Simple tool to evaluate energy demand and indoor environment in the early stages of building design

A simplified building simulation tool to evaluate energy demand and thermal indoor environment in the early stages of building design is presented. Simulation is performed based on few input data describing the building design, HVAC systems and control strategies. Hourly values for energy demand and indoor temperature are calculated based on hourly weather data. Calculation of the solar energy transmitted through windows takes into account the dependency of the total solar energy transmittances on the incidence angle, shades from far objects and shades from the window recess and overhangs. Several systems including heating, cooling, solar shading, venting, ventilation with heat recovery and variable insulation can be activated to control the indoor temperature and energy demand. Predicted percentages of dissatisfied occupants are calculated for a given time period to support decisions concerning the thermal indoor environment. The simplified building simulation tool gives reliable results compared to detailed tools and needs only few input data to perform a simulation. The tool is therefore useful for preliminary design tasks in the early design stages where rough estimates of the building design are given and rough estimates of energy use and thermal indoor environment are needed for decision support.     

Daylighting and energy analysis of private offices with automated interior roller shades

This paper presents a comprehensive analysis to study the balance between daylighting benefits and energy requirements (control of solar gains) in perimeter private office spaces with interior roller shades taking into account glazing properties, shading properties and control together with window size, climate and orientation in an integrated daylighting and thermal manner. Daylight autonomy and useful daylight illuminances were computed as a function of façade design parameters. A thermal simulation module using the explicit finite difference thermal network approach runs at the same time step and calculates heating, cooling and lighting source energy consumption as well as surface temperatures and operative temperature. Based on the daylighting results, lighting internal gains (continuous dimming control) are simultaneously input to the thermal module. The model also considers the air in the gap between shade and interior glass as a separate thermal node.Detailed results for Chicago and Los Angeles showed that windows with visible transmittance higher than 50% have the ability to allow enough daylight into the space for all locations and orientations for window-to-wall ratios higher than 50%. Useful daylight illuminances between 500 and 1000 lux were considered in detail – it was found that this index can be maximized for specific window-to-wall ratios and that depends on the glazing properties and fabric properties for each orientation. Moreover, the complex interactions of the studied parameters and their impact on the heating, cooling and lighting energy performance revealed an interesting result: windows occupying 30–50% of the façade can actually result in lower total energy consumption for most cases with automated shading. This illustration of daylighting benefits can be realized only if the integration of daylighting and thermal climate-based analysis is modeled efficiently and depends on glazing and shading properties and control. Finally, best designs for each orientation and location were pointed out based on both daylighting and thermal results.     

DAYLIGHTING TECHNOLOGIES IN NON-DOMESTIC BUILDINGS

Natural daylight is an inexpensive and very efficient light source provided that the amount of daylight entering a building is controlled according to demand. In commercial buildings electricity for lighting can be cut by 50-75% using daylighting design techniques in combination with efficient artificial lighting. New lighting control technologies and advanced computer simulation tools lo optimize large buildings makes it possible to exploit these energy savings.

Daylight is a very efficient light source, providing more light for less input of thermal energy than any other artificial light source. Efficient shading systems are now emerging systems that can control the admission of daylight to the room according to requirement, and avoid overheating. Some of these systems, such as reflective light shelves, will also contribute to a better distribution of the daylight available by redistributing some daylight to the back of the room. However, more work is needed to develop and test such combined daylight and shading systems.

The use of daylight to reduce electric lighting must be seen as an integrated part of the overall energy optimization of the building. An efficient control of the use of daylight and artificial lighting will not only reduce electricity use for lighting. Additionally, the use of electricity for ventilation and cooling can be reduced also, because the internal heat gains provocating these electricity uses are reduced. This calls for an integrated design approach to the overall energy design of the building, involving the architect and the engineer from the very beginning of the design phase.

Visual comfort of office buildings receives increasing attention, partially because of the VDU's (Visual Display Units) of the computers, that are now almost standard equipment of every work place. The performance requirements for both daylighting systems and artificial lighting systems have been sharpened, and the attention to this fact is crucial in future development of lighting systems.     

