Energy Performance Gap Research Articles

An intelligent semantic system for real-time demand response management of a thermal grid

“Demand Response” energy management of thermal grids requires consideration of a wide range of factors at building and district level, supported by continuously calibrated simulation models that reflect real operation conditions. Moreover, cross-domain data interoperability between concepts used by the numerous hardware and software is essential, in terms of Terminology, Metadata, Meaning and Logic. This paper leverages domain ontology to map and align the semantic resources that underpin building and district energy management, with a focus on the optimization of a thermal grid informed by real-time energy demand. The intelligence of the system is derived from simulation-based optimization, informed by calibrated thermal models that predict the network’s energy demand to inform (near) real-time generation. The paper demonstrates that the use of semantics helps alleviate the endemic energy performance gap, as validated in a real district heating network where 36% reduction on operation cost and 43% reduction on CO2 emission were observed compared to baseline operational data.

Using smart technologies to identify occupancy and plug-in appliance interaction patterns in an office environment

There has been a widely documented phenomenon identifying an energy performance gap between the building’s design and operational phases. This result has been attributed to the stochastic behaviours exhibited by the occupants, who are assumed to follow deterministic and routine schedules. With the recent advancements in smart monitoring technologies, the increasing affordability of wireless sensors has allowed researchers to collect detailed information on the occupants’ dynamic behaviours. However, past applications of such technologies have been highly intrusive and limit the validity of the data collected due to the Hawthorne effect. Therefore, this paper proposes a non-intrusive data collection methodology using a comprehensive range of wireless smart meters, Bluetooth beacons, and questionnaires to capture the occupants’ movement and appliance interaction patterns. The feasibility of the approach is demonstrated during a two-week data collection effort in a university office. By combining the occupants’ presence with appliance energy consumption data, the authors were able to identify the occupants’ appliance interaction patterns. An extension of this work includes the use of the data collected to identify different occupancy and appliance interaction profiles, which contributes to the development of an appliance interaction model that addresses the energy performance gap caused by occupants’ appliance interaction.

Harvesting big data from residential building energy performance certificates: retrofitting and climate change mitigation insights at a regional scale

The reduction of energy consumption and the increase in energy efficiency is currently an important cornerstone of EU policy. Energy performance certificates (EPCs) were implemented as one of the tools to promote this agenda, and are used for the energy performance assessment of buildings. In this study, the characteristics of the Portuguese dwelling stock are regionally analysed using data from approximately 523,000 Portuguese residential EPCs. Furthermore, a bottom-up building typology approach is used to assess the regional energy needs impact of retrofitting actions and to estimate the heating and cooling energy performance gaps of the whole dwelling stock, as well as the potential CO2 emissions resulting from the gaps’ potential offset due to increase thermal comfort. The results show that Portuguese residential buildings have very low energy performance, with windows and roofs being identified as the most energy inefficient elements. Roof retrofitting has the highest potential for the reduction of energy needs. The estimated heating and cooling energy performance gap amount to very significant percentages, due to the poor performing building stock but also very low energy consumption levels, with probable consequences for the thermal comfort of occupants. Assuming the current energy mix, carbon emissions would be 9.8 and 20.2 times higher associated with heating and cooling, respectively, if the actual final energy consumption were to match the estimated theoretical values derived from building regulation. This study demonstrates several application cases and leverages the potential of the individual EPC, increasing the detail in the dwelling stock characterization and energy performance estimation, revealing its value for energy retrofit and climate change mitigation assessments, as well as establishing the ground for future work related to building retrofits, energy efficiency measure implementation, climate change mitigation, thermal comfort, and energy poverty studies.

