Actual Energy Performance Research Articles

Adverse condition and critical event prediction in commercial buildings: Danish case study

Over the last two decades, there has been a growing realization that the actual energy performances of many buildings fail to meet the original intent of building design. Faults in systems and equipment, incorrectly configured control systems and inappropriate operating procedures increase the energy consumption about 20% and therefore compromise the building energy performance. To improve the energy performance of buildings and to prevent occupant discomfort, adverse condition and critical event prediction plays an important role. The Adverse Condition and Critical Event Prediction Toolbox (ACCEPT) is a generic framework to compare and contrast methods that enable prediction of an adverse event, with low false alarm and missed detection rates. In this paper, ACCEPT is used for fault detection and prediction in a real building at the University of Southern Denmark. To make fault detection and prediction possible, machine learning methods such as Kernel Density Estimation (KDE), and Principal Component Analysis (PCA) are used. A new PCA–based method is developed for artificial fault generation. While the proposed method finds applications in different areas, it has been used primarily for analysis purposes in this work. The results are evaluated, discussed and compared with results from Canonical Variate Analysis (CVA) with KDE. The results show that ACCEPT is more powerful than CVA with KDE which is known to be one of the best multivariate data-driven techniques in particular, under dynamically changing operational conditions.

A critical review on questionnaire surveys in the field of energy-related occupant behaviour

Occupants perform various actions to satisfy their physical and non-physical needs in buildings. These actions greatly affect building operations and thus energy use. Clearly understanding and accurately modelling occupant behaviour in buildings are crucial to guide energy-efficient building design and operation, and to reduce the gap between design and actual energy performance of buildings. To study and understand occupant behaviour, a cross-sectional questionnaire survey is one of the most useful tools to gain insights on general behaviour patterns and drivers, and to find connections between human, social and local comfort parameters. In this study, 33 projects were reviewed from the energy-related occupant behaviour research literature that employed cross-sectional surveys or interviews for data collection from the perspective of findings, limitations and methodological challenges. This research shows that future surveys are needed to bridge the gaps in literature but they would need to encompass a multidisciplinary approach to do so as until now only environmental and engineering factors were considered in these studies. Insights from social practice theories and techniques must be acquired to deploy robust and unbiased questionnaire results, which will provide new, more comprehensive knowledge in the field, and therefore occupant behaviour could be better understood and represented in building performance simulation to support design and operation of low or net-zero energy buildings.

Disaggregating high-resolution gas metering data using pattern recognition

Growing concern about the scale and extent of the gap between predicted and actual energy performance of new and retrofitted UK homes has led to a surge in the development of new tools and technologies trying to address the problem. A vital aspect of this work is to improve ease and accuracy of measuring in-use performance to better understand the extent of the gap and diagnose its causes. Existing approaches range from low cost but basic assessments allowing very limited diagnosis, to intensively instrumented experiments that provide detail but are expensive and highly disruptive, typically requiring the installation of specialist monitoring equipment and often vacating the house for several days. A key challenge in reducing the cost and difficulty of complex methods in occupied houses is to disaggregate space heating energy from that used for other uses without installing specialist monitoring equipment. This paper presents a low cost, non-invasive approach for doing so for a typical occupied UK home where space heating, hot water and cooking are provided by gas. The method, using dynamic pattern matching of total gas consumption measurements, typical of those provided by a smart meter, was tested by applying it to two occupied houses in the UK. The findings revealed that this method was successful in detecting heating patterns in the data and filtering out coinciding use.

BIM-based process management model for building design and refurbishment

A conceptual model of BIM-based design and refurbishment, based on pre-built indicators and allowing the assessment of the building energy demand and eco-building parameters, is presented. The new approach presented in this model creates a knowledge-based decision-making environment for refurbishment strategies and quality control, in this way creating the preconditions to bridge the gap between expected and actual energy performance. The model with integration of new BIM-based optimization subsystems enables energy management and optimization processes. For a comprehensive evaluation of refurbishment measures, it is suggested to include energy efficiency, eco-efficiency, and economic parameters.

