Dynamic Energy Simulation Tool Research Articles

On the effects of the mean radiant temperature evaluation in the assessment of thermal comfort by dynamic energy simulation tools

The European Directive 844/2018, the EN 16798–1 and −2, and the ISO 17772 Standards establish that when designing a new building or energy retrofitting an existing building, the Indoor Environmental Quality must be considered. One aspect of IEQ is thermal comfort, which is affected by the mean radiant temperature, tr. This variable is the only one that an HVAC system cannot control directly. In fact, it depends on the temperatures of the surfaces surrounding the subject which are influenced by the air temperature. It can be calculated using the methods envisaged by the ISO EN 7726 standard or alternative approximate methods.It is therefore important to understand whether the differenttr calculation methods affect the PMV value and, therefore, the classification of the thermal environment according to the EN 16798-1 Standard. For many years, building dynamic energy simulation software tools which integrate energy analyses with the evaluation of thermal comfort have been used for the design and verification of the energy performance of buildings. This paper compares different methods of calculating the mean radiant temperature used by Energy Plus with the Design-Builder interface and analyses the influence of the results on the evaluation of thermal comfort in three buildings.

Assessment of Building Energy Simulation Tools to Predict Heating and Cooling Energy Consumption at Early Design Stages

Recent developments in dynamic energy simulation tools enable the definition of energy performance in buildings at the design stage. However, there are deviations among building energy simulation (BES) tools due to the algorithms, calculation errors, implementation errors, non-identical inputs, and different weather data processing. This study aimed to analyze several building energy simulation tools modeling the same characteristic office cell and comparing the heating and cooling loads on a yearly, monthly, and hourly basis for the climates of Boston, USA, and Madrid, Spain. First, a general classification of tools was provided, from basic online tools with limited modeling capabilities and inputs to more advanced simulation engines. General-purpose engines, such as TRNSYS and IDA ICE, allow users to develop new mathematical models for disruptive materials. Special-purpose tools, such as EnergyPlus, work with predefined standard simulation problems and permit a high calculation speed. The process of reaching a good agreement between all tools required several iterations. After analyzing the differences between the outputs from different software tools, a cross-validation methodology was applied to assess the heating and cooling demand among tools. In this regard, a statistical analysis was used to evaluate the reliability of the simulations, and the deviation thresholds indicated by ASHRAE Guideline 14-2014 were used as a basis to identify results that suggested an acceptable level of disagreement among the outcomes of all models. This study highlighted that comparing only the yearly heating and cooling demand was not enough to find the deviations between the tools. In the annual analysis, the mean percentage error values showed a good agreement among the programs, with deviations ranging from 0.1% to 5.3% among the results from different software and the average values. The monthly load deviations calculated by the studied tools ranged between 12% and 20% in Madrid and 10% and 14% in Boston, which were still considered satisfactory. However, the hourly energy demand analysis showed normalized root mean square error values from 35% to 50%, which were far from acceptable standards.

Estimating cooling loads of Arizona State University buildings using microclimate data and machine learning

In hot arid urban climates, building cooling equipment consumes the greatest share of energy out of all building end-use equipment. For existing buildings, dynamic system-based building energy simulation tools have provided valuable information on the impact of microclimates on cooling energy use. However, such models require in-depth information on building model parameters and often suffer from modeler bias even when sufficient calibration indices are satisfied. This study presents a data-driven approach for predicting the cooling loads of three university buildings in Arizona using simulated microclimate data. A microclimate model ENVI-met generated the input micro-scale weather data for each building. The ENVI-met simulation was validated using in-situ observations during the summer of 2018. Multiple machine learning algorithms were implemented. A final model was selected and used as baseline to predict cooling loads for each building in the dataset. The model predicts chill water tons per square meter using microclimate variables that include mean air temperature, mean absolute humidity, shading levels, and direct shortwave radiation. The black-box model was explained using an advanced machine learning model interpretation library in Python: SHAP. The baseline model predicted cooling loads with a prediction accuracy score of 0.98 using the tree-based algorithm Random Forest. Sensitivity analyses and scenario results showed that cooler microclimates reduced cooling loads for the modeled buildings. The developed framework will be used in future study extensions to explore the impacts of simulated microclimate scenarios generated by ENVI-met.

