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Abstract: In this paper, the energy performance of a central atrium is investigated and compared with the energy performance of a courtyard with the same geometric proportions. The atrium and the courtyard design used for the analysis are square in plan and surrounded by the building on all four sides. The glazing type and percentage for the courtyard walls and atrium skylight are varied in the analysis. Weather data from four cities representative of climatic conditions of cold, temperate, hot-humid and hot-dry were used. The results show that, in general, the open courtyard building exhibits a better energy performance for the shorter buildings. As the building height increases, however, at some point the enclosed atrium exhibits a better energy performance. This “break even” point for the number of stories depends on different factors like glazing and climate parameters discussed above. [Copyright &y& Elsevier]

Abstract: Despite government targets that imply 400,000 installed microCombined Heat and Power (microCHP) units by 2010, market penetration is as yet negligible in the UK. This paper reports new experimental data to underpin decisions affecting the uptake of this technology. A simple computer model of the time distribution and use of the electricity output from microCHP, based on trials with a real installation in a UK dwelling, is coupled with a stochastic model of domestic electrical load. It predicts the proportion of output that would be consumed locally, for six household scenarios comprising three different types of house and two levels of occupation and appliance use. The results show that the proportion of microCHP electrical output exported to the electricity distribution network (up to 62%) will be higher than has been estimated by previous studies, and that this is sensitive to the thermal properties of the house and the lifestyle of the occupants. The significance of these results is examined to suggest how careful marketing and the use of half-hourly metering may be used to maximise the benefits of this technology to consumers and the environment. [Copyright &y& Elsevier]

Abstract: To answer to an increasing need in the lighting simulation domain, the CIE technical committee 3.33 defined recently a set of test cases to be used for assessing the accuracy of lighting computer programs. These test cases have the advantage of avoiding or reducing the uncertainties in the validation reference data by using simple analytical scenarios or by applying reliable experimental protocols. This paper presents an application example of these test cases to two existing lighting computer programs. Thirty-two different testing scenarios were used covering different aspects of the lighting simulation domain: direct artificial lighting, direct daylighting and diffuse reflections and inter-reflections. This work showed the usefulness of the CIE simple test cases in identifying the strengths and weaknesses of the tested programs and the accuracy and the capabilities of the programs in simulating different aspects of the lighting propagation were clearly verified. However, the need to expand the CIE set of test cases to other aspects of light and daylighting design has been noted. [Copyright &y& Elsevier]

Abstract: A general method for realistic performance evaluation of solar control properties of facades for facades with sun-shading or other solar control systems has been developed. It is particularly designed to be used for venetian blinds. It can be used used ‘stand-alone’ or within building simulation programs. The new method has proven to be of great practical value to planning teams of huge office buildings in Germany, Austria and Switzerland. The method is presented in detail in this paper. It can be used either ’stand-alone’ (without building simulation) for comparisons of different facade variants or within building simulation programs. Some parts of the proposed methodology could be used in standards (e.g. EN13363) or to improve the accuracy of building simulation programs which are currently on the market. Practical experience with the new methodology led to insights which are the basis for the design of two new products. These new products are compared with state of the art products in [T.E. Kuhn, Solar control: comparsion of two new systems with the state of the art on the basis of a new general evaluation method for facades with venetian blinds or other solar control systems, Energy and Buildings, in press] on the basis of the new methodology. [Copyright &y& Elsevier]

Abstract: Light envelopes are more and more frequently used in modern buildings but they do not present sufficient thermal inertia. A solution to increase this inertia is to incorporate a phase change material (PCM) in this envelope. This paper presents the performance of a test-cell with a new structure of light wallboards containing PCMs submitted to climatic variation and a comparison is made with a test-cell without PCMs. To improve the wallboard efficiency a vacuum insulation panel (VIP) was associated to the PCM panel. This new structure allows the apparent heat capacity of the building to be increased, the solar energy transmitted by windows to be stored without raising the indoor cell temperature, and the thickness of the wallboard to be decreased compared with that of traditional wallboards. An experimental study was carried out by measuring temperature and heat fluxes on and through the wallboards. The indoor temperature, which has a special importance for occupants, was also measured. A numerical simulation with the TRNSYS software was carried out in adding a new module representing the new wallboard. It showed a good agreement with experimental results. This new tool will allow users to simulate the thermal behaviour of buildings having walls with PCMs. [Copyright &y& Elsevier]

Abstract: Through a case study, this research explores an approach, which uses computer simulation technology, to evaluate different energy conservation alternatives and to assist facility managers to select reliable and feasible solutions. The subject facility is located in the Southeast region of the United States. One of the major challenges and operation goals of the General Services Administration, who manages the facility, is for that facility to achieve the Energy Star designation. However, due to the complexity of the facility, the requirements from building occupants, as well as other difficulties, finding a path for optimizing the operation of the facility in order to achieve the Energy Star designation is not always easy. This project uses eQuest, a simulation software tool, to create a “virtual environment”, in which the operations of the HVAC (heating ventilation air-conditioning) system and the lighting of the facility are studied. Subsequently, recommendations initially made by experts through traditional energy audit approaches are evaluated in the “virtual environment” in order to determine the best solution to achieve the goal of the facility managers. This paper discusses major aspects of the project, including the challenges, the values and the limitations of applying computer simulation techniques in such a facility with complicated structural, occupancy and operation features. [Copyright &y& Elsevier]