A Bayesian Dynamic Method to Estimate the Thermophysical Properties of Building Elements in All Seasons, Orientations and with Reduced Error

The performance gap between the expected and actual energy performance of buildings and elements has stimulated interest in in-situ measurements. Most research has employed quasi-static analysis methods that estimate heat loss metrics such as U-values, without taking advantage of the rich time series data that is often recorded. This paper presents a dynamic Bayesian-based method to estimate the thermophysical properties of building elements from in-situ measurements. The analysis includes Markov chain Monte Carlo (MCMC) estimation, priors, uncertainty analysis, and model comparison to select the most appropriate model. Data from two case study dwellings is used to illustrate model performance; U-value estimates from the dynamic and static methods are within error estimates, with the dynamic model generally requiring much shorter time series than the static model. The dynamic model produced robust results at all times of year, including when the average indoor-to-outdoor temperature difference was low, when external temperatures had large daily variation, and measurements were subjected to direct solar radiation. Further, the probability distributions of parameters may provide insights into the thermal performance of elements. Dynamic methods such as that presented herein may enable wider characterisation of the performance of building elements as built, supporting work to reduce the performance gap.

Modelos predictivos del consumo energético de climatización asociado a soluciones de fachadas en Madrid a partir de la monitorización en módulos de ensayo

Este trabajo pretende realizar aportaciones de interés para reducir la brecha existente entre el comportamiento energético real y previsto en edificios. Tiene como principal objetivo establecer modelos predictivos que relacionen el consumo eléctrico de climatización para mantener unas determinadas condiciones operacionales en el ambiente interior, según sea el clima exterior, en función de la solución de fachada. Esos modelos predictivos se obtienen para módulos de ensayo en la que toda su envolvente es adiabática, a excepción de la fachada que se quiere ensayar. Tres soluciones de fachada han sido consideradas: una base que se corresponde con una solución de doble hoja de ladrillo con cámara de aire intermedia, la solución más común en viviendas plurifamiliares en España que fueron construidos entre 1940 y 1980, previamente a la primera normativa que, con carácter global, limitaba la demanda energética en los edificios; y dos soluciones de rehabilitación de la fachada anterior muy frecuentemente utilizadas: Fachada Ventilada y ETICS. Usando los datos de monitorización de los consumos eléctricos de equipos de climatización en esos tres módulos, se generan esos modelos predictivos, tanto para el periodo de verano como el de invierno, que son rectas de regresión lineal cuyas ecuaciones se enuncian, así como sus principales parámetros estadísticos.

Building Energy Assessment and Computer Simulation Applied to Social Housing in Spain

The actual energy consumption and simulated energy performance of a building usually differ. This gap widens in social housing, owing to the characteristics of these buildings and the consumption patterns of economically vulnerable households affected by energy poverty. The aim of this work is to characterise the energy poverty of the households that are representative of those residing in social housing, specifically in blocks of apartments in Southern Europe. The main variables that affect energy consumption and costs are analysed, and the models developed for software energy-performance simulations (which are applied to predict energy consumption in social housing) are validated against actual energy-consumption values. The results demonstrate that this type of household usually lives in surroundings at a temperature below the average thermal comfort level. We have taken into account that a standard thermal comfort level may lead to significant differences between computer-aided energy building simulation and actual consumption data (which are 40–140% lower than simulated consumption). This fact is of integral importance, as we use computer simulation to predict building energy performance in social housing.

