Intelligence in buildings: the potential of advanced modelling

“Intelligence” in buildings usually implies facilities management via building automation systems (BAS). However, present-day commercial BAS adopt a rudimentary approach to data handling, control and fault detection, and there is much scope for improvement. This paper describes a model-based technique for raising the level of sophistication at which BAS currently operate. Using stochastic multivariable identification, models are derived which describe the behaviour of air temperature and relative humidity in a full-scale office zone equipped with a dedicated heating, ventilating and air-conditioning (HVAC) plant. The models are of good quality, giving prediction accuracies of ±0.25 °C in 19.2 °C and of ±0.6% rh in 53% rh when forecasting up to 15 minutes ahead. For forecasts up to 3 days ahead, accuracies are ±0.65 °C and ±1.25% rh, respectively.

The utility of the models for facilities management is investigated. The “temperature model” was employed within a predictive on/off control strategy for the office zone, and was shown to substantially improve temperature regulation and to reduce energy consumption in comparison with conventional on/off control. Comparison of prediction accuracies for two different situations, that is, the office with and without furniture plus carpet, showed that some level of furnishing is essential during the commissioning phase if model-based control of relative humidity is contemplated.

The prospects are assessed for wide-scale replication of the model-based technique, and it is shown that deterministic simulation has potential to be used as a means of initialising a model structure and hence of selecting the sensors for a BAS for any building at the design stage. It is concluded that advanced model-based methods offer significant promise for improving BAS performance, and that proving trials in full-scale everyday situations are now needed prior to commercial development and installation.     

Robustness of a methodology for estimating hourly energy consumption of buildings using monthly utility bills

The evaluation of building energy consumption under typical meteorological conditions requires building energy profiles on an hourly basis. Computer simulations can be used to obtain this information, but generating simulations requires a significant amount of experience, time, and effort to enter detailed building parameters. This paper considers a simple methodology for using existing EnergyPlus benchmark building energy profiles to estimate the energy profiles of buildings with similar characteristics to a given benchmark model. The method utilizes the building monthly energy bills to scale a given benchmark building energy profile to approximate the real building energy profile. In particular, this study examines the robustness of the methodology considered with respect to the parameter discrepancies between a given building and the corresponding EnergyPlus benchmark model used to estimate its profile. Test buildings are defined by perturbing several combinations of the parameters defined in the benchmark building model. The test buildings examined are similar to the EnergyPlus, medium sized office, benchmark building in Baltimore, MD, and a total of 72 distinct test building configurations are examined. The analysis reveals that the methodology can significantly reduce the errors introduced by discrepancies from the EnergyPlus benchmark model.     

Exergoeconomic analysis and optimization of a solar-assisted heating system for residential buildings

In this study, an exergoeconomic model was developed for analysis and optimization of solar heating systems with residential buildings. The optimum collector area (_Ac$A_{\mathrm{c}}$) and storage volume (V$V$) for solar-assisted heating system in the Elaz??, Turkey (38.7^°N)$(38.7^{°}\mathrm{N})$, weather conditions were obtained using MATLAB optimization toolbox. The energy and exergy losses in each of the components of a solar heating system with seasonal storage were also determined. The results showed that the exergy loss and total cost increased with increasing per house collector area for the trapeze and cylindirical tanks. It was found that the total cost of the cylindrical tank system was higher than that of the other trapeze tank system. The exergy loss at the cylindrical tank was 19.8%, while the exergy loss at the trapeze tank was 8.3%.     

Developing future hourly weather files for studying the impact of climate change on building energy performance in Hong Kong

The concern on climate change leads to growing demand for minimization of energy use. As building is one of the largest energy consuming sectors, it is essential to study the impact of climate change on building energy performance. In this regard, building energy simulation software is a useful tool. A set of appropriate typical weather files is one of the key factors towards successful building energy simulation. This paper reports the work of developing a set of weather data files for subtropical Hong Kong, taking into the effect of future climate change. Projected monthly mean climate changes from a selected General Circulation Model for three future periods under two emission scenarios were integrated into an existing typical meteorological year weather file by a morphing method. Through this work, six sets of future weather files for subtropical Hong Kong were produced. A typical office building and a residential flat were modeled using building simulation program EnergyPlus. Hourly building energy simulations were carried out. The simulated results indicate that there will be substantial increase in A/C energy consumption under the impact of future climate change, ranging from 2.6% to 14.3% and from 3.7% to 24% for office building and residential flat, respectively.     

