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Complex fenestration systems (CFS) have become standard elements in facade design of high performance buildings. They include, for example, shading devices to control illumination, solar heat gains, glare and view-out, and photovoltaic elements imbedded in glazing layers to produce electrical energy on site. However, current methodologies to evaluate the thermal performance of CFS are limited to few products and types. This article develops a general methodology to compute the thermal performance of CFS. The methodology assumes each system layer as porous with calculated effective radiation and thermal properties. A new thermal penetration length model was developed to account for the effects of porous layers on the convective film coefficients of adjacent gas spaces, and applied to various types of shading devices. This methodology is validated using the available measurement and computational fluid dynamics (CFD) simulation results for the U-factor of double-glazed windows with between-pane and internal...

Complex fenestration systems (CFS) include windows featuring complex glazing such as translucent and transparent insulation, solar control films, patterned or decorative glass, in-between pane shades, etc. CFS are believed to exhibit superior energy performance, but may have adverse effects on environmental features important for building-occupant satisfaction requirements such as the outdoor view (connection to outside), indoor view (feeling of privacy), luminance (major factor for discomfort glare), and light diffusion quality (relates to uniformity of illuminance on work plane). This article is part of a larger effort to rate complex fenestration systems for energy performance and indoor environment quality (IEQ). In the end, IEQ ratings must be derived from direct studies of how building occupants perceive the indoor environment conditions created by the installed fenestration product. As a first step, this work tackles the theoretical development of new metrics to rate CFS with regards to IEQ, namely the view impairment index, luminance index, and light diffusion quality index. The new indices are applied to some typical CFS, namely a diffuse window, and a clear window combined with an interior shading screen, and integrated perforated Venetian blinds. The results show that the diffuse window may increase the luminance by more than 100% under clear sky conditions when compared with a clear window with a similar light transmittance. White colored Venetian blinds may increase the window luminance by up to 50% and reduce the outdoor view by up to 66% as compared with a clear window with a similar light transmittance.

Efficient radiant heating and cooling systems are promising technologies in slashing energy bills and improving occupant thermal comfort in buildings with low energy demands such as houses and residential buildings. However, the thermal performance of radiant systems in buildings has not been fully understood and accounted for in currently available building energy simulation software. The challenging tasks to improve the applicability of radiant systems are the development of an accurate prediction model and its integration in the energy simulation software. This paper addresses the development of a semi-analytical model for radiant heating and cooling systems for integration in energy simulation software that use the one-dimensional numerical modeling to calculate the heat transfer within the building construction assemblies. The model combines the one-dimensional numerical model of the energy simulation software with a two-dimensional analytical model. The advantage of this model over the one-dimensional one is that it accurately predict the contact surface temperature of the circuit-tubing and the adjacent medium, required to compute the boiler/chiller power, and the minimum and maximum ceiling/floor temperatures, required for moisture condensation (ceiling cooling systems), thermal comfort (heating floor systems) and controls. The model predictions for slab-on-grade heating systems compared very well with the results from a full two-dimensional numerical model.

This is one of two papers that outlines the methodology used to develop, through computer simulation, skylight design tools for thermal and energy performance of atriums in cold climates. The methodology identified important design alternatives that included skylight and atrium physical variables, and a series of thermal and energy performance outputs that may serve as selection criteria for an energy-efficient design. New prediction models were developed to overcome some computer-simulation limitations, which included models to deal with airflow between an atrium and its adjacent spaces and temperature stratification within an atrium space. The developed airflow network model is a technique used to predict the mutual influence between the atrium and its surrounding spaces without requiring additional geometrical information on the surrounding spaces. The developed temperature stratification model is consistent with airflow network models and the zone concept used in building thermal-simulation programs since it takes into account radiation (overlooked in airflow network models) and convection heat transfer at the same time. This was done through treating fictitious surfaces that separate the thermal zones in a similar way as real surfaces. Fictitious surfaces were assigned a high emissivity, high solar transmittance, high thermal conductivity and convection film coefficient of 10 W / m 2 ° C . These values were found to yield reasonable solar radiation absorption, convection and radiation heat balances for the real surfaces irrespective of the number of the thermal zones. The developed models were integrated into a simulation computer program, and then validated against field measurements of a case study atrium. The predicted indoor temperatures were within ±2°C of the measured ones in both winter and summer days.

