+---
+title: HVAC Instrumentation and Control Devices
+category: Mechanical / Controls & Testing
+toc_depth: 3
+description: >
+ When to use: Specifying the field layer of HVAC control devices for commercial,
+ institutional, and light-industrial buildings (new construction or major renovation):
+ space, duct, immersion, and outdoor temperature/humidity sensors; differential-pressure
+ transmitters for duct static, hydronic, and filter applications; CO2 sensors for
+ demand-controlled ventilation; occupancy sensors in the HVAC loop; airflow measurement
+ stations; unitary/terminal thermostats; and electric valve and damper actuators furnished
+ under the controls scope. Covers device selection, accuracy, enclosure, mounting,
+ termination, and field calibration/verification for devices wired to BAS field
+ controllers over hardwired, BACnet MS/TP, BACnet/IP, or Modbus RTU networks.
+ Not intended for: BAS controllers, network architecture, programming, and sequences of
+ operation (use [[sync/building-automation-system]]); testing, adjusting, and balancing
+ (use [[sync/testing-adjusting-and-balancing]]); functional performance testing and
+ commissioning (use [[sync/commissioning]]); industrial process control valves and
+ positioners (use [[sync/control-valves-and-actuators]]); industrial process
+ instrumentation and flow measurement (use [[sync/process-instrumentation]] and
+ [[sync/flow-measurement]]); the damper, louver, and damper-body assemblies the actuator
+ mounts on (use [[sync/louvers-and-dampers]]); ductwork and hydronic piping (use
+ [[sync/hvac-ductwork]] and [[sync/hydronic-piping]]); control wiring conductors and
+ raceways (use [[sync/conductors-and-cables]] and [[sync/raceways-and-conduit]]); VFD
+ speed-reference points (use [[sync/hvac-variable-frequency-drives]]); lighting-only
+ occupancy sensors (use [[sync/lighting-controls]]); and fire alarm duct smoke detectors
+ (use [[sync/fire-alarm-systems]]).
+---
+
+# Scope {toc}
+
+## This standard governs the field layer of the HVAC controls system: the sensing elements, transmitters, thermostats, and actuators that gather signals for and execute commands from the building automation system. {note}
+
+## It begins at the field controller's terminal strip and extends outward to the point of measurement or actuation. Everything from the controller inward — the controller itself, the network, programming, and the written sequences of operation — belongs to [[sync/building-automation-system]]. Drawing the boundary at the controller terminal keeps two different trades and two different submittal reviews from overlapping at the most error-prone seam in a controls installation. {note}
+
+## The devices covered are the physical instruments a technician can touch, calibrate, and replace. {note}
+
+## This includes space temperature sensors and wall thermostats; duct, mixed-air, immersion, and outdoor temperature and humidity sensors; differential-pressure transmitters for duct static, hydronic, and filter applications; CO2 sensors for demand-controlled ventilation; occupancy sensors tied into the HVAC loop; airflow measurement stations; and electric valve and damper actuators furnished under the controls scope. {note}
+
+## Devices shall be furnished, installed, terminated, field-calibrated, and point-to-point verified under this section prior to testing, adjusting, and balancing.
+
+## Devices shall be compatible with the building automation system controllers and network protocols specified in [[sync/building-automation-system]].
+
+## Each device shall be selected to satisfy the sensor inputs and actuator outputs required by the project's sequences of operation.
+
+## ASHRAE Guideline 36 is the best single reference for determining which inputs and outputs a given system type requires; the sequences themselves are owned by the BAS standard, but the device list must satisfy them. {note}
+
+## The following work is explicitly excluded from this standard and is governed elsewhere. {note}
+
+## The boundaries below are stated as scope exclusions, not obligations, because no one performs them under this section. {note}
+- BAS controllers, network architecture, operator workstations, programming, sequences of operation, scheduling, alarming, trending, and cybersecurity — [[sync/building-automation-system]].
+- Testing, adjusting, and balancing, including instrument-calibrated airflow and water-flow measurement by a TAB agency — [[sync/testing-adjusting-and-balancing]].
+- Building commissioning and functional performance testing of integrated systems — [[sync/commissioning]].
+- Industrial and process modulating control valves and valve positioners — [[sync/control-valves-and-actuators]].
+- Process pressure, level, and temperature instrumentation with process-grade RTDs and thermowells — [[sync/process-instrumentation]].
+- Industrial and process flow measurement instruments — [[sync/flow-measurement]].
