RACA Journal I March 2026 www. refrigerationandaircon. co. za 11
LOCAL INNOVATION
BSIMAC: SA-BUILT HVAC DESIGN AND ENERGY SIMULATION PLATFORM WITH GLOBAL POTENTIAL
By Eamonn Ryan
When mechanical engineer and long-time HVAC practitioner Alec Johannsen established his private consultancy in 1991, his focus was on HVAC installations and consulting. This article is Part 1, to be followed by Part 2 in the April issue.
But as computing hardware matured and building-energy demands became more sophisticated, Johannsen recognised a gap in the market: a need for a software tool that fused practical HVAC system design with annual‐energy simulation, underpinned by sound theoretical modelling.
The result is BSIMAC( not an acronym) – a software package that has grown gradually since the late 1990s into one of South Africa’ s widely adopted tools for HVAC design and buildingenergy analysis( www. bsimac. co. za).
Today, BSIMAC boasts approximately 150 active users – engineers, architects and simulation specialists – who rely on it for design, compliance and‘ what-if’ analysis. Its longevity speaks to more than just utility: it signals a strategic positioning in the evolving global built-environment and HVAC marketplace.
“ Over the years, my consultancy evolved to cover a broad remit – HVAC installations, energy efficiency work and software development in related fields. With a background in applied thermodynamics and after more than two decades in privatepractice engineering, I eventually found myself transitioning into the software side of things,” says Johannsen.
“ Back in the late 1990s, as personal computers became more accessible, I realised that many of the HVAC and energy-analysis tools available at the time were either too simplistic, relying on empirical shortcuts, or they were built as research engines rather than practical design platforms. Even the commercial packages lacked the flexibility, methodological transparency, or everyday usability that real-world consulting work demanded.
“ That’ s what pushed me to start developing BSIMAC – initially as a tool specifically for air-conditioning system design. Over time, I expanded it to include annual building-energy simulation as well. That dual mode of operation has remained one of BSIMAC’ s key differentiators.”
DUAL‐FUNCTION APPROACH: DESIGN AND ANNUAL SIMULATION
One of BSIMAC’ s core strengths lies in its architecture that supports two complementary design pathways:
• Design mode: targeted at HVAC engineers doing system sizing, cooling / heating load calculations for selected design days.
• Annual simulation mode: targeted at energy analysts and building designers who need to simulate an entire year( 8 760 hours) of operation under typical or average conditions, to assess energy use, and compliance with energy-regulations.
“ Shifting from design to full annual simulation is actually quite straightforward conceptually. You use the same building model, the same equipment, the same thermal zones – the difference is simply in the time horizon. Instead of modelling just a few peak days, you simulate every hour of the year, and you work with average rather than
Alec Johannsen. extreme weather data.
“ The real beauty is that you don’ t have to build separate models for sizing and simulation. You can reuse the entire design framework, which makes the process far more efficient and coherent.”
This distinguishes BSIMAC from many competing platforms that are either design-oriented( load calculators) or simulation-oriented, but rarely both in one integrated, practitioner-centric tool.
A milestone in BSIMAC’ s evolution occurred in 2012, when it received formal certification under the South African standard route for annual energy simulation( via Agrément South Africa) for compliance modelling. Johannsen explains that this made BSIMAC eligible for use in the performance and reference building routes of energy-compliance – allowing architects / designers to deviate from prescriptive envelope and insulation rules provided that the building’ s actual simulated energy-use meets targets.
This regulatory linkage significantly boosted the software’ s market penetration, because thermal modelling is usually the preferred compliance route throughout the building industry.“ Once a tool is certified, it becomes a trusted instrument for regulatory filings and design approvals. BSIMAC has been used in many thousands of applications over the years – for both design work and full building-energy simulation – and that level of adoption speaks to the confidence users have in it,” says Johannsen. RACA Continued in Part 2 …
Supplied by Alec Johannsen business
RACA Journal I March 2026 www. refrigerationandaircon. co. za 11