Lessons Learned from Building-Performance Digital Twins
AMPLIFY VOL. 36, NO. 4
Among the many fascinating applications of digital twins, using them to create a virtual replica of how a real building is performing at a given time ranks high. These building-performance digital twins start by using physics principles to predict how a building will perform, taking into account its envelope, mechanical systems, and energy usage. Real-time data collected from smart meters, wireless meters connected to the Internet of Things, and building management systems (BMSs) is added to create a hybrid physics data model of the building. Machine learning (ML) and artificial intelligence (AI) methods can additionally be used to fill any data gaps (e.g., algorithms that extrapolate data over a 12-month period) and to predict things like internal occupancy or external weather patterns.
Building-performance digital twins can also be calibrated to an energy-efficiency standard such as the International Performance and Measurement and Verification Protocol (IPMVP).1 The calibrated digital twin can then be used to derive insights into energy-conservation measures, including operational and behavioral measures, shallow and deep retrofit measures, pathways to net zero or positive energy, and end-of-life considerations.
Where a live connection to metered data is available, the digital twin can be deployed to monitor systems in real time to ensure the building is performing according to its design intent. This type of monitoring can be used to close gaps between the building’s operational performance and design standards like Leadership in Energy and Environmental Design (LEED), Building Research Establishment Environmental Assessment Methodology (BREEAM), nearly zero-energy building (NZEB), and Passivhaus.
This article presents the results from an Innovate UK–funded project called eDigit2Life (Project Ref: 105871). The project involved the creation of a number of performance digital twins based on buildings on the campus of the University of Glasgow, Scotland.
University of Glasgow Digital Twins
Building-performance digital twins were created for two new buildings on the university campus: the James McCune Smith Learning Hub (JMS) and the Advanced Research Centre (ARC), completed in 2021 and 2022, respectively, as well as for the university’s library, which was completed in 1968.
For this article, we have chosen JMS and the library to discuss (see Figures 1 and 2). Figure 3 shows the campus-level digital twin, with the energy consumption of each building simulated using OpenStreetMap data and information on the buildings from the University Estates team. These buildings have not been calibrated, but they provide benchmark data from which the university can derive simple insights.
For the new buildings, the design team used the modeling software tool Revit to create a building information model (BIM). The mechanical, electrical, and plumbing engineers converted the BIM to an energy model using Integrated Environmental Solutions (IES) Virtual Environment (VE) dynamic simulation modeling software and created an initial model to ensure the building would comply with the relevant industry standards for energy performance.
The eDigit2Life team took the compliance model and updated it to include information on each building’s energy-usage patterns and the unregulated loads that had not been considered in the compliance model. (Note that UK compliance models mostly focus on building assets such as the envelope and major systems. Thus, they are not representative of building energy usage and occupant behavior once in operation.)
Using information from the as-built documentation, the team added occupancy profiles based on building use and investigated small power electrical equipment loads. Next, data was collected from the BMS and design profiles (e.g., space temperatures, equipment efficiencies, lighting loads, and HVAC flow/return temperatures) and added to the model. The resulting hybrid physics-data model was calibrated according to IPMVP to create the building-performance digital twin.
For the existing building, a geometry model was created based on available architectural drawings (e.g., BIM or Revit model). An energy audit of each building was carried out to collect the additional data required for a thermal template of the model.
Information relating to the energy heat and flows of the building is important when creating a building-performance digital twin. For example, to create an accurate model, the team must know the heating set-point and set-back temperatures, the schedule for the heating controls, and the amount of domestic hot water consumption for each zoned area.
Data on other factors contributing to internal heat gains should also be gathered, including equipment that emits heat (computers, monitors, lighting) and the number of people in the spaces. Small power electrical equipment, plug loads, lighting types, and occupancy profiles are all very important to creating accurate building-performance digital twins. None of this information would be contained in a standard BIM.
Next, a calibrated model was created using information from the energy audit and accounting for unregulated loads, bringing it into close correlation with the metered data (see Figures 4 and 5).
Opportunities from Building-Performance Digital Twins
Building-performance digital twins can be used for a variety of purposes:
Monitoring operational energy on an ongoing basis to ensure the design intent of the building is being met
Ensuring optimum energy performance while maintaining healthy environmental levels in the building (e.g., thermal comfort, ventilation, day lighting, glare)
Testing a range of interventions and refurbishment options on existing buildings to work toward net-zero goals
Monitoring compliance with sustainability regulations, such as environmental, social, and governance (ESG) regulations; EU taxonomy for sustainable activities; EU Climate Benchmarks regulation; and EU Sustainable Finance Disclosure Regulation
Creating net-zero energy plans or decarbonization pathways for single buildings or, where applicable, groups of buildings across a portfolio or campus
Identifying solutions for fossil fuel divestment for individual buildings or groups of buildings (e.g., net-zero energy or positive-energy blocks)
A calibrated model for the library was created in the same way as for JMS. Figures 6 and 7 show the calibration of monthly and time-series data.
