Detailed building energy modeling using OpenStudio and EnergyPlus
OpenStudio is an open-source, cross-platform software development kit (SDK) for building energy modeling (BEM). Developed by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL), OpenStudio provides a comprehensive platform for creating and analysing whole-building energy models.
EnergyPlus is DOE's state-of-the-art whole-building energy simulation engine that powers OpenStudio. It calculates heating, cooling, lighting, ventilation, and other energy flows in buildings, providing detailed insights into building performance.
Our Simplicity projects use these industry-leading tools to optimise building design for energy efficiency while maintaining comfort and functionality.
We benchmark a typical Simplicity build against traditional methodologies in terms of energy consumption and cost. Lake Road, Northcote is used as the example Simplicity Building, compared against a code-minimum baseline, an enhanced standard (better insulation and windows), and a CLT building.
Key Finding: The Simplicity build system demonstrates the most cost-effective and energy-efficient balance when considering both initial construction and operational performance. Our in-situ concrete approach provides superior thermal mass benefits while minimising construction complexity.
The same comparison repeated across our four projects — Reiputa, Waiatarua, Lake Road and Morningside Drive — showing how each successive design improves on the last. Results come from the OpenStudio energy simulations of the actual projects (entered via the Admin page).
Interactive 3D visualisation of the building model geometry, thermal zones, and surface properties.
A single Northcote N12 apartment (~65 m²) as the unit of analysis — showing where electricity is consumed, what that means in operational carbon, and how the choice of building fabric (in-situ concrete vs CLT) changes the heating and cooling load over the building’s life.
Individual appliances roll up into four end-use categories used across all OpenStudio simulations — consistent across projects and comparable against NZ benchmarks.
To complement the whole-building energy model, we are developing Therm thermal-bridge analysis for each key junction detail — wall corners, slab edges, window reveals. These isothermal simulations quantify how heat migrates through the fabric beyond what simplified R-value calculations capture. The corrected U-values and linear thermal-bridge psi (ψ) values feed directly into the EnergyPlus construction definitions.
The two diagrams below illustrate the concept: temperature isotherms flowing from the warm interior through the wall construction to the cold exterior, and why in-situ concrete mass with a well-placed insulation layer changes the gradient — and therefore the annual heating/cooling load — so significantly compared to a CLT or timber-frame alternative.
At a wall corner two exterior surfaces converge, creating a zone of higher heat flux than mid-wall. Therm quantifies this as a linear thermal bridge (ψ value) applied as a correction to the EnergyPlus whole-building model.
In-situ concrete is embodied-carbon intensive at construction — but it pays back through reduced operational carbon across the 50+ year building life. Higher thermal mass means the building absorbs heat during the day and releases it overnight, cutting the hours the heat pump runs and lowering annual electricity demand and associated grid emissions.
Complete Nezo OpenStudio energy analysis reports for each project, including annual energy consumption breakdown, monthly profiles, and HVAC system performance metrics. Select a project to view its report.