The impact of shading design and control on building cooling and lighting demand

Shading should be considered as an integral part of fenestration system design for commercial and office buildings, in order to balance daylighting requirements versus the need to reduce solar gains. In this paper, the simultaneous impact of glazing area, shading device properties and shading control on building cooling and lighting demand was calculated using a coupled lighting and thermal simulation module. The interactions between cooling and lighting energy use in perimeter spaces were evaluated as a function of window-to-wall ratio and shading parameters. An exterior roller shade was used as an example. The impact of shading device type, properties and control on building cooling and lighting energy demand was quantified and analyzed. The simulation results indicate that, if an integrated approach for automatic control of motorized shading is used in conjunction with controllable electric lighting systems, substantial reduction of energy demand for cooling and lighting could be achieved in perimeter spaces, depending on climatic conditions and orientation.     

Quantifying the potential of automated dynamic solar shading in office buildings through integrated simulations of energy and daylight

The façade design is and should be considered a central issue in the design of energy-efficient buildings. That is why dynamic façade components are increasingly used to adapt to both internal and external impacts, and to cope with a reduction in energy consumption and an increase in occupant comfort. To gain a complete picture of any façade’s performance and subsequently carry out a reasonable benchmarking of various façade alternatives, the total energy consumption and indoor environment need to be considered simultaneously. We quantified the potential of dynamic solar shading façade components by using integrated simulations that took energy demand, the indoor air quality, the amount of daylight available, and visual comfort into consideration. Three types of façades were investigated (without solar shading, with fixed solar shading, and with dynamic solar shading), and we simulated them with various window heights and orientations. Their performance was evaluated on the basis of the building’s total energy demand, its energy demand for heating, cooling and lighting, and also its daylight factors. Simulation results comparing the three façade alternatives show potential for significant energy reduction, but greater differences and conflicting tendencies were revealed when the energy needed for heating, cooling and artificial lighting were considered separately. Moreover, the use of dynamic solar shading dramatically improved the amount of daylight available compared to fixed solar shading, which emphasises the need for dynamic and integrated simulations early in the design process to facilitate informed design decisions about the façade.     

Assessment of fixed shading devices with integrated PV for efficient energy use

The use of external fixed shading devices to adjust solar influx radiation and to save energy is well known. However, fixed shading devices can reduce daylight availability, increase artificial light needs and block the beneficial winter solar radiation.This paper is part of a research on the characteristics of the optimum shading device. The aim is to investigate the balance between the energy needs for heating and cooling the space that the shading device is used for and the energy that is used for lighting the same space and the energy that the shading device can produce.In order to investigate the balance between the above mentioned parameters, thirteen types of fixed shading devices have been studied and categorized according to their energy performance, for a single occupant office room. The same office room is tested for two different Mediterranean latitudes in Athens and in Chania, Crete in Greece and for two different south facing windows’ sizes.The thermal behavior of the devices is assessed through computer simulation application and the daylight analysis is assessed with both computer simulation and physical modeling. Stable parameters were the internal loads in the office room, the south orientation of the façade and the type of glazing. Variable parameter was the type of the fixed shading device.The study shows that all shading devices with integrated south facing PV can efficiently produce electricity which may be used for lighting. The study highlights the fact that shading devices such as Surrounding shading, Brise–Soleil full façade and Canopy inclined double work efficiently against thermal and cooling loads and may be used to produce sufficient electricity and control daylight. The study defines the geometrical parameters that will be incorporated to the overall characteristics of the optimum fixed shading device and proposes new fields of development for the BIPV technologies.     

Lighting and energy performance of solar film coating in air-conditioned cellular offices

In subtropical Hong Kong, the principal objectives of fenestration design include eliminating direct sunlight and decreasing cooling loads. To avoid the problems of glare, excessive brightness and thermal discomfort, occupants may block the windows with internal shading devices, resulting in poor daylighting performance and very small amount of electric lighting energy savings. Recently, the advances in thin film coatings for window glass products provide a means of substantially reducing heat gain without proportionally reducing daylight transmittance. It has been suggested that film coatings together with photoelectric lighting control systems could minimise the electric lighting and cooling requirements without causing undue visual and thermal discomfort to the occupants. This paper presents field measurements on solar control film coatings in fully air-conditioned offices in Hong Kong. Solar heat gains, indoor illuminance levels and the electricity consumption by the fluorescent luminaires were systematically recorded and analysed. Measurements were made for two cellular offices, one with solar control film coating on the window glass and the other without. The findings showed that the solar film coating could cut down energy expenditures for air-conditioned buildings, especially for spaces with large glazing areas subject to substantial amount of direct sunlight. Results are presented and the design implications discussed.     