Using this digital twin, three scenarios were modeled for improved performance:
Adjusting start/stop times and closing upper floors during low-occupancy periods
Basic electrical retrofit, including replacing all lighting fixtures with LED fixtures and implementing power management software
HVAC equipment upgrades, including better control of ventilation systems
The building-performance digital twin predicted reductions of 15% on energy and carbon emissions, 9% reductions for the electrical retrofit, and 23% for HVAC upgrades. The university is hoping to begin scenario one once the current exam schedule has completed; the other two scenarios are being considered alongside a range of other campus-wide energy-saving initiatives.
The eDigit2Life project started in April 2020, just on the cusp of the COVID-19 pandemic. The initial plan was to examine only new buildings, but because of construction delays from the pandemic, the project leaders decided to expand the scope and examine several existing buildings. This turned a negative situation into an opportunity to demonstrate the benefits of digital twins for both types of buildings and discover many important lessons.
Need to Connect Design & Standards
Currently, compliance models are created during the design stage of the building lifecycle and are not used beyond that stage. Additionally, there are many ways to measure performance, and minimum performance standards are well-known to produce large gaps between design and operation. Similarly, when adjustments are made for occupant comfort, changes are sometimes made that go against the design intent of the building, such as increasing set-point temperatures. Furthermore, design-stage modeling, however accurate, is always based on historical data, briefing assumptions, occupancy assumptions, and behavioral assumptions.
Thus, clients of building projects need to be educated that minimum compliance standards will not achieve sustainable outcomes and efficient buildings in operation and governments, and standardizing bodies need to be aware of the dangers of using compliance metrics as operational targets.
Need to Connect Procurement & Construction
The building construction process is currently siloed. Procurement practices are based on outlined specifications that do not include information on the building’s final intended use. For example, for the new JMS and ARC buildings on the University of Glasgow campus, the proposed BMS was specified at the design stage with the intent to access the BMS data using a live connection that would enable operational energy monitoring, ensuring the building performed to its design intent. Unfortunately, a remote server to enable remote access of the data was not included in the contract. This demonstrates a need to include building “in-use” scenarios in the specifications of different equipment to ensure the procurement team has all the information it needs to make the best decisions. Similarly, when equipment such as air-handling units break or reach end of life, the procurement team may simply select the replacement equipment based on lowest cost. The performance digital twin could be used to demonstrate how a slightly more expensive unit would provide better ROI and lower carbon emissions, contributing to the university’s sustainability goals and long-term investment plan.
Need to Connect Facilities & Energy Management
Often, building-operation roles are siloed and lack communications workflows. For instance, a typical facilities manager is responsible for fixing things as they break (reactive maintenance), while a typical energy manager is responsible for energy performance. However, in many organizations, these two departments do not work closely together due to organizational separations for historically valid reasons. The University of Glasgow addressed this by creating a sustainability team that includes representatives from facilities, energy management, and IT.
Need for Stronger Focus on Ongoing Operations Costs
In many construction projects, too much emphasis is placed on capital expenditure during the building design phase, leaving out important considerations about the operation cost of running the building. In cases where the building is being constructed for sale to a third party, it is more obvious why operational costs are not a concern, but these omissions sometimes occur when the building is being constructed by the intended building occupant. Most often, a lack of industry-shared knowledge and/or expertise are the cause.
For instance, the estimated operational cost is often linked to compliance metrics. These are not a true reflection of the building’s operation because small power loads and other plug loads, which can be considerable, are not included in the compliance model. Performance digital twins are an ideal way to solve this type of problem, ensuring the final building in operation performs to its design intent.
Need to Focus Sooner on Sustainability
During construction, the sustainability focus tends to be on reducing waste, using sustainable materials, and ensuring speed of delivery. Further education for all on the impact on the building’s final operation is required. Performance digital twins can help demonstrate impacts of pre-operation decisions on building-efficiency metrics.
Need to Base Plant Equipment Sizes on Average Operations
Chartered Institution of Building Services Engineers (CIBSE) loads are designed to ensure mechanical plants are sized to perform optimally at peak times. This can lead to specifying and installing oversized systems, as peak loads may only occur a few days per year. This project highlights the need to look beyond CIBSE loads and base plant equipment sizes on more realistic average annual operation figures. This would allow for a certain level of tolerance in times of extreme external temperatures (e.g., two or three very hot days in July that are out of step with climatic norms). Performance digital twins can easily provide the data needed to make that determination, thus avoiding equipment oversizing.
Need for Governance Around BMS Data Fees
Performance digital twins require large amounts of data, and the more comprehensive that data is, the more accurate the twin will be. Preprocessing of data and connections with protocols such as Haystack and Brick can help streamline the import of data from the BMS, but there are barriers that can block the performance digital twin from being built in the first place.
