Battery energy storage systems (BESS) will most likely play an important role in enabling integration of small-scale renewable energy sources, from residential and smaller commercial enterprises, into the electricity networks. With benefits ranging from greater use of cleaner energy sources to potential cost savings, battery energy storage systems can ensure security and continuity of supply. This paper assesses battery storage technologies based on their technical capability and economic viability for effective renewable energy integration. An overview of current technologies and their performance characteristics is reviewed before modeling. Simulink models containing generic battery blocks and other standard blocks, form a basis of assessment for the technical capabilities. HOMER models for stand-alone photovoltaic systems with battery storage are evaluated for economic assessment.
Overheating is a major problem in many modern buildings due to the utilization of lightweight constructions with low heat storing capacity. A possible answer to this problem is the emplacement of phase change materials (PCM), thereby increasing the thermal mass of a building. These materials change their state of aggregation within a defined temperature range. Useful PCM for buildings show a phase transition from solid to liquid and vice versa. The thermal mass of the materials is increased by the latent heat. A modified gypsum plaster and a salt mixture were chosen as two materials for the study of their impact on room temperature reduction. For realistic investigations, test rooms were erected where measurements were carried out under different conditions such as temporary air change, alternate internal heat gains or clouding. The experimental data was finally reproduced by dint of a mathematical model.
With good design practices and life-cycle cost optimization, the specific fan power for individual (SFPI) fans will be between 0.5 and 1 kW m−3−1. Data from nearly 1000 audited fans in Sweden show that the average measured SFPI weighted by drawn motor power is 1.5 kW m−3 s−1 and the situation appears to be similar in other countries. Contract forms used by Swedish builders and consultants' design practices are analyzed here to search for an explanation of the low performance of installed systems. Identified as two major barriers to efficient system design are the lack of performance specifications when procuring systems and the incentive structure in the building sector. As a consequence, duct design methods, rules of thumb, and vendor recommendations do not lead to system optimization. The broad minima in life-cycle costs over a range of air-handling unit sizes show that potential economic welfare losses from efficiency standards are likely to be smaller than the losses that result from today's design practices.
In this study, a building with a volume of 351 m3 and a net floor area of 117 m2 is considered as a case study with the indoor and exterior air temperatures of 20 and 0 °C, respectively. For the heating applications, four options are studied with (1) a heat pump, (2) a condensing boiler, (3) a conventional boiler and (4) a solar collector, which are driven by renewable and non-renewable energy sources. An energy and exergy analysis is employed to assess their performances and compare them through energy and exergy efficiencies and sustainability index. Energy and exergy flows are investigated and illustrated. Also, the energetic and exergetic renewability ratios are utilized here along with sustainability index. The results show that overall exergy efficiencies of heat pump, condensing boiler, conventional boiler and solar heating systems are found to be 3.66, 3.31, 2.91, and 12.64%, while the sustainability index values for the four cases considered are calculated to be 1.039, 1.034, 1.030 and 1.144, respectively. So, solar collector-based heating system gives the highest efficiency and sustainability index values.
Heat losses from buildings through contact with the ground, especially in the case of large buildings, have a strong influence on energy demand. Various methods for calculating these heat losses are available, including one method that is defined by the EN ISO 13370 standard. Due to the complexity of this method, we have developed a method that is presented in this paper. Using our method we have calculated weight factors for buildings with and without basements with a variety of thermal transmittances for the contact between the building and the ground. Also, the number of influential parameters used in EN ISO 13370 is reduced. Our simplified method is particularly appropriate for use in the process of designing the thermal insulation for buildings and determining the specific heat losses from buildings.
The European and International Standard UNE-EN ISO 13790 presents a set of calculation methods for the evaluation and design of energy and thermal performance of buildings. These methods have diverse range of details for calculating the energy use of heating and cooling in different building zones, as well as for calculating the heat transfer and solar heat gains of special elements, such as ventilated solar walls (Trombe walls). In this article, the authors have revised the aforementioned document in order to check the proposed mathematical models and their implementation within Mediterranean climates. This assessment pinpoints the existence of some errors in the equations provided in EN ISO 13790 under steady state conditions. Concurrently, the corrected equations are shown and new correlations are proposed for the ratios δ and ω which are more suitable for Mediterranean climates.
The purpose of this 1991 investigation was to gather data on the prevalence and size of duct leakage for a dispersed sample of Arkansas houses. Information on the praticality, cost and success of duct sealing procedures are included. This study also illustrates the use of a simple, but very powerful, diagnostic tool, which we call the “pressure pan”. The concept evolved from experiments by others to find pressure fields (generated by forced-air systems) inside wall cavities. The procedure directs repair efforts and provides follow-up quality control. The calculations of energy savings achieved after sealing the duct systems are based on direct metering of the daily consumption of the electricity or gas for space heating and hourly outside temperatures. The study reports that, before repair, the average duct system leakage at 50 pascals in cubic feet per minute was 621 (0.293 cubic meters per second at 50 pascals), which represents an average of 21.6% of the total leakage of the study houses. For that sample, the average reduction in energy consumption after repair was 21.8%; 31.3% for heat pumps and 19.7% for gas furnaces. Converting the energy reduction data into dollars and considering the repair costs results in very positive simple payback and benefit-to-cost ratio.
