Showing papers in "Journal of Building Performance Simulation in 2013"

The urban weather generator

Abstract: The increase in air temperature produced by urbanization, a phenomenon known as the urban heat island (UHI) effect, is often neglected in current building energy simulation practices. The UHI effect can have an impact on the energy consumption of buildings, especially those with low internal heat gains or with an inherent close interaction with the outdoor environment (e.g. naturally-ventilated buildings). This paper presents an urban weather generator (UWG) to calculate air temperatures inside urban canyons from measurements at an operational weather station located in an open area outside a city. The model can be used alone or integrated into existing programmes in order to account for the UHI effect in building energy simulations. The UWG is evaluated against field data from Basel (Switzerland) and Toulouse (France). The error of UWG predictions stays within the range of air temperature variability observed in different locations of the same urban area.

A model predictive control optimization environment for real-time commercial building application

Abstract: A model predictive control (MPC) environment is described. The environment integrates Matlab and EnergyPlus with a modified particle swarm optimizer to predict optimal building control strategies. A supporting framework is described which couples the environment to a building automation system, allowing real-time optimization considering operator overrides and updated weather forecasts. Challenges unique to integration with EnergyPlus for real-time optimization are discussed. Application of the environment is demonstrated in two simulation cases. First, the environment is used to determine hourly cooling set points minimizing daily energy cost for EnergyPlus's Benchmark Large Office building. Results suggest 5% cost savings during the study period. Second, the environment is used to determine hourly supply water temperature and circulator availability that minimize daily energy consumption for a small office building having a thermally activated building system (TABS). Compared to the base case, energy sa...

A validation of the Radiance three-phase simulation method for modeling annual daylight performance of optically-complex fenestration systems

Abstract: A new capability that enables annual simulation of optically complex fenestration systems has been added to Radiance. The method relies on bidirectional scattering distribution function (BSDF) input data, which are used in an efficient matrix calculation to compute time-step performance given TMY data. The objective of this study was to explain the value of this capability to designers and developers of innovative daylighting systems and to demonstrate its speed and accuracy via comparisons of simulated to measured illuminance data for a daylight-redirecting optical louver system. The method was shown to provide valid results that accurately replicate real-world conditions with an absolute mean bias error below 13% and a root mean square error below 23%. Routine application of this new capability will not be hindered by slow computational speed for illuminance calculations. Instead, the capability will be dependent on the availability of BSDF data for daylighting, shading and fenestration systems.

Building models for Model Predictive Control of office buildings with Concrete Core Activation

Abstract: Model predictive control (MPC) is a good candidate to exploit the energy cost savings potential of concrete core activation (CCA), while guaranteeing thermal comfort. A bottleneck for practical implementation is the selection and identification of the building control model. Using grey box models, this article studies the impact of model structure and identification data set on the MPC control performance for an office building with CCA. Results for a one-year simulation show: (1) a second-order model can achieve equal control performance as a fourth-order one, (2) inclusion of solar or internal gains in the identification data set improves the model accuracy in general, especially for the fourth-order models and (3) MPC with a second-order model reduces electricity consumption by 15% compared to a reference controller, hereby deploying information about past operative temperature prediction errors and this without the need for solar or internal gains predictions.

A hierarchical Bayesian framework for calibrating micro-level models with macro-level data

Abstract: Owners of housing stocks require reliable and flexible tools to assess the impact of retrofits technologies. Bottom-up engineering-based housing stock models can help to serve such a function. These models require calibrating, using micro-level energy measurements at the building level, to improve model accuracy; however, the only publicly available data for the UK housing stock is at the macro-level, at the district, urban, or national scale. This paper outlines a method for using macro-level data to calibrate micro-level models. A hierarchical framework is proposed, utilizing a combination of regression analysis and Bayesian inference. The result is a Bayesian regression method that generates estimates of the average energy use for different dwelling types whilst quantifying uncertainty in both the empirical data and the generated energy estimates. Finally, the Bayesian regression method is validated and the use of the hierarchical Bayesian calibration framework is demonstrated.

Model predictive control for buildings: a quantum leap?

Abstract: The promise of harnessing the predictive and diagnostic powers of a well-calibrated building energy model for improved building operations is attracting a growing number of building sciences resear...