This paper presents an analysis of the impact of selected design alternatives on the thermal and energy performance of atriums based on the methodology outlined in the accompanying paper. Computer simulation programs were used to predict the impact of the selected design alternatives on the design performance outputs of atriums. Design alternatives focused on fenestration glazing types, fenestration surface area, skylight shape, atrium type, and interaction of the atrium with its adjacent spaces. Design performance outputs, evaluated with respect to a basecase design, included seasonal solar heat gain, cooling and heating peak loads and annual cooling, heating and total (heating plus cooling) energy. Design tools were developed to quantify the impact of the design alternatives on the performance outputs. The design tools were cast into two-dimensional linear relationships with the glazing U-value and SHGC as independent parameters. The results for the enclosed atriums showed that the annual cooling energy ratio increased at a rate of 1.196 per unit of SHGC ratio and decreased at a rate of 0.382 per unit of U-value ratio. However, the annual heating energy ratio increased at a rate of 1.954 per unit of U-value ratio and decreased at a rate of 1.081 per unit of SHGC ratio. Similar trends were also found for the three-sided and linear atriums. Pyramidal/pitched skylights increased the solar heat gain ratio by up to 25% in the heating season compared to flat skylights. The effect of the skylight shape on the annual cooling and heating energy may be positive or negative, depending on the glazing U-value and SHGC ratios and the atrium type. Atriums open to their adjacent spaces reduced the annual cooling energy ratio by up to 76% compared to closed atrium spaces. However, open atrium spaces increased the annual heating energy ratio by up to 19%.

The topic of this paper is part of a project to develop software to analyze the optical characteristics and daylighting performance of conventional and tubular skylights. Skylights are found in many building types, such as commercial and institutional buildings, houses, shopping malls, hotels, etc. However, skylight manufacturers lack design tools to predict the optical performance of skylight products. Prediction of skylight optical characteristics is a difficult task, due to the complexity of skylight shapes that change with design requirements. This paper presents an analytical model to compute the overall optical characteristics of barrel vault skylights under direct beam light. The model is based on a ray-tracing technique, and can handle skylights with different glazing types (gables opaque, or glazed with different glazing types from the top surface of the skylight), different shapes (short/long with high/low-rise profiles) and different orientation (north-south, west-east, or any direction). Applications of the model showed that barrel vault skylights transmit much more light at high incidence angle on a horizontal surface than similar flat skylights. The skylight length-to-radius ratio (L/R) has a significant impact on the optical characteristics. Short skylights (L/R = 2) with uniform glazing transmit approximately the same amount of light at any sun position. However, long skylights (L/R = 5) transmit about 64 percent more light when the sun is perpendicular to the skylight axis than when the sun is parallel to the skylight axis. Short skylights with clear gables and tinted top transmit substantially more light than flat skylights with similar tinted glazing, particularly when the sun is parallel to the skylight axis.

This paper presents a comparison study between simulation and filed measurements of thermal parameters of an atrium building in Ottawa, Canada. The selected atrium was an enclosed three-storey building with a pyramidal skylight. The atrium was fully conditioned and has open corridors at each storey connecting it to adjacent spaces. The atrium space was used for circulation and reception while adjacent spaces are offices and meeting rooms. The atrium was monitored in June 1995 and in December 1995 to consider extreme conditions of the outdoor climate. The simulation results were obtained using ESP-r computer program. The comparison included those of predicted and measured solar radiation entering the atrium space at the rooftop, and predicted and measured indoor temperatures of the atrium floors. Results for the solar radiation showed good agreement between the measured and predicted values. When the mechanical system was turned off, the predicted temperatures were within ±2°C of the measured temperatures in winter. In summer, however, the predicted temperatures were 2–3°C higher than the measured temperatures.

