Education

Practical lessons for techs new to the industry. All of these are based on things I struggled with when I was new. This includes how a system actually works, why it's piped or wired the way it is, and what the equipment is doing. Not calculators (those live in Tools). If you have any requests or corrections, feel free to reach out.

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LESSON :: PID BASICS READ

What proportional, integral, and derivative actually do on an HVAC loop — with three small sims you can play with one knob at a time.

PIDP · I · D3 Mini Sims

LESSON :: CONTROLLER WIRING READ

Controller Wiring

How a field point lands on a DDC controller — 24 VAC power and the shared common, the input and output types, and the wiring gotchas that bite. Pairs with the Controller Wiring Simulator.

Wiring24 VAC + CommonUI / BI / AO / BOField Gotchas

LESSON :: COMMISSIONING READ

Controls Commissioning

Proving a controller does what its sequence of operations says — point-to-point checkout of every AI, AO, BI, and BO, override discipline, interlock and reset testing, and trend logs as proof over time.

CommissioningPoint-to-PointAI · AO · BI · BOOverrides

LESSON :: HYDRONIC LOOPS READ

How water gets around a building — 2-pipe direct vs. reverse return, and why the closely-spaced tees on a boiler aren't a piping mistake.

HydronicsDirect ReturnReverse ReturnPrimary / Secondary

LESSON :: LOAD PIPING READ

Two-way vs three-way valves at the load — variable vs constant system flow, when each one fits, and how the choice shapes the rest of the loop.

Hydronics2-Way Valves3-Way ValvesVariable / Constant

LESSON :: VFDS READ

What a variable frequency drive does, the cube-law energy story, and the run-command vs. speed-reference parameters every controls tech meets — with a widget for the configuration mistake that catches everyone.

DrivesCube LawRun / Speed SourceWidget

LESSON :: PUMP CONTROL READ

How the BMS controls a hydronic pump — pump curves and the operating point, DP control with a remote sensor, and DP setpoint reset. Pairs with VFDs and Load Piping.

HydronicsPump CurveDP ControlSetpoint Reset

LESSON :: EQUIPMENT STAGING READ

Equipment Staging

How a BMS staging sequence decides how many parallel pumps to run, when to add or drop one, and which pump leads — with widgets for staging delays and lead/lag rotation.

SequencingStage Up / DownLead / LagRotation

LESSON :: BALANCING READ

Hydronic Balancing

Getting design flow to every load — calibrated balancing valves, automatic balancing valves, and PICVs. With a widget that shows what each one does when system pressure swings.

HydronicsManual / Auto / PICVDesign FlowWidget

LESSON :: COIL SELECTION READ

Where the design flow a balancer chases actually comes from — the load-to-flow chain (q = ṁ·cp·ΔT), why the chosen ΔT sets the GPM, and the coil levers (rows, fins, face velocity, approach) that meet the capacity.

HydronicsLoad → FlowDesign ΔTRows · Face Velocity

LESSON :: REFRIGERANT CYCLE READ

Refrigerant Cycle Basics

How a vapor-compression system moves heat — the four components, high side vs low side, and the saturation P-T relationship behind every refrigerant sensor reading.

HVAC4 ComponentsHigh vs Low SideP-T

LESSON :: SUPERHEAT & SC READ

Superheat & Subcooling

The two measurements that prove a refrigerant cycle is running right — what each measures, the sensors that compute them, and what abnormal readings tell you.

HVACSuperheatSubcoolingFault Direction

LESSON :: TXV VS EEV READ

The two metering-device designs that hold superheat at a target — the TXV's mechanical force balance and the EEV's controller-driven stepper loop.

HVACTXVEEVForce Balance

LESSON :: PSYCHROMETRICS READ

Psychrometrics Basics

The seven properties on a psychrometric chart, what each one tells a controls engineer, and the gotchas that bite — with a pool-room widget that shows why dew point is the number to watch.

HVAC7 PropertiesPool-Room WidgetDew Point

LESSON :: AHUS READ

Follow one parcel of air through an air handler — return and relief, the mixing box at minimum outside air, filter, coils, and the supply fan — with a sensor-strip widget that walks the unit like a BMS graphic.