+- Louver and damper bodies, including volume-control, fire, and smoke dampers; only the actuator mounted on the body is covered here — [[sync/louvers-and-dampers]].
+- HVAC ductwork materials and construction — [[sync/hvac-ductwork]].
+- Hydronic piping materials and specialties — [[sync/hydronic-piping]].
+- Control conductors, signal cable, and control wire — [[sync/conductors-and-cables]].
+- Raceways and conduit methods for control wiring — [[sync/raceways-and-conduit]].
+- HVAC variable-frequency drives and their integral speed-reference points — [[sync/hvac-variable-frequency-drives]].
+- Lighting occupancy sensors used solely for lighting control — [[sync/lighting-controls]].
+- Fire alarm duct smoke detectors installed and tested under the fire alarm contract — [[sync/fire-alarm-systems]].
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+| Standard | Title |
+|----------|-------|
+| ANSI/ASHRAE 135-2024 | BACnet — A Data Communication Protocol for Building Automation and Control Networks |
+| ANSI/ASHRAE/IES 90.1-2022 | Energy Standard for Buildings Except Low-Rise Residential Buildings |
+| ANSI/ASHRAE 62.1-2022 | Ventilation and Acceptable Indoor Air Quality |
+| ASHRAE Guideline 13-2015 | Specifying Direct Digital Control Systems |
+| ASHRAE Guideline 36-2021 | High-Performance Sequences of Operation for HVAC Systems |
+| NFPA 70 | National Electrical Code (Articles 725, 800, 430) |
+| NFPA 90A-2024 | Standard for the Installation of Air-Conditioning and Ventilating Systems |
+| UL 916 | Energy Management Equipment |
+| UL 60730-1 | Automatic Electrical Controls — General Requirements |
+| NEMA 250-2020 | Enclosures for Electrical Equipment (1000 V Maximum) |
+| IEC 60529 | Degrees of Protection Provided by Enclosures (IP Code) |
+| ISA-5.1-2009 | Instrumentation Symbols and Identification |
+| ANSI/ISA-51.1-1979 (R1993) | Process Instrumentation Terminology |
+| AMCA 500-D | Laboratory Methods of Testing Dampers for Rating |
+
+# Submittals {toc}
+
+## The Contractor shall submit the following action submittals for review and approval prior to procurement:
+- Product data for each sensor, transmitter, thermostat, and actuator type, including accuracy, range, output signal, supply voltage, and enclosure rating.
+- A device schedule cross-referenced to the control drawings by ISA-5.1 tag number, listing service, location, range, and accuracy for each point.
+- Shop drawings showing sensor mounting details, immersion well lengths, averaging-element insertion depths, and actuator-to-damper or actuator-to-valve linkage.
+- Actuator torque calculations for each damper, including damper area, blade-seal friction allowance, and applied safety factor.
+- Wiring termination diagrams showing field device to controller terminal assignments and circuit classification per NFPA 70 Article 725.
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - Product data for each device type
+ - Device schedule keyed to ISA-5.1 tags
+ - Mounting and insertion shop drawings
+ - Damper actuator torque calculations
+ - Wiring termination diagrams
+default:
+ - Product data for each device type
+ - Device schedule keyed to ISA-5.1 tags
+ - Mounting and insertion shop drawings
+ - Damper actuator torque calculations
+ - Wiring termination diagrams
+```
+
+## The Contractor shall submit the following informational submittals:
+- NIST-traceable factory calibration certificates for all CO2 sensors and for temperature transmitters serving air-handler supply-air and mixed-air points.
+- Manufacturer installation instructions for each device type.
+- A field calibration and point-to-point verification report for every installed device, completed before TAB begins.
+
+```datasheet
+label: Informational Submittals Required
+type: checkbox
+options:
+ - Factory calibration certificates (CO2 and critical TT)
+ - Manufacturer installation instructions
+ - Field calibration and point-to-point report
+default:
+ - Factory calibration certificates (CO2 and critical TT)
+ - Manufacturer installation instructions
+ - Field calibration and point-to-point report
+```
+
+## The Contractor shall submit the following closeout submittals:
+- Operation and maintenance data including recommended recalibration intervals for CO2 and humidity sensors.
+- A final as-installed device schedule reflecting field changes, with tag numbers reconciled to the control and mechanical drawings.
+
+```datasheet
+label: Closeout Submittals Required
+type: checkbox
+options:
+ - O&M data with recalibration intervals
+ - Final as-installed device schedule
+default:
+ - O&M data with recalibration intervals
+ - Final as-installed device schedule
+```
+
+# Quality Assurance {toc}
+
+## Devices shall be the products of manufacturers regularly engaged in the production of HVAC field instrumentation and actuators.