The use of normative energy calculation beyond building performance rating

Abstract: Standardized building performance assessment is best expressed with a so-called normative calculation method, such as defined in the Committee for Standardization/International Organization for Standardization (CEN/ISO) calculation standards. The normative calculation method has advantages of simplicity, transparency, robustness and reproducibility. For systematic energy performance assessment at various scales, i.e. at the unit of analysis of one building up to a large-scale collection of buildings, the authors' group developed the Energy Performance Standard Calculation Toolkit (EPSCT). This toolkit calculates objective indicators of energy performance using either the monthly or hourly calculation method as specified in the CEN/ISO standard for building energy calculation. The toolkit is the foundation for numerous single, medium-scale and large-scale building energy management applications. At the largest level, applications should be able to manage hundreds or thousands of buildings. The paper introd...

Analysis of local optima in predictive control for energy efficient buildings

Abstract: We study the problem of heating, ventilation and air conditioning (HVAC) control in a typical commercial building. We propose a model predictive control (MPC) approach which minimizes energy cost while satisfying occupant comfort and control actuator constraints, using a simplified system model and incorporating predictions of future weather and occupancy inputs. In simplified physics-based models of HVAC systems, the product between air temperatures and flow rates arising from energy balance equations leads to a non-convex MPC problem. Fast computational techniques for solving non-convex optimization can only provide certificates of local optimality. Local optima can potentially cause MPC to have worse performance than existing control implementations, so deserve careful consideration. The objective of this article is to investigate the phenomenon of local optima in the MPC optimization problem for a simple HVAC system model. In the first part of the article, simplified physics-based models and MPC desig...

Hybrid residential end-use energy and greenhouse gas emissions model – development and verification for Canada

Abstract: This article presents the Canadian Hybrid Residential End-Use Energy and GHG Emissions Model (CHREM), a model based upon building performance simulation, and compares its estimates with residential sector energy consumption surveys and the estimates of other models. The CHREM advances the state of the art of residential sector energy consumption and green house gas (GHG) emissions modelling by three new contributions: (i) the use of a database of 16,952 unique house descriptions of thermal envelope and energy conversion system information that statistically represent the Canadian housing stock; (ii) a ‘hybrid’ modelling approach that integrates the neural network and engineering modelling methods to estimate the energy consumption of the major end-uses, providing the capacity to model alternative and renewable energy technologies, such as solar energy and energy storage systems; and (iii) a method for the accumulation and treatment of energy consumption and GHG emissions results as a function of end-use a...

Quantitative risk management for energy retrofit projects

Abstract: This article presents a risk analysis method based on Bayesian calibration of building energy models. The Bayesian approach enables probabilistic outputs from the energy model, which are used to quantify risks associated with investing in energy conservation measures in existing buildings. This article demonstrates the applicability of the proposed methodology to support energy saving contracts in the context of the energy service company industry. A case study illustrates the importance of quantifying relative risks by comparing the probabilistic outputs derived from the Bayesian approach with standard practices endorsed by International Performance Measurement and Verification Protocol and ASHRAE guideline 14.

Approximating model predictive control with existing building simulation tools and offline optimization

Abstract: Model predictive control (MPC) is an established control technique in other fields and holds promise for improved controls in high-performance buildings. It has been receiving increasing attention in buildings research but has yet to find its way into common practice. This is due, at least in part, to a mismatch between the tools and techniques used in most MPC development and those commonly found in building design and operation. This article investigates the use of offline optimization with common building simulation tools to approximate MPC with lookup tables. Particular attention is paid to methods for limiting problem dimensionality. The approach is presented through three illustrative case studies, and its benefits and range of applicability are discussed.

Heating and cooling in high-rise buildings using facade-integrated transparent solar thermal collector systems

Abstract: New facades of high-rise buildings often include renewable energy converters to allow “green building” operation. At the same time, numerous tenants value visual transparency. Transparent solar thermal collectors (TSTCs) aim at decreasing the non-renewable primary energy demand and increasing the visual transparency at the same time. On the one hand, this paper presents the main modelling challenges that arise when considering building facades and especially integrated TSTC systems. New transient systems simulation (TRNSYS) [Beckman, W. A., L. Broman, A. Fiksel, S. A. Klein, E. Lindberg, M. Schuler, and J. Thornton. 1994. “TRNSYS The Most Complete Solar Energy System Modelling and Simulation Software.” Renewable Energy 5 (1–4): 486–488] types have been especially developed for this purpose. A simplified model is presented for comparison purposes. On the other hand, the overall performance for a building with facade-integrated TSTC, as measured by its non-renewable primary energy demand, is treated. This i...