A comparison between new European technical standards and dynamic simulation tools for chiller modelling

In the last years, new technical standards for the assessment of the energy efficiency of technical building systems were developed by the European Committee for Standardization (CEN). These procedures were conceived as to combine the easiness of the calculation methodologies and their related assumptions with a sufficient level of accuracy. While the former objective is often achieved, the latter is a challenging task as the procedures sometimes fail to simulate in a proper way the actual performance of the technical systems. On the other hand, the detailed procedures applied by detailed dynamic energy simulation tools are more precise and complex; however, for their application, they need a wide range of input data that are often hard to collect. For this reason, simplified procedures are now commonly applied, above all in the case of existing buildings. Nevertheless, these procedures need to be deeply analysed and validated. In this paper, the main standard calculation procedures addressed to chillers and specified in EN 16798-13:2017 were analysed, with a focus on the required input data and the calculation procedures. The same approach was then applied to the more detailed calculation methods used in the dynamic tools EnergyPlus and TRNSYS, and the results were compared. The theoretical analysis was then followed by a case study approach. A reference office building, representative of the Italian building stock, was selected and analysed in two different Italian climatic zones. The determination of the thermal energy need for cooling was performed by means of EnergyPlus, while the assessment of the energy demand related to technical building systems was performed both with EnergyPlus and with the standard procedures. This paper is part of a wider research activity finalised to the analysis of the technical building systems calculation procedures, taking into account different generation systems and thermal coupling modes between the technical systems and the building itself.

An optimized solution for retrofitting building façades: Energy efficiency and cost-benefit analysis from a life cycle perspective

The study aims to conduct a comprehensive cost-benefit analysis (CBA) for incremental energy star ratings in Melbourne and Perth by upgrading the thermal performance of the building façade. CBA is performed over 20, 40, and 60 years by considering the refurbishment of an existing building façade or a newly constructed house to ensure the highest energy efficiency at the lowest reasonable cost. The hybrid approach of using a dynamic energy simulation tool (FirstRate5) and @RISK optimizer provides a feasible solution for obtaining a specific star rating. This study shows energy saving costs can offset the additional investment of insulation levels and energy-efficient glazings. However, life cycle energy savings are minimized after a certain point of supplementary yield insulations, such as ceilings R(6) and walls R(3). Hence the results are evaluated in terms of financial appraisals, such as net present value (NPV), benefit-cost ratio (BCR), internal rate of return (IRR), and other indicators for incremental star-rated designs. The results of the financial appraisals recommend upgrading the obligatory star rating from 6-star to 8-star is a cost-effective solution irrespective of climate and time horizon. Sensitivity indices of design variables exhibit the significance of functionality and cost implications in the established energy rating scheme. Possible economic recession (at > 7%) due to COVID and the Ukraine war, the investment coefficient (r ≤ −0.56) with NPV increases significantly against energy savings cost (r ≥ 0.8). Given the present energy rating scheme, these findings provide an exhaustive perception of policy implications.

Analysis of future carbon-neutral energy system – The case of Växjö Municipality, Sweden

In line with the Swedish target of carbon neutrality by 2045, the municipality of Växjö in Kronoberg County has set its own target to be carbon neutral in 2030. Currently, the Municipality's partially decentralized energy system relies heavily on interconnected electricity supply from the national grid, and fuels imports from other parts of Sweden. Under this circumstance, several concerns arise, including: in which ways future demand changes induce supply changes, and whether a future carbon-neutral energy system will be less costly in a sustained-electricity supply condition. In this study, techno-economic evaluations are conducted for different carbon-neutral scenarios for Växjö’s future energy system in 2030 and 2050, using an hour-by-hour dynamic energy simulation tool of EnergyPLAN. Projections for the future energy demands for Växjö were developed and modeled, based on the development strategies and on the national sustainable future scenarios in Sweden. Results for the Växjö’s carbon-neutral scenarios showed that the current energy system is sufficient to satisfy future heat demand. However, fulfilling demands of electricity for all sectors and fuels for transport and industry is a challenge. In the short term and at increased energy demand and price, being carbon neutral is technically viable without major changes in energy supply technologies. However, in the long term, investment for intermittent renewable energy resources, together with carbon capture and storage is considered to be viable financially. Therefore, planning for a carbon-neutral Växjö based on local investments showed to be a feasible strategy.