+
+## Electronic thermostats, room sensors, and energy-management controllers shall be listed under UL 916.
+
+## Thermostats and space sensors shall comply with the applicable safety requirements of UL 60730-1.
+
+## A factory calibration certificate is not a substitute for field verification. {note}
+
+## Field-installed sensors are frequently shipped uncalibrated or drift during shipping and handling. Requiring a NIST-traceable factory certificate establishes the as-shipped baseline; the field verification below confirms the device still reads true after installation. Both are required for the critical points. {note}
+
+## Installed sensor accuracy shall be field-verified to within 1.5 times the manufacturer's rated accuracy over the device's operating range.
+
+## Sensors failing the field verification tolerance shall be replaced, not adjusted, before TAB begins.
+
+## Sensor accuracy shall be re-verified after TAB completion at points affected by balancing.
+
+## Sensor tag numbers shall follow ISA-5.1 format.
+
+## Sensor tag numbers shall be identical across the control, mechanical, and electrical contract documents.
+
+## A supply-air temperature transmitter on AHU-1 carried as TT-AHU-1-SA on one drawing set and as something else on another is a guaranteed installation error and a recurring source of controls RFIs. Tag consistency is a quality-assurance requirement, not a drafting nicety. {note}
+
+# Environmental and Service Conditions {toc}
+
+## Enclosure type shall be selected for the installed environment per NEMA 250.
+
+## Enclosure selection is a function of where the device lives, not of the device itself. The same transmitter may be Type 1 in a dry electrical room and Type 4X on a corrosive rooftop. IEC 60529 IP ratings are an acceptable equivalent basis where a manufacturer rates only to the IP code: IP54 is roughly equivalent to NEMA Type 12, and IP65 to NEMA Type 4. {note}
+
+## Devices in dry, conditioned interior locations shall be furnished in NEMA Type 1 enclosures.
+
+## Devices in mechanical rooms, boiler rooms, and exterior locations shall be furnished in NEMA Type 4 enclosures.
+
+## Devices in pool, chemical, or other corrosive environments shall be furnished in NEMA Type 4X (stainless) enclosures.
+
+## Devices in classified hazardous locations shall be furnished in explosion-proof enclosures listed to UL 1203.
+
+```datasheet
+label: Device Enclosure Type by Location
+type: select
+options:
+ - "NEMA Type 1 (dry interior)"
+ - "NEMA Type 4 (mechanical room, exterior)"
+ - "NEMA Type 4X (corrosive / washdown, stainless)"
+ - "Explosion-proof, UL 1203 (classified hazardous)"
+default: "NEMA Type 1 (dry interior)"
+```
+
+## Devices shall be rated for the temperature, humidity, and vibration of their installed location without degradation of stated accuracy.
+
+# Power and Signal {toc}
+
+## Sensor and device power shall be 24 VAC or 24 VDC Class 2 per NFPA 70 Article 725.41.
+
+## Class 2 power limiting keeps the field wiring inside the energy thresholds that permit plenum-rated cable without conduit in many jurisdictions and bounds the fault energy at the sensing element. The conductors and raceways themselves are governed by [[sync/conductors-and-cables]] and [[sync/raceways-and-conduit]]; this standard fixes only the device-side voltage and circuit class. {note}
+
+## For two-wire 4-20 mA loop-powered devices, maximum loop resistance shall be verified against the specified supply voltage before installation.
+
+## A 4-20 mA loop has a finite voltage budget. If the sum of the device burden, the wiring resistance, and the controller input resistance exceeds what the supply can drive, the transmitter saturates below 20 mA and the reading clips at the top of the range. This is checked on paper at submittal, not discovered at startup. {note}
+
+## Sensor supply voltage shall be selected to match the device input requirement.
+
+```datasheet
+label: Sensor Supply Voltage
+type: radio
+options:
+ - "24 VAC, Class 2"
+ - "24 VDC, Class 2"
+default: "24 VAC, Class 2"
+```
+
+## Device output signal type shall match the receiving BAS controller input.
+
+```datasheet
+label: Analog Sensor Output Signal
+type: select
+options:
+ - "4-20 mA"
+ - "0-10 VDC"
+ - "2-10 VDC"
+ - "RTD (1000 Ω platinum, direct)"
+ - "Thermistor (10k Ω, direct)"
+ - "BACnet MS/TP (network)"
+default: "4-20 mA"
+```
+
+# Temperature Sensors {toc}
+
+## 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}
+
+## Space temperature sensors shall be furnished as the selected element type.