Reflections on the use of renewable power sources and nuclear energy in Portugal

This paper analyses the current energy balance of Portugal, considering the actual sources which are mainly traditional fossil fuels, hydroelectric power and renewables. Other potential sources are also discussed and taken into consideration in view of the previewed evolution of the country in energetic terms. Among these, nuclear power, once regarded as an option, is now being re‐considered. This paper also sums up the main issues to be considered in a future debate on the subject.     

Energy retrofit of historical buildings: theoretical and experimental investigations for the modelling of reliable performance scenarios

The paper suggests a multi-criteria approach for the energy refurbishment of historical buildings, proposing methodologies for the performance analysis, coupling several experimental and numerical studies. The target consisted in a rigorous evaluation procedure, in order to guarantee the necessary reliability of a numerical model of the system “building envelope/technical plants”, on which testing the technical and economical convenience of energy retrofit solutions.The paper collects the long work carried out by several Institutions during the last years, on Building “Palazzo dell’Aquila Bosco-Lucarelli”, a historical building located in Benevento (Southern Italy), currently analyzed in order to define the technical adoption of possible improving actions.The carried out studies, beyond the proposition of an operational methodology, are aimed to evidence a best-practice specified for the Italian territorial context, which has several historical buildings needing restoration.Carefully applied investigations, based on various methodologies and through several instrumentations, allowed the definition of a numerical model correspondent to the real building, defined also comparing the results with the historical requests of gas and electricity. Moreover, dynamic energy simulations tested the effectiveness, singularly and coupled, of several solutions for the building energy optimization. A significant potentiality of energy and economic optimization has been demonstrated.     

A new methodology for the design of low energy buildings

The Kyoto protocol binded the developed countries to reduce the greenhouse gas emissions at least by 5% by 2008-2012 in order to tackle global warming and climate change. Some of the measures of the governments to achieve this goal are to promote new buildings construction and to retrofit existing buildings while satisfying low energy criteria. This means improving energy efficiency of buildings and energy systems, developing sustainable building concepts and promoting renewable energy sources.The design of a low energy building requires parametric studies via simulation tools in order to optimize the design of the building envelope and HVAC systems. These studies are often complex and time consuming due to a large number of parameters to consider. Hence, this paper aims to set up a methodology that simplifies parametrical studies during the design process of a low energy building. The methodology is based on the Design of Experiments (DOE) method which is a statistical method widely used in industry to perform parametric studies that reduces the required number of experiments.     

An integrated modeling tool for simultaneous analysis of thermal performance and indoor air quality in buildings

To analyze the thermal performance and indoor air quality (IAQ) in building simultaneously and quickly, we have developed an integrated modeling tool to simulate the dynamic indoor multi-parameters distributions and concentrations. The tool can take the parameters including indoor temperature, indoor humidity, and pollutant concentrations (e.g., volatile organic compounds (VOC) CO₂, particulate matter (PM)), as well as the heating/cooling load of heating, ventilating, and air-conditioning (HVAC) system into account. It couples a new zonal approach based on room air age. This paper presents the basic concept and flow chart in developing the modeling tool, and demonstrates the tool's application in a hypothetical health care building. The tool could be used for design of HVAC system with IAQ control devices and for the simultaneous analysis of thermal performance and IAQ in buildings.     

A study on modeling and performance assessment of a heat pump system for utilizing low temperature geothermal resources in buildings

Low and moderate geothermal resources are found in most areas of the world. A very efficient way to heat and air-condition homes and buildings is the utilization of ground source heat pumps (GSHPs), also known as geothermal heat pump (GHPs), to obtain heat energy from low temperature geothermal resources.     

Automatic generation of energy conservation measures in buildings using genetic algorithms

Building energy simulations are key to studying energy efficiency in buildings. The state-of-the art building energy simulation tools requires a high level of multi disciplinary domain expertise from the user and many technical data inputs that curb the usability of such programs. In this paper an IT tool is presented, which has the capability of predicting a building's energy utilization configuration based on the reported annual energy and a few non-technical inputs from the user; and correspondingly generates cost effective energy conservation measures for the intended savings.The approach first identifies the system variables that are critical to a building's energy consumption and searches for the combination of these parameters that would give rise to the annual energy consumption as reported by the facility. Genetic algorithms are utilized to generate this database. A statistical fit is formulated between the system variables and the annual energy consumption from the database. Using this correlation, system configuration for the target energy efficiency is determined with corresponding energy conservation measures. A cost analysis is carried out to prescribe the most cost effective energy conservation measures. Competency of the tool is demonstrated in the paper through case studies on three geographies with different climate conditions.     

