PERFORMANCE | MEASUREMENT AND VERIFICATION IPMVP Option D offers robust measurement and verification to give building services engineers and their clients a better insight into how a design energy performance rating can be validated during operation. Nazli Dabidian explains how TO CLOSE THE PERFORMANCE GAP, CHOOSE OPTION D T here have been various attempts within the UK building industry to address the issue of real energy performance. These include the Design for Performance1 framework which is mainly based on the Australian Nabers2 Leti self-declaration,3 and the new Breeam 2018 additional energy credits under Ene01.4 To understand how buildings are performing compared with the theoretical performance calculated during the design stage, building managers can use a measurement and verification protocol that has been established by the US Department of Energy. The International Performance Measurement and Verification Protocol (IPMVP),5 promoted by the Efficiency Valuation Organisation,6 assesses investment in energy and water efficiency, demand management and renewable energy projects. The Guide to Energy Performance Contracting Best Practice7 is closely related to the IPMVP, and can be used in conjunction with it. Measurement and verification is more easily achieved for existing buildings when an energy efficiency strategy is being implemented to reduce energy consumption. This is because the buildings energy consumption before implementation of that strategy can be monitored and measured, and used as the baseline. When commissioning a major refurbishment or new development, however, the client could and perhaps should expect the same level of commitment to achieving the calculated energy performance rating during operation. So how can delivered building performance be evaluated against the theoretical performance calculated at the design stage? In a retrofit project, the baseline is clear it is the monitored energy performance of the existing building. For new construction, such a baseline does not exist; instead, designers use various other measures for example, compliance with Part L of Building Regulations to establish a theoretical energy performance for the building. In the past decade in the UK, Energy Performance Certificates (EPCs) have also been used. The problem is that, after completion and handover, actual operating conditions can differ significantly from those assumed at the design stage. Option D of the IPMVP, using a calibrated simulation, offers a solution to this. How it works Dynamic thermal modelling of the building is carried out during design and, for more accuracy, the HVAC schematic may be added to the model. For unknown operational items, such as occupant density or operational hours, assumptions will be used. This model is the unadjusted design stage baseline. Once the building is in operation, the model can be modified to match the actual operational conditions, including the small power density, occupancy, operational time and weather data. All elements of the model including the specifications, efficiencies and controls are adjusted to represent the existing building. The modifications will be made so the results represent the operational energy performance. Sub-metering is invaluable in model calibration; sufficient sub-metering of the building systems will allow the models disaggregated energy output to be compared with the operational sub-meters. Once the model is calibrated and the team is satisfied with its accuracy, the two models can be compared. The difference between the adjusted baseline and the calibrated operational energy consumption will represent any discrepancy between the energy performance targeted during design and that achieved in operation. 42 April 2019 www.cibsejournal.com CIBSE Apr19 pp42-43 Measurement protocol.indd 42 22/03/2019 16:57