Optimal spacing for double-skin roofs

Double-skin design is known as an effective way to reduce the building's solar heat gain. In this study, inclined parallel plates with upper plate heated by a lighting system are used to simulate double-skin roofs exposed to solar irradiation. Heat transfer experiments were carried out for different inter-plate spacing and different inclined angles. In some of our test runs, a radiant barrier is also installed on top of bottom plate to further cut down the building's heat gain. The Nusselt numbers reduced from our test data are consistently matched with Azevedo and Sparrow's correlation. The optimal inter-plate spacing, when the most heat gain is blocked out, can be directly obtained from our test data which is very close to the sum of both plate's thermal boundary layer thicknesses.     

Enhancing the sustainability and energy conservation in heritage buildings: The case of Nottingham Playhouse

Today, there is a growing interest in developing energy efficient buildings since it is estimated that buildings account for about 40% of the total primary energy consumption in the world. In relation to existing buildings, energy efficiency retrofits have become an important opportunity to upgrade the energy performance of commercial, public and residential buildings that may reduce the energy consumption, demand and cost. In this paper we cover the energy efficiency deep retrofit process that has been carried out for Nottingham Playhouse theatre building for the aim of enhancing its environmental performance and analysing the energy efficiency gained after implementing certain proposed modifications. It is a nationally protected historic building, listed as Grade II1 on The National Heritage List for England (NHLE). The building has had insulation enhancement, doors modifications, solar energy installations, energy-saving lights, in addition to improved heating and air conditioning system. The paper presents a novel methodology; and its results indicate significant improvements in the building's energy performance which is demonstrated using infrared thermographic images and data logger sensors where significant energy savings to the building's thermal performance are obtained. The energy saving measures have been completed while maintaining the heritage building's general appearance and architectural features, which have received a Commendation Certificate from The Nottingham Civic Society for this achievement.     

Fast computer graphics techniques for calculating direct solar radiation on complex building surfaces

Direct solar radiation has a major influence on a building's thermal behaviour. Current simulation engines are not up to the challenge of accurately modelling solar gains for buildings with complex or curved geometry and buildings sited in dense urban areas. Accurate thermal performance prediction for buildings in early stages of design is hindered by excessive computation time and incompatibility between architectural models and building energy simulation software. This paper proposes using a combination of modern computer graphics rendering techniques and parametric B-spline interpolation methods to quickly and accurately calculate solar gains over a full year based on sparse data with a continuous interpolation method. These new procedures accommodate complex building geometries and intricate shadow patterns and can accelerate shading calculations by several orders of magnitude. Faster calculations allow studies to be made at the early stages of design when modifications can have the greatest impact on a building's thermal behaviour.     

A life-cycle energy analysis of building materials in the Negev desert

Environmental quality has become increasingly affected by the built environment—as ultimately, buildings are responsible for the bulk of energy consumption and resultant atmospheric emissions in many countries. In recognizing this trend, research into building energy-efficiency has focused mainly on the energy required for a building's ongoing use, while the energy “embodied” in its production is often overlooked. Such an approach has led in recent years to strategies which improve a building's thermal performance, but which rely on high embodied-energy (EE) materials and products. Although assessment methods and databases have developed in recent years, the actual EE intensity for a given material may be highly dependent on local technologies and transportation distances. The objective of this study is to identify building materials which may optimize a building's energy requirements over its entire life cycle, by analyzing both embodied and operational energy consumption in a climatically responsive building in the Negev desert region of southern Israel—comparing its actual material composition with a number of possible alternatives. It was found that the embodied energy of the building accounts for some 60% of the overall life-cycle energy consumption, which could be reduced significantly by using “alternative” wall infill materials. The cumulative energy saved over a 50-year life cycle by this material substitution is on the order of 20%. While the studied wall systems (mass, insulation and finish materials) represent a significant portion of the initial EE of the building, the concrete structure (columns, beams, floor and ceiling slabs) on average constitutes about 50% of the building's pre-use phase energy.     

