But the truth is very simple:
NO global standard (ASHRAE, IEC, ANSI) forces you to use a specific sensor type in BMS.

🟢🟢So what do standards actually tell us?

🟢 What ASHRAE REALLY Specifies
1. Accuracy requirements
2. Sensor placement (where to mount in duct/pipe/room)
3. Response time
4. Environmental protection (IP rating, insulation, shielding)
5. Calibration & test methods

🟢But they do not say:
“Use Pt1000 for water”
“Use 10k Thermistor for duct”
“Use Ni1000 for return air”
These choices are driven by engineering judgement + controller capability + project specifications.

🟢 Related Standards You Should Know
1. ASHRAE Guideline 36 - sensor accuracy & placement
2. ASHRAE Standard 41.1 - temperature measurement method
3. ASHRAE Handbook - application guidance (air vs water sensors)
4. IEC 60751 - platinum RTD accuracy classes
5. UL 873 - safety for temperature devices

None of them specify which resistance type to use.

🟢 So How Do We Decide Which Sensor to Use?
Here’s the industry-recommended best practice
a. Pt1000 (Platinum RTD)
1. Best for chilled water & hot water lines
2. High accuracy, stable, long cable runs
3. Used in BTU meters & critical applications
b. 10kΩ Thermistor (Type II / Type III)
1. Most common for comfort sensing
2. Supply air / return air / mixed air / room sensors
c. 2.2kΩ Thermistor
1. OEM units, VAV boxes, general duct sensing
d. Ni1000
1. Mainly for legacy Siemens/JCI systems

🟢 Final Takeaway
1. Standards tell you HOW to measure temperature.
2. They don’t tell you WHICH sensor to choose.
3. Sensor type selection is always engineering-driven.

If you're designing, submittal reviewing, or commissioning BMS systems, understanding this difference helps you avoid project conflicts and ensures accurate control.