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Overheating in built environments during climate extreme heat events is a major concern to human health, particularly for people vulnerable to prolonged exposure to heat and humidity. However, currently available methods for assessing the risk of overheating lack robust procedures to evaluate the effects of overheating on the comfort and health of vulnerable occupants residing in the various different dwellings. This paper developed a general methodology to define and characterise overheating events and evaluate the risk to reduced comfort and undesirable health effects of building occupants exposed to extreme heat events. Criteria to declare overheating were developed based on heat-related health outcomes related to limits for body dehydration and core temperature of healthy average-age and older adults. The methodology was then applied to a case study of a residential building with typical local construction practice for cold climates and compared with existing methods for assessing risk from exposure to extreme heat events. The results showed that all the methods predicted that highly insulated and airtight buildings are more prone to overheating than older buildings that are less well insulated and airtight. However, only the proposed methodology described in this paper predicted that natural ventilation through opening windows significantly reduced the overheating risk to below the threshold value. Furthermore, multi criteria methods might be difficult to apply in practice in that it is not guaranteed to violate all the criteria to declare a building space is not overheated. The proposed methodology sets the groundwork for establishing a benchmark model from which different overheating metrics can be compared.

The objective of this work was to compare the hygrothermal responses and the moisture performance of four wood-frame walls as predicted by four hygrothermal (HAM) simulation tools, namely: DELPHIN, WUFI, hygIRC and COMSOL. The four wall systems differ only in their cladding type; these were fibreboard, vinyl, stucco and brick. Three Canadian cities having different climates were selected for simulations: Ottawa, Ontario; Vancouver, British Columbia and Calgary, Alberta. In each city, simulations were run for 2 years. Temperature and relative humidity of the outer layer of OSB sheathing were compared amongst the four simulation tools. The mould growth index on the outer layer of the OSB sheathing was used to compare the moisture performance predicted by the respective hygrothermal simulation tools. Temperature profiles of the outer layer of the OSB sheathing were all in good agreement for the four HAM tools in the three locations. For relative humidity, the highest discrepancies amongst the four tools were found with stucco cladding where differences as high as 20% could be found from time to time. Mould growth indices predicted by the four HAM tools were similar in some cases but different in other cases. The discrepancies amongst the different HAM tools were likely related to: the material property processing, how the quantity of wind-driven rain absorbed at the cladding surface is computed and some implementation details. Despite these discrepancies, The tools generally yielded consistent results and could be used for comparing the impacts of different designs on the risk of premature deterioration, as well as for evaluating the relative effects of climate change on a given wall assembly design.

Overheating in buildings arising from climatic extreme heat events has been identified as a health concern to vulnerable occupants. However, there have been very limited studies to generate suitable weather data to evaluate by simulation the overheating risk and its effect on the comfort and health of occupants. This paper develops a methodology to identify reference summer weather years (RSWY) for overheating risk analysis. The methodology includes generation of historical climate data, and development of a heat stress metric for the definition and characterization of heat events. The Standard Effective Temperature was selected among a short list of popular metrics, modified and named t-SET to account for transient heat events, activity levels of occupants, and thermoregulatory controls of sleeping subjects. The t-SET model predictions compared well with measured body temperatures of subjects undergoing multi-stage activities under hot conditions. The t-SET index was used to generate RSWY for selected Canadian cities.

The two-node bioheat model is widely used in thermal comfort standards and design tools. In recent years, there have been many new experimental studies and thermoregulatory models developed under stressful heat or cold conditions, but those have not been tested under the two-node model structure. Furthermore, limited validation studies of the two-node model revealed significant discrepancies in the prediction of skin temperature. This study collects relevant thermoregulatory models (six for sweating, three for skin blood flow and shivering, and four for sweat evaporation efficiency) and devises a methodology to compare the accuracy of various model combinations against experimental data. An improved model is developed and validated under heat and cold exposure conditions. The RMSE method is used to compare the accuracy of various model combinations and to optimize the proposed thermoregulatory model constants. The results reveal that only several model combinations can be considered as accurate for the core and skin temperature predictions, amongst which are the proposed models at the first rank.

Exposure to hot and humid conditions results in physiological changes in metabolism, cardiac output and thermoregulation of the young adult and these changes deviate with elderly due to aging. The elderly population is more vulnerable than the healthy and young population due to age-weakened physiology and thermoregulatory functions. There are, however, limited bioheat models addressing such changes due to hot exposure in the young and the elderly. This paper develops robust bioheat models for young and elderly while incorporating the physiological changes under exposure to heat-stressful conditions for both age groups the age-related changes in physiology and thermoregulation to an elderly human. However, due to a large variability of thermoregulation among the elderly population, a sensitivity analysis revealed that the average elderly is characterized by metabolic rate and cardiac output, which are lower than those of the young by 21% and 14.4%, respectively. Moreover, the thresholds of the onset of vasodilation and sweating are delayed from those of young adults by 0.5 °C and 0.21 °C, respectively. The elderly and young bioheat models were validated with number of independent published experimental studies under hot exposures in steady and transient conditions. Model predictions of core and mean skin temperatures showed good agreement with published experimental data with a discrepancy of 0.1 °C and 0.5 °C, respectively.