Strategies for minimizing building energy performance gaps between the design intend and the reality

The disparity found between the predicted energy consumption in the design stage of buildings and the energy use during operation is known as energy performance gap. According to recent studies, the actual energy consumption can be twice to five times higher than predicted by the model. Building energy performance gap can have significant financial and environmental impact. This study aims to address this issue by interacting with professionals in the industry to identify the factors that contribute to the building energy performance gap, and to explore strategies that can help minimise the gap in major office buildings. Semi-structured interviews with 13 building energy professionals were conducted to gather and analyse the relevant design factors that contribute to the gap. Possible strategies of managing the factors were also identified through the semi-structured interviews. The interview responses were analysed qualitatively using Nvivo software, and as a result, 8 factors of energy performance gap were identified, as follows: (i) Inaccurate design parameters, (ii) Failure to account for uncertainties, (iii) Lack of accountability, (iv) Poor communication, (v) Lack of knowledge and experience, (vi) Inefficient and over-complicated design, (vii) Lack of post-construction testing, and (viii) Lack of feedback. Recommendations were drawn from the strategies identified from the study, and a framework on how to address the energy performance gap in the design process was proposed. The framework has three categories, namely strategies for better regulation and better accountability, strategies for project team for accurate energy models, better communication and lack of expertise, and suggestions for training to set training requirements for upskilling the industry workforce.

Bridging energy performance gaps of green office buildings via more targeted operations management: A system dynamics approach

In China, one of the major causes of energy performance gaps observed in green office buildings is the incompetent operations management, which is not distinguished from that of traditional buildings on both facilities and occupants. In this paper, a system dynamics model was established to simulate the interactions (primarily through communications) between facility managers and occupants and to find out targeted operations management strategies to narrow energy performance gaps. The model identifies different types of occupants and uses the Monte Carlo method to address the uncertainty between energy consumption and indoor environment quality satisfaction of occupants. Through a comparison of scenarios in which different types of occupants were each involved, differences in energy performance gaps were found and more-targeted operations management strategies were tailored. The model was applied to a specific case in China. The results indicate that facility managers could pay less attention to austerity occupants while paying more attention to communications with standard occupants to enhance their energy-saving awareness. The results also reveal that the wasteful occupants have the most potential for narrowing the gaps, which can be realized by combining communications and the heating, ventilation and air conditioning (HVAC) system equipment with zonal control.

Mapping the energy performance gap of dwelling stock at high-resolution scale: Implications for thermal comfort in Portuguese households

An aging building stock and low-efficiency heating, ventilation and air conditioning (HVAC) systems may be preventing the adequate energy performance (EP) of Portuguese dwellings. This study aims to estimate and analyze the EP gap of the occupied main residence Portuguese residential dwelling stock, for thermal comfort attainment, at high geographical resolution scale, i.e. for every civil parish. A building typology approach was applied to estimate the heating and cooling (H&C) theoretical final energy consumption (TFEC) for thermal comfort. An energy consumption statistics-based approach was used to estimate the H&C real final energy consumption (RFEC). The EP gap is the percentual difference between the TFEC and RFEC. Three scenarios were tested, looking deeper into southern European space H&C patterns, considering varied conditioned areas and occupancy schedules. This study provides a methodological framework for zooming in the assessment of the dwelling stock EP for a whole country, allowing for a comparative analysis between regions, as the different regional EP gap drivers are identified. For nominal conditions, every civil parish has an EP gap higher than 60%, for both H&C, related to poor energy efficiency of the building stock and low H&C energy consumptions. The scenarios demonstrated a bridging of several civil parishes’ EP gap, possibly resulting from temporal space climatization patterns. High remaining EP gaps suggest the civil parishes in the north and center inland regions are the most vulnerable in the winter and summer seasons, potentially due to significant energy poverty levels.

Collaboration between designers and contractors to improve building energy performance

Improvement of building energy performance is crucial in achieving energy conservation goals. Previous studies have indicated that effective collaboration among stakeholders can help to address the building energy performance gap. However, only a few studies have examined the effects of underlying collaboration between designers and contractors. To fill this research gap, this study proposes an evolutionary game model to investigate the underlying logic of the collaboration by analyzing the dynamic behaviors of designers and contractors. First, the main possible drivers and barriers of the collaboration between designers and contractors were identified through a literature review and an expert interview. Second, a Nash equilibrium model was utilized to analyze the decision of designers and contractors under different scenarios. The results show that the best means to promote the collaboration is “reducing collaboration costs”, followed by “increasing the collaboration benefits” and “decreasing the loss caused by a lack of collaboration”. Based on the parameter discussion of the evolutionary game model, five solutions were proposed for the effective collaboration between designers and contractors. This study helps to clarify the dynamic collaboration decision process of designers and contractors, who are considered players with bounded rationality. The proposed evolutionary game model provides a theoretical basis for quantitative research on the collaboration between designers and contractors. This study could help researchers to consider the dynamics of collaboration among stakeholders in building projects, and it could also help practitioners to select proper strategies for improved collaboration.

