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.     

Double skin façades for warm climate regions: Analysis of a solution with an integrated movable shading system

The analysis of a glass double skin façade equipped with integrated movable shading devices is presented, employing three different modelling levels: optics of materials, fluid dynamics of the double skin façade and building energy balance; the aim is to optimize both winter and summer energy performance. The model is developed for a façade oriented towards the south and taking into account the climatic data of central Italy; the solar radiation path with its multiple reflections at the different interfaces have been taken into account employing a ray tracing method. Simulations have been validated by the comparison with data of a similar experimental apparatus and they show that the winter configuration of the proposed façade allows a satisfactory solar heat gain in spite of the presence of shading systems. In summer, the solar heat is mainly absorbed by the external part, and even if a natural convection occurs, there is no significant influence on the inner skin and on the internal environment, thus reducing building cooling requirements. The façade performance was compared with traditional enclosures such as glazed and opaque walls in an office room in central Italy, showing that in the entire year the façade proposed significantly improves the building energy behavior, especially compared to opaque walls and when the configuration with air recovery is considered.     

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.     

Comparative life cycle analysis for green façades and living wall systems

Greening the building envelope focusing on green façades with vegetation is a good example of a new construction practice. Plants and partly growing materials in case of living wall systems (LWS) have a number of functions that are beneficial, for example: increasing the biodiversity and ecological value, mitigation of urban heat island effect, outdoor and indoor comfort, insulating properties, improvement of air quality and of the social and psychological well being of city dwellers.This paper discusses a comparative life cycle analysis (LCA) situated in The Netherlands for: a conventional built up European brick façade, a façade greened directly, a façade greened indirectly (supported by a steel mesh), a façade covered with a living wall system based on planter boxes and a façade covered with a living wall system based on felt layers. Beside the environmental benefits of the above described greening systems, it is eventually not clear if these systems are sustainable, due to the materials used, maintenance, nutrients and water needed.A LCA is used to analyze the similarity and differences in the environmental impacts in relation with benefits estimated for two climate types for building energy saving (reduction of electrical energy used for building cooling and heating).     

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 thermal performance of double skin façade with Tillandsia usneoides plant curtain

Tillandsia usneoides (Spanish moss) is a natural “air plant” characterised with rootless and soilless. It can be intertwined into plant curtain of arbitrary shape installed in the air cavity of double skin façade (DSF) as intermediate shade. The research project aims in researching Tillandsia usneoides (TU) plant curtain and defining the shading effect and thermal performance of the double skin façade with Tillandsia usneoides plant curtain in hot summer in Shanghai, China. The instantaneous solar heat gain and the instantaneous solar heat gain coefficient (ISHGC) of double skin façade with different Tillandsia usneoides density were obtained. The experimental data prove that the ISHGC decreases with the increase of plant density and solar radiation of outside environment. The minimum value of instantaneous solar heat gain coefficient is 0.24 for double skin façade with plant density of 750 g/m². Further analysis on temperature distribution of each layer of double skin façade indicates that plant curtain can contribute to creation of comfortable indoor climate and energy saving because it decreases the temperature of interior façade. The change of plant density will not influence the temperature stratification of double skin façade. However, the increase of plant density exacerbated the overheating of outside air cavity of DSF. More effective measures such like watering the TU plant curtain should be considered to solve this problem.     

Performance and influence of numerical sub-models on the CFD simulation of free and forced convection in double-glazed ventilated façades

Double-glazed façades (DGF) are an attractive option in contemporary architecture and are increasingly used in commercial buildings. They offer some advantages compared with single façade systems but require careful design. The solar-collector-like construction leads to high temperatures in the façade cavities and the possibility of the building overheating. This is undesirable effect, especially in Mediterranean climates. A possible solution for reducing thermal overheating is to use the air channel between the two layers of glass to evacuate the solar radiation absorbed by the façade. A suitable simulation procedure for modeling these façades would be very useful for designing buildings of this type.     

Façades and summer performance of buildings

External cooling loads of a building façade are caused mainly by shortwave irradiance transmission, but also secondary heat flows from the internal glass panes and through ventilation gains from the façade. In a double façade with sun-blinds in the air gap, thermal energy is produced through absorption on the blinds. The work quantifies the thermal performance of single and double façades under summer conditions using laboratory and full scale building experiments. The experimental results were used for model validation and parameter studies were done using dynamic building simulation tools.     