Building leakage analysis and infiltration modelling for an Italian multi-family building

Abstract: The presented paper aims at detailing the results of an investigation that was recently conducted in Italy to evaluate the contribution infiltration makes to meeting ventilation needs in a recently renovated apartment building and the corresponding energy costs. It is years that increasing importance has been placed on the energy efficiency in residential buildings as about 70% of the existing Italian residential building stock was built before 1976 (i.e. before any measure related to the energy efficiency in buildings). As existing dwellings have been traditionally considered ‘leaky’, the actions for improving their energy efficiency have often determined tighter buildings, raising concerns about whether the amount of infiltration is sufficient to provide occupants with acceptable indoor air quality (IAQ). The current state of knowledge on infiltration in multi-family buildings in terms of measuring procedures, corresponding air change rates and airflow patterns was reviewed. The air tightness of a three...

Extraction of supervisory building control rules from model predictive control of windows in a mixed mode building

Abstract: Rule extraction is a promising technique for developing or fine-tuning supervisory control strategies in buildings. Three data mining techniques are examined that extract rules from offline model predictive control (MPC) results for a mixed mode building operated during the cooling season: generalized linear models (GLM), classification and regression trees (CART), and adaptive boosting. All rules were able to recover approximately 90% of the original optimizer energy savings under open loop tests, but the GLM-based rules saw significant performance degradation under simulated tests. CART and boost rules only degraded in performance by a few percentage points, still retaining the vast majority of optimizer savings (84% and 93% for the CART and boost rules, respectively). The results demonstrate that the proposed rule extraction techniques may allow building automation systems to achieve near-optimal supervisory control strategies without online MPC systems, although further research is required to broadly...

Advances in hygrothermal building component simulation: modelling moisture sources likely to occur due to rainwater leakage

Abstract: Moisture control design of building envelope components by hygrothermal simulation is state-of-the-art today. For architects and engineers, there are several simulation tools available which comply with the European Standard EN 15026 and/or the North-American moisture control standard ANSI/ASHRAE 160. Numerous investigations have shown that hygrothermal simulation models are clearly superior to steady-state dew-point calculations in predicting the climate dependent moisture behaviour of construction assemblies. However, compared to real life, there remains a major deficit: most models assume a perfectly assembled and installed building component without any cracks or gaps that may cause unintended moisture entry. This draw-back has been recognized and new approaches have been developed to allow for imperfections by introducing source terms in the models, e.g. accounting for the effects of rainwater penetration. The magnitude of these moisture sources is still a matter of discussion because they should rep...

Moisture flow modelling within the ESP-r integrated building performance simulation system

Abstract: Moisture plays a central role in the provision of healthy buildings, both in relation to indoor humidity levels, which impacts on air quality and thermal comfort, and in relation to interstitial/surface condensation leading to fabric deterioration and mould growth, which impacts on performance and occupant well-being. Integrated building performance simulation (IBPS) provides a means to ensure that due consideration is given to these aspects at the design stage as designers attempt to deploy new approaches to energy demand reduction and sustainable supply. This paper describes how building space and construction moisture flow is modelled within the ESP-r system in a manner that is appropriately coupled to other domain models representing the heat, power, air and light flows within building/plant systems of arbitrary complexity (but with the focus here only on those domains that impact directly on moisture flow). The purpose of the paper is to describe the role of moisture flow modelling within IBPS, the b...

Hygrothermal implications of low and zero energy standards for building envelope performance in the UK

Abstract: Driven by climate change legislation and high rates of fuel poverty, the UK faces multiple challenges both in new build and upgrading the existing stock. How these challenges are addressed will have long-term impacts on the building fabric, occupant comfort and wellbeing. Building performance simulation has an important role to play in this process, yet it is widely recognized that over-simplification in the modelling of physical phenomena leads to substantial sources of error. Moisture is a major cause of damage in buildings, and the Glaser method is a widely used steady-state method used to calculate the vapour pressure difference in a building's envelope. Although known for its limitations, it is the principal method used to assess moisture response in the UK. This paper evaluates the current situation in the UK, addressing fuel poverty targets, advanced energy saving standards and changing boundary conditions and their compounding implications for building envelope performance.

Exterior condensations on façades: numerical simulation of the undercooling phenomenon

Abstract: This article intends to apply existing numerical models of exterior boundary conditions on the simulation of exterior condensation on facades (undercooling phenomenon) finished with external thermal insulation composite systems. The results of three hygrothermal models were compared, regarding the temperature on the exterior surface of a west facade. The climatic conditions from Porto city were used. We analysed in detail how the simulation of the undercooling phenomenon is influenced by the numerical treatment of the radiative balance on the exterior surface. The numerical results show that these programs are useful tools in assessing the exterior condensation on facades and the importance of radiative balance on the exterior surface temperature. However, some differences were observed in the calculated values due to different parameters included in the radiative balance of the models.

