BUILDING PERFORMANCE | ENERGY TRACKING VISIBLE PERFORMANCE Making building performance visible is the aim of a new tool that tracks the impact of design changes on energy intensity and cost. Roderic Bunn and John Field describe the tool and its advantages for use on Soft Landings projects The OpEC tool tracks changes to loads caused by, for example, an increase in planned hours of operation T he performance gap remains a chronic shortcoming in the way we deliver buildings. Clients and builders alike have little idea how a building is likely to perform as its coming out the ground. Its energy use and emissions cannot come as a shock. The emerging performance needs to be made visible so that corrective actions can be made, or energy penalties accepted. To help delivery teams tackle this issue, the authors have developed an Excel-based spreadsheet that aims to provide the functionality necessary for the assessment of operational energy and carbon dioxide emissions as a project progresses through delivery and into operation. Called the Operational Energy and Carbon (OpEC) spreadsheet, the new tool is designed to track changes to power loads. It is part of a project enabled by the Construction Innovation Hub (the Hub) and defines operational energy and carbon dioxide emissions information exchanges for Government Soft Landings (GSL) and other soft landings projects. The OpEC is, essentially, a more powerful version of CIBSE TM22 Energy assessment and reporting methodology, a spreadsheet method originally developed for post-occupancy evaluation. It is also consistent with the energy analysis conventions of CIBSE TM54: 2013 Evaluating operational energy performance of buildings at the design stage. Power estimations made using the TM54 approach can be used to populate the OpEC spreadsheet. Thermal loads, typically calculated in dynamic simulation models (DSM), can be imported and updated as required. What make the OpEC tool particularly powerful are its programmed macro functions. These enable each iteration involving a change to a load and its operating parameters to be saved within the memory of the spreadsheet. Changes can be recorded in one spreadsheet rather than being dispersed over several files. Each change is captured individually, and the energy saving (or penalty) of a change is summarised in terms of kilowatt hours, kilograms of carbon dioxide, and energy cost (based on a userselected unit cost of electricity, and fossil gas or biofuel as appropriate). Figure 1 is a snapshot of how this works. In the example, a projects power loads have been input as single-line entry items. Where a modification to an entry is needed for example, as information becomes available on the actual wattage of an installed product or its usage factor the user can record the different value using a change macro function. The cell value is subsequently modified and recorded as a colour overlay unique to the cell. Changes to the spreadsheet can be on rated wattage, and in-use and out-of-hours usage factors. Hours of use and days per week in use can be altered for individual loads. All changes to installed loads (kW), hours of use or intensity of use (kWh) and cost (p/kWh) during subsequent project stages can be tracked and reported as changes occur. The iterations are automatically captured in tables, histograms and line graphs (see Figures 2 and 3). Even though a high number of iterations can be recorded in the OpEC tool, the file size will never get bigger than a couple of megabytes, which cant be said of a DSM. Unlike DSM, the OpEC tool does not require a high level of skill; many functions and outputs are automated. Alterations to loads in the OpEC tool The OpEC tool enables penalties to be made visible to all, so they can be accepted or quickly reversed 34 October 2021 www.cibsejournal.com CIBSE Oct21 pp34-36 OpEC energy tracking tool.indd 64 24/09/2021 14:21