Using Simulation to Unlock Retrofit Potential in Existing HVAC Systems

Retrofitting without simulation is guesswork

Many retrofit decisions are still made using static rules of thumb: oversizing margins, generic payback tables, or incomplete as-built data.

But buildings don’t operate on paper—they operate in real-time, under dynamic load, with unpredictable user behaviour and legacy quirks.

Simulation brings the full system into view—exposing performance gaps, bottlenecks, and upgrade opportunities you can’t see with conventional tools.

‍

Why simulate existing HVAC systems?

Retrofitting without simulation can lead to:

Fixing visible symptoms while missing root causes
Replacing equipment that isn’t the real problem
Unexpected results from flow or control conflicts
Missed efficiency gains from low-cost interventions
Difficulty justifying upgrades without clear data

Simulation avoids these pitfalls by modelling the system as it actually operates. It captures hourly load variation, tracks ΔT behaviour across all circuits, and maps hydraulic flow and pressure zones.

It also accounts for how components interact under part-load conditions, and reveals return temperature profiles along with system losses.

This level of insight allows engineers to design, diagnose, and optimise with precision—before problems appear on site.

‍

Spotting bottlenecks that undermine performance

Through simulation, you can uncover what static design tools often miss.

Overloaded or underused branches become immediately visible, along with valve authority problems and short-circuiting flows.

On top of that, simulation helps identify oversized or poorly sequenced pumps, and zones with delivery mismatches or sluggish response also surface clearly.

Most critically, simulation exposes the hidden causes of high return temperatures (often the key reason behind poor heat pump or condensing performance).

‍

What the simulation workflow looks like

Using a platform like Hysopt, the process involves:

Importing system data: As-built layouts, component specs, BMS trends
Building a digital twin: System-wide hydraulic and thermal model
Running simulations: Seasonal load variation, part-load conditions, control logic testing
Scenario analysis: Test impact of control changes, balancing, flow strategies, or equipment swaps
Prioritised recommendations: Ranked list of interventions by cost, complexity, and ROI

See how Hysopt supports simulation-driven retrofit planning

‍

Real result: from static drawings to dtrategic action

In a university retrofit, the initial plan focused on replacing the heat pump to improve efficiency.

However, simulation revealed that 35% of the energy loss stemmed from ΔT collapse and poor flow management.

By rebalancing the system and adding variable flow, energy use dropped by 28%—without installing a new generation plant.

The insight didn’t come from assumptions, but from system simulation that exposed the real causes behind the inefficiency.

‍

FAQ: Simulation tools for retrofit planning

Do I need a full BIM model to simulate?

No. Basic schematics and component specs are often enough. Simulation fills in the performance picture.

How accurate is the output?

Very. Hysopt simulations match measured system behaviour within a 5–10% range when calibrated with operational data.

Can I simulate phased retrofits?

Yes. You can model and compare individual, staged, or bundled upgrades—ideal for budget-constrained projects.

Design based on data—not just diagrams

Simulation transforms retrofit planning from reactive fixes into proactive strategy. You don’t just see what’s broken—you see how the whole system behaves and where the biggest wins are hiding.

Want more info about using simulation tools to assess and improve existing HVAC systems? Here’s everything you need.