Ventilation is essential for the maintenance of good indoor air quality, although there is evidence to suggest that energy loss through uncontrolled or unnecessary air infiltration is excessive. In this study, estimates are presented for air change (ventilation and infiltration) energy use in non-industrial buildings for 13 countries. Various methods are used for the estimates, but they are mainly based on calculating the total annual enthalpy change needed for the conditioning of air. The potential for reduced energy use by improved ventilation control is also briefly reviewed. Considering the non-industrial building stock of the 13 countries collectively, the total annual loss of heating energy due to air change is estimated to amount to 48% of delivered space conditioning energy (including heating equipment losses). The results emphasise that air change related energy losses are as important as conduction and equipment losses (including ‘flue’ losses) in dissipating delivered space conditioning energy from buildings.In addition, estimated financial expenditures, as well as carbon dioxide emissions associated with this energy use are indicated. The financial expenditures are derived from the air change energy estimates using published International Energy Agency (IEA) energy pricing information. The magnitudes of the carbon dioxide emissions have been based on published IEA estimates of total emissions from energy-related sources for each country.
A daylighting study of classrooms in three california climates was made using the DOE-2.1B Building Energy Analysis Computer Program. The daylighting configurations studied were unilateral, clerestory, and top-lighting designs. The climates studied were Fresno, Oakland, and Mount Shasta.It was found that daylighting could produce lighting energy savings in excess of 80%, and total building energy savings in excess of 30% in all climates analyzed. It was also found that the less than optimum daylighting designs studied still used less energy than classrooms having no daylighting features.For Fresno, unilateral designs should use approximately 50% glass, with the glass oriented either north or south, provided the south is shaded. The glass should be mounted on the wall as high as possible. Clerestories should run the length of the classroom and should be 0.6 m (2 ft) high, assuming additional windows comprise 30% of the wall area. Skylights can be between 1% and 5% of the total roof area.For Oakland, unilateral designs should use approximately 70% glass, with the glass oriented in any direction, provided orientations other than north are shaded. Clerestories should be 1.2 m (4 ft) high. Skylights should be between 3% and 5% of the roof area.For Mount Shasta, unilateral designs should use approximately 50% glass, with the glass facing south with an overhang. A northern orientation performs almost identically. Clestories should also face south and have an overhang, but again northern orientations perform almost as well. Skylights should be between 3% and 5% of the roof area.Skylights save the greatest amount of energy in all three climates.
The 2000 W society, achievable through cuts in resource consumption and per capita CO2 emissions, is closely related to the goals of sustainable development. This study identifies the specific targets that need to be met both globally and by Switzerland to realize the vision. As a major energy consumer, the buildings sector will have to make a substantial contribution to meeting these targets. The report starts by examining the energy-saving potential of individual residential buildings through different combinations of building standard and building services system. Various building concepts already available today offer considerable potential and, as individual solutions, often achieve the targets of the 2000 W society. Yet, as the impact of such individual solutions on the building stock is dampened by a range of factors (e.g. long refurbishment cycles, low energy prices, scepticism of investors towards new technology), the effective gains fall far short of the theoretical potential. As the considered implementation scenarios and building stock projections show, the average buildings-sector targets required for the 2000 W society are nonetheless attainable. However, in order to tap the potential in the residential buildings sector, there is an urgent need for immediate action at various levels (e.g. through financial incentive systems, consumer information campaigns).
The significance of the residential building sector in terms of energy consumption is well acknowledged. In this view the knowledge of the way the residential building stock of Cyprus behaves in terms of energy consumption is quite valuable since it will assist policy makers to formulate targeted measures aiming the improvement of energy efficiency and setting current legal standards and benchmarks in the energy performance certificate, a requirement of the 2002/91/EC Directive. Unfortunately, the existing knowledge on this subject is quite poor. As a remedy a research project supported by a national research grant is in operation since December 2008. This paper presents the outline, goals and methodology of this research project and the findings regarding the energy behaviour and other characteristics of the residential building stock of Cyprus. From the analysis of the results for 500 residential buildings, it seems that the energy demand and primary energy required is lower than that of other European countries. Moreover, it seems that the age of residential buildings has low correlation with the energy demand while in contrast with other Northern and Central European countries, it is clear that the contribution of cooling energy requirements to the overall energy demand is quite significant.
In order to meet new tighter building energy requirements introduced in Denmark in 2006 and prepare the way for future buildings with even lower energy consumption, single-family houses were built with the purpose to demonstrate that it is possible to build typical single-family houses with an energy consumption that meets the demands without problems concerning building technology or economy. The paper gives a brief presentation of the houses and the applied energy-saving measures. The paper also presents results from measurements of the overall energy use, indoor climate and air tightness. Furthermore, results from detailed calculations of the utilization of electricity-related heat gains are presented. Looking at the energy consumption in relation to the new energy requirements, the paper concludes that the single houses can relatively easily keep the future energy demands. The energy consumption of the houses is on a level corresponding to a classification as “low-energy house class 2” or an energy consumption of 75% of the required maximum energy consumption. With minor modifications, some houses could be classified as “low-energy building class 1” corresponding to an energy consumption of only 50% of the required and almost the level of typical passive houses.
