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Understanding the difference between Building Simulation Software and Hysopt

This blog explains the key differences and compatibilities between building simulation software and Hysopt, showing how the two complement each other to deliver more reliable, efficient, and verifiable HVAC systems.

When introducing Hysopt in new markets, we often face the same question: “So, you’re just another building simulation tool?” The confusion is understandable. Building simulation software such as IES, TAS, HAP, or Trace 3D has been a cornerstone in building design for decades. But Hysopt is not a building simulation tool. In fact, our role in the workflow is very different – and that’s exactly where our added value lies.

Consider this: a building simulation tool might tell you a new office will consume 1.2 million kWh annually. But it won’t show you whether the heating system is oversized, whether the distribution network is balanced, or how much carbon you can save with smarter control. That’s where Hysopt comes in.

This blog explains the key differences and compatibilities between building simulation software and Hysopt, showing how the two complement each other to deliver more reliable, efficient, and verifiable HVAC systems.

What building simulation software does

Building simulation software is designed to model the whole building. It predicts energy consumption, heating and cooling loads, comfort levels, daylighting, and other environmental conditions. For example, a consultant might use IES to estimate annual kWh consumption or hours of overheating risk for a proposed school.

These tools are widely used by architects and engineers to:

  • Demonstrate compliance with regulations
  • Compare energy efficiency strategies
  • Optimise the building envelope and services on a macro level

Their strength lies in analysing overall performance across different design scenarios. However, their system design functionalities are often limited or simplified, which leaves a gap when it comes to the detailed hydraulic and thermodynamic performance of HVAC systems.

What Hysopt does – and doesn’t do

Hysopt focuses on the HVAC systems themselves – the heating and cooling distribution, generation, and control. Our software uses a physics-based approach to simulate, calculate, and optimise HVAC systems with a level of accuracy that spreadsheets or “rules of thumb” simply cannot achieve.

What Hysopt does:

  • Provides traceable, verifiable system performance
  • Helps avoid oversizing and underperformance
  • Identifies optimisation opportunities such as energy savings and carbon reduction
  • Automates (complex) calculations, saving engineers significant time compared to spreadsheets or manual methods
  • Supports consultants, contractors, and owners with transparent decision-making

What Hysopt doesn’t do:

  • We don’t model building envelopes, comfort, or daylight.
  • We don’t replace building simulation tools – instead, we take their output (loads, conditions) as input to design and optimise the HVAC system.

Here’s how it compares at a glance:

Building Simulation Software Hysopt
Scope Whole building performance (energy, comfort, daylight) HVAC system performance (hydronics, generation, controls)
Outputs kWh consumption, peak loads, comfort hours Flow rates, pressure drops, energy efficiency, system sizing
Stage of use Design development, compliance Conceptual through detailed design
Strengths Macro-level analysis, regulatory compliance Detailed, verifiable system performance
Limitations Limited system modelling accuracy Not for envelope or comfort modelling

This distinction is critical: Hysopt complements building simulation software by bridging the gap between high-level building predictions and the real-world performance of HVAC systems.

When Hysopt can be used in the workflow

Besides the technical stage, one of the most powerful aspects of Hysopt is that it can be applied in the conceptual stage, even before a full building design is in place. Using early load estimates from building simulation, Hysopt enables consultants and contractors to:

  • Explore different HVAC concepts with confidence – compare system options side by side, with quantified performance data rather than assumptions.
  • Simulate system performance under realistic conditions – test how designs behave dynamically across seasonal variations and part-load operation.
  • De-risk projects by ensuring systems will deliver as promised – provide verifiable evidence to clients and stakeholders before major investment decisions are made. To see how this works in real projects, explore our solutions page.

Aligned with the RIBA Plan of Work, Hysopt is particularly valuable from Stage 2 (Concept Design) onwards, supporting better decisions well before systems are locked in.

In markets like Canada, where traditional spreadsheets and rules-of-thumb dominate, this represents a huge step-change. In the UK, growing demand for traceable and verifiable performance (driven by NABERS UK, CIBSE TM63, and net zero targets) makes Hysopt a vital addition to the toolkit.

The bigger picture

Rather than competing with building simulation software, Hysopt fills the missing link. By combining building-level predictions with physics-based HVAC system optimisation, the industry can deliver higher-performing, lower-carbon, and more reliable buildings.

Ready to see the difference for yourself? Request a free trial today and discover how Hysopt can bring certainty to your HVAC projects.

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