. In this work the modelling of the test building using a dynamic thermal simulation program (ESP-r) is presented and the main results discussed. In order to study the rainscreen ventilated façade three different multi-zone models were defined and the comparison with the experimental results has been used in order to select the best ESP-r air flow network for the modelling of this kind of envelope component. The thermal analysis of this envelope component evidenced that the ventilated façade is able to reverse the direction of the heat flux through the envelope in regions characterized by large solar irradiation during the winter and moderate wind velocity, when the indoor-outdoor air temperature difference is small, thereby reducing the energy consumption required for indoor heating.     

Building simulation as an assisting tool in decision making: Case study: With or without a double-skin façade?

Implementation of double-skin façades in buildings has been an object of broad application in the recent years. In this presentation, a planned office building in the city-centre of Trondheim, Norway, is used as a case for considering whether a double-skin should be applied to the east façade in order to reduce the heating demand, thus making the double-skin façade a profitable investment. The building is modeled both with and without a double-skin façade with the building energy simulation program ESP-r. This paper describes how a double-skin façade with controllable windows and hatches for natural ventilation can be implemented in the simulation program. The simulation results indicate that the energy demand for heating is about 20% higher for the single-skin façade with the basic window solution compared to the double-skin alternative. However, by switching to windows with an improved U-value in the single-skin alternative, the difference in energy demand is almost evened out. The number of hours with excessive temperatures is, in contrast to other studies on the subject, not significantly higher for the double-skin alternative. However, the predicted energy savings are not sufficient to make the application of a double-skin façade profitable.     

Thermal comfort and IAQ characteristics of naturally/mechanically ventilated and air-conditioned bedrooms in a hot and humid climate

The characteristics of thermal comfort and indoor air quality (IAQ) in bedrooms, occupants’ perceptions and their impact on sleep quality are not often studied. It becomes even more interesting if climatic conditions allow Naturally/Mechanically Ventilated (NMV) concepts as opposed to Air-conditioning (AC) and this becomes very significant from an energy perspective. This paper reports our findings from such a study conducted in a hot and humid climate. Objective measurements of thermal comfort and IAQ were carried out during sleeping period in 12 NMV and 12 AC bedrooms over a period of 2 months. Questionnaire responses were sought from each subject at the end of the objective measurements to assess their perceptions on thermal comfort and indoor air quality of the bedrooms during sleep and their sleeping conditions. Although the “Historical” and “Immediate” responses for the NMV and AC bedrooms indicate that there was a good level of acceptability for both Thermal Comfort and Perceived Air Quality (PAQ), it was found that NMV bedroom was a better sleeping environment. The subjects’ immediate perception of PAQ and thermal comfort were reasonably correlated with their historical perceptions. The subjects’ perception of PAQ was fairly closely correlated to their perception of Thermal Comfort. There was a considerable increase in the carbon dioxide level in an AC bedroom relative to a NMV bedroom. However, there was no clear evidence to substantiate that sleeping duration decreased with increasing level of carbon dioxide, but the findings do suggest that high level of carbon dioxide may hinder the duration of sleep.     

Difficulties and limitations in performance simulation of a double skin façade with EnergyPlus

Currently, several whole-building simulation tools (e.g., esp-r, EnergyPlus, TRNSYS, TAS, IES VE, IDA ICE, VA114, BSim, etc.) are used to assess the energy performance of double-skin façade (DSF) buildings. The aforementioned tools are well suited to assess energy performance of conventional building systems or whole buildings; however, it is questionable whether such tools can accurately describe the transient heat and mass transfer phenomena that occur in the complex three-dimensional geometry of DSFs. This paper describes an empirical validation of the EnergyPlus simulation tool for performance simulation of a DSF. A series of experiments were conducted for cavity airflow and thermal behavior of the DSF and then compared with simulation outputs. In this paper, it is shown that there are significant differences in both thermal and airflow behavior of DSFs between the measurements and simulation predictions by EnergyPlus. This study investigates three cases causing the differences and elucidates what should be considered when modeling DSFs using EnergyPlus.     

Thermal acceptability assessment in buildings located in hot and humid regions in Brazil

The objective of this paper was to perform an analysis on thermal acceptability in naturally ventilated (NVB) and air-conditioned buildings (ACB) located in hot and humid climates in Brazil. Experiments were carried out in April and November 2005 with 1.301 questionnaires based on ISO 10551:1995(E). Indoor and outdoor climatic variables were monitored simultaneously. The results revealed that 53% of the occupants of NVB and 78% of ACB were thermally satisfied. However, some restrictions were observed with the applications of the following methodologies: ISO/FDIS 7730:2005(E); ANSI/ASHRAE Standard 55:2004; Adaptive Temperature Limits (ATG) and prEN15251: 2005(E). Differences were observed between thermal sensation (TSV) and predicted mean vote (PMV) and between the subject's percentages expressing thermal unacceptability of the environment and the PPD calculated according to ISO/FDIS 7730:2005(E).     