A review of daylight illuminance determinations and energy implications

Daylighting is recognized as an important element in architecture and a useful strategy in energy-efficient building designs. Daylight gives a sense of cheeriness and brightness that can have a significant positive impact on the people. There is a scope for integrating daylight with electric light to reduce building energy use. The amount of daylight entering a building is mainly through window openings, which create in the indoor environment a more attractive and pleasing atmosphere, in addition to maximise visual access to the pleasant views of the outside world. Determinations of the exterior and interior daylight and lighting energy savings are key issues to demonstrate the benefits based on daylighting designs. This paper provides a review of daylight illuminance determinations and the lighting energy reductions due to daylighting schemes. The study includes daylight measurements, prediction of daylight illuminance under various sky conditions and potential electric lighting energy savings from daylight-linked lighting controls. The article aims at providing building professionals, practitioners and researchers more information and a better understanding of daylight for promoting effective daylighting designs and evaluations.     

引进日光 关掉电灯

公共建筑自然采光的意义不仅在于节省照明能耗,减少碳排放,而且为室内的视觉作业提供舒适、健康的光环境,是良好的室内环境质量不可缺少的重要组成部分。文章介绍了新型自然采光技术——管道式日光照明装置,在与灯光照明、传统天窗采光和光纤集光照明等的比较中说明管道式日光照明装置的技术原理、结构功能和应用。     

Daylighting performance evaluation of a bottom-up motorized roller shade

This paper presents an experimental and simulation study for quantifying the daylighting performance of bottom-up roller shades installed in office spaces. The bottom-up shade is a motorized roller shade that opens from top to bottom operating in the opposite direction of a conventional roller shade, so as to cover the bottom part of the window, while allowing daylight to enter from the top part of the window, reaching deeper into the room. A daylighting simulation model, validated with full-scale experiments, was developed in order to establish correlations between the shade position, outdoor illuminance and work plane illuminance for different outdoor conditions. Then, a shading control algorithm was developed for application in any location and orientation. The validated model was employed for a sensitivity analysis of the impact of shade optical properties and control on the potential energy savings due to the use of daylighting. The results showed that Daylight Autonomy for the bottom-up shade is 8–58% higher compared to a conventional roller shade, with a difference of 46% further away from the façade, where the use of electric lighting is needed most of the time. The potential reduction in energy consumption for lighting is 21–41%.     

Simulation of façade and envelope design options for a new institutional building

This paper presents a simulation case study of façade and envelope preliminary design options for the new Engineering building of Concordia University in Montreal. A major principle of the analysis was to create a high quality building envelope in order to optimally control solar gains, reduce heating and cooling energy demand and reduce electricity consumption for lighting, while at the same time maintain a comfortable and pleasant indoor environment. The stated approach of the design team was to aim for an energy-efficient building, employing innovative technologies and integrating concepts such as daylighting and natural ventilation. Detailed energy simulations were therefore performed from the early design stage, in order to present recommendations on the choice of façade, glazings, shading devices, lighting control options, and natural ventilation. Integrated thermal studies, a daylighting analysis and the impact of the above on HVAC system sizing were considered. Simulation results showed that, using an optimum combination of glazings, shading devices and controllable electric lighting systems, the energy savings in perimeter spaces can be substantial. Perimeter heating could be eliminated if a high performance envelope is used. The building is currently being commissioned.     

Thermal mass and night ventilation as passive cooling design strategy

We calculated the influence of thermal mass and night ventilation on the maximum indoor temperature in summer. The results for different locations in the hot humid climate of Israel are presented and analyzed. The maximum indoor temperature depends linearly on the temperature difference between day and night at the site. The fit can be applied as a tool to predict from the temperature swing of the location the maximum indoor temperature decrease due to the thermal mass and night ventilation. Consequently, the fit can be implemented as a simple design tool to present the reduction in indoor temperature due to the amount of the thermal mass and the rate of night ventilation, without using an hourly simulation model. Moreover, this design tool is able to provide for the designer in the early design stages the conditions when night ventilation and thermal mass are effective as passive cooling design strategy.     