Variable-Load Heat Pumps: Impact of the Design and Control Parameters on the Actual Operation Conditions

Nowadays heat pumps (HPs) represent the main alternative to traditional heating systems for the transition to nearly zero-energy buildings. Though HPs are a well-known technology, the estimation of their actual energy performance is still under discussion. Indeed, the proper choice of the HP design parameters (e.g. size, rated supply temperature) and the adopted control strategy can assume a paramount role to cover the mismatch between declared and actual performance of the system. Objective of this work is to analyze this mutual dependence in an operating system to provide guidelines for the design of a residential heating system with a HP. Through a dynamic energy simulation tool, a variable-load air-to-water HP is used to cover the thermal demand of a residential building. The effect of the reciprocal influence of different design choices (e.g. rated heating capacity or design supply temperature) and control strategies (e.g. climatic regulation) is analyzed by simulating different scenarios. To complete the evaluation, the impact of a thermal energy storage is also assessed. The study allows to identify guidelines for the design of different system configurations and results seem to confirm the impact of the investigated parameters on the seasonal performance of the system.

A Life Cycle Cost Analysis of Structural Insulated Panels for Residential Buildings in a Hot and Arid Climate

In hot and humid climatic conditions, cooling tends to dominate building thermal energy use. Cooling loads can be reduced through the adoption of efficient building envelope materials, such as Structural Insulated Panels (SIPs). This study quantifies the life cycle cost and operational energy of a representative case-study house in Bahrain using SIPs and hollow concrete blocks (HCBs) for the envelope over a period of 50 years. Operational energy is calculated using a dynamic energy simulation tool, operational costs are calculated based on the energy demand and local tariff rates, and construction costs are estimated using market prices and quotations. The life cycle cost is quantified using the Net Present Cost technique. Results show that SIPs yield a 20.6% reduction in cooling energy use compared to HCBs. For SIP costs of 12 and 17 USD/m2, the SIP house was cheaper throughout, or had a higher capital cost than the HCB house (breaking even in year 33), respectively. We propose policy recommendations with respect to material pricing, electricity tariffs, and energy efficiency, to improve the operational energy efficiency of houses in Bahrain and similar countries along the Arabian Peninsula.

Designing and assessing solar energy neighborhoods from visual impact

The optimal diffusion of Building Integrated PhotoVoltaics (BIPV) in cities requires diligent planning to arrange temporal and spatial distribution of energy, while preserving the aesthetics of city landscapes. Benefitting from an increasing quality of 3D models of cities, a comprehensive methodology to estimate potential energy generation from visually-acceptable PV, energy use from buildings, and economically viable micro-grid operation is proposed, by combining validated dynamic energy simulation tools into an open-source computational platform. The platform intends to be useful for urban planners and officials in charge of planning a large-scale BIPV installation into an existing neighborhood: simulations are carried out at the city scale, inclusive of façade potential, shading from vegetation and detailed roof shapes with super-structures.Social acceptability is investigated through a novel visual impact assessment methodology and grid integration solutions are analyzed with reference to their associated costs. Under a conservative scenario, a median of 10 kW hAC-electricity / m2 heated floor area per year is available from BIPV production in Geneva (Switzerland), covering 32 % electricity demand for space heating from heat pumps, or, alternatively, almost 10 times the one for space cooling. Visual impact has demonstrated not to be concurrent to grid integration constraints at the current stage, but rather to contribute to filtering building envelope surface and avoid grid curtailment of excess electricity. In the near future, with an increased grid efficiency, visual impact is expected to become a crucial criterion to limit the integration extent.