A new and innovative look at anti-insulation behaviour in building energy consumption

This paper presents the findings of a case study with building simulation using EnergyPlus dynamic thermal simulation software, in which wall insulation was varied together with cooling set-point temperature in a hot and dry climate of Botswana. Against the established norm that adding wall insulation reduces annual fuel consumption, it is shown in this paper that this is not always the case: there are instances where adding wall insulation directly increases annual fuel consumption. Initial cost of insulation aside, as the cooling set-point temperature is gradually increased, the building switches from an “insulation reduces cooling load” to an “insulation increases cooling load” behaviour. In other words, the well established knowledge that “the lower the u-value the better” gets overridden by “the higher the u-value the better”. We termed this a “point of thermal inflexion”. Simple graphical demonstration of the existence of this point is presented in the paper. According to the findings, design engineers and building economics related professionals who quantify investment on insulation can get disastrous results if they assume that all buildings behave pro-insulation since a building may behave anti-insulation.     

Criteria for use of groundwater as renewable energy source in geothermal heat pump systems for building heating/cooling purposes

Environmental protection measures are conducted directly by the use of renewable energy sources. The energy development of cities in Europe is aimed at the sustainable use of renewable energy sources in order to achieve the substitution of fossil fuels and the reduction of the hazardous gas emission into the atmosphere. Geothermal resources of medium and low enthalpy in Europe being used for obtaining heat energy are providing about 6600 MW_t, currently having the growth trend of 50 MW_t annually. The use of geothermal low enthalpy, namely of subgeothermal groundwater resources, has even higher annual growth rate, and if such a trend is kept till the year 2010, the produced energy will amount about 8000 MW_t. Criteria of the groundwater use as a hydrogeothermal energy resource in heat pumps are complex, and they deal with aspects of incoming temperatures and groundwater quantities. The precise limit temperature of groundwater that would separate the direct use of geothermal energy (only by the use of heat exchangers), and indirectly by the use of a heat pump has not been determined in the professional and scientific practice of Serbia so far. Taking into account that relatively small number of new flat is being built in Serbia nowadays, if we want to save energy it is necessary to carry out the energy reconstruction of the existing flats whose number is estimated to be more than 2.8 million. By the application of subgeothermal energy and the use of heat pumps, energy consumption would be significantly reduced.     

A study on estimating the energetic and exergetic prices of various residential energy sources

In choosing the type of any energy sources for residential and other uses, their prices play in general a big role. These prices are based on energy values. Besides this, the application of the exergy, which is a way to a sustainable future, is more meaningful in providing information for long-term planning of resource management. In the present study, energy and exergy prices of various energy sources are investigated. The energy sources considered include coal, natural gas, furnace oil, diesel oil, liquefied petroleum gas (LPG) and wood, while electric resistance along with heat pump and district heating are also covered. In this context, chemical exergy relations of these energy sources are presented first. The prices of various energy sources in the Turkish residential sector, which is given as an illustrative example, are then used in the calculations. Finally, the energy and exergy prices are compared with each other, while the main conclusions are listed. The highest unit energy price is that of diesel oil, while the lowest one is that of natural gas. The differences between the energy and exergy prices are small for all energy carriers.     

An integrated empirical and modeling methodology for analyzing solar reflective roof technologies on commercial buildings

Buildings impact the environment in many ways as a result of both their energy use and material consumption. In urban areas, the emission of greenhouse gases and the creation of microclimates are among their most prominent impacts so the adoption of building design strategies and materials that address both these issues will lead to significant reductions in a building's overall environmental impact. This report documents the energy savings and surface temperature reduction achieved by replacing an existing commercial building's flat roof with a more reflective ‘cool roof’ surface material. The research methodology gathered data on-site (surface temperatures and reflectivity) and used this in conjunction with the as-built drawings to construct a building energy simulation model. A 20-year cost benefit analysis (CBA) was conducted to determine the return on investment (ROI) for the new cool roof construction based on the energy simulation results. The results of the EnergyPlus™ simulation modeling revealed that reductions of 1.3–1.9% and 2.6–3.8% of the total monthly electricity consumption can be achieved from the 50% cool roof replacement already implemented and a future 100% roof replacement, respectively.This corresponds to a saving of approximately $22,000 per year in energy costs at current prices and a consequent 9-year payback period for the added cost of installing the 100% cool roof. The environmental benefits associated with these electricity savings, particularly the reductions in environmental damage and peak-time electricity demand, represent the indirect benefits of the cool roof system.     