Intelligent building energy management system using rule sets

The current study presents an intelligent decision support model using rule sets based on a typical building energy management system. In addition, the model's impact on the energy consumption and indoor quality of a typical office building in Greece is presented. The model can control how the building operational data deviates from the settings as well as carry out diagnosis of internal conditions and optimize building's energy operation. In this context, the integrated “decision support model” can contribute to the management of the daily energy operations of a typical building, related to the energy consumption, by incorporating the following requirements in the best possible way: (a) the guarantee of the desirable levels of living quality in all building's rooms and (b) the necessity for energy savings.     

Modeling of an integrated solar system

The feasibility of using low-cost solar collection and storage technology to provide energy for residential units is investigated. Different construction strategies were compared including traditional housing practice against newly innovative ideas such as low radiant heating system, desiccant dehumidification, integrated low-cost solar collection, and phase-change material (PCM) storage. The selected building, located in Blacksburg, VA, integrated a solar thermal roof collection system consisting of a low-temperature flat-plate collector integrated within a concrete building envelope linked to a PCM storage tank. For the considered location and weather conditions (Blacksburg, VA), the proposed collection and storage solar system can supply 88% of the building's space heating and hot water needs averaged throughout the year saving the homeowner approximately 61.5% of the annual heating bills. However, the use of a storage system is not economical for the considered conditions. The paper also shows a month-by-month demand and supply distributions for the modeled building's heating and hot water needs.     

Life-cycle assessment of a 100% solar fraction thermal supply to a European apartment building using water-based sensible heat storage

Providing 100% of a building's heating and hot water using a solar thermal system in a European climate has been shown to be both practically feasible and functionally successful for a new apartment building in Switzerland. The research conducted a life cycle assessment of the solar thermal system and compared the results with an air-source heat-pump, ground-source heat pump, natural gas furnace, oil furnace and a wood-pellet furnace. Using a range of lifetime scenarios it was found that the solar thermal system displays potentially significant advantages over all other systems in terms of reductions for purchased primary energy (from 84 to 93%) and reductions in GHG emissions (from 59 to 97%). However, due to the heavy industrial processes and the particular metals used in manufacturing, the solar thermal system was shown to have a higher demand for resources which, in relation to the natural gas system, can be by a factor of almost 38. Potential impacts on ecosystem quality were marginally worse than for the heat-pump and fossil fuel systems due to resource use impacts whilst potential human health impacts were similar to the heat pump systems but better than the fossil and biomass fuelled systems.     

Simulation of coupled heat and moisture transfer in air-conditioned buildings

The simultaneous heat and moisture transfer in the building envelope has an important influence on the indoor environment and the overall performance of buildings. In this paper, a model for predicting whole building heat and moisture transfer was presented. Both heat and moisture transfer in the building envelope and indoor air were simultaneously considered; their interactions were modeled. The coupled model takes into account most of the main hygrothermal effects in buildings. The coupled system model was implemented in MATLAB-Simulink, and validated by using a series of published testing tools. The new program was applied to investigate the moisture transfer effect on indoor air humidity and building energy consumption under different climates. The results show that the use of more detailed simulation routines can result in improvements to the building's design for energy optimisation through the choice of proper hygroscopic materials, which would not be indicated by simpler calculation techniques.     

Experimental research on performance of the solar heat gain (SHG) insulation panel

Recently, research on energy efficiency for buildings has been performed due to a shortage of energy and increased concern about the environment. Building envelopes have vital roles in energy efficiency. Insulation depth, opening designs, double skins and other methods have been discussed to improve the performance of building envelopes. Among these methods, the use of opaque insulation has a role for blocking the inner heat loss, but also for inefficiently blocking the natural solar heat coming to the inside of a building. This paper looks at a way of bringing solar heat to the inside of a building, which is impossible with normal insulation. The research measures the amount of heat gain and provides the possibility of energy savings through solar heat in a test building.     

Thermal monitoring and indoor temperature predictions in a passive solar building in an arid environment