Potential of emerging glazing technologies for highly glazed buildings in hot arid climates

In order to improve the sustainability of buildings one of the challenges is to address the role of the building envelope as the key climate moderator between the internal and external environments. The envelope is exposed to the elements and needs to control air exchange as well as sunlight and sound passing through to the occupants. Therefore, it has a major impact not only on the energy utilisation within the space it controls but also on the quality of comfort. However, inside highly glazed modern buildings, achieving good comfort is often at the cost of high-energy consumption. Therefore, in the light of ever increasing energy costs, improved façade design can contribute to a reduction of operational costs. The aim of this paper is to explore technical, economic, environmental and indoor comfort implications of emerging glazing technologies for energy control of highly glazed buildings in arid Middle Eastern climates, which is one of the harshest climates for this building type. The work includes predictions through thermal simulation of the impact of electrochromic glazing, holographic optical elements (HOE), aerogel glazing and thin film photovoltaics on two example buildings. Potential reductions in cooling demand are assessed.     

Investigation on energy performance of double skin façade in Hong Kong

Double skin façade can be defined as a building façade covering one or several stories with multiple skins. The skins may be air tight or ventilated. With sophisticated study and design, buildings constructed with double skin façade can have better thermal performance than the conventional single skin façade. This paper reports the findings on the energy performance of double skin façade applied to a typical office building under the climatic condition in Hong Kong. An experimental setup was established and the measured data were used to verify the theoretical model developed via the EnergyPlus simulation program. The validated model was then used to evaluate the energy performance of double skin façade with various configurations including glazing type (clear, absorptive or reflective glass), glazing position (inner or outer pane) and glazing layers (single or double glazing material). The results indicate that a double skin façade system with single clear glazing as the inner pane and double reflective glazing as the outer pane can provide an annual saving of around 26% in building cooling energy, as compared to a conventional single skin façade with single absorptive glazing. However, the long payback period of 81 years makes the double skin façade system economically infeasible. Support and motivation are needed from the local government in order to foster successful and widespread application of the double skin façade system in buildings.     

The most efficient position of shading devices in a double-skin facade

In recent years, there has been a great deal of interest in double-skin facades due to the advantages claimed for this technology in terms of energy saving in the cold season, protection from external noise and wind loads and their high-tech image.     

Combined thermal acceptability and air movement assessments in a hot humid climate

In the ASHRAE comfort database [1], underpinning the North American naturally ventilated adaptive comfort standard [2], the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that the main complaint related to air movement was a preference for ‘more air movement’ 3 and 4. These observations suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds are available. If that were the case, would it be reasonable to expect temperature and air movement acceptability levels at 90%? This paper focuses on this question and combines thermal and air movement acceptability percentages in order to assess occupants. Two field experiments took place in naturally ventilated buildings located on Brazil’s North-East. The fundamental feature of this research design is the proximity of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. Almost 90% thermal acceptability was found within the predictions of the ASHRAE adaptive comfort standard and yet occupants required ‘more air velocity’. Minimum air velocity values were found in order to achieve 90% of thermal and air movement acceptability. From 24 to 27 °C the minimum air velocity for thermal and air movement acceptability is 0.4 m/s; from 27 to 29 °C is 0.41–0.8 m/s, and from 29 to 31 °C is >0.81 m/s. These results highlight the necessity of combining thermal and air movement acceptability in order to assess occupants’ perception of their indoor thermal environment in hot humid climates.     

Air movement acceptability limits and thermal comfort in Brazil's hot humid climate zone

In hot humid climates, natural ventilation is an essential passive strategy in order to maintain thermal comfort inside buildings and it can be also used as an energy-conserving design strategy to reduce building cooling loads by removing heat stored in the buildings thermal mass. In this context, many previous studies have focused on thermal comfort and air velocity ranges. However, whether this air movement is desirable or not remains an open area. This paper aims to identify air movement acceptability levels inside naturally ventilated buildings in Brazil. Minimal air velocity values corresponding to 80% and 90% (V80 and V90) air movement acceptability inside these buildings. Field experiments were performed during hot and cool seasons when 2075 questionnaires were filled for the subjects while simultaneous microclimatic observations were made with laboratory precision. Main results indicated that the minimal air velocity required were at least 0.4 m/s for 26 °C reaching 0.9 m/s for operative temperatures up to 30 °C. Subjects are not only preferring more air speed but also demanding air velocities closer or higher than 0.8 m/s ASHRAE limit. This dispels the notion of draft in hot humid climates and reinforce the broader theory of alliesthesia and the physiological role of pleasure due to air movement increment.     

Numerical investigation on thermal performance and correlations of double skin façade with buoyancy-driven airflow

This paper briefly reviews the primary parameters for a double skin façade (DSF) design. The research presents an integrated and iterative modeling process for analyzing the thermal performance of DSF cavities with buoyancy-driven airflow by using a building energy simulation program (BESP) along with a computational fluid dynamics (CFD) package. A typical DSF cavity model has been established and simulated. The model and the modeling process have been calibrated and validated against the experimental data. The validated model was used to develop correlations that can be implemented in a BESP, allowing users to take advantage of the accuracy gained from CFD simulations without the required computation time. Correlations were developed for airflow rate through cavity, average and peak cavity air temperature, cavity air pressure, and interior convection coefficient. The correlations are valuable for “back of the envelope” calculation and for examining accuracy of zonal-model-based energy and airflow simulation programs.     