The impact of defects on energy performance of buildings: Quality management in social housing developments

Construction defects in the domestic sector, especially occurring in the building fabric, are acknowledged to contribute to the energy performance gap of buildings. Discontinuity of insulation layers, gaps in the vapor/air barriers and thermal bridging through building elements lead to undesired heat loss, and thus to the increase of energy use for space heating. This study set out to investigate how quality management systems related to energy performance of buildings are defined and implemented in social housing projects in the UK. The analysis of evidence collected from a number of Housing Association case studies suggests that in the majority of the projects, the deployed quality management procedures focused on visual quality issues, allowing defects with the potential to impair the thermal performance of the dwellings to remain uncorrected. Despite a range of quality control procedures administered by the client, contractor and independent agents, they did not systematically appraise such defects during the construction stage. Apart from one case study, the quality management systems implemented in the projects lack an objective definition of the compliance methodology when addressing to the energy performance quality criteria.

Comparative Analysis of the Energy and CO2 Emissions Performance and Technology Gaps in the Agglomerated Cities of China and South Korea

This paper presents a comparative analysis of the technology gap, energy efficiency, and CO2 emission performance of the agglomerated cities in Eastern and Central China and South Korea under economic heterogeneity. The potential reductions of energy and CO2 emission are estimated from agglomerated city perspectives. The global meta-frontier non-radial direction distance function is used to conduct an empirical analysis of agglomerated cities among Eastern, Central China and South Korea. The results show the potential reduction of 7.58 billion tons of CO2 emissions in Korea and another potential reduction of 1930.62 toe energy for the research period in China, if Korea and China proactively collaborate with each other. The empirical results conclude several unique findings and their implications. First, there are significant differences between the Chinese and Korean cities, in energy efficiency, CO2 emission performance, and meta-technology gaps. Korean cities play a leading role at benchmarking efficiency level with meta-frontier technology. Second, there is no significant difference between total-factor and single-factor performance indexes in the Korean cities, because South Korea requires large capital stocks to replace energy in the production process. However, the opposite is true for Eastern and Central China cities. Finally, there is huge potential for the Chinese cities to reduce energy and CO2 emissions by “catching up” internally as well as by the collaborative efforts with Korean cities.

Occupant behaviour and thermal comfort in buildings: Monitoring the end user

Studies indicate that the energy performance gap between real and calculated energy use can be explained for 80% by occupant behaviour. This human factor may be composed of routine and thermoregulatory behaviour. When occupants do not feel comfortable due to high or low operative temperatures and resulting high or low skin temperatures, they are likely to exhibit thermoregulatory behaviour. The aim of this study is to monitor and understand this thermoregulatory behaviour of the occupant. This is a detailed study of two females living in a rowhouse in the city of Heerlen (Netherlands). During a monitoring period of three weeks over a time span of three months the following parameters were monitored: activity level, clothing, micro climate, skin temperatures and thermal comfort and sensation. Their micro climate was measured at five positions on the body to assess exposed near body conditions and skin temperature. Every two hours they filled in a questionnaire regarding their thermal comfort and sensation level (7-point scale), clothing, activities and thermoregulatory behaviour. The most comfortable (optimal) temperature was calculated for each person by adopting a biophysical model, a thermoneutral zone model. This study shows unique indivual comfort patterns in relation to ambient conditions. An example is given how this information can be used to calculate the buildings energy comsumption.