Efficient venetian blind control strategies considering daylight utilization and glare protection

This paper presents the development of new venetian blind control strategies considering daylight provision, lighting energy use and visual comfort. A hybrid ray-tracing and radiosity method is used to calculate transmission through the window-blind system and interior illuminance distributions taking into account specular and diffuse material properties. Work plane illuminances are used to extract daylighting metrics, while directional light distribution and respective luminance values are used to calculate glare potential. Four types of control strategies were evaluated – a cut-off angle control, a daylight-redirecting control, and two glare protection control modes. Using the common “cut-off” angle may result in a strong second reflection that might significantly affect visual discomfort depending on view direction and profile angle. Proper rotation of the tilt angle and consideration of specular characteristics can minimize this effect and redistribute daylight deeper into the space, although glare problems cannot be eliminated in some cases. Moreover, two additional control strategies were developed based on glare probability and sky conditions: the first is a model-based control derived from real time glare simulation results. The second is a “simplified” control that uses pre-calculated correlations between glare probability and transmitted illuminance to establish binary set points that can be used in model-predictive control algorithms.A detailed daylighting analysis was performed in order to evaluate set points for blind control actions, annual daylighting metrics, lighting energy use and daylight glare probability and duration. Different room sizes, glazing properties, blind material characteristics and orientations were studied. The results showed that diffuse blinds do not reduce the risk of glare when light redirection is desired; double-sided slats with a diffuse top and a specular bottom surface are better in this regard. Fixed angles at 60° or higher provide satisfactory results for most cases, although there is a penalty in daylighting efficiency. The two glare protection control algorithms proved to be efficient in providing high daylight autonomy values without the risk of glare for all studied cases.     

INTEGRATED PREDICTIVE ADAPTIVE CONTROL OF HEATING,COOLING, VENTILATION,DAYLIGHTING AND ELECTRICAL LIGHTING IN BUILDINGS

The present energy consumption of European Buildings is higher than necessary, given the developments in control engineering. Optimization and integration of smart control into building systems can save substantial quantities of energy on a European scale while improving the standards for indoor comfort. Many tools are available for the simulation of one or some of the following aspects: (a) heating, cooling and indoor thermal comfort, (b) ventilation and indoor air quality, (c) daylighting, electrical lighting and light quality, (d) installations, local control and fault detection, (e) Genetic optimized Neuro-Fuzzy control. The interaction between these aspects, however, is very relevant and cannot be neglected. Therefore, an integrated software tool is required. TNO together with the University of Delft develops such an integrated tool. This paper describes the first results of the utilization of this tool and the development of an integrated, predictive, adaptive building system for indoor climate control.     

Overall energy performance of semi-transparent single-glazed photovoltaic (PV) window for a typical office in Hong Kong

This paper develops an overall methodology for investigating the thermal and power behaviors of semi-transparent single-glazed photovoltaic window for office buildings in Hong Kong. In order to estimate its overall energy performance, this study is conducted in terms of total heat gain, output power and daylight illuminance. Three simulation models are established, including one-dimensional transient heat transfer model, power generation model and indoor daylight illuminance model. A typical office room reference is chosen as case study, and the weather data from 2003 to 2007 from the Hong Kong Observatory are used as the simulation inputs. By incorporating the simulation results, the overall energy performance can be evaluated in terms of electricity benefits corresponding to five orientations of the studied typical office. The priority of office orientation considering overall energy performance is: south-east, south, east, south-west and west. The findings show that thermal performance is the primary consideration of energy saving in the entire system whereas electricity consumption of artificial lighting is the secondary one. The overall annual electricity benefits are about 900 kWh and 1300 kWh for water-cooled and air-cooled air-conditioning systems respectively. The application of semi-transparent PV glazed window can not only produce clean energy, but also reduce building energy use by reducing the cooling load and electrical lighting requirements, which definitely benefits our environmental and economic aspects.     