Air SystemsMixing BoxCoils · FanSensor Strip

LESSON :: ECONOMIZERS READ

When an air handler should cool with outside air instead of the coil — the linked damper assembly, dry-bulb vs enthalpy changeover with a live explorer widget, integrated staging, and the field failure modes.

Air SystemsFree CoolingChangeoverExplorer Widget

LESSON :: BUILDING PRESSURE READ

Building Pressure

Why a building goes positive or negative — the air ledger, barometric relief vs power exhaust vs return-fan tracking, and a live ledger widget where you balance the building yourself.

Air SystemsAir LedgerPower ExhaustLedger Widget

LESSON :: UNIT IDENTIFICATION READ

Unit Identification

Standing in front of an unfamiliar air-side unit — three field questions, the RTU / AHU / MAU / split lineup, nameplate and schedule literacy, and a lineup-walker widget with mysteries to solve.

Air SystemsRTU · AHU · MAUNameplatesLineup Walker

LESSON :: VAV SYSTEMS READ

One cold trunk, thirty throttles — the flow ring and CFM = K·√VP, pressure independence, minimums and reheat, and a widget that starves a DX coil.

Air SystemsBoxes · ReheatFlow RingsBox Walker

LESSON :: DUCT STATIC READ

Duct Static Control

How the supply fan finds its speed — one sensor two-thirds down the trunk, setpoint reset, the safeties, and why a healthy static can hide a collapsed airflow.

Air SystemsFan · VFDSetpoint ResetLoop Driver

LESSON :: AIR BALANCING READ

Commissioning the air side to design flow — verifying box CFM against a traverse, setting box min, max and reheat, proportional balancing against the index zone, and building pressure.

Air SystemsFlow Rings · K√VPMin · Max · ReheatProportional

LESSON :: DOAS READ

Dedicated Outdoor Air (DOAS)

The unit that conditions 100% outdoor air and decouples ventilation and latent load from sensible — the deep coil and reheat, energy recovery, dew-point control, and terminals that handle the space.

Air SystemsLatent / SensibleDeep Coil · ReheatDew-Point Control

LESSON :: FUNCTION BLOCKS READ

Function-Block Basics

What a function block and a wiresheet are, why building-controls sequences are built from boxes-and-wires, and how a sheet evaluates — paired with the Function-Block Editor.

LogicWiresheetEvaluation Order

LESSON :: MODBUS READ

What Modbus is, how a request looks on the wire, the four data tables, the function codes that read and write them, and what an exception response means.

Modbus4 Data TablesFunction CodesExceptions

LESSON :: MODBUS DECODING READ

Modbus Decoding

Why a Modbus value comes back wrong even when the read succeeded — the 5-digit register trap, signed vs unsigned, the four byte orders, and scaling.

Modbus5-Digit TrapSigned / UnsignedByte Order

LESSON :: BACNET VS MODBUS READ

BACnet vs Modbus

Two protocols side by side — self-describing objects versus raw registers, discovery, COV versus polling, priority versus last-write, and where a gateway bridges them.

Objects vs RegistersDiscoveryCOV vs PollGateways

LESSON :: BACNET READ

BACnet on the wire — the self-describing object model, the services that read and write properties, the priority array, and Who-Is / I-Am discovery.

BACnetObject ModelPriority ArrayWho-Is / I-Am

LESSON :: BACNET SERVICES READ

BACnet Services

The verbs of BACnet — confirmed vs unconfirmed, the service families, and BIBBs and device profiles that say which services a device actually supports.

BACnetServicesBIBBsDevice Profiles

LESSON :: BACNET NETWORKING READ

BACnet Networking

BACnet networking — the three layers of addressing, the BVLL/NPDU/APDU frame, BBMDs and Foreign Device Registration, and reading the EBO hex blob.

BACnet3 Addr LayersBVLL / NPDU / APDUBBMD / FDR

LESSON :: BACNET MS/TP READ

Why devices fall off an MS/TP trunk — the token ring and Max_Master, MAC address vs device instance, termination / biasing / polarity, and a symptom-to-layer table.

BACnetToken RingMax_MasterTermination