+
+```datasheet
+label: Space Temperature Sensor Element
+type: radio
+options:
+ - "10k Ω thermistor"
+ - "1000 Ω platinum RTD"
+ - "4-20 mA transmitter"
+ - "BACnet MS/TP network sensor"
+default: "10k Ohm thermistor"
+```
+
+## Space temperature sensors shall hold their rated accuracy over the full 40°F to 95°F operating range.
+
+## An accuracy figure with no stated span is meaningless: a device can be ±0.5°F at 70°F and ±3°F at the ends of its range. Stating the operating span over which the accuracy must hold is what makes the specification enforceable. {note}
+
+## Space temperature sensor accuracy shall meet the selected class.
+
+```datasheet
+label: Space Temperature Sensor Accuracy
+type: radio
+options:
+ - "Standard, ±1.0°F (±0.5°C)"
+ - "High-accuracy, ±0.5°F (±0.25°C) for critical/laboratory spaces"
+default: "Standard, ±1.0°F (±0.5°C)"
+unit: °F
+```
+
+## Space temperature sensors shall be located to read representative occupied-zone conditions.
+
+## Poor sensor placement is the single most common cause of comfort complaints that no amount of controller tuning can fix. Sensors on exterior walls read the wall, not the room; sensors under a supply diffuser read the supply air; sensors near a radiant panel or in direct solar gain read the source, not the occupant. {note}
+
+## Space temperature sensors shall be mounted a minimum of 5 ft from any heat source and 18 in from the nearest supply register per ASHRAE Guideline 13.
+
+## Space temperature sensors shall not be located on exterior walls, above ceiling supply diffusers, adjacent to radiant panels, or in positions subject to direct solar radiation.
+
+## Space sensor location shall be coordinated with the architectural reflected ceiling and elevation drawings. [[drawing: space sensor mounting locations]]
+
+## Duct and mixed-air temperature sensors shall be averaging type with the selected insertion length.
+
+```datasheet
+label: Duct Averaging Temperature Sensor Insertion Length
+type: select
+options:
+ - "12 in"
+ - "18 in"
+ - "24 in"
+default: "18 in"
+unit: in
+```
+
+## Duct, mixed-air, immersion, and outdoor temperature sensors shall hold ±0.5°F accuracy at 70°F.
+
+## Factory calibration certificates shall be furnished for air-handler supply-air and mixed-air temperature sensors.
+
+## Mixed-air sensors shall be of sufficient averaging length to span the full duct cross-section.
+
+## Mixed air stratifies: the cold outdoor stream and the warm return stream do not blend completely within the mixing box. A short single-point sensor placed in either stream reports a temperature that does not exist anywhere the air is actually delivered, which corrupts every economizer and freeze-protection decision downstream. A serpentine averaging element that crosses the full duct face is the only reliable way to read true mixed-air temperature. {note}
+
+## Immersion temperature sensors in hydronic piping shall be furnished with thermowells of the selected insertion length.
+
+```datasheet
+label: Immersion Sensor Thermowell Insertion Length
+type: select
+options:
+ - "2.5 in"
+ - "4 in"
+ - "6 in"
+default: "4 in"
+unit: in
+```
+
+## Immersion sensors in systems above 140°F, or in any system requiring sensor replacement under pressure, shall be installed in thermowells.
+
+## A thermowell lets a sensor be pulled and replaced without draining the system or scalding the technician, and it isolates the element from the pressure boundary. Thermowell length and insertion depth must match the pipe diameter and the sensor element length so the tip sits in the flowing stream, not in a stagnant boundary layer at the wall. Coordinate the immersion taps with [[sync/hydronic-piping]]. {note}
+
+## Outdoor air temperature and humidity sensors shall be furnished in a NEMA 4X housing with a passive radiation shield.
+
+## A bare outdoor sensor in sunlight reads the solar load on its own housing, not the air, and can run many degrees high on a clear day. A ventilated radiation shield is what makes an outdoor reading usable for economizer and reset logic. {note}
+
+# Humidity Sensors {toc}
+
+## Humidity sensing technology shall be capacitive thin-film polymer.
+
+## Capacitive thin-film elements are the building-controls standard: they recover from saturation, resist contamination better than bulk-polymer elements, and hold accuracy over a wide range. Bulk-polymer elements are cheaper but drift faster and are reserved for non-critical monitoring. {note}
+
+## Humidity sensor accuracy shall meet the selected class.