For example, BMS manufacturers and system installers can require building owners to pay a fee for every BMS data point provided to another system, creating a significant barrier to accessing the data needed to deliver an accurate performance digital twin.
Building-owner education is needed to help ensure contracts do not block access to their data, and governance may be required to prevent BMS manufacturers from impeding decarbonization of the built environment. How this governance would be applied to ensure it is still lawful needs to be examined.
Need for Mandated Measurement & Verification
As mentioned previously, when using CIBSE guides, building-services systems can be oversized, which has a negative impact on operational efficiency. More evidence on the real performance of buildings is therefore required. This can only be achieved through better measurement and verification of a building’s performance, which is currently not mandated.
Proposed Methodology: Enabling Performance Digital Twins
Figure 8 identifies recommendations to the Royal Institute of British Architects (RIBA) Plan of Work2 stages that would facilitate performance digital twin adoption. These recommendations would lead to buildings that perform as their design intended, helping decarbonize the built environment.
At a high level, the goal is to ensure operational efficiency is considered during all stages of the construction lifecycle and that performance digital twins are used to enable iterative design approaches throughout. Interoperability between tools and technologies is a key requirement to achieving these goals.
Representatives from IT, facilities, and energy management should be included throughout the process, starting with initial predesign conversations. Energy-performance metrics should be included at the early concept design stage to reduce the risk of costly interventions later on.
Fit-out design should happen much earlier than is typical: during the technical design stage. Even if the end use of the building is not fully known, the building will have designated zones of use (e.g., toilet, kitchen, common area, office, meeting room). Standard fit-out designs should be allocated to these spaces (including plug loads, appliances, and other small power loads) and incorporated into the energy modeling as soon as possible. This can be used in an iterative manner to size the plant and to inform the final fit-out design to ensure optimum operation of the final installed systems.
Use cases for the mechanical plant, environmental machinery, and all equipment should be included with fit-out specifications to ensure the procurement team is aware of the final use for all equipment. Following this, the building should be commissioned to the as-built performance and recommissioned on a regular basis to ensure no changes have been made that could negatively affect the building in operation.
Once the building is in operation, a central committee comprising IT, procurement, facilities, and energy management teams should be created. Measurement and verification should be carried out on a continuous basis, and the data should be held in a central repository to inform future design.
Recommendations for Governance Models & Standardization Bodies
Based on our work on the eDigit2Life project, we believe there are several ways governments and/or standards bodies could support the use of digital twins in building design, construction, and operation:
More education across project delivery and design teams is required with respect to: (1) compliance modeling and what it should be used for and (2) why performance gaps occur and, therefore, the importance of measurement and verification.
The methods for achieving compliance need to be reexamined to go beyond looking at the building as an asset, to take into account the building’s final fit-out, occupancy, and user behavior.
Whoever is responsible for the capital expenditure of the building should also be responsible for the operational expenditure for the first few years of the building in operation.
Building owners should have access to their energy data at all times and should not have to pay extra to receive it.
There should be governance on knowledge sharing of measurement and verification data. This could be held by a centralized body like CIBSE that can access the data, perform research into future energy design and standards, and publish the findings for all.
Performance digital twins can combine physics data, metered data, and AI/ML methods to provide building owners with insights into the performance of a building or group of buildings. Those insights can be used to improve performance and help building owners reduce energy use and carbon emissions as well as plan future decarbonization.
The eDigit2Life project involved creating a number of performance digital twins for buildings on the University of Glasgow campus that were used to derive insights for better performance management.
The project proved that the technology to create performance digital twins exists, and those twins can contribute to the decarbonization of our built environment. However, the project uncovered multiple nontechnical barriers currently preventing their proliferation:
The need for operational-performance discussions to take place at the very beginning of any new building or building-renovation project.
The need for iterative design to take place throughout the building process, including: (1) early energy and compliance analysis during initial concept design and (2) beginning fit-out design during technical design development. This would inform better system sizing.
The need for operational use cases to be included in equipment specifications so that procurement teams can purchase the precise equipment needed.
The need to establish a centralized committee focused on sustainability and energy performance that meets frequently from the beginning of the project and continues until regular building operations begin.
The project also exposed the need for more education on the purpose of compliance models, increased measurement, verification and data analysis, and compliance modeling that advances beyond the current approach (which tends to look at a building only as an asset). Other recommendations include mandated approaches to ensure operational expenditure is considered in design and mandates to enable access to the building’s energy data by the building owner.
1 “International Performance Measurement and Verification Protocol (IPMVP).” Efficiency Valuation Organization (EVO), accessed April 2023.
2 “RIBA Plan of Work.” Royal Institute of British Architects (RIBA), accessed April 2023.