This paper addresses the dual challenge of designing sustainable low-energy buildings while still providing thermal comfort under warmer summer conditions produced by anthropogenic climate change—a key challenge for building designers in the 21st century. The main focus is towards buildings that are ‘free running’ for some part of the summer, either being entirely naturally ventilated or mixed-mode (where mechanical cooling is only used when thought to be essential). Because the conditions in these buildings will vary from day to day it is important to understand how people react and adapt to their environment. A summary is made of recent developments in this area and of the climate data required to assess building performance. Temperatures in free running buildings are necessarily closely linked to those outside. Because the climate is changing and outside summer temperatures are expected to increase, the future will offer greater challenges to the designers of sustainable buildings aiming to provide either entirely passive or low-energy comfort cooling. These issues are demonstrated by predictions of the performance of some case study buildings under a climate change scenario. The examples also demonstrate some of the important principles associated with climate-sensitive low-energy design.
The goal of performing sensitivity analysis of a simulation model is to determine the effect of input variation and the effect of input uncertainty on the output data. Sensitivity analysis is an unavoidable step in model validation, and it is also generally useful in performing simulations. The user must know the influence of the accuracy of the data that is input to the program. This paper presents a methodology for performing sensitivity analysis as well as the tools that implement this methodology, MISA and LiSA, that were developed within the IEA-ECBCS Annex 23 `Multizone air flow modeling'. The basic concepts of sensitivity analysis as well as the main characteristics of the developed tool are presented. More detailed information are available in the final report of the sub-task 3 `Evaluation of COMIS' of the Annex 23 [J.-M. Fürbringer, C.-A. Roulet, R. Borchiellini, Evaluation of COMIS, final report IEA.ECB&CS Annex 23 Multizone Air flow Modelling, LESO-PB, EPFL, 1015 Lausanne, Switzerland, 1996.].
The EU-27 residential building stock offers high potential for energy efficiency gains. The policies already in place or proposed to improve the energy efficiency and thus the environmental performance focus on new buildings and major renovations of existing buildings. However, there might be additional measures that could lead to further energy efficiency improvements. In particular, the installation of roofs or windows that show a high thermal efficiency outside major renovations offer a large improvement potential. In this study, the potential environmental and economic impacts of two types of such policy options were analysed: first, measures that require high energy efficiency standards when roofs or windows have to be replaced; and, second, measures that accelerate the replacement of building elements. The results suggest that the two policies offer the potential for substantial additional energy savings. In addition, the installation of energy efficient building elements comes at negative net cost. When the replacement of building elements is accelerated, however, the additional costs do not outweigh the energy cost savings.
This paper describes the modelling approach used to accurately evaluate the effect of thermal bridges on the energy performance of buildings. The heat transfers in the intersections of walls were initially modelled in Sisley software. These models were then reduced and integrated in Clim 2000. The simulation results were compared against the models obtained from thermal regulation values. For standard wall configurations, it was seen that the detailed modelling of heat transfers provides an additional accuracy of about 5% in terms of the evaluation of the building’s heat losses.
Good heating, ventilating and air conditioning (HVAC) control ensures comfort. It is usually also the most cost-effective way to improve energy efficiency of air-conditioned buildings. In this article, the comfort enhancement and energy saving potential with new control strategies are determined for the Human Science Building (HSB) at the University of Pretoria. A new software tool, QUICKcontrol, was used to perform the complex and fully integrated building, HVAC and control simulations. Various control strategies were investigated. These included air-bypass, reset control, setback control, improved start–stop times, economiser control and CO2 control. The simulation models were firstly verified against measurements to ensure accurate and realistic retrofit simulations. It was then possible to ensure comfort and to predict savings of 60% in HVAC power consumption. This resulted in a simple payback period of 9 months. Preparing input data took about 2 days, while setting up the simulation model took another day. The typical run time for the fully integrated building, HVAC system and control simulation took approximately 90 s per day on an Intel™ Pentium 133 MHz personal computer.
Recently accepted revisions to ASHRAE Standard 55—thermal environmental conditions for human occupancy, include a new adaptive comfort standard (ACS) that allows warmer indoor temperatures for naturally ventilated buildings during summer and in warmer climate zones. The ACS is based on the analysis of 21,000 sets of raw data compiled from field studies in 160 buildings located on four continents in varied climatic zones. This paper summarizes this earlier adaptive comfort research, presents some of its findings for naturally ventilated buildings, and discusses the process of getting the ACS incorporated into Standard 55. We suggest ways the ACS could be used for the design, operation, or evaluation of buildings, and for research applications. We also use GIS mapping techniques to examine the energy-savings potential of the ACS on a regional scale across the US. Finally, we discuss related new directions for researchers and practitioners involved in the design of buildings and their environmental control systems.
