controlsfreak.dev /// FIELD REFERENCE LIVE
Jump to Signal Scaling BACnet/IP Hex Thermistor Psych Chart Electrical Calc All tools →

Field tools for those in building automation/controls, advanced HVAC, and many other adjacent fields. Built by a building automation programmer.

The math you don't want to redo in the mechanical room, on the roof, or at the panel — airflow and duct sizing, coils and psychrometrics, valve and pump sizing, signal scaling, BACnet/IP, and Modbus — plus explainers that walk a whole system end-to-end. No login, no ads, no tracking; view-source still works, and these pages will still run ten years from now.

Browse tools → Start with the explainers →

Three weeks in or thirty years in — the explainers start from the ground up.

Featured · Refrigerant Loop Simulator — now with heat-pump mode →

Live · AHU-1 supply-air temperature loop RUN
55.0 °F supply air 55.1 °F · valve 62 % Open the full PID Tuner →

The supervisor reads the supply-air sensor; the controller holds it at setpoint by modulating the cooling valve. Drag the setpoint and watch the loop chase it — then open the full PID Tuner to tune one yourself.

LIVE AHU-1 · holding setpoint v3.74.5 ·

Guides

REF :: BACNET OK
The BACnet reference hub →
Everything BACnet in one place — the lessons run in a start-here reading order (object model, services, networking, MS/TP, and BACnet vs Modbus), alongside the field tools that decode the units, errors, objects, and priorities a controller reports.
Start Here5 Lessons6 Tools
REF :: FORCED AIR OK
The forced-air reference hub →
The whole air side in one place — the lessons run from the air handler out to the VAV box and its commissioning, plus dedicated outdoor air, and the airflow, coil, and fan tools that measure, size, and check the air a system actually moves.
Start Here8 Lessons13 Tools
REF :: HYDRONICS OK
The hydronics reference hub →
The whole water side in one place — the lessons run from the loop and load piping through pump control and balancing, the valve, flow, and pump tools that size the water a system moves, and a live loop-builder sandbox.
Start Here5 Lessons4 Tools + Sim
REF :: REFRIGERATION OK
The refrigeration reference hub →
The refrigerant circuit in one place — the lessons run from the vapor-compression cycle through superheat and subcooling to the metering devices that hold it, plus the P-T and superheat calculator and a live loop simulator.
Start Here3 Lessons1 Tool + Sim

Tools by Category

TOOL :: HVAC LIVE
HVAC tools →
Psychrometric chart, economizer ratio, air mixing, coil sizing, coil freeze risk, dew point, refrigerant P-T, and power / energy conversion — the airside, refrigerant, and unit-conversion math on one filtered view.
PsychrometricsCoilsEconomizer8 tools
TOOL :: PROTOCOLS LIVE
Protocol tools →
Modbus register decoding and function codes, BACnet/IP hex addressing, the BACnet object reference, vendor-ID lookup, the engineering-units decoder, the error-code decoder, and the priority-array resolver — the bus-level conversions you hit mid-integration.
ModbusBACnet8 tools
TOOL :: SIGNALS LIVE
Signal tools →
Analog signal scaling (mA / V ↔ engineering units) and thermistor / RTD curves — the field-wiring math for getting a real number off a point.
Analog I/OSensors2 tools
TOOL :: AIRFLOW LIVE
Airflow tools →
Velocity pressure, duct traverse, airside load, equipment airflow check, minimum outdoor air, and duct sizing — measuring, checking, and sizing the air an air handler actually moves.
Velocity PressureDuctwork6 tools
TOOL :: ELECTRICAL LIVE
Electrical tools →
Control-transformer VA sizing, wire-run voltage drop, and a field quick-calc for Ohm's-law and power checks — the control-power and wiring math for panel work.
TransformersVoltage Drop3 tools
TOOL :: HYDRONICS LIVE
Hydronic tools →
Valve Cv sizing, valve authority, waterside load, and pump / fan affinity laws — sizing the wet side and predicting what speed changes do to flow, head, and power.
ValvesPumps4 tools

Browse

SECTION :: TOOLS OK
Calculators & lookups →
Calculators and lookups for the parts of the job that come up over and over — conversions, sizing checks, protocol decoding, and the reference tables that are never around when you need them. Open one, get an answer, get back to work.
CalculatorsLookupsConverters31 Tools
SECTION :: SIMULATORS OK
Run the models →
Running models you can poke at in the browser — bump the setpoints, force the faults, and watch loops, logic, and equipment respond live. Get a feel for the controls before you're standing in front of the real thing.
Hands-onSandboxesLive Models7 Simulators
SECTION :: EDUCATION OK
Learn the fundamentals →
A connected set of explainers, not a glossary — lessons on the loops, systems, and protocols behind the day-to-day work, each asking one question and answering it with diagrams, worked examples, and the occasional interactive widget.
ExplainersDiagramsWidgets40 Lessons
SECTION :: PRACTICE OK
Quiz yourself →
Active-recall quizzes that pair with the lessons, plus broader field drills — interview-and-cert-style scenarios, protocol quirks, and troubleshooting. New to the field? Surviving Your First Months is the gentlest place to start.
QuizzesField DrillsActive Recall41 Total

About

Role Controls Programmer
Industry BAS / Building Automation
Location Northeast U.S.
REV 2026-05-24
Status Active

Hi, I'm a controls programmer based in the Northeast U.S. This is a side project I'm working on while exploring vibe coding. There's a genuine gap in easy reference websites and educational resources for this trade. This site started as just a way to have some easy reference tools in one place, but has expanded to include much more. Teaching those in the trade has been a passion of mine since I began to grow my own knowledge. With this project I aim to do that with a broader audience. I try to verify the accuracy of everything on this site the best that I can, but if anything is incorrect, please contact me and I will ensure I fix the accuracy issue. If there are any specific tools or topics you want to see covered, I want to hear about it!

The path here was a little roundabout. I started college for electrical engineering, and pretty quickly realized that learning the theory without getting my hands on it didn't sit right — I wanted to be doing the work, not just reading about it. Between electronics, electrical, and mechanical tinkering going back to when I was a kid, controls turned out to be the place where all of that overlapped. I left school to find a controls role, and the field's been the right fit since.

Day-to-day, the work splits between new-construction programming, retro-commissioning on existing systems, and the troubleshooting calls that always seem to pile up alongside. Most of it lands on institutional and education buildings — schools, universities — and light industrial sites. The teaching impulse that ended up shaping this site started kicking in once new hires began showing up on jobs alongside me; walking somebody through their first sequence of operations, or just showing them what a real panel actually looks like behind the door, turned out to be some of the more satisfying parts of the trade.

Bug reports, tool requests, or feedback — get in touch.