Climify.org: an online solution for easy control and monitoring of the indoor environment

Real energy performance of new and retrofitted buildings often consistently differs from expectations. While occupants might complain about poor indoor climate, the energy use in such buildings is often higher than expected, leading to the well-known phenomenon called “Energy Performance Gap”. In the past years, monitoring of buildings, both in terms of energy use and indoor climate conditions, was realised mostly for office buildings only, and at high financial costs. However, the exponential growth in availability of IoT devices, over the last years, opens now new scenarios for low-cost monitoring and control solutions of buildings. Yet, modern IoT devices are often only accessible online through the vendors’ software, although some devices make use of open communication protocols and can, therefore, be connected to open platforms such as openHAB. However, the use of open platforms is still connected to a big efforts for many final users. We, therefore, propose climify.org, an open platform for plug and play connection of IoT sensors and actuators, for easy monitoring and controlling of buildings and buildings’ HVAC systems. The platform climify.org offers, at time of writing, three main applications. The first application is an IoT device installation app, to be used on portable devices (e.g. mobile phones or tablets of system administrators): this app allows easily installing and locating a sensor or an actuator, within a building. The second application is an online service for data visualisation and HVAC control: while the monitoring data can be plotted, the service offers several data evaluation methods; moreover, the settings of the connected actuators can be modified and controlled. The third application can be installed on portable devices (mobile phones and tablets of buildings’ occupants) and allows occupants to provide feedback on their perception of the indoor climate through several questionnaires’ formats. Through the three applications developed within climify.org, we aim at providing the best indoor climate and the lowest energy use through a low-cost solution.

Namenski geometrijski dizajn zastakljivanja za analizu energetske efikasnosti zgrada

Geometry is an important architectural design issue in the assessment of a building model's energy performance using Building Performance Simulation tools. The commonly used window-to-wall ratio method, while providing a fast and automatic way of modelling glazing, is prone to geometrical inaccuracies, which can contribute to the energy performance gap between modelled and monitored buildings. To alleviate these challenges, this paper presents a mechanism for creating a bespoke glazing design on curved surfaces based on the concept of UV-mapping. The glazing can be designed on a 2D planar vector drawing as a set of interconnected curves, which are then mapped unto the UV space of the subdivided and planarised input wall as the glazing. It is hypothesised that a building model with a bespoke glazing design, while more time consuming, allows a more aesthetically representative and geometrically accurate glazing design, thus minimising the energy performance gap.

Parameters that influence the probability on lower-than-expected energy savings - a pre- and post renovation energy consumption analysis of 90,000 renovated houses in the Netherlands

Thermal renovations are considered to be an effective measure to reduce residential energy consumption. However, they often result in lower-than-expected energy savings. In this paper, we investigate some parameters that influence the probability on lower-than-expected energy savings. We do this by comparing actual pre- and post-renovation energy consumption of 90,000 houses in the Netherlands. The results of this study confirm that the effect of the parameters differ per renovation measure. For every renovation measure, the energy performance gap post renovation plays a significant role. This implies that the use of actual energy consumption data to determine the potential energy savings could therefore help to reduce the number of renovations resulting in lower-than-expected energy savings. Also, the energy efficiency state of the building pre-renovation plays an important role. One should take into account that renovations of energy inefficient buildings more frequently result in lower-than-expected energy savings than renovations of relatively energy efficient buildings. For the type of house we found that multifamily houses more often result in lower than expected savings when building installations are improved, while single-family houses renovations more frequently result in lower energy savings than expected when the building envelope insulation is improved. These insights can contribute to the decision making process whether or not to take a certain renovation measures, they can also help to manage expectations on housing stock level and individual building level.

Hit2Gap Project: Highly Innovative building control Tools Tackling the energy performance gap

Measurement campaigns have shown major discrepancies in buildings energy performance between planned energy demand and real energy consumption, while nowadays most of the newly constructed offices buildings are equipped with BMS systems, integrating a more or less extended measurement layer providing large amounts of data. The HIT2GAP project has developed a new generation of building monitoring and control tools based on advanced data treatment techniques allowing new approaches to assess building energy performance data, getting a better understanding of building’s behaviour and hence a better performance. From a strong research layer on data, HIT2GAP solution builds on existing measurement and control tools that are embedded into a new software platform for performance optimization. The HIT2GAP solution is applied as a novel intelligent layer offering new capability of the existing BMS systems and offering the management stakeholders opportunities for services with a novel added value. Applying the solutions to groups of buildings also allows to test energy demand vs. local production management modules. This solution is being tested in various pilot sites across Europe. HIT2GAP work has been carried out with a permanent concern about market exploitation of the solutions developed within the project. This paper will present the project solution in detail and showcase the achievement so far in the real case demo sites.