The 65-node thermoregulation model was developed, based on the Stolwijk model. The model has 16 body segments corresponding to the thermal manikin, each consisting of four layers for core, muscle, fat and skin. The 65th node in the model is the central blood compartment, which exchanges convective heat with all other nodes via the blood flow. Convective and radiant heat transfer coefficients and clothing insulation were derived from the thermal manikin experiments. A thermoregulation model combined with radiation exchange model and computational fluid dynamics (CFD) is proposed. The comprehensive simulation method is described.
This paper describes existing International Standards Organization (ISO) standards and current activity concerned with thermal comfort. It describes how an ISO standard is produced from a new work item proposal to publication as an International Standard. ISO Standards should be valid, reliable, useable, and with sufficient scope for practical application. The existing thermal comfort standard—EN ISO 7730—is considered in terms of these criteria as well as ISO 8996 (metabolic rate) and ISO 9920 (clothing). The work of ISO/TC 159 SC5, ‘ergonomics of the physical environment’, is presented in Appendix A. The proposed revision of EN ISO 7730 is presented in detail. The revised standard will be based on requirements for general thermal comfort (predicted mean vote (PMV), operative temperature) and local thermal discomfort (radiant temperature asymmetry, draught, vertical air temperature differences, floor surface temperatures). One critical issue is the effect of air velocity. Increased air velocity has a beneficial effect at warm temperatures, but it may result in draught sensation in cooler temperatures. Another issue is the extent to which requirements of humidity need to be included in a standard for thermal comfort. Several recent research projects dealing with adaptation, influence of air velocity and the effect of humidity have been responsible for keeping the standards up to date.
The revised Turkish thermal insulation standard (TS 825) was described and then compared with the ISO 9164, EN 832 and German regulation. The TS 825 was an application of ISO 9164 as it uses the same equation, same restriction and same flexibility. The main differences in the calculation methods presented in the standards were 'the acceptance of the climate data', 'the calculation method of the internal heat gains', the calculation method of solar heat gains' and 'the acceptance of air change rate values'. It was found that the parameters described in the regulation were not significant for modern buildings.
In the present study, abrasion resistance and compressive strength of concrete specimens containing SiO2 and Al2O3 nanoparticles which are cured in different curing media have been investigated. Portland cement was partially replaced by up to 2.0wt.% SiO2 and Al2O3 nanoparticles and mechanical properties of the produced specimens were measured. Increasing the nanoparticles content have found to increase the abrasion resistance of the specimens which were cured in water and saturated limewater, while this condition was not observed for compressive strength in both curing media. The enhancement of abrasion resistance was more for the specimens containing SiO2 nanoparticles in both curing media. Since, abrasion resistance and compressive strength of the specimens follow a similar regime by increasing the nanoparticles content when they are cured in saturated limewater, some experimental relationships has been presented to correlate these two properties of concrete for this curing medium. On the whole, it has been concluded that the abrasion resistance of concrete does not only depend on the corresponding compressive strength.
This research investigates the possibility to use highly absorbing materials to dampen indoor RH% variations. The practical MBV of sodium polyacrylate, cellulose-based material, perlite and gypsum is evaluated for a daily cyclic exposure that alternates high (75%) and low (33%) RH% levels for 8 h and 16 h, respectively. The adjustment velocity to RH% variations and the presence of hysteretic phenomena are also presented. The cellulose-based material proves to be the most suitable for moisture buffering applications. Starting from this material’s properties, the effect of thickness, vapour resistance factor (μ) and mass surface exchange coefficient (Zv) on sorption capacity is evaluated by the use of a numerical model.
The paper contributes to the system design of solar thermal absorption chillers. A full simulation model was developed for absorption cooling systems, combined with a stratified storage tank, steady-state or dynamic collector model and hourly resolved building loads. The model was validated with experimental data from various solar cooling plants.As the absorption chillers can be operated at reduced generator temperatures under partial load conditions, the control strategy has a strong influence on the solar thermal system design and performance. It could be shown that buildings with the same maximum cooling load, but very different load time series, require collector areas varying by more than a factor 2 to achieve the same solar fraction. Depending on control strategy, recooling temperature levels, location and cooling load time series, between 1.7 and 3.6 m2 vacuum tube collectors per kW cooling load are required to cover 80% of the cooling load.The cost analysis shows that Southern European locations with higher cooling energy demand lead to significantly lower costs. For long operation hours, cooling costs are around 200 € MWh−1 and about 280 € MWh−1 for buildings with lower internal gains and shorter cooling periods. For a Southern German climate, the costs are more than double.
In the last few years, thermal comfort research in summer has significantly increased the electricity consumption in buildings. This is mainly due to the use of conventional air conditioning systems operating with mechanical vapor compression. Solar cooling systems appear to be an interesting solution to solve this problem. But the understanding of this technology has to be refined through fundamental studies by developing numerical simulations. Moreover, the study of pilot plants is a practical method to gain experience by analyzing all the processes behind solar cooling technology. This paper presents an experimental study of a solar cooling absorption system implemented in Reunion Island, located in the southern hemisphere near the Capricorn Tropic. The particularity of this project is to achieve an effective cooling of classrooms, by a solar cooling system without any backup systems (hot or cold). The aim of this experimental study is to define the limits of the use of such system under tropical climate conditions without setting a set point temperature. Indoor thermal comfort is achieved by a self-stabilizing operating system that maintains the indoor temperature 6 °C below the outdoor temperature. During some critical periods of the year, when the outdoor temperature is very high and when the solar cooling system cannot provide enough refrigerating production, thermal comfort inside the building is achieved by using ceiling fans. Firstly we will present the installation and the choices we made in the control and design process. In the second part, an analysis of the experimental results will be presented.