COMPARISON OF GREEN HOME ENERGY PERFORMANCE BETWEEN SIMULATION AND OBSERVATION: A CASE OF VIRGINIA, UNITED STATES

The United States has a long-term goal to reduce 50% of energy usage in buildings based on 2010 consumption levels. Home energy efficiency is often measured by laboratory experiments and computational simulation. Thus, there is little to no quantifiable evidence showing the extent of energy efficiency homes can achieve within the larger context of green building standards. The objective of this research is to identify actual home energy performance as an effect of green building technologies by comparing energy use from real-world observations and energy modeling. Results indicate a significant reduction of energy consumption at 43.7% per unit or 43.4% per square foot (i.e., 0.093 m2) and substantial financial savings at $628.4 per unit or $0.80 per square foot (i.e., $8.6 per m2) annually. Savings account for 2% of median annual household income or 46% of energy cost expenditures for an American home. Results also identify the construction type as a significant factor, yet building technology is not the only factor influencing a home's energy efficiency. The findings contribute to the body of knowledge in three aspects: (1) simulated energy usage is higher than actual energy usage; (2) energy modeling via simulation tools is particularly accurate for new construction; and (3) energy modeling, especially for existing buildings, is not accurate due to largely varying occupant behaviors.

Creating paradigms for nearly zero energy hotels in South Europe

According to the European Directive on the Energy Performance of Buildings recast, hotels and other buildings of a certain size, frequently visited by the public, should set an example in environmental and energy performance. Moreover, being energy intensive buildings, they are at high priority for becoming nearly Zero Energy Buildings. Even though they represent a specific category, along with restaurants, till today there is a lack of credible data for this type of buildings, especially taking into account the wide range of different typologies (coastal, mountain, urban, rural or business, resort, spa/wellness, bed & breakfast). This paper presents the results of the actual energy performance of six south European countries (Greece, Croatia, France, Romania, Italy and Spain) plus one north (Sweden) for comparison, analyzed in the framework of the nearly Zero Energy Hotels (neZEH) project. The project focused on providing technical assistance to existing pilot hotels for refurbishing into nearly Zero Energy Buildings, demonstrating the sustainability of investments towards zero energy and undertaking training and capacity building activities at regional, national and European level. The results showed that the primary energy use for the hosting functions across all sixteen pilot hotels can decrease dramatically—from an average of 277 kWh/m2/y to an average of 102 kWh/m2/y; an average reduction of 63%. At the same time, Renewable Energy Sources share for the hosting functions can be increased from an average of 18% to an average of 46%. The analysis also showed that hotel non-hosting functions, i.e., other facilities that require special indoor environmental conditions, such as spa, kitchen etc. are more critical than the hosting functions; their primary energy use can decrease from an average of 727 kWh/m2/y to an average of 374 kWh/m2/y.

Heat energy from a shallow geothermal system in Glasgow, UK: performance evaluation design

This study reports on the actual energy and economic performances of a water source heat pump recently installed and operated at a Glasgow Subway station in the UK using subsurface water ingress to provide heating and domestic hot water. This follows from a previous publication that detailed the empirical measurements and design of a heating system designed on the basis of a 15-month monitoring period of the water flow and temperature. The perennial water flow at a relatively high temperature enabled the system to operate more efficiently than a typical heat pump system with boreholes or trenches. The performance of the water source heat pump has been monitored for a 4-month period, and the coefficient of performance as well as the energy saving is reported in the present study. The findings of this study not only indicate the energy, carbon dioxide and financial benefits of the heating system, but also highlight key issues during the operation in such a demanding underground environment. Further renewable heat potentials for the rest of the subway network and opportunities to commercialise the excess heat energy output are explored.