This article presents a simulation study to predict the energy performance of the Central Sunlighting System (CSS) installed in open-plan offices. Several simulation tools are combined to conduct the simulations. SkyVision calculates the daylight luminous flux and the lighting and solar heat gains of the CSS. A set of coefficients pre-calculated using Radiance relates the desktop illuminances to the CSS luminous fluxes. DaySim is used to compute the daylight illuminance from the perimeter windows. ESP-r is used to compute the heating and cooling energy use of the office spaces. The results show that the CSS may save a significant amount of energy in North American climates. Energy savings from the combination of daylighting from windows and the CSS for typical, four-cubicle, open-plan offices range from 44% to 57% for lighting, 8% for cooling and from 14% to 23% for the total (lighting, cooling and heating) energy.

This article presents the development of a sufficiently accurate and reliable optical model to predict the lighting and thermal performance of the central sunlighting system (CSS). The model is based on the ray tracing technique to compute the amount of sunlight flux transmission through the light guide to interior spaces of buildings, and absorption of solar radiation within the components of the CSS, which may become solar heat gains indoors. The model is validated using a detailed ray tracing technique and field measurements carried out on a previous prototype. The validation results show that the model predictions are in good agreement with the ray tracing and measurement results. The model can be integrated in existing fenestration design tools, or in whole-building energy simulation software, with significantly lower calculation time compared to the full integration of suitable lighting simulation software.

The daylight coefficient (DC) method is a powerful and efficient method to perform annual daylight illuminance simulation. A set of coefficients are calculated for a given room space and static fenestration systems prior to simulation start. Time series of indoor daylight illuminances are obtained by only knowing the sky luminance. However, for rooms with dissimilar dynamic complex fenestration systems (such as windows with movable shadings) whose optical behaviour (transmission, reflection and scattering) may change during simulation, the efficiency of the DC method may be compromised as another whole set of coefficients must be re-calculated. This study presents the development of a new methodology to compute the DC set for rooms with dissimilar complex fenestration components only once prior to simulation start. A validation study is carried out, in which the daylight illuminances in an office space equipped with a clear window and internal Venetian blinds are compared using predictions from the presen...

By admitting natural light deep into a building and connecting occupants with the outside, skylights can improve the aesthetic look of buildings and increase occupant satisfaction. In addition, by allowing the entry of natural light electric light levels can be reduced thereby leading to energy savings. However, the potential energy benefits and amenities of skylights have not been fully exploited in today’s building design due to some theoretical and technical challenges. The lack of design tools is one of the major hurdles building designers face to adopt such products and quantify their energy benefits. The optical characteristics of skylights are the significant factors affecting their energy benefits. Recognizing this gap, the SkyVision tool was developed to assist skylight manufacturers and building designers in developing appropriate skylight designs for given building types and daylighting applications. This paper describes the models implemented in SkyVision to compute the optical characteristics of barrel-vault skylights with clear, fully translucent or partially diffusing glazing under beam and diffuse light. The models are based on the ray-tracing technique. Under diffuse light, two models are developed: (1) a luminance-based model when the sky luminance distribution is known; and (2) an illuminance-based model when the illuminance on a horizontal surface is known. The second model is simpler and faster and more suitable for annual performance calculation. Experimental measurements of the skylight transmittance were conducted under real sky conditions to validate the model predictions. The actual measurements compared reasonably well with the model predictions. The predictions from the luminance-based and illuminance-based models showed good agreement with each other. When applied to an example study, the models predicted that vault skylights with clear glazing are more effective than flat skylights with similar glazing in boosting the beam light transmittance, particularly in winter days. Translucent vault skylights are more effective than flat skylights with similar glazing in reducing solar heat gains, particularly in summer days. Translucent skylights may out-perform transparent skylights, particularly during sunny days in winter.