The optimal use of fuel and electricity in a direct-fired absorption chiller system is important in achieving economical operation. Previous work on the control schemes mainly focused on the component local feedback control. A system-based control approach, which allows an overall consideration of the interactive nature of the plant, the building and their associated variables is seen to be the right direction. This paper introduces a new concept of integrating neural network (NN) and genetic algorithm (GA) in the optimal control of absorption chiller system. Based on a commercial absorption unit, neural network was used to model the system characteristics and genetic algorithm as a global optimization tool. The results appear promising.
The report describes the design, modelling and performance of an active solar cooling system in northern Italy. Various aspects related to active solar cooling, like energy storage, room comfort, modelling and the LiBrH2O absorption cycle are discussed.The cooling system consists essentially of: an array of 36 m2 of flat plate collectors with a black chrome selective surface; a LiBrH2O absorption machine with a refrigerating power of 4 kW; and two storage devices of 0.3 and 2 m3 water. The system is installed in the JRC Solar Laboratory in Ispra.The results of one summer of operation are presented together with the results of the simulation model. The overall system efficiency, defined as the fraction of the solar irradiation which is converted into cooling effect, is calculated for the whole cooling season and is found to be 11%. This value lies close to the measured values for this parameter.
An analysis is undertaken to show the effects of a range of coating absorptivity values on the improvement of heat transfer across a Trombe wall (which is used for passive solar heating) and to its enclosure. The analysis shows that enhanced heat delivery to the enclosure of a Trombe wall system is feasible with the application of an absorptive coating of a superior nature – characterized by high absorptivity and very low emissivity – on the heat-receiving surface of the wall and thus can be seen as a heat transfer enhancement technique.
The CDM potential in an academic institution hosting 2500 students is analyzed through the introduction of renewable energy technologies (Solar Water Heater, Solar Steam Cooking) and adoption of energy efficient technologies (Compact Fluorescent Lighting, Energy Efficient Air Conditioners). The baseline emission has been calculated for each technology. A detail investment analysis has been carried out for each of these measures. The impact of revenue generated by selling carbon credits through the clean development mechanism (CDM), on the economic viability of the project activity is analyzed along with sensitivity analysis.Out of the four cases analyzed, energy efficient lighting and energy efficient air conditioners do not require CDM benefits for their viability hence they fail to prove the additionality. Solar steam cooking having negative value of IRR does not pass the additionality criterion for CDM. The solar water heater generating 48.13 tCO2/year is identified as the candidate CDM project. The total amount of CO2 that can be saved from emitting to the atmosphere by employing the renewable and energy efficient technologies is 311.34 tCO2/year. The CERs generated by this project are insufficient to cover the validation/ verification and registration expenses. For converting the CDM potential into reality, bundling of the similar activities with nearby academic institutes can be considered.
The energy renovation of existing buildings is an important tool for the reduction of energy consumption in the building sector, the improvement of prevailing indoor thermal comfort conditions and also for the improvement of environmental conditions in urban areas. At the same time, it is a technical, economic and social problem, due to the way in which many cities have been built and the restrictions imposed by economic constrains that tantalise most countries in South-Eastern Europe, and also Greece. It applies particularly in Northern Greece, with its cold and prolonged heating season, where a series of studies was carried out since 1994 to approach the problem and develop viable proposals. Public and mixed-use buildings form a significant part of the building stock and are therefore a primary candidate for energy saving measures, especially as they also play the role of a ‘pilot-demonstrator’ for the private owned buildings. However, due to the low energy prices that prevailed over the last 10 years, and as energy saving measurements are capital intensive investments, little was done in that direction. The recent sharp increase in oil prices proved that this was a short-sighted policy. In the following paper are presented the results of a study that aimed to determine the potential of energy saving renovation measures, in a representative sample of buildings under realistic conditions, to evaluate the feasibility of these measures, and also the way in which this feasibility is being analysed, under the rapidly changing economic conditions.
In his recent papers, Oke has challenged urban climatologists to establish quantitative and readily understood guidelines which might assist planners in the design of climatically rational cities, and has shown by example how such an approach might be taken for street canyon geometry. This study pursues Oke's arguments relating canyon structure to solar access within the canyon space using a numerical simulation methodology to explore the dependence of irradiance on the canyon facets, on a pedestrian within the canyon and the net irradiance at the canyon top on aspect ratio, street orientation, city latitude, season and sky condition. In addition, wall, floor and pedestrian ‘access indices’ are defined as the relevant irradiances divided by the equivalent horizontal surface, open-site solar irradiance, and it is suggested that such quantities, if presented in a form convenient to the planning practitioner, might constitute one type of parameter of use in an urban planning context.