In this paper, results of a long-term temperature monitoring in a passive solar house, located at the Sede-Boqer Campus of the Ben-Gurion University, in the Negev region of Israel are presented. Local latitude is 30.8°N and the elevation is approximately 480 m above sea level. The climate of the region is characterized by strong daily and seasonal thermal fluctuations, dry air and clear skies with intense solar radiation. The monitored building consists of a two storey, passive solar house and belongs to a student dormitory complex located at the Sede-Boqer Campus. Formulae were developed, based on part of the whole monitoring period, representing the measured daily indoor maximum, average and minimum temperatures. The formulae were then validated against measurements taken independently in different time periods. In managing the building, the main objective in the winter was to bring up the indoor temperature by direct and indirect solar gains while in the summer it was to keep the temperature down. Therefore, analysis of the data and development of predictive formulas of the indoor temperatures were done separately for the winter and for the summer. Measured data of each season were then divided into two sub-periods, the first one used to generate formulas based on measured data (generation) and the second for testing the predictability of the formulas by independent data (validation). In general, a fairly good agreement was verified between onsite measurements and results of the formulae, with regard to daily indoor maximum, average and minimum temperatures. The issue of using outdoor temperatures measured in the adjacent street canyon instead of those registered at the local meteorological site for evaluating the building's cooling demand is also addressed in the paper. The developed formulae were here used for estimating the building's thermal and energy performance in summer, taking into account: (1) solely climatic data from the meteorological station; (2) climatic data from the meteorological station, except for outdoor ambient temperature, which was monitored adjacent to building. Results indicated that the calculation of the building's energy demand for air-conditioning based on temperature data collected at the meteorological station would yield half of the cooling degree-days externally and about two-thirds of that internally, as compared to adopting measured canyon temperatures for such calculations.     

Study on thermal performance of semi-transparent building-integrated photovoltaic glazings

This paper presents a one-dimensional transient heat transfer model, the Semi-transparent Photovoltaic module Heat Gain (SPVHG) model, for evaluating the heat gain of semi-transparent photovoltaic modules for building-integrated applications. The energy that is transmitted, absorbed and reflected in each element of the building-integrated photovoltaic (BIPV) modules such as solar cells and glass layers were considered in detail in the SPVHG model. Solar radiation model for inclined surface has been incorporated into the SPVHG model. The model is applicable to photovoltaic (PV) modules that have different orientations and inclinations. The annual total heat gain was evaluated by using the SPVHG model. The impacts of different parameters of the PV module were investigated. It was found that solar heat gain is the major component of the total heat gain. The area of solar cell in the PV module has significant effect on the total heat gain. However, the solar cell energy efficiency and the PV module's thickness have only a little influence on the total heat gain. The model was also validated by laboratory tests by using a calorimeter box apparatus and an adjustable solar simulator. The test results showed that the simulation model predicts the actual situation well.     

Optimization of the form of a building on an oval base

The aim of this work is to analyze the possibility of optimizing an abstract, symmetrical with respect to the north–south axis form of a building with vertical walls and windows, and constant volume and height. The external south partitions of the building are walls with whole windowpanes. The heat losses through walls, floors, roof and the gain of solar radiation through transparent partitions with respect to their direct correlation with the shape of building form are next taken into consideration. The gain of solar energy for the north part of the building have been disregarded.     

Energy simulations for glazed office buildings in Sweden

Highly glazed buildings are designed by architects to be airy, light and transparent with more access to daylight. Their energy efficiency, however, has become questioned. Therefore, energy simulations of single skin office buildings in Sweden were carried out, using a dynamic energy simulation tool. In order to study the impact of glass on the energy use during the occupation stage, office building alternatives with 30, 60 and 100% window to external wall area were studied. Other varied parameters were the building's orientation, the plan type (open and cell plan offices), the control set points and the façade elements (type and size of windows, type and position of shading devices, etc.). The main conclusion is that careful design is needed to ensure low energy use and good thermal comfort, especially for highly glazed office buildings. Careful design of glazed office buildings has to be based on detailed thermal simulations. Especially in fully glazed buildings (in which the façade is more “sensitive” to climatic conditions), proper combination of control set points, glazing and solar shading are crucial for the energy performance.     