Ceiling mounted personalized ventilation system in hot and humid climate—An energy analysis

This study is to evaluate energy saving potential of ceiling mounted personalized ventilation (PV) system in conjunction with background mixing ventilation compared with mixing ventilation system alone and with mixing ventilation system when occupants are provided with individually controlled desk fans for generating additional air movement at each desk. Control strategy applied includes different number of personalized ventilation air terminal devices used and different PV airflow rates supplied. Energy calculation is based on design conditions in Singapore, representing a hot and humid climate. The results reveal that increasing room temperature can save cooling energy when the combination of PV with ceiling mounted personalized ventilation nozzles and background mixing ventilation is used. In this case the energy for transport of air increases but the total energy decreases, i.e. energy can be saved due to elevated room temperature. Comparing with mixing ventilation plus desk fans, ceiling mounted personalized ventilation cannot only realize better cooling effect but also decrease the total energy consumption.     

Productivity model in hot and humid environment based on heat tolerance time analysis

Thermal environment is one of the most important factors that have impact on workers' productivity. There are many hot and humid workshops in China, whose thermal environment characteristics are the high temperature, high humidity and little radiation intensity. Working in hot and humid environment for a long time not only can extremely do harm to human body health, but also probably induce accidents due to the fall of productivity. In this paper, human body experiment and statistics analysis with the software of EXCEL were applied to establish a heat tolerance time model and a productivity model in hot and humid environment. Firstly, a chamber stimulating hot and humid environment was built and the experiment on heat tolerance and productivity in this chamber was completed. Heat tolerance time and productivity in different environments were tested with the change of air temperature and humidity in the environment chamber. According to the experiment results, regressive formulas for heat tolerance time changing with thermal environment parameter (WBGT) in three conditions of physical labour intensity were provided by statistics methods respectively. On this basis, the function of productivity changing with heat tolerance time and thermal environment parameter (WBGT) in three conditions of physical labour intensity using multiple linear regression analysis tool of EXCEL were obtained finally. F-test was also applied to verify the significance of all the established regression equations. The result shows that the effect of curve regression is significant and the regression function gives important statistic meaning and practical value to work time determination and productivity prediction in hot and humid environment.     

Enhancement of stack ventilation in hot and humid climate using a combination of roof solar collector and vertical stack

In the hot and humid climate, stack ventilation is inefficient due to small temperature difference between the inside and outside of naturally ventilated buildings. Hence, solar induced ventilation is a feasible alternative in enhancing the stack ventilation. This paper aims to investigate the effectiveness of a proposed solar induced ventilation strategy, which combines a roof solar collector and a vertical stack, in enhancing the stack ventilation performance in the hot and humid climate. The methodology selected for the investigation is physical experimental modelling which was carried out in the actual environment. The results are presented and discussed in terms of two performance variables: air temperature and air velocity. The findings indicate that the proposed strategy is able to enhance the stack ventilation, both in semi-clear sky and overcast sky conditions. The highest air temperature difference between the air inside the stack and the ambient air (T_i−T_o) is achieved in the semi-clear sky condition, which is about 9.9 °C (45.8 °C–35.9 °C). Meanwhile, in the overcast sky condition, the highest air temperature difference (T_i−T_o) is 6.2 °C (39.3 °C–33.1 °C). The experimental results also indicate good agreement with the theoretical results for the glass temperature, the air temperature in the roof solar collector’s channel and the absorber temperature. The findings also show that wind has significant effect to the induced air velocity by the proposed strategy.     

Thermal perception,adaptation and attendance in a public square in hot and humid regions

Highly relevant to an individual's thermal perception, the thermal environment in outdoor public spaces impacts the use of such spaces. Thermal adaptation, which involves physiological, psychological and behavioral factors, also plays an important role in assessment of thermal environments by users. Given that these issues have rarely been addressed for outdoor environments in hot and humid regions, this study examines user thermal comfort in a public square in Taiwan. Physical measurements were taken and a questionnaire survey was used to assess the thermal comfort of subjects. The number of people visiting the square was also counted. Analytical results indicate that the thermal comfort range and neutral temperature of subjects was higher than those of people in a temperate region. Additionally, local subjects preferred a cool temperature and weak sunlight, and adapted to thermal environments by seeking shelter outdoors. Analytical results confirm the existence of thermal adaptation and illustrate the characteristics of, and variances in, thermal adaptation. During the cool season, the number of people visiting the square increased as the thermal index value increased. However, the number of people frequenting the square decreased as the thermal index increased during the hot season. These experimental results were compared with those for temperate regions, indicating that the human energy balance model cannot fully explain the influence of climate on use of public spaces; that is, psychological and behavioral factors also play important roles in outdoor thermal comfort. Study findings also elucidate design of outdoor public spaces in hot and humid regions.