Transient diffusion of indoor air and contaminant elements affects human comfort and health within short periods of time. This paper presents the method of exposure prediction under such conditions using the scales of accessibility of supplied air (ASA) and accessibility of contaminant source (ACS). These two scales describe the spreading performance of supplied air and indoor pollutants, respectively, and they can be figured out by computational fluid dynamics (CFD) simulation and then used to predict contaminant dispersion when flow field keeps unchanged. The new method in the form of an algebraic equation makes clear how the ventilating parameters affect the final indoor contaminant distribution. It can also be used to predict the possible health impact on occupants since this method covers both the concentration and the exposure duration of contaminants. A tracer gas measurement was conducted to validate the application model, and results show good agreement. Case study results show that transient diffusion differs very much from that under constant conditions, and this prediction method helps to flexibly control the ventilation system to meet specific requirements.
The dispersion of accidentally released gases in a built-up area was determined in a boundary layer wind tunnel. A geometrically similar model of a part of an industrial plant in West Germany was used. The leak positions and the wind directions were varied.It is shown that the dispersion is determined essentially by the complex flow conditions near the buildings. The angle between wind direction and street direction as well as the roughness of the industrial area are found to be important parameters for flow and dispersion of gases. The results are compared with data obtained for the same source configuration but for a uniformly rough surface. It is shown that in comparison to uniformly rough surface diffusion the spread rate of the diffusion plume is increased by a factor of up to 2, and the position of the plume axis is shifted.
A program of laboratory studies into thermal comfort requirements is presented. Two studies used groups of 16 subjects over a range of conditions (warm to cool) to investigate the effects of gender over 3 h exposures in simulated living room/office environments. It was found that for identical levels of clothing and activity, there were only small differences in the thermal comfort responses of male and female subjects for neutral and slightly warm conditions. For cool conditions, female subjects tended to be cooler than males. An experiment to investigate the effects of heat acclimation on thermal comfort requirements involved six male subjects providing thermal comfort responses in neutral and slightly warm environments over 2 days. They then carried out an acclimatization program over 4 days, for 2 h per day, exercising in a hot (45 °C, 40% relative humidity) environment. Thermal comfort responses were then recorded in two sessions over 2 days in identical conditions to the pre-acclimation session. It was found that changes in thermal comfort responses were small and likely to be of little practical significance. An investigation into the behavior of people to maintain thermal comfort by adjusting their clothing was conducted using eight male and eight female subjects. Seated subjects reduced or increased their clothing level by using a wardrobe of clothing that was familiar to them. It was found that subjects can adjust their clothing to maintain thermal comfort, but within limits. Upper limits (clothing off) will be determined by modesty and acceptability. Lower limits (clothing on) will be determined by clothing design and acceptability. A low air temperature limit of 18 °C in freely available clothing may provide a working hypothesis. A laboratory study of thermal comfort requirements for people with physical disabilities compared responses with those of people without physical disabilities. It was found that there are few group differences between thermal comfort requirements of people with and without physical disabilities. However, there is a greater necessity to consider individual requirements for people with physical disability.
Tri-generation is a novel application of energy technologies which simultaneously produces heat, refrigeration and electricity. An expression for the calculation of the thermodynamic performance of a generic tri-generation scheme is presented. A brief first-law analysis involving an energy conversion ratio and newly defined heating-to-cooling and electric-to-cooling load ratios to usual system component thermodynamic parameters (such as coefficient of performance or prime mover thermal efficiency) was carried out. To illustrate the usefulness of the criterion, a tri-generation pilot plant set up in an office building was studied.
To better quantify the effects of conservation measures, degree-day-based techniques are commonly used to isolate weather-induced changes in building energy use. In this paper, we use a building energy simulation model, which allows us to hold fixed all influences on energy use besides weather, to evaluate several degree-day-based techniques. The evaluation is applied to simulated electricity and natural gas consumption for two large office building prototypes located in five U.S. climates. We review the development of degree-day-based, weather-normalization techniques to identify issues for applying the techniques to office buildings and then evaluate the accuracy of the techniques with the simulated data. We conclude that, for the two office building prototypes and five U.S. locations examined, most techniques perform reasonably well; accuracy, in predicting annual consumption, is generally better than 10%. Our major finding is that accuracy among individual techniques is overwhelmed by circumstances outside the control of the analyst, namely, the choice of the initial year from which the normalization estimates are made.
A prototype predictive controller, based on the theory of optimal stochastic control, was developed and installed in a non-residential building in Delémont (Switzerland). This building is very well insulated (U = 0.65 W/m2K for windows) and, moreover, equipped with an active floor heating and cooling system. Solar and free gains supply more than 50% of its heating energy during winter. The controller determines, with the aid of the predicted free gains, the heat to supply for the next hour in order to optimise comfort and minimise energy consumption over a period of 24 h. The performance of this controller is compared with that of an advanced external temperature controller installed in the same building. A detailed energy balance of the building is presented for both controller types. The maximal energy savings observed in favour of the predictive controller amount to 24% during the cold season (October through April) and even reach 31% during the hot season (May through September). The thermal comfort was evaluated through questionnaires filled in by the occupants, but also thanks to an analysis based on temperature monitoring in the building. The analysis results show that comfort was maintained by the predictive controller.