Energy performance optimization of buildings using data mining techniques

The operational energy consumption of buildings often does not match with the predicted results from the design. One of the most dominant causes for these so-called energy performance gaps is the poor operational practice of the heating, ventilation and air conditioning (HVAC) systems. To improve underperforming HVAC systems, analysis of operational data collected by the building management system (BMS) can provide valuable information. In order to completely use and interpret operational data, the building sector is urging for methods and tools. Data mining (DM) is identified as an emerging powerful technique with great potential for discovering hidden knowledge in large data sets. In this study, the performance of HVAC systems was analysed using regression analysis as DM technique. This leads to valuable insights to control and improve the building energy performance. The results show that a reduction of 7-13% on the heating demand and 41-70% on the cooling demand can be obtained.

Comparison of EnergyPlus and IES to model a complex university building using three scenarios: Free-floating, ideal air load system, and detailed

The energy performance gap is one of the most discussed issues in the design community since energy modeling became an integral part of the building design process. Different limitations apply to almost every building performance simulation (BPS) software available today and to have confidence in the predictions of whole-building energy models it is necessary to have a thorough understanding of various features, specific capabilities, and disadvantages of BPS tools. The main contribution of this work is the use of three methods of evaluation with different levels of complexity, free-floating, ideal air load system, and detailed method to analyze and compare the capabilities of EnergyPlus and IES to model complex LEED silver multi-purpose university building. Consequently, this study provides new information regarding capabilities of two extensively used BPS tools to model advanced and innovative buildings, and in particular HVAC systems that are increasingly becoming used in high-performance commercial and institutional buildings worldwide. The difference between the total energy consumptions of the EnergyPlus and IES models developed according to the final construction drawings was approximately 2.1%, whereas differences between the heating and cooling loads of the EnergyPlus and IES models with ideal air load systems were 6 MWh (1.7%) and 0.86 MWh (7.8%), respectively. The high consistency between the models’ aggregated predictions are particularly pertinent and encouraging for certification programs such as LEED, which take into account aggregated energy consumption data in their assessments. The findings also emphasize the importance of the modeler's assumptions regarding the modeling of HVAC systems and their impact on the model's predictions.

Measuring and modelling retrofit fabric performance in solid wall conjoined dwellings

There remains a significant number of occupied and uninsulated solid wall dwellings in the UK. Deep retrofit is often required for these buildings to become energy efficient but it is difficult to determine how these buildings will respond to retrofit without a detailed understanding of their fabric thermal performance Greater certainty can however be achieved by combining theoretical models and practical field tests, prior to the design of retrofit programmes. This type of approach can then be used to inform and optimize the design of retrofit interventions. This paper presents results from a series of in situ fabric performance tests undertaken on two no-fines concrete, conjoined dwellings pre- and post-retrofit and demonstrates how empirical data can be used to inform and calibrate the thermal performance of dynamic simulation models (DSMs). This is a particularly pragmatic calibration method as it eliminates the need for actual weather data, which is expensive and prohibitive to collect and collate. The DSM inputs and outputs were compared with those obtained from Standard Assessment Procedure (SAP) calculations. The results illustrate how the fabric performance of no-fines concrete can vary between similar house types within the same development. This research also validates the effectiveness of the calibration methodology that uses the whole house Heat Transfer Coefficient (HTC) as the qualifying metric. Furthermore, results also emphasize the importance of appropriately characterizing the physical properties of existing buildings before designing retrofit strategies. This paper contributes to the growing knowledge base concerned with the energy performance gap. In this instance, SAP predicts higher absolute savings then measured in situ which is problematic when assessing the financial viability of retrofits.