Estimation of mould growth levels on rendered façades based on surface relative humidity and surface temperature measurements

Many façades made with thin rendering on thermal insulation have problems with biological growth. In this study, surface temperature and surface relative humidity were monitored over a 20-month period on test house façades with different constructions (thermal inertia), surface colour and compass directions. This data were used to test three theoretical indices of biological growth with the aim of indicating the potential of mould growth on different types of rendered façades. The results show that thin renderings on thermal insulation have significantly higher surface humidities compared to façade constructions with higher thermal inertia, and therefore have a higher potential for mould growth. The colour is the most important factor for the surface humidity levels on south-facing façades (in the northern hemisphere) as darker surfaces absorb more solar radiation and therefore have a higher average temperature. On a north-facing façade the heat storage capability of the façade and its effect on the surface temperature is most important.     

A numerical model to evaluate the thermal behaviour of active transparent façades

Active transparent façades constitute a building envelope component that is becoming more and more common in high-rise office buildings. Many designers have opted for a ventilated façade, claiming that this technology is sustainable, reduces energy consumption and enhances indoor comfort conditions, but these claims have often proved to be wrong. From the thermofluid-dynamic analysis point of view, few design procedures or sufficiently detailed, reliable and easy to use simulation software are available for ventilated façades. A numerical model that has been developed to simulate the thermal behaviour of mechanically ventilated active transparent façades is presented in this paper. The model, developed in the Simulink/Matlab^® environment, simulates the façade in both steady-state and transient conditions and provides the temperature of the different layers of the façade structure and the corresponding heat fluxes as output data. The model has been validated by comparing the simulation results with experimental data obtained in the laboratory. A test has also been performed on a real façade under actual operating conditions. The model performance has resulted to be quite promising. The accuracy of the prediction of the temperature is good, while the simulations of the heat fluxes are slightly less reliable for some operative conditions.     

Experimental evaluation of a climate façade: Energy efficiency and thermal comfort performance

The results of an extensive experimental campaign on a climate façade with a mechanically ventilated air gap, carried out at the Department of Energetics at the Politecnico di Torino, are presented. Measurements were performed utilizing the TWINS (Testing Window Innovative Systems) test facility, which consists of two outdoor cells, one used for reference purposes, and the other which adopts different active façade configurations. The energy efficiency of the façade and the thermal comfort implications have been evaluated considering the ability to pre-heat the ventilation air in the winter season, and the ability to remove part of the solar load during the summer season; the normalized daily energy passing through the façade and the normalized surface temperature of the inner glass were analysed. The improvement in performance obtained by varying the configuration and operative conditions (changing the air flow rate, the shading device and the internal glazing) has been investigated.     

Airflow assessment in cross-ventilated buildings with operable façade elements

This paper presents an experimental study of basic cross-ventilation flow characteristics that are essential inputs for accurate natural ventilation modelling and design. The study focuses on a generic single-zone building model tested in a wind tunnel under isothermal flow conditions (wind-driven ventilation). An advanced experimental method based on particle image velocimetry (PIV) was developed to investigate the air velocity field in buildings with cross-ventilation. It was found that airflow patterns in rooms with cross-ventilation are complex and cannot be predicted by simplified macroscopic models such as the orifice equation. Inlet-to-outlet ratio and relative location of openings on a building façade are important parameters to be considered, in addition to the wall porosity. This study provides new insights that enable improved design and control of operable façade elements to enhance space cooling using natural ventilation.     

Vertical greening systems and the effect on air flow and temperature on the building envelope

The use of horizontal and vertical greening has an important impact on the thermal performance of buildings and on the effect of the urban environment as well, both in summer and winter. Plants are functioning as a solar filter and prevent the adsorption of heat radiation of building materials extensively. Applying green façades is not a new concept; however it has not been approved as an energy saving method for the built environment. Vertical greening can provide a cooling potential on the building surface, which is very important during summer periods in warmer climates. In colder climates evergreen species create an external insulation layer and contribute to energy savings and loss of heat. In this study an analysis of the effect on air flow and (air and surface) temperature of vertical greening systems on the building level is presented. An experimental approach was set up to measure the temperature (air and surface) and the air flow near and on different types of green façades and a living wall system to evaluate the influence of wind velocity and its effect on the thermal resistance. A comparison between measurements on a bare façade and a plant covered façade has taken, in the beginning of autumn, to understand the contribution of vegetation to the thermal behaviour of the building envelope.     

Indoor thermal environmental conditions near glazed facades with shading devices – Part I: Experiments and building thermal model

This paper presents an experimental study of indoor thermal environment near a full-scale glass facade with different types of shading devices under varying climatic conditions in winter. Interior glazing and shading temperature, operative temperature and radiant temperature asymmetry were measured for façade sections with roller shades and venetian blinds at different positions. Interior glass surface temperatures can be high during sunny days with low outdoor temperature. Shading systems significantly improved operative temperature and radiant temperature asymmetry during cold sunny days, depending on their properties and tilt angle. During cloudy days the impact was smaller, however the shading layers could still decrease the amount of heat loss through the façade. A transient building thermal model, which also calculates indoor environmental indices under the presence of solar radiation, was developed and compared with the experimental measurements. Part II of this paper uses this validated model with a transient, two-node thermal comfort model (including transmitted solar radiation) for assessment of indoor environmental conditions with different building envelope and shading properties, façade location and orientation.     