This paper describes the present state of the project SNOW-SIM at Narvik Institute of Technology. The project is aimed at finding methods for simulations of wind and snowdrift around building construction. The purpose of this project is to develop an integrated planning environment suitable for determining wind loads and snow deposition in planning construction in the cold climate areas. Such problems are now mostly solved by using wind tunnel experiments, rough assumptions or by experience. Calculations in two and three dimensions are performed on commercial fluid dynamic software based on Navier-Stokes equations. This paper deals with wind loads on buildings, ventilation of the attic of a small house, and flow patterns around groups of buildings. The velocity is shown as a vector plot around the structures, and the wind pressure is given as characteristics pressure values on surfaces. Flow patterns around buildings are visualized by streamlines. Simulations of snow accumulations are done with a generalized drift-flux model which is described in the paper. Drifts around snow fences are simulated in two dimensions and compared with full-scale measurements. Three-dimensional snow deposition is calculated around a group of houses with snow deposition expressed as surfaces.
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.
Eight different algorithms predicting the performance of earth-to-air heat exchangers are evaluated. The sensitivity of the methods to the inlet air temperature, air velocity, pipe length, pipe radius and the pipe depth is examined. Two different types of experiments have been designed and performed, and experimental results have been compared with the set of predicted values. The relative accuracy of each algorithm is estimated and reported for both cases.
Solid desiccant air-conditioning systems present a promising solution, in terms of performance level and environmental protection, pointing out their potential to be coupled with thermal solar or waste heat energy source. Nevertheless, these systems are characterized by constraints to the load they can satisfy, through the trade-off between the dehumidification cooling capacity and the latent load of the conditioned space. On that level, one has to note that, for steady environmental conditions, the conditioned space does not present unique value of load, but range of load, corresponding to an array of acceptable temperature and (usually relative) humidity values. In this work a methodology is proposed for the definition of the system's achievable working range under specific set of space (comfort) requirements. Through this approach, the systems present greater potential for covering the space requirements, thus presenting more possibilities on a design basis, and more flexible control strategies, as well. The proposed methodology is presented and discussed through the case study of a solar desiccant air-conditioning system coupled to a typical residential building.
In tropical countries, the greatest thermal gain occurs through the roof of a house. In Brazil, the use of an asbestos-cement roof without a ceiling is very common. Thus, there is intense heat transfer to the internal environment, which may cause thermal discomfort to the inhabitants. One way to reduce the heat flux is the use of radiant barriers, which reduce the heat flux through radiation. The use of this type of barrier in Brazil began in the mid-1990s and since then it has become popular for the thermal insulation of building roofs. However, there is a drawback regarding the experimental methods for the evaluation of the energy efficiency of these sheets. Many manufacturers show only the thermal conductivity, or give sparse information on the percentage reduction in radiated heat. There is currently no Brazilian normalization regarding the effective reductions in heat due to the use of these sheets. This study presents a compact apparatus for the determination of the efficiency of insulation sheets based on the use of heat flux transducers. Also, two models using thermal resistances which give simple correlations of great usefulness are presented. The sensitivity of the efficiency in relation to the several variables involved can be verified by exploring these correlations algebraically. Test results for different types of insulation sheets are reported and compared with the theoretical models.
In this paper, one-dimensional coupled heat and mass transfer through a plane geometry porous building component submitted to intertropical climatic conditions is studied. An analytical method using the periodic solution approach has been proposed to evaluate the heat and moisture transfer process in building materials. Results are discussed using the three climatic regions of Cameroon (2–13 °N). With latitude of 11°, it offers examples of practically whole range of intertropical climates. Influence of latitude on various temperature and moisture content through the building component has been presented. The results are in good agreement with the experimental data and other analytical solutions published in the literature.
This paper presents application range and functionality of thermally activated building systems (tabs). Tabs are increasingly used for energy efficient and economical cooling and heating of commercial buildings. Thereby, the building structure is used as thermal storage allowing the use of renewable energy sources. Based on a simulation study for a typical office building the aspects of thermal comfort, maximum permissible heat gains in the room and the re-cooling of the building mass are analysed. It is shown that depending on the maximum permissible daily room temperature amplitude with tabs typical heat gain profiles with peak loads up to around 50 W/m2 floor area can be managed. However, the transitional (mid-season) periods with already high solar gains and still restricted comfort range, in most cases will be decisive for the dimensioning of tabs, thus limiting maximum loads to lower values. The results also show that processes on the room side are almost unaffected from the processes on the supply side. In the cooling case, this allows for the re-cooling period of the fabric being extended to 24 h a day with accordingly “high” supply temperatures and peak load reductions of up to 50%. The results given may serve as orientation guide whether a tabs may be applicable in a specific building, and provides relevant parameters for the dimensioning of tabs.
