DYNAMIC MODELLING | RIGHT-SIZING HVAC SIZING THE OPPORTUNITY Integrated design and dynamic modelling can help overcome the problem of HVAC oversizing, says Autodesks Steven Butler O versizing of HVAC systems is a 224bn problem globally, according to a joint study by Autodesk and the Rocky Mountain Institute (RMI).1 This found that using traditional static-load and rule-of-thumb approaches to system sizing can result in a 50% oversizing of systems.2 This reduces occupiable space, raises capital and operating costs, and decreases occupant comfort. Right-sizing is the process of designing systems that can treat occupiable spaces during normal conditions, while allowing a small amount of overrun for exceptionally hot or cold days. This article looks at how integrated building design and dynamic modelling can support this. To succeed, these methods need the right approach and inputs, and an iterative and collaborative process. HVAC right-sizing will also be crucial to meet the ambitious goal of decarbonising Europes building stock by 2050.3 Around 75% of buildings in the EU were built before 1990, and an estimated 97% need an upgrade,4 putting mechanical, electrical and plumbing professionals in a strong position to improve the energy performance of existing and new building stock. For a typical commercial building in the EU, right-sizing could reduce greenhouse gas emissions by as much as 0.44 metric tonnes of CO2-equivalent per year.5 The approach: design-assist and dynamic modelling BIM has lowered barriers to early-stage energy analysis dramatically. With the design file now providing the basis for analysis from early stages including concept design the opportunity for the engineer to engage as a collaborative adviser arises much sooner. By automating aspects of energy simulation, including creation of the analytical model, software has further opened the door for this change in practice. Insight building performance analysis software gives Revit users a guide to better building energy and environmental performance throughout the building life-cycle. Engineers can use its sensitivity analysis to guide clients and architects to the most desirable energy conservation measures. The software shows how prospective design changes affect heating and cooling loads, and energy use intensity. Using the model and integrated building performance analysis data eliminates the need to build a separate model for energy analysis. On upload, a range of potential design outcomes are simulated through energy cost-range factors, to help engineers identify key energy performance drivers quickly, and dynamically compare design scenarios. Interaction with performance indicators, benchmarks, factors, ranges and specifications gives real-time cause-and-effect feedback early in the project. By using the cloud, dynamic modelling can be performed early and often. Beginning the process in the conceptual design phase and carrying it through the entire design phase allows decisions to be made at the right time, with the right information potentially minimising loads and optimising equipment selection to achieve better building performance with right-sized designs. Insight supports a variety of workflows, including whole-building energy and lighting analysis, solar radiation and shading, daylighting, and heating and cooling loads analysis. HVAC right-sizing will also be crucial to meet the ambitious goal of decarbonising Europes building stock by 2050 52 March 2020 www.cibsejournal.com CIBSE Mar20 pp52-53 Right sizing.indd 52 21/02/2020 15:03