HVAC Sensor & Flow Switch Selection Guide
For the shared principles behind how every sensor works, see our How HVAC Sensors Work guide.
A building automation system is only as good as the sensors feeding it. This guide walks through matching the right sensor or switch to the question a control loop actually needs answered.
Step 1: What Question Does the Control Loop Need Answered?
| Question | Device type | Guide |
|---|---|---|
| Is fluid flowing, yes or no? | Flow switch | Paddle Water Flow Switches |
| Has a pressure differential crossed a threshold? | DP switch | Differential Pressure Switches |
| What is the actual airflow velocity? | Air velocity sensor | Air Velocity Sensors |
| What is the room/duct humidity level? | Humidity sensor/transmitter | Humidity Sensors |
| What is the temperature at this point? | Temperature sensor (wall/duct/immersion/outdoor) | Temperature Sensors |
| Should ventilation respond to occupancy or air quality? | CO2/enthalpy/occupancy sensor | CO2, Enthalpy & Occupancy Sensors |
| What current is a motor or pump drawing? | Current sensor | Current Sensors |
Step 2: Switch/Threshold vs Sensor/Continuous Output
Decide whether the control loop needs a simple threshold alarm (switch) or a continuous value for monitoring and modulating control (sensor/transmitter). This distinction repeats across every device category — flow switches vs flow sensors, DP switches vs DP transmitters, and so on.
Step 3: Match the Installation Format to the Application
- Wall-mounted for occupied-space readings (temperature, humidity, occupancy)
- Duct-mounted for airstream readings (temperature, humidity, air velocity)
- In-line/insertion for fluid flow and pressure (flow switches, DP switches)
- Outdoor for ambient conditions feeding economizer logic
Step 4: Confirm Signal Compatibility with the BMS
Sensors and transmitters output different signal types — dry contact, 4-20mA, 0-10V, or digital protocols like Modbus or BACnet. Confirm the device’s output matches what the building automation system’s input modules can accept before specifying.
Step 5: Consider Combined Devices
Several product lines Jaideo carries combine multiple measurements in one device — temperature and humidity together, or CO2 alongside general air quality — reducing installation points and wiring compared to specifying separate single-function devices.
Putting It Together
Sensor and switch selection comes down to identifying the control question, choosing switch vs continuous sensor, matching installation format, and confirming signal compatibility. Jaideo Automation can help specify the right combination for your BMS integration.
Frequently Asked Questions
What is the difference between a switch and a sensor in HVAC controls?
A switch gives a simple on/off signal when a threshold is crossed, while a sensor or transmitter provides a continuous value suitable for monitoring and modulating control.
What signal types do HVAC sensors commonly output?
Common output types include dry contact for switches, and 4-20mA, 0-10V, or digital protocols like Modbus or BACnet for sensors and transmitters, which must match the building automation system’s input modules.
Can one device measure more than one HVAC parameter?
Yes. Several combined sensors measure temperature and humidity together, or CO2 alongside broader air quality, reducing the number of installation points needed.