Development and experimental validation of a simulation model for open joint ventilated façades

The investigation of the thermal and fluid dynamical behaviour of open joint ventilated façades is a challenging task due to the complex airflows generated inside of the naturally ventilated cavity by the existence of open joints. For this reason, the use of advanced fluid measurement and simulation techniques is highly recommended. This paper focuses in the development and experimental validation of a simulation model for these façade systems. More specifically, different turbulence and radiation models available in the commercial computational fluid dynamic codes have been tested on a three-dimensional model and the results have been compared to particle image velocimetry measurements. The correlation between experimental and numerical data has been used in order to select the simulation procedure for this type of façades. Best fittings have been found when using the RNG k-epsilon turbulence model and the Discrete Ordinate radiation model. Using the selected scheme, parametrical simulations have been performed to investigate the effect of increasing the cavity height, and correspondingly, the number of slabs. Results show that ventilation air flow inside the cavity is enhanced by incident radiation as well as by the height of the façade.     

The energy savings potential of using dynamic external louvers in an office building

This research is aimed at exploring the influence of external dynamic louvers on the energy consumption of an office building located in Abu Dhabi-UAE. The IES-VR software was used to predict the energy consumption of a representative office module in order to evaluate the overall energy performance of employing external louvers on the south, east and west oriented façades. The use of dynamic façades was compared to another simpler method of using light-sensor controlled light dimmers. The results show that the potential energy savings using light dimming strategy only was 24.4%, 24.45% and 25.19% for the south, east and west oriented façades, respectively. The proposed dynamic louvers system with light dimming strategy achieved energy savings of 34.02%, 28.57% and 30.31% for the south, east and west orientations, respectively. Detailed analysis of the results showed that the façade's optimal static angle was −20° for the south oriented façade and 20° for the east and west oriented façades. Using these fixed optimal angles resulted in slightly lower energy savings than that of the dynamic façades. This would seem to be a good tradeoff between savings in energy running cost and the investment required to install, operate and maintain a dynamic façades system.     

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.     

On-line parameter estimation and optimal control strategy of a double-skin system

To reduce the potential problems of window systems such as undesired heat gain (loss), glare, and thermal discomfort due to asymmetric radiation, double-skin systems have been introduced. The current problem with double-skin systems is that their operation requires an adequate simulation model to realize optimal control of the system. The estimation of the parameters in the lumped model developed in a previous study [1] was based on ‘laborious’ off-line calibration procedure. This effort has to be repeated for every different size, different type, or differently oriented façade system. Different façade components are characterized by different thermal and optical properties of glazing and blind slats, system configurations [height, width, depth], other simulation variables, etc. For each type the parameter set in the lumped model has to be established through a calibration procedure. In view of micro climate variations even same type systems within one façade but on different heights may have to be calibrated separately. In order to avoid the laborious off-line calibration of every single façade component, an on-line self-calibrating procedure is developed in this paper. The true advantage of the technique is that every component can be pre-wired and ready to be hooked to the calibration set-up when it is brought to the site. The paper will explain the simulation model, selection of calibration parameters, and the process of on-line self-calibration, model validation and application of optimal control. It is shown that the on-line self-calibrating simulation model far outperforms the off-line calibrated model. Consequently, the plug and play self-calibration technique will render the current in-situ ‘laborious’ off-line calibration process obsolete.     

Reducing the acoustical façade load from road traffic with green roofs

Noise annoyance by road traffic is a major issue in urbanized regions. In this study, the influence of a green roof on the façade noise load was investigated numerically for road traffic at close distance. Consistent positive effects of the presence of a green roof are observed at non-directly exposed (parts of) façades. A sufficient green roof area is needed to obtain significant reductions in total A-weighted road traffic noise level. With increasing traffic speed, the green roof effect increases for light vehicles. In case of heavy vehicles, this dependence is less strong. In a street canyon situation, the façade load in the non-exposed canyon is largely influenced by both the roof slope and the presence of a green roof. A flat roof generally results in the best average shielding. A green roof is especially interesting in case of a saddle-backed roof. With a good choice of green roof parameters, the shielding of a flat green roof can be approached.     

Low energy architecture for a severe US climate: Design and evaluation of a hybrid ventilation strategy

Natural ventilation, relying on openings in the façade, is applicable to a limited range of climates, sites and building types. Advanced naturally ventilated buildings, such as those using stacks to encourage buoyancy driven airflow, or hybrid buildings, which integrate both natural and mechanical systems, can extend the range of buildings and climate within which natural ventilation might be used.