Introducing the qualitative performance gap: stories about a sustainable building

ABSTRACTIn the design and operations industries, the performance gap is a common discrepancy found between predicted building energy performance and actual energy performance. The performance gap is considered to have negative impacts for the brand of ‘green’ buildings, designers and operators. A socially based analogue is proposed here: the qualitative performance gap, defined as the perceived gap between what inhabitants expect and their actual experience of the building environment. This concept is explored at a regenerative Living Lab: the Centre for Interactive Research on Sustainability (CIRS) in Vancouver, Canada. ‘Official’ and ‘lived’ stories about the building were interpreted from sources of building information and interviews. Expectations about and forgiveness of building performance were gained from pre- and post-occupancy evaluations and interviews. The solution to the qualitative performance gap is not to eliminate it, but, in line with the concept of interactive adaptivity, to use the gap to generate new stories and new consequences for human wellbeing. The qualitative performance gap is thus conceived as positively generative, of new stories of place and identity. This work recommends crafting an ‘official story’ of social aspirations, and a communication feedback loop amongst designers, operators and building inhabitants, transparently sharing successes and failures.

Energy performance and the discrepancy of multiple NetZero Energy Homes (NZEHs) in cold regions

A NetZero Energy Home (NZEH) is designed, modelled, and constructed to produce as much energy as it consumes on an annual basis, with the required energy generated from renewable resources. However, the actual performance of an NZEH may vary from the design objective, and the performance of a given NZEH may differ from other NZEHs. In order to examine the actual energy performance and identify discrepancies among multiple NZEHs, a research project has been initiated in which six NZEHs in Edmonton and Calgary, Canada, built by Landmark Group of Companies, are monitored, assessed, and compared in this research. Complete annual data has been collected for four of the NZEHs to date, and the results show the average energy balance, excluding the NZEH with a period of non-occupancy (listed for sale), reaches −1.4%, which is very near the targeted balance. The actual energy performance is analyzed and compared for the monitored NZEHs by category, including space heating, domestic hot water (DHW) heating, ventilator, and base loads (including major appliances). Overall, space heating and cooling are found to account for more than 50% of the total energy usage of the NZEHs, except for one listed for sale; all the base loads of the analyzed NZEHs are lower than the base load predicted in HOT2000 (19.5 kWh/day). The factors contributing to energy performance variations are also analyzed by category in this paper. This research thus addresses the actual energy performance and discrepancies among multiple NZEHs in cold regions; the research results can be referenced to improve building operation and future design of NZEHs.

Energy balance and life cycle assessment of small size residential solar heating and cooling systems equipped with adsorption chillers

Solar heating and cooling systems for space heating and cooling are experiencing a growing trend and interest. However, the actual energy and environmental performance of small/medium size installations is not clearly foreseeable. In this paper, an analysis of such systems using adsorption chillers in different European climates is presented. Solar systems have been simulated in TRNSYS and compared to a conventional system employing a vapour compression unit. The results have been used for a Life Cycle Assessment (LCA) study, determining the potential impact during the whole life of the system, from raw materials supply to its end-of-life. The LCA has been carried out by using the LCA tool developed in the framework of the International Energy Agency SHC Task 48. Results showed that the useful life of the system is a key parameter: for a useful life of 10 years, the conventional system performs better than the renewable-based one for almost all the locations. However, if a longer life is achieved (15 or 20 years), solar systems show environmental advantage under almost all the climatic conditions: the environmental benefits of using a solar system during the operation step counterbalance the additional impact generated during the other life-cycle steps.

Exploration of the Bayesian Network framework for modelling window control behaviour

Extended literature reviews confirm that the accurate evaluation of energy-related occupant behaviour is a key factor for bridging the gap between predicted and actual energy performance of buildings. One of the key energy-related human behaviours is window control behaviour that has been modelled by different probabilistic modelling approaches. In recent years, Bayesian Networks (BNs) have become a popular representation based on graphical models for modelling stochastic processes with consideration of uncertainty in various fields, from computational biology to complex engineering problems. This study investigates the potential applicability of BNs to capture underlying complicated relationships between various influencing factors and energy-related behavioural actions of occupants in buildings: in particular, window opening/closing behaviour of occupants in residential buildings is investigated. This study addresses five key research questions related to modelling window control behaviour: (A) variable selection for identifying key drivers impacting window control behaviour, (B) correlations between key variables for structuring a statistical model, (C) target definition for finding the most suitable target variable, (D) BN model with capabilities to treat mixed data, and (E) validation of a stochastic BN model. A case study on the basis of measured data in one residential apartment located in Copenhagen, Denmark provides key findings associated with the five research questions through the modelling process of developing the BN model.