Thermal performance of lightweight concrete applications in building envelopes in Lebanon

Innovative building materials are being used in building envelopes for reducing their heating and cooling needs. This paper aims to assess the thermal impact of using lightweight concrete in Lebanese building constructions by pouring an 8 cm thickness of lightweight concrete on the roof and the slab and replacing traditional hollow concrete block by lightweight concrete blocks. Thermal properties of two different samples were experimentally determined: the first one (558 kg/m3) used for the roof and the slab and the second one (1074 kg/m3) used for the walls. Then numerical simulations were carried out for a Lebanese traditional detached house using the characteristics of these two samples. The thermally improved Light Weight Concrete building (LWC) was compared to a traditional Lebanese house base case (BC) using a dynamic building energy simulation tool in the four different Lebanese climate zones: coastal, mid-mountain, mountain, and inland zones. The results highlight the effectiveness of integrating LWC to building envelopes by reducing energy consumption and improving thermal comfort in both winter and summer climate conditions and in the different Lebanese climatic zones. The paper demonstrates that the use of LWC in the vertical walls replacing the traditional hollow blocks can reduce the heating needs by up to 9% and by up to 13% for cooling needs. On the other hand, adding a LWC roof screed has a very high impact on cooling and heating energy consumption, which can reach up to 74% in cooling energy savings and up to 24% in heating energy savings.

Updated Typical Weather Years for the Energy Simulation of Buildings in Mediterranean Climate. A Case Study for Sicily

Building energy simulations are normally run through Typical Weather Years (TWYs) that reflect the average trend of local long-term weather data. This paper presents a research aimed at generating updated typical weather files for the city of Catania (Italy), based on 18 years of records (2002–2019) from a local weather station. The paper reports on the statistical analysis of the main recorded variables, and discusses the difference with the data included in a weather file currently available for the same location based on measurements taken before the 1970s but still used in dynamic energy simulation tools. The discussion also includes a further weather file, made available by the Italian Thermotechnical Committee (CTI) in 2015 and built upon the data registered by the same weather station but covering a much shorter period. Three new TWYs are then developed starting from the recent data, according to well-established procedures reported by ASHRAE and ISO standards. The paper discusses the influence of the updated TWYs on the results of building energy simulations for a typical residential building, showing that the cooling and heating demand can differ by 50% or even 65% from the simulations based on the outdated weather file.

DIGITAL ENERGY SIMULATION OF BUILDINGS PROTECTED BY MUNICIPAL HERITAGE POLICIES IN THE FRAMEWORK OF ENERGY RENOVATION PROJECTS

Abstract. The energy simulation is a key tool when designing renovation actions on buildings. In the framework of the InterregMed SHERPA project, bound to trigger and manage energy renovations in public buildings, the digital analysis of an educational building affected by the municipal heritage protection has been carried out. The building is the CIPFP Blasco Ibáñez, catalogued as a monument of local interest in Valencia (Spain) city planning, where the heritage value of its facades (main and interior), roof and internal spatial structure is identified.The methodology used consists in performing an energy audit of the building in order to be able to customize a digital energy model. By means of an hourly dynamic energy simulation tool, the current status of the building and its systems can be determined, and energy renovation actions can be outlined. The use of digital analysis tools is of utmost interest in buildings declared as municipal heritage sites since enables the study to be performed in a non-intrusive manner. Several points of energy improvement are identified. There are some actions that can be performed without affecting parameters protected by the heritage status, and some others which need to be modified in order to be compliant with it. Furthermore, the digital analysis through energy simulation tools also allows to perform detailed calculations about the energy, environmental and economic savings associated with the measures. The assessment has proved the need to promote research and testing of new solutions and technologies to improve the energy efficiency of heritage buildings.

Application and Validation of a Dynamic Energy Simulation Tool: A Case Study with Water Flow Glazing Envelope

The transparent materials used in building envelopes significantly contribute to heating and cooling loads of a building. The use of transparent materials requires to solve issues regarding heat gain, heat loss, and daylight. Water flow glazing (WFG), a disruptive technology, includes glazing as part of the Heating, Ventilation and Air Conditioning (HVAC) system. Water is transparent to visible wavelengths, but it captures most of the infrared solar radiation. As an alternative to fossil fuel-based HVAC systems, the absorbed energy can be transferred to the ground through borehole heat exchangers and dissipated as a means of free-cooling. Researchers of the Polytechnic University of Madrid have developed a software tool to calculate the energy balance while incorporating the dynamic properties of WFG. This article has studied the mathematical model of that tool and validated its ability to predict energy savings in buildings, taking spectral and thermal parameters of glazing catalogs, commercial software, and inputs from the measurements of the prototypes. The results found in this article showed that it is possible to predict the thermal behavior of WFG and the energy savings by comparing the thermal parameters of two prototypes. The energy absorbed by the water depends on the mass flow rate and the inlet and outlet temperatures.