Estimation of exterior vertical daylight for the humid tropic of Kota Kinabalu city in East Malaysia

In tropical regions natural daylight has been a fundamental factor in building design. It is the most efficient way of lighting a building in the daytime and has a great potential for energy conservation in buildings. In Malaysia there are a limited available data of measured illuminance which is the case of several regions in the tropics. Using established models it is possible to predict the luminous efficacy and then estimate the monthly mean hourly exterior illuminance. In this study two different models were chosen. The Perez and Du Mortier–Perraudeau–Page–Littlefair models were selected for the prediction of hourly exterior horizontal illuminance for the city of Kota Kinabalu in East Malaysia. Comparison between the two models were made. The vertical hourly illuminance was predicted also using Perez approach. The potentiality of daylight in four orientations was discussed. This study highlights the importance of Sunpath diagram on daylight illuminance during the conceptual design stage. The results in this study is hoped to contribute further insight into the potentiality of daylighting of tropical sky.     

Calculation procedure of the shading factor under complex boundary conditions

Together with the evolution of buildings and systems, energy assessment models have become more and more detailed, requiring a precise evaluation of the building loads and gains.For an accurate analysis of solar heat gains, technical standards introduce an external shading reduction coefficient of the incident solar radiation, called shading factor. Its value is provided for simple geometries, which are usually not suitable to properly describe a real environment. In addition, the relations adopted to evaluate the shading factor are based on simplified hypotheses, which cause non-negligible errors when compared to more complex algorithms.The objective of this study is the development of a calculation procedure of the shading factor under complex boundary conditions. The algorithms have been implemented in a software tool written in Matlab language. It can provide for the value of the shading factor on a generically oriented and tilted surface. After setting the site and the time for the simulation, generic-shaped windows can be modelled. The external environment, which can be imported from DXF files, can include a horizon profile, generic-shaped obstructions and vegetation. The calculation can be performed for every sky condition: clear, average or generic. In addition, the simulation can be run to obtain instantaneous, daily average or monthly average shading factor values.     

Theoretical solution for light transmission of a bended hollow light guide

Hollow light guides with very high reflective inner surfaces are novel daylight systems that collect sunlight and skylight available on the roof of buildings transporting it into deep or windowless interiors in building cores. Thus the better utilization of daylight can result in energy savings and wellbeing in these enclosed indoor spaces. An analytical complex solution of a straight tube system was solved in the HOLIGILM method with a user-friendly tool available on the http://www.holigilm.info. An even more difficult light flow transport is to be determined in bended tubes usually placed on sloped roofs where a bend is necessary to adjust the vertical pass through the ceilings.This paper presents the theoretical derivation of the model with its graphical representation and coordinate system respecting backward ray-tracing bend distortions. To imagine the resulting illuminance on the horizontal plane element in the interior, the virtual ray (i.e. luminance in an elementary solid angle) has to pass the ceiling diffuser interface, the inner mirror like tube with a bend, through a roof cupola attachment to the element of the sky and sun light source. Due to this complexity and the lengthy derivation and explanations more practical applications will be published later in a separate contribution.     

Daylighting in the tropics

Traditional adaptations of tropical/sub tropical buildings to high ambient irradiance from high elevations are outlined. Generally, these adaptations result in severe shading of window apertures, greatly reducing access to daylight. Some examples of optical systems designed to improve daylighting in tropical buildings are discussed. These include angle selective glazing, light guiding shades, vertical and horizontal light pipes, switchable glazing and angle selective skylights. The simulation of these devices within packages such as RADIANCE is also discussed.     

Application of automated blind for daylighting in tropical region

This paper reports an experimental and simulation study on application of automated Venetian blind for daylighting in tropical climate. A horizontal blind system operating automatically under programmed control was constructed and integrated onto the glazed windows to form a window system with an automated blind in a room of a laboratory building. A dimming controller was also integrated to the lighting system of the room. Different operation schemes of the window system were devised and tested in the attempt to maximize energy savings while maintaining the quality of the visual environment in the room. Intensive measurement of illuminance of the interior space was undertaken during the experiments. A methodology for calculation of interior daylight illuminance and associated glare corresponding to the configurations of the experiments was adopted. The method was coded into a computer program. Results of calculation from the program agree well with those from experiments for all the schemes of operation conducted. The program was used to simulate the situation when each scheme of operation was implemented for a whole year. It was found that such window system with automated blind enabled energy savings of 80%, but a more sophisticated scheme also helped maintain the interior visual quality at high level.