Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: HVAC Instrumentation and Control Devices
…234 unchanged lines
## Temperature sensing element type shall be selected for the service.
−## For most building points a 10k Ohm thermistor gives adequate accuracy at the lowest cost and is the default for space sensing. A 1000 Ohm platinum RTD is more linear and stable over a wide span and is preferred for immersion and critical air-handler points. A 4-20 mA transmitter is used where the run length or electrical noise makes a direct-resistance signal unreliable, and a BACnet MS/TP network sensor is used where the project's network architecture favors device-level addressing. {note}
+## For most building points a 10k Ω thermistor gives adequate accuracy at the lowest cost and is the default for space sensing. A 1000 Ω platinum RTD is more linear and stable over a wide span and is preferred for immersion and critical air-handler points. A 4-20 mA transmitter is used where the run length or electrical noise makes a direct-resistance signal unreliable, and a BACnet MS/TP network sensor is used where the project's network architecture favors device-level addressing. {note}
## Space temperature sensors shall be furnished as the selected element type.
…7 unchanged lines
- "4-20 mA transmitter"
- "BACnet MS/TP network sensor"
−default: "10k Ohm thermistor"
+default: "10k Ω thermistor"
```
…192 unchanged lines
## An outdoor CO2 reference sensor shall be provided where required to baseline high-occupancy DCV calculations.
−## ASHRAE 62.1 DCV math assumes a 400 ppm outdoor baseline. Actual outdoor CO2 at grade in dense urban locations runs 450 to 600 ppm, so a fixed 400 ppm assumption systematically under-ventilates. A measured outdoor reference removes that error in high-occupancy buildings; smaller projects in clean-air locations may omit it. {note}
−
```datasheet
label: Outdoor CO2 Reference Sensor
…5 unchanged lines
```
+## ASHRAE 62.1 DCV math assumes a 400 ppm outdoor baseline. Actual outdoor CO2 at grade in dense urban locations runs 450 to 600 ppm, so a fixed 400 ppm assumption systematically under-ventilates. A measured outdoor reference removes that error in high-occupancy buildings; smaller projects in clean-air locations may omit it. {note}
+
# Occupancy Sensors {toc}
## Occupancy sensors tied into the HVAC control loop shall use the selected sensing technology.
−## Passive infrared (PIR) alone detects motion and is adequate where occupants move regularly. Dual-technology sensors add ultrasonic or microwave detection and hold occupancy through low-motion activity such as seated desk work, preventing the HVAC from prematurely dropping a still-occupied zone to setback. This sensor is the HVAC loop's occupancy input only; sensors used solely for lighting are governed by [[sync/lighting-controls]]. {note}
−
```datasheet
label: HVAC Occupancy Sensor Technology
…5 unchanged lines
```
+## Passive infrared (PIR) alone detects motion and is adequate where occupants move regularly. Dual-technology sensors add ultrasonic or microwave detection and hold occupancy through low-motion activity such as seated desk work, preventing the HVAC from prematurely dropping a still-occupied zone to setback. This sensor is the HVAC loop's occupancy input only; sensors used solely for lighting are governed by [[sync/lighting-controls]]. {note}
+
## Occupancy sensors shall provide a discrete output to the HVAC controller for occupied/unoccupied determination.
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## Airflow measurement stations (AFMS) shall use the selected sensing technology.
−## A pitot-array (flow-cross) station averages velocity pressure across the duct and is robust and inexpensive, but loses accuracy at very low velocities where velocity pressure becomes negligible. A thermal-dispersion array measures mass flow directly and holds accuracy down to very low velocities, at higher cost, and is preferred for outdoor-air and minimum-ventilation measurement where the flow is small and the accuracy matters most. {note}
−
```datasheet
label: Airflow Measurement Station Type
…5 unchanged lines
```
+## A pitot-array (flow-cross) station averages velocity pressure across the duct and is robust and inexpensive, but loses accuracy at very low velocities where velocity pressure becomes negligible. A thermal-dispersion array measures mass flow directly and holds accuracy down to very low velocities, at higher cost, and is preferred for outdoor-air and minimum-ventilation measurement where the flow is small and the accuracy matters most. {note}
+
## Airflow measurement stations shall be furnished with a factory calibration certificate traceable to the as-built duct configuration.
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- Transmitters (1 of each type)
```