Abstract: Validation and verification of building simulation programs and load calculation programs is of continuing interest. Dynamic thermal behavior data, including conduction transfer function (CTF) coefficients, thermal response factors and periodic response factors, are used to calculate transient heat conduction through building constructions. Computational inaccuracy sometimes occurs in calculating CTF coefficients and response factors. In this paper, a method for verification of the CTF coefficients and response factors over the whole frequency range is introduced. This method is based on the equivalence of dynamic models for a linear system and the frequency characteristics of building transient heat transfer models. Bode diagrams and error criteria are proposed to verify the CTF coefficients and response factors. Some examples are given to demonstrate the methodology. [Copyright &y& Elsevier]

Abstract: In this paper, we develop statistical models of the thermal transmittance of 2D thermal bridges (ψ). We aim to give building designers plain and practical tools for the evaluation of the most common 2D thermal bridges. Three examples are considered: a slab-on-grade floor–wall junction, a floor–wall junction and a roof–wall junction. For each case, we perform computer simulations of the thermal transmittance, ψ, for several values of the most important variables. Then, we fit these numerical results to a nonlinear regression model. The results appear to be good with relative errors less than 5%. [Copyright &y& Elsevier]

Abstract: Real-time computer simulation is required in a number of applications, where the simulated dynamic systems are directly coupled with systems in the real world or with other systems also running in real-time. Typical problems of real-time simulations are that the dynamics of the modeled system are not represented in enough detail, either by not sampling the inputs or not producing output values frequently enough or both. Increasing the sampling frequencies may lead, as an additional problem, to real-time violations caused by insufficient computing power. The latter problem is amplified if the real-time is accelerated to achieve a kind of fast motion and reduce experiment times. In this paper, we show how the first problem can be solved by automatic frequency adjustment, minimizing the number of computations and how the remaining second problem can be reduced by trading a graceful degradation of accuracy against the computing power requirements automatically. Experiments show that simulation times could be reduced by a factor of 100 without unacceptable simulation errors. [Copyright &y& Elsevier]

Abstract: Glass façades, particularly in high-rise buildings, increase in energy consumption for heating, cooling and ventilation. This causes too high running cost of mechanical systems. Double skin glass façade is a system that decreases these disadvantages, by providing natural ventilation, preventing solar heat gain, controlling daylight, etc. This paper aims to investigate the appropriateness of double skin glass façades in moderate climate, such as Istanbul, in terms of the energy and cost efficiency when compared to single skin glass façades. For this purpose, an approach is proposed to determine the efficient alternatives. It comprises to generate standard façade alternatives by considering the objectives, constraints and performance criteria, and to evaluate their energy and cost efficiency for both single and double skin glass façades. In conclusion, the most energy efficient double skin glass façade is about 22.84% more efficient than the most energy efficient single skin glass façade is. Additionally, the most cost efficient single skin glass façade is about 24.68% more efficient than the most cost efficient double skin glass façade is. [Copyright &y& Elsevier]

Abstract: One of the primary goals of the radiant heating and cooling community for the past two decades has been the fair and accurate comparison of radiant space conditioning systems with conventional forced air systems. The desire of the community was to give architects and engineers the ability to compare the energy consumption of different system types while requiring the systems to produce equivalent thermal environments. Unfortunately, radiant systems, though relatively simple in concept, are relatively complex from a modeling standpoint. A rigorous model must include fundamental laws of thermodynamics and properly account for heat transfer due to radiation, convection, and conduction. In addition, the model must do this in a generic way within a program that is capable of modeling buildings of any size and type and their associated HVAC systems. Such challenges are not easily overcome and require careful attention to detail as well as a solid foundation from which to build. This paper summarizes a model which addresses these concerns and provides a radiant system model within a popular building energy simulation program. [Copyright &y& Elsevier]

This paper describes the application of a building simulation program to construct a decision-support tool for use by policy makers addressing the needs of the Scottish domestic sector. It is argued that the generic nature of the tool renders it suitable to support the cumulative roll-out of upgrade measures in the long term, both within and outwith the UK. The tool is then used to appraise the impact of the upgrade measures that might be applied to the Scottish housing stock. [Copyright &y& Elsevier]

This paper reports the technical feasibility and economic viability of a hybrid solar/wind grid connected system for electrical and thermal energy production, covering the energy demand of a typical residence in the city of Xanthi (Greece). The technical characteristics of the solar and wind energy subsystems are given. The energy output provided by the hybrid energy system was estimated using a simulation program, which is based on the Monte Carlo method, for reading the solar radiation and wind potential data. The auxiliary energy supply is based on the output of a combined-cycle natural gas power plant, recently constructed in the Thrace region. The economic analysis of the proposed hybrid solar/wind system is performed using the life cycle savings (LCS) method and the payback period (PBP) of the initial capital cost is determined. [Copyright &y& Elsevier]

Tree-shade alters building cooling and heating loads by reducing incident solar radiation. Estimates of the magnitude of this effect, and how it is influenced by urban forest structure (e.g. tree size and location), are difficult due to the complexity inherent in tree–sun–building interactions. The objective of this paper is to present a simplified method for making these estimates appropriate for neighborhood and larger scales. The method uses tabulated energy use changes for a range of tree types (e.g. size, shape) and locations around buildings (lookup tables), combined with frequency of occurrence of trees at those locations. The results are average change in energy use for each tree type that are not explicitly dependent on tree location. The method was tested by comparison to detailed simulations of 178 residences and their associated trees in Sacramento, California. Energy use changes calculated using lookup tables matched those from detailed simulations within ±10%. The method lends itself to practical evaluation of these shading effects at neighborhood or larger scales, which is important for regional assessments of tree effects on energy use, and for development of tree selection and siting recommendations for proposed energy conserving planting programs. [Copyright &y& Elsevier]