+
+```datasheet
+label: Humidity Sensor Accuracy
+type: radio
+options:
+ - "Standard, ±3% RH (capacitive)"
+ - "Precision, ±2% RH (data center, archival)"
+default: "Standard, ±3% RH (capacitive)"
+unit: "% RH"
+```
+
+## Combined temperature/humidity elements shall be furnished where both points are required at the same location.
+
+```datasheet
+label: Humidity Sensor Configuration
+type: radio
+options:
+ - "Combined temperature/humidity element"
+ - "Separate humidity element"
+default: "Combined temperature/humidity element"
+```
+
+## Duct-mounted humidity sensors shall be located a minimum of three duct widths downstream of any cooling coil.
+
+## Air leaving a cooling coil at part load is at or near saturation, and condensate carried onto a capacitive element destroys it. Locating the sensor well downstream gives the air room to mix and warm above its dew point before it reaches the element. {note}
+
+## Duct-mounted humidity sensors in condensation-prone locations shall include a condensation-protection provision such as a hydrophobic filter or heated element.
+
+# Differential-Pressure Transmitters {toc}
+
+## Differential-pressure transmitters shall be electronic piezoresistive type.
+
+## Piezoresistive transmitters are stable, have no moving linkage to wear, and provide a clean analog or network output. Mechanical pressure switches and gauges are reserved for simple local indication and high/low limit safeties, not for the modulating control and reset inputs this section covers. {note}
+
+## Differential-pressure transmitter range shall be selected so the design setpoint falls at 50% to 60% of full scale.
+
+## A transmitter operating at the bottom of its range wastes resolution and amplifies sensor noise into the control loop; one operating near full scale clips during transients. Placing the design setpoint near mid-scale gives headroom in both directions and the best signal-to-noise for reset control. {note}
+
+## Duct static pressure transmitters shall be furnished with the selected range and ±1% full-scale accuracy.
+
+```datasheet
+label: Duct Static Pressure Transmitter Range
+type: select
+options:
+ - "0 to 1 in WC (terminal duct)"
+ - "0 to 3 in WC (AHU supply duct)"
+ - "0 to 5 in WC"
+default: "0 to 3 in WC (AHU supply duct)"
+unit: in WC
+```
+
+## Duct static pressure sensors shall be located approximately two-thirds of the way down the longest duct run, not at the air-handler discharge.
+
+## ASHRAE Guideline 36 requires the static pressure sensor be located remote from the fan. Sensing at the discharge makes the static-pressure-reset logic travel a much wider band than necessary and starves the terminal boxes at the end of the run, the exact opposite of what duct static reset is meant to achieve. {note}
+
+## Duct static pressure sensor location shall be coordinated with the ductwork layout. [[drawing: duct static sensor location]]
+
+## Building (room differential) static pressure transmitters shall be furnished with a ±0.25 in WC range and ±1% full-scale accuracy.
+
+## Hydronic differential-pressure transmitters shall be furnished with the selected range and ±0.5% full-scale accuracy.
+
+```datasheet
+label: Hydronic Differential-Pressure Transmitter Range
+type: select
+options:
+ - "0 to 30 PSI (chilled/hot water ≤150 PSI systems)"
+ - "0 to 50 PSI"
+default: "0 to 30 PSI (chilled/hot water ≤150 PSI systems)"
+unit: PSI
+```
+
+## Filter differential-pressure transmitters shall be ranged to read clean-to-final pressure drop across the served filter bank.
+
+# CO2 and Demand-Controlled Ventilation {toc}
+
+## CO2 sensors shall be non-dispersive infrared (NDIR) type.
+
+## NDIR is the only technology accurate and stable enough for ventilation control. Dual-beam NDIR, which uses a reference wavelength to cancel lamp aging and window fouling, is preferred over single-beam for long-term stability without constant recalibration. {note}
+
+## ASHRAE 90.1-2022 Section 6.4.3 mandates demand-controlled ventilation for zones with a design occupant density of 25 people or more per 1000 ft². {note}
+
+## Where the energy code triggers DCV, CO2 sensing is the input that drives it, so the sensor selection below is code-driven, not optional, for those zones. ASHRAE 62.1-2022 governs the ventilation calculation the DCV logic executes. {note}
+
+## CO2 sensors shall be furnished with the selected technology and range.