In an office building equipped with a thermally activated building component system (TABS) detailed in situ measurements have been performed. The measurements presented in this paper have been concentrated on the concrete core conditioning (CCC) system, which is used for heating and cooling the building. Plastic pipes with circulating water have been placed in the concrete slab. One coil of the thermally activated concrete slab has been measured in detail using 80 measurement points. The measurements include temperature measurements at different heights of the concrete slabs as well as in the suspended floor and in both adjacent rooms. Furthermore the supply and return water temperature, the volume flow for the coil as well as the heat flow at the surface of the concrete slab have been measured. The measurements have been analyzed in the frequency-domain with help of a Fourier-transform. The temperature measurements and the volume flow have been utilized to validate a FEM-program working in the frequency-domain and a simplified RC star network placed in the time-domain simulation environment TRNSYS. The simplified RC-network has been previously validated with help of the FEM-program working in frequency-domain. For the validation of the FEM-program the measured time series have been transformed into Fourier-series and then used as input to the FEM-program performing the calculation in frequency-domain.
This work compares the experimental results obtained for the energy performance study of a ground coupled heat pump system with the design values predicted by means of standard methodology. The system energy performance of a monitored ground coupled heat pump system is calculated using the instantaneous measurements of temperature, flow and power consumption and these values are compared with the numerical predictions. These predictions are performed with the TRNSYS software tool following standard procedures taking the experimental thermal loads as input values. The main result of this work is that simulation results solely based on nominal heat pump capacities and performances overestimate the measured overall energy performance by a percentage between 15% and 20%. A sensitivity analysis of the simulation results to changes in percentage of its input parameters showed that the heat pump nominal coefficient of performance is the parameter that mostly affects the energy performance predictions. This analysis supports the idea that the discrepancies between experimental results and simulation outputs for this ground coupled system are mainly due to heat pump performance degradation for being used at partial load. An estimation of the impact of this effect in energy performance predictions reduces the discrepancies to values around 5%.
This paper presents the results of an extensive literature review on the topic of thermal adaptation in the built environment. The adaptive approach to modeling thermal comfort acknowledges that thermal perception in ‘real world’ settings is influenced by the complexities of past thermal history and cultural and technical practices. An important premise of the adaptive model is that the person is no longer a passive recipient of the given thermal environment, but instead is an active agent interacting with the person—environment system via multiple feedback loops. Thermal adaptation can be attributed to three different processes—behavioral adjustment, physiological acclimatization and psychological habituation or expectation. Both climate chamber and field evidence indicates that the slower process of acclimatization is not so relevant to thermal adaptation in the relatively moderate conditions found in buildings, whereas behavioral adjustment and expectation have a much greater influence. One of the most important findings from our review of field evidence was the distinction between thermal comfort responses in air-conditioned vs. naturally ventilated buildings, most likely resulting from a combination of past thermal history in the buildings and differences in levels of perceived control.
Investigating thermal comfort conditions in outdoor urban spaces, has thrown some light on the complexity of the issues involved, demonstrating that a quantitative approach is insufficient in describing comfort conditions outdoors. It revealed that although microclimatic parameters strongly influence thermal sensation, they cannot fully account for the wide variation between objective and subjective comfort evaluation, whereas, psychological adaptation seems to becoming increasingly important. This paper concentrates on the issue of psychological adaptation: naturalness, expectations, experience (short-/long-term), time of exposure, perceived control and environmental stimulation, and presents an attempt to try and evaluate the relative impact of each of these parameters. Understanding the interrelationship between the different parameters of psychological adaptation would be of interest in order to compare their relative significance, and to assess their design role, that is whether design considerations would influence these parameters, or vice versa, whether they could influence design decisions. An awareness of these issues would be valuable to architects, planners and urban designers, not by the way of limiting possible solutions, rather by enriching the design possibilities.
Building energy use in India is rising phenomenally. Indian codes prescribe a very narrow comfort temperature range (23–26 °C) for summer. Ventilation controls alone consume 47% of total energy in residences. Thermal comfort field studies in Indian residences were not attempted. The author conducted a field study in apartments in Hyderabad, in summer and monsoon seasons in 2008. This paper presents the occupants’ methods of environmental and behavioural adaptation and impediments in using controls.Only about 40% of the occupants were comfortable in summer due to inadequate adaptive opportunities. The comfort range obtained in this study (26.0–32.5 °C), was way above the standard. Fanger's PMV always overestimated the actual sensation.The occupants used many adaptation methods: the environmental controls, clothing, metabolism and many behavioural actions. Use of fans, air coolers and A/cs increased with temperature, and was impeded by their poor efficacy and noise, occupant's attitudes and economic affordability. A/c and air cooler usage was higher in top floors. Behavioural adaptation was better in summer and was restricted in higher economic groups always. Thermal tolerance was limited in subjects using A/cs and resulted in “thermal indulgence”. This study calls for special adaptation methods for top-floor flats.
While most of the existing artificial neural networks (ANN) models for building energy prediction are static in nature, this paper evaluates the performance of adaptive ANN models that are capable of adapting themselves to unexpected pattern changes in the incoming data, and therefore can be used for the real-time on-line building energy prediction. Two adaptive ANN models are proposed and tested: accumulative training and sliding window training. The computational experiments presented in the paper use both simulated (synthetic) data and measured data. In the case of synthetic data, the accumulative training technique appears to have an almost equal performance with the sliding window training approach, in terms of training time and accuracy. In the case of real measurements, the sliding window technique gives better results, compared with the accumulative training, if the coefficient of variance is used as an indicator.