Experimental and numerical study to evaluate the effect of thermostat settings on building energetic demands during the heating and transition seasons

Occupant behavior towards heating and cooling system setting is a very complex process that has been under investigation in the past years. As most of dynamic energy simulation tools consider energy consumption as fully deterministic with fixed and unrealistic schedules, the ability to predict properly the energy consumption is poor because of occupant interaction with indoor environment. In this study, the occupant in residential buildings is modeled as a probabilistic process. The occupant behavior related to thermostat settings is studied through experimental measurements collected in eleven buildings in France over a period of one year, by monitoring various parameters, including indoor air temperature, ambient temperature, indoor and outdoor relative humidity and indoor CO2. The occupant attitude was classified into three groups, active, normal and passive, according to the number of setting changes per year. The Logistic regression is adopted to calculate the probability of changing the thermostat setting by an occupant, in terms of different environment parameters. The results yield to a proposed model that can be implemented in simulation software, in order to take into account the occupant behavior in the assessment of realistic energy consumption.

Analysis of Night-Time Pre-Cooling in a School Building

The content of this paper is a theoretical case study of a school building where the impact of night pre-cooling on operative temperature during summer period is analyzed. The classroom under pitched roof was selected for case study purposes. There are glass surfaces on roof and in external wall. We compare two types of building constructions. On the one hand side there is the wooden lightweight construction. On the other hand side there is the heavyweight construction made of reinforced concrete. The mechanical ventilation system provides for the required air change rate in classroom during whole day. The results from energy simulation show positive impact of night pre-cooling in combination with heavyweight building construction on maximum operative temperature in classroom during summer period. The results are output from dynamic energy simulation tool DesignBuilder.

Effects of the room temperature sensor position and radiator sizing on indoor thermal comfort and energy performances

In this paper, a simplified zonal model for the evaluation of the spatial distribution of the air temperature in a thermal zone is presented. This model, in which the air flow is caused only by buoyancy forces, is implemented in ALMABuild. The model is used for the analysis of the effect of the temperature sensor positioning on the control system behaviour and on the indoor comfort conditions. This analysis is performed considering a multi-zone building composed by three offices, focusing the evaluation to the central one. The office is heated by means of a radiator in which the hot water flow rate is varied by a valve controlled via a room temperature sensor. By means of numerical simulations, indoor comfort conditions, energy consumptions and control system response are evaluated for three different sensor positions (far from the radiator, in the middle of the office, close to the radiator), two radiator sizes (one obtained by imposing a high supply water temperature, 80 °C, the other a low supply temperature, 60 °C) and two control strategies (weather compensation and fast restart). The results presented in this study and demonstrate how complete dynamic energy simulation tools can provide to the designer important information, like the room temperature sensor position that should be close to the emitter and far from cold external walls, for the optimal design of HVAC systems.

Automatised and georeferenced energy assessment of an Antwerp district based on cadastral data

Municipalities play a key role in supporting Europe's energy transition towards a low-carbon economy. However, there is a lack of tools to allow municipalities to easily formulate a detailed energy vision for their city. Nevertheless, most municipalities have access to georeferenced cartographic and cadastre information, including that on basic building characteristics. This article describes an innovative method to calculate and display the current hourly thermal energy demand for each building in a district based on basic cartography, cadastre, and degree-day values. The method is divided into two main blocks: (1) input data processing to obtain geometric information (e.g. geolocation, building and facades’ dimensions) and semantic data (e.g. use, year of construction), and (2) district energy assessment to calculate the thermal energy demand using data obtained in block 1. The proposed method has been applied and tested in the historical district of Antwerp. The reliability and thoroughness of the results obtained using the method are demonstrated based on two different validations: (1) comparison of the results with those calculated using an existing dynamic energy simulation tool, and (2) comparison of the results with the real gas consumption of a partial sector of the selected district. The first validation shows that the average difference between the two methodologies is less than 11% for the heating demand, less than 11% for the cooling demand, and less than 15% for the domestic hot water demand. The second validation shows a 24% difference between the real natural gas consumption and that obtained by new methodology. Finally, the results have been presented to the municipality of Antwerp, which plans to use the method to design the district heating expansion within the city centre. Furthermore, sensitivity assessment was used to determine the relevance of the main input parameters considered in this method, such as the base temperature, energy system schedules, window-to-wall ratio, and solar gains.