Methodological proposal for monitoring energy refurbishment. Indoor environmental quality in two case studies of social housing in Madrid, Spain

Energy performance analysis of two dwellings is discussed with a view to energy refurbishment. Both form part of State-developed multi-family social housing in Madrid. Their non-insulated double wall façades are typical of the buildings erected in Spain between 1940 and 1980, i.e., from the end of the Spanish Civil War to the entry into effect of code NBE-CT-79 on thermal conditions in buildings.A methodology is proposed to characterise existing conditions in this type of housing and identify the main factors for proposing improvement measures. Data were gathered on design, user behaviour, indoor environmental quality, construction systems and energy consumption. The analysis focused on user well-being, including factors such as usage and indoor environmental quality to tailor the approach adopted to actual performance.The results of applying the methodology to two standard dwellings to determine actual energy performance revealed significant differences from the standards set out in the legislation, as well as shortcomings in indoor environmental quality, inaccuracies in assumptions about user behaviour and flaws in construction system quality.

How do French social housing tenants interpret normative descriptive feedback connected with energy? / ¿Cómo interpretan los inquilinos de vivienda social en Francia los mensajes normativos descriptivos respecto al consumo de energía?

Energy-efficient houses are designed to reduce electricity. However, a gap between theoretical and actual energy performance of buildings is often observed. Achieving energy efficiency through regulatory norms is insufficient, and ways must be found to change people’s behaviours. In this line, normative feedback could be a powerful tool to reduce residential energy consumption. In the present research, 14 low-energy buildings were equipped to measure energy consumption. Their occupants received descriptive normative messages used to promote household energy saving. We were interested in the quantitative impact of normative feedback on household consumption, but also in the way in which these households receive the information linked to normative feedback and how they adapt to it. The results showed that energy-efficient houses are not an environment in which people could learn new practices if they do not have knowledgeable pre-requisites. A normative feedback can help change habits only for people who have the knowledge regarding energy issues that allows them to understand the feedback. For most households, the information is not understood and does not lead to behavioural change.

Actual energy performance of student housing: case study, benchmarking and performance gap analysis

While recent studies have shown an important gap between design and real energy use of multifamily buildings, this study analyses the energy performance gap for student housing. A very high energy performance (VHEP) student residency was analysed in detail, followed by a comparison of energy and water consumption with student residencies and other dwellings in Geneva. The analysis shows that for this VHEP residency the limit values according to the actual thermal regulations and MINERGIE label are exceeded: actual heat demand is 98 MJ/m2.a for heating (without double-flow ventilation) and 116 MJ/m2.a for hot water while the MINERGIE-index is 137 MJ/m2 (38 kWh/m2.a). Nevertheless, its thermal energy consumption (IDC=224 MJ/m2.a) is similar to other VHEP buildings, and half of Geneva's average values. The study points to factors which highly influence real performance of VHEP buildings and concludes that there is a huge optimisation potential during use phase of a building.

Realising Operational Energy Performance in Non-Domestic Buildings: Lessons Learnt from Initiatives Applied in Cambridge