As a consequence of global warming and rapid urbanization around the globe, the magnitudes and frequencies of extreme heat events (EHEs) are increasing and this trend is expected to continue into the future. In this study, the added benefit of modelling climate at convection-permitting spatial resolutions (grid spacing

It has been acknowledged that as outdoor temperature and relative humidity increase past threshold values, so do older people mortality and morbidity rates. Similarly, there exist indoor conditions of temperature (Tamb) and relative humidity (RH) that would pose a health-risk to older people when they are exposed to these conditions for extended periods. However, these indoor conditions need to be identified to set protective measures for this vulnerable population. The aim of this work is to develop heat stress indices for older people similar to the standard effective temperature (SET) for a wide range of indoor conditions, activity levels and clothing insulation. A robust and validated bioheat model for older people was used to predict thermal responses and deduce the limits of Tamb and RH that would present a heat-related health risk when the core temperature exceeds 38 °C, or percentage of body water loss exceeds 2%, or when skin wettedness and SET exceed given thresholds. The results were consistent with published experimental data. At relatively cool ambient conditions, Tamb < °C, older people have higher mean skin temperatures and feel cooler than younger people. At Tamb ≥ 25 °C, older people have lower mean skin temperatures and SET values become greater than younger ones, indicating that older people would rate their indoor conditions more stressful than younger people.

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...

The need for energy conservation in buildings has spurred innovations in window technologies. These products include windows combined with shading devices, and windows featuring complex glazing such as switchable glazing, diffuse glazing, translucent and transparent insulation, patterned or decorative glass, etc. Current fenestration simulation tools for energy performance product ratings do not cover complex fenestration products. This paper addresses the development of detailed calculation models to compute the optical characteristics of complex fenestration products made up of a mixture of clear and scattering glazing layers. The models take into account not only the optical properties of the individual glazing layers making up the window product, but also the haze and gloss properties of the glazing layers. Specific optical models are developed to compute the optics of a clear substrate with applied or laminated scattering film, and composite film made up of a number of homogeneous materials with known optical properties. A general optical model was also developed for screen-like glazing panes such as insect/shading screens, roller blinds, drapery sheets, honeycomb transparent insulation and fibreglass translucent glazing.

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.

Domes have become increasingly popular in modern building designs. Glazed domes are used to bring daylight and solar heat into the indoor space. For domes with multiple spaced layers of glazings, there is little information available on natural convection heat transfer within these layers. This information is required for the evaluation of the dome thermal performance (e.g., the U-factor). This paper presents a numerical study on heat transfer by laminar natural convection within multi-layer domes with uniform spacing heated from the outside. The flow and temperature fields within the domed enclosure were obtained using the control volume approach combined with the fully implicit scheme. Correlations for the heat transfer as a function of the dome shape and the gap spacing between the layers were developed under steady-state conditions. The results showed that the convection heat transfer for fully hemispheric domes (half of spheres) may reach more than 13% higher than that for low profile domes (hemispherical caps) for small gap spacings (gap spacing-to-radius ratio δ δ >0.3). The critical gap spacing that yields the maximum heat transfer was quantified for each dome shape.

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.

Daylighting and thermal loads are very important design issues for skylight design, especially in large spaces such as atria. However, the trade-off between daylighting and thermal performance of skylights has been difficult to solve, due to a lack of daylighting and thermal design tools. A mathematical model was developed to predict the visible/solar transmittance, absorptance and reflectance of multi-glazed domed skylights for both direct and diffuse radiation- The model is based on tracking the beam and diffuse radiation transmission through the dome surface. Since all building energy simulation and fenestration rating tools are limited to planar skylights, the model was translated into a simple method in which domed skylights were substituted by optically equivalent planar skylights. The results showed that domed skylights yield slightly lower visible/solar transmittance at low sun zenith angles, and substantially higher visible/solar transmittance at high sun zenith angles, or near the horizon, than ...

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.

Domed skylights are important architectural design elements that deliver daylight and solar heat into buildings, and connect the building's occupants to the outdoor environment. Despite the widespread use of domed skylights, there is limited information on the convective heat transfer within cavities of multi-glazed domes. This information is required to evaluate the thermal performance of domed skylights for product rating purposes, or to evaluate the heat loss or gain of installed skylights in buildings. This article presents a numerical study on the laminar natural convection in horizontal concentric domed cavities heated from the inside surface. A commercial CFD package is used to solve for the flow and temperature fields. The results show that for large cavity gap spacing-to-radius ratios, the cavity flow is mono-cellular and steady state. For small gap spacing ratios, however, the cavity flow may be multi-cellular and transient periodic. Practical correlations for the heat transfer coefficient as a ...

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.