New Surrogate Model for Wind Pressure Coefficients in a Schematic Urban Environment with a Regular Pattern

Natural ventilation and the use of fans are recognized as sustainable design strategies to reduce energy use while reaching thermal comfort. A big challenge for designers is to predict ventilation rates of buildings in dense urban areas. One significant factor for calculating the ventilation rate is the wind pressure coefficient (Cp). Cp values can be obtained at a high cost, via real measurements, wind tunnel experiments, or high computational effort via computational fluid dynamic (CFD) simulation. A fast surrogate model to predict Cp for a schematic urban environment is required for the integration in building performance simulations. There are well-known surrogate models for Cp. The average surface pressure coefficient model integrated in EnergyPlus considers only a box-shaped building, without surrounding buildings. CpCalc, a surrogate model for Cp, considers only one height of neighbouring buildings. The Toegepast Natuurwetenschappelijk Onderzoek (TNO) Cp Generator model was available via web interface, and could include several box-shaped buildings in the surrounding area. These models are complex for fast integration in a natural ventilation simulation. For optimization processes, with thousands of simulation runs, speed is even more essential. Our study proposes a new surrogate model for Cp estimation based on data obtained from the TNO CP Generator model. The new model considers the effect of different neighbouring buildings in a simplified urban configuration, with an orthogonal street pattern, box-shaped buildings, and repetitive dimensions. The developed surrogate model is fast, and can easily be integrated in a dynamic energy simulation tool like EnergyPlus for optimization of natural ventilation in the urban areas.

Validation of dynamic building energy simulation tools based on a real test-box with thermally activated building systems (TABS)

Empirical validation and code-to-code comparison of more than one building simulation tool has seldom been done in literature. Therefore this paper presents the first detailed comparison of 1D building energy simulation tools with 3D CFD simulation and measurement data from a test bed (Test-Box), exposed to natural environmental conditions. Dymola (library: IDEAS), EnergyPlus, IDA ICE and TRNSYS –four commonly used tools– were selected for comparison against highly accurate real measurement data and dynamic CFD results. This paper evaluates the performance of mentioned above 1D simulation tools and in particular their implemented Thermally Activated Building Systems (TABS) models. The mean error, RMSE, standard deviation and maximal error for the room air, the ceiling surface and concrete temperature of the Test-Box model results are acceptable for all tools. The time course of the room air temperature follows the measurement data relatively well for all four tools. However, the negative bias (Dymola -0.92 K, EnergyPlus -2.18 K, IDA ICE -0.37 K and TRNSYS -1.13 K) indicates a general overestimation for all tools. Furthermore, the paper reflects the properties of simulation tools regarding the modelling language, GUIs, co-simulation capabilities and their recommended field of application.

Comparison between monitored and simulated data using evolutionary algorithms: Reducing the performance gap in dynamic building simulation

A correct thermal building design is a key issue on the viewpoint of energy-efficiency targets established by the United Nations Framework Convention on Climate Change. Dynamic energy simulation tools are often used to predict the thermal performance of new buildings or to recommend energy retrofit packages for refurbishment. To reduce uncertainties in model input definition, the dynamic calibration models assumes a crucial role in the accuracy of energy modelling. Thus, the research goal consists in the development of a calibration approach to reduce the differences between building simulation and real monitored data (performance gap) using a hybrid evolutionary algorithm in dynamic building simulation. A University building has been monitored over one year and the registered data was used to calibrate the numerical model and to validate the calibration methodology proposed. The results attained reveal agreement between predicted and real data with a CV RMSE index attained between 4.5 and 5.4.