The gap between the intended and actual energy performance of buildings is increasingly well documented in the non-domestic building sector. Recognition of this issue has led to the availability of a large range of initiatives that seek to ensure energy efficient building operation. This article reviews the practical implementation of three such initiatives in a case study building at the University of Cambridge. The notionally high-performance office/laboratory building implemented two voluntary design frameworks during building planning and construction: the voluntary rating scheme BREEAM and a bespoke Soft Landings framework called the Cambridge Work Plan. The building additionally meets the energy reporting criteria for the EU Energy Performance of Buildings Directive (EPBD), a legislative requirement for many publicly owned buildings in the UK. The relative impact of these three approaches for optimising building energy performance is reviewed through a mixed methods approach of building occupant and operator interviews, document analysis and energy performance review. The building’s core functions were revealed to consume 140% more energy than the building logbook estimate for the same needs. This difference, referred to widely as the energy performance gap, is larger than the majority of reported UK university buildings in the energy reporting database CarbonBuzz. The three implemented initiatives are demonstrated to be inadequate for reducing the energy performance gap in the case study, thus a number of alternative energy efficiency approaches are additionally reviewed. Common to the three approaches used in the case study is a lack of verification of actual building performance despite ambitious sustainability targets, due to a heavy focus on the design-stage and few follow-up mechanisms. The paper demonstrates the potential of energy efficiency initiatives that are focussed on operational performance as a core criterion (such as the Living Building Challenge) together with those that ensure the creation of realistic energy estimates at the design stage (such as the Chartered Institution of Building Services Engineers (CIBSE) Technical Memorandum 54).

An ANN-GA Semantic Rule-Based System to Reduce the Gap Between Predicted and Actual Energy Consumption in Buildings

This paper addresses the endemic problem of the gap between predicted and actual energy performance in public buildings. A system engineering approach is used to characterize energy performance factoring in building intrinsic properties, occupancy patterns, environmental conditions, as well as available control variables and their respective ranges. Due to the lack of historical data, a theoretical simulation model is considered. A semantic mapping process is proposed using principle component analysis (PCA) and multi regression analysis (MRA) to determine the governing (i.e., most sensitive) variables to reduce the energy gap with a (near) real-time capability. Further, an artificial neural network (ANN) is developed to learn the patterns of this semantic mapping, and is used as the cost function of a genetic algorithm (GA)-based optimization tool to generate optimized energy saving rules factoring in multiple objectives and constraints. Finally, a novel rule evaluation process is developed to evaluate the generated energy saving rules, their boundaries, and underpinning variables. The proposed solution has been tested on both a simulation platform and a pilot building – a care home in the Netherlands. Validation results suggest an average 25% energy reduction while meeting occupants’ comfort conditions.

Comparative building performance evaluation of a ‘sustainable’ community centre and a public library building

This paper uses a forensic building performance evaluation approach to undertake a comparative evaluation of the in-use energy and environmental performance data (collected over two years) of two civic buildings located in Southeast England – a small community centre (<1000 m2) and a medium-sized public library building (∼4500 m2), which are designed to high sustainability standards (EPC A rating) and low heating demand met by on-site low/zero carbon technologies. Although both buildings achieved measured air-permeability rates of ∼5 m3/h.m2, they encountered similar issues related to poor documentation of ‘as-built’ drawings, poor handover and guidance, problems with integrating and maintaining new technologies (heat pumps, biomass boilers and solar thermal), lack of calibration of sub-meters, and issues with automatic window controls. However, the actual annual energy use of the community centre is similar to the design prediction, while it is almost double the prediction in the case of the library building. This is because the community centre management team overcame some of the issues through their continuous engagement and interest in the building’s performance, whereas the management team of the Library building failed to engage with energy management, resulting in disuse of the biomass boiler and solar thermal system. Practical application: Comparative building performance evaluation (BPE) systematically reveals the similarities and differences in the actual energy and environmental performance of two ‘sustainable’ civic buildings. Careful management of heating and electricity loads, good occupant control over the indoor environment and high performance of low-carbon technologies in the Community Centre results in the building performing better than good practice benchmark. Regular changes in facility management (FM) staff result in inadequate energy management and control over heating, ventilation and lighting, that undermines occupant comfort and leads to excessive energy use in the library building. For civic buildings to perform as designed, it is vital that metering, sub-metering and controls are set up, commissioned and used properly by the FM team. Design teams should ensure that easy-to-understand user guides are made available before handover for FM and occupants.