Normalising domestic space heating demand using post hoc models

Current evidence suggests that the energy performance gap between predicted and actual use of energy in buildings is significantly weighted towards under prediction and can be as high as 200%. High-quality modelled and actual data are needed to ensure like for like comparisons when investigating the energy performance gap. Internal temperature ( ti) normalisation is a key process to ensure like for like comparisons but is often hampered by the lack of the original model due to the time lag between design, construction and occupancy. Here, we demonstrate the use of models created after data collection – i.e. post hoc – as a substitute for original models in evaluating the energy performance gap. The robustness of the internal temperature normalisation factor ( fti) is tested using measured data from 20 Passivhaus homes. The data from each home are inputted into 10 Passive House Planning Package and 10 Standard Assessment Procedure models with highly different domestic and non-domestic building configurations, creating 400 model variants. Each variant is further split into four cases of varying internal gains and solar radiation creating a total of 1600 variants. Results demonstrate that fti is resilient to differences in building configuration, solar radiation levels and varying internal gains (SEM < 0.02). Even though SEM increases when measured internal temperatures are below base assumptions, the impact of this error on the computed space heating demand is at most 4%. This suggests that post hoc models can be a substitute for actual models in evaluating the energy performance gap and that limited site data can still yield robust results. Practical application: Identifying the causes of the energy performance gap (the difference between modelled and measure energy demand) is complex. Normalising space heating demand for internal temperatures means that some differences between modelled and actual space heating demand can be accounted for. Building models such as Passive House Planning Package (PHPP) and Standard Assessment Procedure (SAP) are readily available and allow variations in climate and temperature data to be inputted. This research demonstrates that in practice any PHPP and SAP model can be used for normalisation, not just one that is building specific and that some parameters (internal temperature) are more important than others. This provides a simple and easily accessible approach to temperature normalisation that can be applied by industry to domestic dwellings.

Mind the energy performance gap: Evidence from green commercial buildings

Energy performance gap refers to the discrepancy between the predicted and the realized energy savings after buildings adopt energy-efficient technologies. This study identifies and analyzes the organizational, behavioral and engineering factors related to the energy performance gap. 117 completed surveys from facility managers in the United States were obtained in 2017. We find that the primary reasons for the energy performance gap are (1) occupants using more energy than designed, (2) more occupants than originally designed, and (3) energy-efficient technology failures. An analysis is conducted using probit models. The results show that LEED and Energy Star buildings are more likely to have tenant lease agreements to eliminate asymmetric information for new tenants. Energy Star buildings are more likely to have sub-metering for air conditioning. However, LEED buildings are associated with factors causing the energy performance gap, such as lack of sub-metering for AC and longer operating hours. Building characteristics such as occupancy rate, building type, ownership and building location influence the impacts of the identified socio-technical factors. Finally, several suggestions to mitigate the energy performance gap are proposed, such as incentives to facility managers, commissioning, energy performance contracting, and occupants’ behavioral change.

Towards a framework to evaluate the ‘total’ performance of buildings

Internationally, buildings are a major contributor to carbon emissions. Despite significant advances in the technology and construction of energy-efficient buildings, in many cases a performance gap between designed and actual performance exists. While much research has investigated the drivers of the building energy performance gap – both static and transient– there has been considerably less research into the total performance gap, defined here as performance gaps in building energy use, occupant satisfaction and Indoor Environmental Quality parameters such as thermal comfort and air quality which may impact on occupant health and wellbeing. This paper presents a meta-analysis of building performance data from buildings in the UK and China – selected due to their contrasting development environments – which illustrate the presence of and complexities of evaluating total performance gaps in both countries. The data demonstrate the need for (1) high end-use, spatial granularity and temporal resolution data for both energy and Indoor Environmental Quality, and (2) developing methodologies that allow meaningful comparisons between buildings internationally to facilitate learning from successful building design, construction methodologies and policy environments internationally. Using performance data from a UK building, a potential forward path is illustrated with the objective of developing a framework to evaluate total building performance. Practical application: While much research has examined building energy performance gaps, Indoor Environmental Quality and occupant satisfaction gaps are rarely included despite their relationship to energy. We use a meta-analysis of energy, indoor environmental quality, and occupant satisfaction data from buildings in the UK and China to illustrating the presence of and complexities of evaluating total performance gaps for buildings in the two countries, and the need for high resolution dynamic buildings data and novel methodologies for comparison between buildings across different contexts. Illustrative case studies are used to demonstrate potential future directions for evaluating ‘total’ building performance.