Improving direct solar shading calculations within building energy simulation tools

Abstract: The calculation of the shadows that building environment, building elements or shading devices may cast on the building envelope, plays a key role in load calculations and building energy simulation. Algorithms for solar shading calculations have direct repercussions on the accuracy of the results and the computational times of building simulation tools. This paper presents an improved method for direct solar shading calculations based on the projection of every polygon on a unique receiving surface and incorporates recent and high efficient algorithms to solve polygon intersections. Firstly, the method is shortly described. Secondly, it is validated by comparisons with other methods, experimental results and European standards. Then, a comparison test between the proposed and conventional methods is presented to assess computational speed improvement. Finally, the main advantages of the proposed method are discussed.

Calibration of a central cooling plant model using manufacturer's data and measured input parameters and comparison with measured performance

Abstract: Several approaches for model calibration are used by consultants and researchers. For buildings with large mechanical cooling plants, the measurement of relevant parameters, the identification of performance values/curves, and their use in the model calibration should receive more attention, especially when the model is intended for ongoing commissioning. These additional steps are presented in this paper using as a case study a university campus central cooling plant. A fair agreement was obtained between measurements and predictions with the calibrated model for water temperature at key locations, the electric power input of cooling equipment, and the coefficient of performance (COP) of chillers and various groups of equipment. The case study proved that it is possible to develop a calibrated model using measurements and manufacturer data, without modifying by trial-and-error some variables or using stochastic approaches.

Total utility demand prediction for multi-dwelling sites by a bottom-up approach considering variations of inhabitants’ behaviour schedules

Abstract: This article reports systematic case studies based on a Total Utility Demand Prediction System presented in the authors’ previous works, in which one can follow a bottom-up approach to accurately calculate the time series utility loads (energy, power, city water, hot water, etc.) for multi-dwelling systems, including residential buildings, residential block areas and even an entire city. This calculation considers the behavioural variations of the inhabitants of the dwellings. In the case studies, we assumed a residential building consisting of 100 independent dwellings to accurately predict various peak demands and seasonal or annual demands. A series of simulations reveals that considering time-varying inhabitant behaviour schedules significantly affects the peak loads. Hence, HVAC COP, inhabitants’ age and their family type significantly influence the peak loads and their accurate time-series.

Nanocomposite materials for rapid-response interior air humidity buffering in closed environments

Abstract: Three different mesoporous silica (MS) samples were selected as template materials for designing novel, high-performance desiccants to give rapid-response temperature and humidity buffering in closed environments. The aim was to investigate how the functional properties of the MS materials can be tuned to suit differing psychrometric conditions in closed environments, and to inform the design process by conducting sensitivity analysis using building performance simulation software. Their humidity buffering performance was compared with other materials using WUFI Pro v5.1 to conduct numerical hygrothermal simulations. The MS materials had more than two orders of magnitude greater humidity buffering than traditional interior building materials (e.g. painted gypsum plaster) due to their high vapour storage capacity and high dynamic vapour sorption (DVS) response rates. Analysis showed that the gradient of the w 50–w 80 portion of the absorption branch isotherm is the most sensitive parameter when using the h...

A dynamic thermal network approach to the modelling of Foundation Heat Exchangers

Abstract: Foundation Heat Exchangers (FHX) are a novel form of ground heat exchanger for residential applications. The recently developed dynamic thermal network approach has been applied to formulate a model of the FHX that includes the basement, pipes and adjacent ground. This response factor approach allows complex three-dimensional geometries, such as this, to be represented and simulated efficiently. The formulation of the method and its application to the FHX is described along with a numerical procedure to calculate the required weighting factor series. An improved method of calculating these data and reducing it to a compact form is presented. Some modification of the original method has also been necessary to implement the boundary conditions associated with the heat exchanger pipes and ground surface. Data from an installation at an experimental house have been used to validate the model.

