PLC Simulator
HVAC vertical

HVAC PLC Simulator

Practice chiller sequencing, damper modulation, and boiler startup control in auto-graded browser scenarios. Write real IEC 61131-3 ladder logic — no install required.

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HVAC control scenarios

The three HVAC control challenges that trip up programmers

Chiller sequencing

Lead/lag chiller selection, runtime equalisation, status feedback, and fault switchover. Practice the logic that keeps cooling plants running efficiently.

Damper modulation

Variable-position analogue outputs (0–100%), setpoint tracking, mixed-air temperature control. Practice proportional damper control with real PID.

Boiler startup sequence

Multi-step startup with safety interlocks: purge timer, ignition sequence, flame proof, high-limit cutout. Practice safety-critical sequential control.

How HVAC PLC control works

A visual map of HVAC PLC concepts

HVAC control is mostly analogue loops (modulating dampers, valves, and fan speed) wrapped in discrete safety interlocks (freeze stat, high-limit, flame proof). These are the building blocks behind the chiller, damper, and boiler scenarios — each one you can write and run yourself in the browser.

HVAC 4-20 mA temperature sensor scaling — a chilled-water or mixed-air temperature transmitter read by the analogue input card and scaled to degrees Celsius in the PLCA 4 to 20 milliamp analog signal from a sensor, read by the analog input card and scaled linearly into engineering units such as degrees Celsius.sensor4-20mAAI cardADC62.5deg C (scaled)10004mA20mAlinear scaling
4–20 mA temperature scaling — the conversion behind every chilled-water and mixed-air loop.
HVAC fan and pump motor control — start/stop seal-in logic driving an air-handler supply fan or chilled-water pump from a PLC outputA 3-wire motor control circuit: Stop and Start pushbuttons, a contactor coil with a seal-in auxiliary contact and an overload contact, driving a motor.StopStartM (seal-in)OLMMmotor
Fan and pump motor control — the start/stop seal-in behind every AHU fan and chilled-water pump.
HVAC boiler purge timer — an on-delay timer enforcing the pre-ignition purge dwell in the boiler startup safety sequenceA TON on-delay timer: the accumulated time bar ramps up toward the preset value, and the done (DN) bit turns on when the accumulator reaches preset.TONPRE 5000ACCACC ramps to PREPREDNdone bit
On-delay timers — the purge dwell and fan-proving delays in the boiler startup sequence.
HVAC digital interlock I/O — freeze stat, high-limit cutout and flame-proof inputs mapped to PLC discrete inputs that gate the modulating control loopsA digital input pushbutton wired to a PLC input card, and a PLC output card driving a lamp, with a sinking versus sourcing hint.I/O CARDINPUTOUTPUTPushbuttonI:0/0LampO:0/0sinking (NPN) vs sourcing (PNP)
Digital interlocks — freeze stat, high-limit, and flame-proof inputs gate the analogue loops.
The PLC scan cycle in HVAC control — read sensor inputs, execute the PID and sequencing logic, update damper and valve outputs, then repeatThe repeating PLC scan cycle: read inputs, execute the ladder logic, update outputs, then housekeeping, looping continuously.1Read Inputs2Execute Logic3Update Outputs4HousekeepingSCANCYCLE
The scan cycle — read sensors, run the PID/sequencing logic, drive dampers and valves, repeat.
An HVAC ladder rung — a chiller enable contact driving the lead-chiller output coil in a lead/lag sequencing programA basic ladder logic rung between two power rails: an examine-if-closed contact (XIC) in series driving an output coil (OTE).L1L2] [StartXIC I:0/0LampOTE O:0/0
A ladder rung — chiller enable logic, the unit behind lead/lag sequencing.

Build these for real in the browser PLC simulator, or start the free curriculum.

HVAC scenarios

Auto-graded HVAC machine scenarios

Chiller Sequencing

Lead/lag control, runtime hours, fault switchover.

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Damper Modulation

Analogue output, setpoint tracking, mixed-air temp.

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Boiler Startup

Purge timer, ignition, flame proof, high-limit interlock.

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PID Temperature

Closed-loop control, Kp/Ki/Kd tuning, trend settling.

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Pump Alternation

Lead/lag pump runtime equalisation, duty/standby.

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Tank Fill

Level sensor, fill valve, pump, overflow alarm.

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How it works

01

Sign up free

No credit card. Two scenarios unlocked immediately.

02

Read the scenario brief

Each HVAC scenario explains the process, I/O list, and control requirements.

03

Write your program

IEC 61131-3 ladder, structured text, or function block. Real execution against the machine model.

04

Get graded

Auto-grader checks your control logic against HVAC test cases. Instant feedback.

Why HVAC controls engineers use this

HVAC-specific scenarios: chiller, damper, boiler — not just traffic lights
Analogue I/O practice with scaled engineering units
PID tuning in a safe environment before commissioning real equipment
Multi-step startup sequence practice with safety interlock verification
Auto-graded — objective pass/fail on every test case
No hardware, no wiring, no site access needed

Try the HVAC scenarios free

Two scenarios free forever. Full access from a monthly rate.

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Keep exploring

Related practice on this site

  • PID control for PLCs — Kp/Ki/Kd tuning for temperature and pressure loops, the maths behind the damper and PID scenarios.
  • PID temperature scenario — tune a closed loop and watch the trend settle, auto-graded.
  • Motor control PLC scenarios — the fan and pump start/stop and lead/lag logic used across HVAC plants.
  • HMI simulator — build the operator screen that shows chiller status, temperatures, and damper position.
  • PLC simulator — open sandbox to write and run analogue and sequencing ladder logic.
Questions

HVAC PLC FAQ

The simulator includes Chiller Sequencing (lead/lag chiller control with status monitoring), Damper Modulation (variable-position damper with analogue output control), and Boiler Startup Sequence (multi-step safety interlock startup). These are typical building automation and HVAC PLC applications.

Practice HVAC PLC programming today

Chiller, damper, boiler scenarios. No install. No credit card.

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