Virtual Building Dataset for energy and indoor thermal comfort benchmarking of office buildings in Greece

The knowledge of building stock energy data of a country is a very significant tool for energy benchmarks establishment, energy rating procedures and building classification boundaries determination, according to the Directive 2002/91/EC and its implementation in EU Member States. The lack of building energy databases in many EU Countries, including Greece, and the difficulties of collecting them lead to the investigation of other potential solutions. The aim of this paper is to present a method of a Virtual Building Dataset (VBD) creation for office buildings in Greece. The philosophy of VBD is based on the creation and simulation of random office buildings that could be found or built in Greece, taking into account the Greek constructional and operational characteristics of office buildings and Greek legislation. The VBD consists of 30,000 buildings (10,000 in each climatic zone) with their detailed constructional and operational data and of their simulation outputs: the annual specific energy consumption for heating, cooling, artificial lighting, office equipment and an indoor thermal comfort indicator. Based on VBD results the energy and indoor thermal comfort benchmarks for office building sector in Greece are assessed and presented.     

Thermoeconomic analysis and optimization of high efficiency solar heating and cooling systems for different Italian school buildings and climates

The paper investigates the energetic and economic feasibility of a solar-assisted heating and cooling system (SHC) for different types of school buildings and Italian climates. The SHC system under investigation is based on the coupling of evacuated solar collectors with a single-stage LiBr-H₂O absorption chiller; auxiliary energy for both heating and cooling is supplied by an electric-driven reversible heat pump. The SHC system was coupled with different types of school buildings located in three different Italian climatic zones. The analysis is carried out by means of a zero-dimensional transient simulation model, developed using the TRNSYS software; the analysis of the dynamic behaviour of the building was also included. An economic model is proposed, in order to assess the operating and capital costs of the systems under analysis. Furthermore, a parametric analysis and a subsequent mixed heuristic-deterministic optimization algorithm was implemented, in order to determine the set of the synthesis/design variables that maximize system profitability. The results are encouraging, as for the potential of energy saving. On the contrary, the SHC economic profitability can be achieved only in case of public funding policies (e.g. feed-in tariffs), as always happens for the great majority of renewable energy systems.     

武汉写字楼的能源管理与节能改造分析

根据2007年武汉市能源审计结果,分析了写字楼的能源管理现状.对某写字楼进行了能耗模拟和节能改造模拟.能耗模拟结果表明,机组选型偏大,系统运行调节存在问题.建议提高系统综合能效比、实施照明控制和安装外遮阳;能耗模拟要考虑周边建筑的阴影.     

Life cycle assessment in buildings: State-of-the-art and simplified LCA methodology as a complement for building certification

The paper presents the state-of-the-art regarding the application of life cycle assessment (LCA) in the building sector, providing a list of existing tools, drivers and barriers, potential users and purposes of LCA studies in this sector. It also proposes a simplified LCA methodology and applies this to a case study focused on Spain. The thermal simulation tools considered in the Spanish building energy certification standards are analysed and complemented with a simplified LCA methodology for evaluating the impact of certain improvements to the building design. The simplified approach proposed allows global comparisons between the embodied energy and emissions of the building materials and the energy consumption and associated emissions at the use stage.The results reveal that embodied energy can represent more than 30% of the primary energy requirement during the life span of a single house of 222 m² with a garage for one car. The contribution of the building materials decreases if the house does not include a parking area, since this increases the heated surface percentage. Usually the top cause of energy consumption in residential building is heating, but the second is the building materials, which can represent more than 60% of the heating consumption.     

建筑节能设计标准变革和建筑物的节能设计

按建筑节能设计标准的不同要求,将我国建筑节能发展历程分成几个不同的阶段。根据墙体材料的实际应用状况和保温隔热材料的发展状况,每个阶段设计重点和采取的设计思路都不同。现在既要满足高节能率又要满足新的消防要求。     

Data collection and analysis of the building stock and its energy performance—An example for Hellenic buildings

The process of building labeling and certification in accordance to the provisions of the European Directive on the Energy Performance of Buildings (EPBD) constitutes a unique opportunity for collecting information on the characteristics of the building stock and its energy performance on a national and European level. Thus, there is a need to handle data from a large stock of buildings and to be able to analyse information and extract practical trends and benchmarks. Stakeholders and technical managers who oversee a number of buildings experience similar needs in order to collect, organize and monitor the energy performance of a large pool of buildings. To facilitate these efforts, a common evaluation database and complimentary software for its exploitation have been developed in the frame of a European project.This paper presents an overview of the database and its available tools, and the main results from a case study on Hellenic buildings that reveals relevant characteristics. The Hellenic database included a sample of 250 buildings from different regions in Greece, with a breakdown that is representative of the national building stock. The main results focus on the buildings’ energy performance, thermal envelope characteristics and the exploitation of solar thermal energy.