Analysis of probabilistic climate projections: heat wave, overheating and adaptation

Abstract: Climate change could substantially impact on the performance of buildings in providing thermal comfort to occupants The recently launched UK climate projections (UKCP09) suggest that all areas of the UK will become warmer in the future with the possibility of more frequent and severe extreme events, such as heat waves This study, as part of the low carbon futures (LCF) project, explores the consequent risk of overheating and the vulnerability of a building to extreme events A simple statistical model proposed by the LCF project elsewhere has been employed to emulate the outputs of the dynamic building simulator (ESP-r), which if directly used with the numerous replicated climates available from a probabilistic climate database could be practically challenging For complex probabilistic climate datasets, we demonstrate the efficiency of the statistical tool in performing a systematic analysis of various aspects of heat waves including: frequency of extreme heat events in changing climate; its impact on

Establishing the zero-carbon performance of compact urban dwellings

Abstract: This paper presents an analysis of the zero-carbon performance of a case-study building which is representative of a growing number of new buildings that are being built on redevelopment sites in inner-city areas in the UK. Compact urban dwellings are apartment style buildings with a floor area of ∼50 m2 per dwelling, often based over two floors. The constraints of this type of building on achieving zero-carbon performance in the context of the Code for Sustainable Homes is discussed and the shortcomings of the code are demonstrated in terms of the target heat and electricity demand targets for the design of the building systems. A graphical representation of the simulation results is used to present the findings. It has been demonstrated that in specific urban contexts, zero-carbon performance as defined within the current UK compliance framework may be very difficult to achieve in practice given the assumptions used in the simulation here. Therefore, it is very likely that zero-carbon compact urban dwel...

Using building simulation to model the drying of flooded building archetypes

Abstract: With a changing climate, London is expected to experience more frequent periods of intense rainfall and tidal surges, leading to an increase in the risk of flooding. This paper describes the simulation of the drying of flooded building archetypes representative of the London building stock using the EnergyPlus-based hygrothermal tool ‘University College London-Heat and Moisture Transfer (UCL-HAMT)’ in order to determine the relative drying rates of different built forms and envelope designs. Three different internal drying scenarios, representative of conditions where no professional remediation equipment is used, are simulated. A mould model is used to predict the duration of mould growth risk following a flood on the internal surfaces of the different building types. Heating properties while keeping windows open dried dwellings fastest, while purpose built flats and buildings with insulated cavity walls were found to dry slowest.

Sensitivity of the predicted convective heat transfer in a cooled room to the computational fluid dynamics simulation approach

Abstract: Computational fluid dynamics (CFD) plays an increasingly important role in the design, analysis and optimization of engineering systems. However, CFD does not necessarily provide reliable results. The most crucial numerical solution error is caused by inadequate grid resolution, and the key modelling error sources in CFD in ventilated indoor environments are turbulence modelling and diffuser modelling. Many researchers already proposed guidelines, but they based their analyses on local variables. In response, underlying study intended to verify the impact of the CFD simulation approach on the convective heat flux, an integral quantity. The authors tested several grids, Reynolds averaged Navier–Stokes turbulence models and diffuser models for three convection regimes in a cooled room. The diffuser modelling had a much larger impact than the grid and the turbulence modelling, as long as the jet dominated the airflow. So, CFD users, who want to model forced/mixed convection airflow indoors, certainly need to...

A novel method to model trees for building daylighting simulation using hemispherical photography

Abstract: The ability to simulate the effect of trees on natural light performance in buildings is contingent upon accurate simulation of light passing through the canopy. Accurate simulations require some assumption of leaf angle distribution (LAD) to compute canopy gap fractions. The ellipsoidal LAD can very closely approximate real plant canopies. The method requires calculation of leaf area density from observed distribution of gap fraction as a function of zenith angle. Two sets of Neem trees were studied (small and large). Hemispherical image acquisition and analysis for both groups was carried out to measure gap fractions. The results helped to develop a 3D tree model that was used to simulate the effect of tree interception of daylight. The illuminance levels were simulated under the tree model and the output results were validated against actual measurements using MBE and RMSE techniques (small trees: MBE = 0.33, RMSE = 0.20; large trees: MBE = 9.68, RMSE = 2.02).

London 2012 Velodrome – integrating advanced simulation into the design process

Abstract: The highly acclaimed London 2012 Velodrome indoor cycling arena, which has achieved BREEAM ‘excellent’, has been designed using a process which integrates considerable levels of complex building simulation across all design stages. This includes a wide range of airflow, thermal, daylight and energy models used to simultaneously support and drive the design as well as quantify the overall performance. Three building simulation competences associated with the integration of advanced simulation into the architectural design process have been identified: simulation competence, integration competence and holistic design competence. The Velodrome has been an exemplar in terms of the use of simulation to positively influence building orientation, form, detailing and performance.

Heat and moisture: issues and applications

Abstract: The statistician George Box once said that ‘essentially, all models are wrong, but some are useful’ (Box and Draper 1987). By ‘wrong’, Box reminds us that the model is not, and never will be the re...