Adaptive biomimetic facades: Enhancing energy efficiency of highly glazed buildings

In this paper, we investigate the design of an adaptive biomimetic facade as a practical solution for enhancing energy efficiency of highly glazed buildings in the hot and humid regions. We present an adaptive facade that reduces solar heat gain and hence the energy consumption of the building, with minimal reduction in visual comfort (i.e., indoor lighting levels and visibility to the outer environment) of the users. The basic module of the facade consists of four shading devices that can be folded along both horizontal and vertical axes. The design enables shading under both high and low sun angles, without blocking visibility to the outdoor environment. To develop the facade, we explore and mimic the physical, physiological and adaptation properties of an Oxalis oregana—a leaf that has the natural ability to track sun path and change its angle/position accordingly. As a case study for the proposed facade, we take an existing 20-story office building in the hot and humid climate of Lahore, Pakistan. Our numerical results indicate that after retrofitting of the designed facade, the building's existing energy load decreases by 32%. Moreover, 50% of the interior space (as opposed to 55% before the retrofitting) still has lighting level within the recommended range of 500–750 lux. The investigation demonstrates that the proposed biomimetic facade can significantly reduce the energy consumption, with minimal reduction in visual comfort, of highly glazed buildings.     

Compensation for differential energy balance across a building incorporating solar energy systems

In order to compensate for imbalance in solar energy between different sides of a building, and the resultant difference in energy availability and (heating/cooling) demand, methods using offsetting were developed to adjust occupiers’ energy bills. In the case of solar electricity generation, a model was considered, in which all the power is routed through common meter(s), so that total electricity generated is recorded. Equal proportions of this metered energy can then be deducted from occupiers’ individual meter readings, to give the net energy use for which each user is billed. Computer-based models were used to calculate the imbalance on those energy demands, which are affected by solar gain, i.e., space heating and cooling. The offset was calculated, such that all users pay the same bill for a given thermostat setting, and are charged more or less, for settings which result in higher or lower energy consumption respectively. Several case studies were performed, in which one building parameter was changed between successive trials. It was found that the offset was different in each case. Therefore, it is necessary to calculate the offset separately for each location, and for each building, depending on those parameters related to solar and thermal energy exchange.     

基于能耗控制的建筑外百叶遮阳优化研究

对透过建筑外百叶遮阳进入室内的太阳辐射得热进行了分析,并以建筑全年能耗为控制指标,提出了总辐射净得益量的概念,对建筑外百叶遮阳结构(百叶倾角和百叶数量)进行了优化,对比分析了优化模型与现用模型全年节能效果。结果表明,南向百叶遮阳的效果与百叶倾角有很大关系,而东西向则不明显;总辐射净得益量概念对于综合评价遮阳设施冬夏季的节能效果具有较好的指导作用。     

Analysis of the influence of installation thermal bridges on windows performance: The case of clay block walls

The building's energy performance is the result not only of material and component performances, but also of the way the components are interconnected. Concerning windows, their energy performance, which is usually evaluated by using the glass and frame heat transfer coefficients and the linear heat transfer coefficients of the glazing spacer, depends also on the frame installation. In this paper the entity of thermal losses due to the frame installation has been evaluated in terms of linear thermal transmittance calculated in accordance with the standard EN ISO 10211:2007 using THERM 5.2. The analysis of thermal bridges between a wooden frame window installed into two different kinds of external clay block walls has been carried out. The linear thermal transmittances have been calculated for three cases regarding the position (external, internal, and intermediate) and three concerning the insulation of the hole perimeter (non insulated, insulated and with insulation over fixed frame). The impact of the window installation on thermal losses has been estimated and its dependence on different sizes has been evaluated. A new graphical representation has been suggested. The frame position and the configuration of the window hole insulation result to have a relevant impact on the overall thermal performance of the considered window.     

Estimating effective solar absorptance in rooms

A model capable of calculating the redistribution of solar energy inside a building's rooms and the room's effective solar absorptance was developed and implemented in a computer code. Best-fit curves of a room's effective solar absorptance are provided as a function of the ratio between the window area and the internal surface area and of the wall absorptance. Moreover, model predictions are compared with an approximate theoretical equation.     

建筑节能与改善功能

建筑节能与改善建筑功能是矛盾对立的两方面, 讲节能, 限制了通风, 产生了房间空气质量问题;而满足了房间空气质量的通风,会产生能量大的损失,经济负担太大,一般住户难以承担。也是国家政策所不允许。所以,处理好这一对矛盾是解决建筑节能的关键问题。中国四合院建筑是既解决建筑节能又改善功能的典型,作者将对此进行论证。对被动太阳房因能量有限是绝对不能通风的,也产生室内空气质量问题,这可采用在四合院建筑形成被动太阳房来解决房间空气质量的问题。还研究了大气长波辐射的利用、强化和减弱的措施。