+
+```datasheet
+label: CO2 Sensor Technology and Range
+type: select
+options:
+ - "Dual-beam NDIR, auto-calibrating, 0-2000 ppm"
+ - "Dual-beam NDIR, 0-5000 ppm"
+ - "Single-beam NDIR, 0-2000 ppm"
+default: "Dual-beam NDIR, auto-calibrating, 0-2000 ppm"
+unit: ppm
+```
+
+## CO2 sensors shall meet an accuracy of ±50 ppm or ±3% of reading, whichever is greater, per ASHRAE 62.1.
+
+## CO2 sensors shall warm up to within stated accuracy in 3 minutes or less.
+
+## Automatic baseline calibration (ABC) shall be disabled in continuously occupied (24/7) spaces.
+
+## CO2 sensors in continuously occupied spaces shall be manually recalibrated every 12 months.
+
+## ABC logic assumes the space empties and falls to outdoor CO2 concentration at least once every seven days, then resets its zero to that low point. A 24/7 facility never reaches that baseline, so ABC drifts its zero upward and reports falsely low CO2, which starves the space of ventilation exactly when it is occupied. In those spaces ABC must be turned off and the sensor calibrated by hand on a schedule. {note}
+
+## ABC selection shall be set per the space occupancy pattern.
+
+```datasheet
+label: CO2 Sensor Auto-Baseline Calibration (ABC)
+type: radio
+options:
+ - "ABC enabled (intermittently occupied spaces)"
+ - "ABC disabled, manual recalibration every 12 months (continuously occupied)"
+default: "ABC enabled (intermittently occupied spaces)"
+```
+
+## 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
+type: radio
+options:
+ - "Provided (high-occupancy / urban baseline)"
+ - "Not provided (assume 400 ppm outdoor baseline)"
+default: "Not provided (assume 400 ppm outdoor baseline)"
+```
+
+# 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
+type: radio
+options:
+ - "Passive infrared (PIR) only"
+ - "Dual-technology (PIR + ultrasonic/microwave)"
+default: "Dual-technology (PIR + ultrasonic/microwave)"
+```
+
+## Occupancy sensors shall provide a discrete output to the HVAC controller for occupied/unoccupied determination.
+
+## Occupancy sensor coverage and mounting location shall be coordinated with the served zone. [[drawing: occupancy sensor coverage]]
+
+# Thermostats {toc}
+
+## Electronic thermostats for unitary and terminal equipment shall be UL 916 listed and shall comply with UL 60730-1.
+
+## Thermostats serving BAS-integrated equipment shall communicate to the controller over the project network protocol.
+
+## A networked thermostat exposes its setpoint, mode, and space temperature to the BAS for scheduling, reset, and trending. A standalone thermostat is an island the operator cannot see or override remotely, acceptable only where the served equipment is genuinely outside the BAS scope. {note}
+
+## Thermostat communication and adjustment scope shall be selected for the application.
+
+```datasheet
+label: Thermostat Type
+type: radio
+options:
+ - "BACnet MS/TP networked thermostat"
+ - "Standalone electronic thermostat (non-networked)"
+default: "BACnet MS/TP networked thermostat"
+```
+
+## User-adjustable setpoint range and override authority shall be limited to the values established by the project's energy and comfort requirements.
+
+# Airflow Measurement Stations {toc}
+
+## 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
+type: radio
+options:
+ - "Pitot-array (flow cross)"
+ - "Thermal dispersion"
+default: "Thermal dispersion"
+```
+
+## Airflow measurement stations shall be furnished with a factory calibration certificate traceable to the as-built duct configuration.
+
+## Airflow measurement stations shall be installed with the manufacturer's required straight-duct distances upstream and downstream.
+
+## A flow station reads accurately only in a developed, non-swirling velocity profile. Mounting it too close to an elbow, transition, or damper produces a distorted profile and a systematically wrong reading no field calibration can correct. The required straight-run distances are part of the device specification, not a field option. {note}
+
+## Airflow measurement station location shall be coordinated with the ductwork layout to provide the required straight runs. [[drawing: AFMS location and straight-run]]
+
+# Damper Actuators {toc}
+
+## Damper actuators furnished under this section mount on damper bodies provided under [[sync/louvers-and-dampers]].
+
+## This section covers only the actuator, its control signal, and its fail-safe behavior. The damper blade, frame, seals, and leakage class belong to the damper standard. The two must be coordinated so the actuator torque matches the damper the manufacturer actually ships. {note}
+
+## Damper actuator torque shall be sized at a minimum of 2 in-lb per ft² of damper area per AMCA 500-D, with a 20% safety factor added.
+
+## The bare-area rule covers the air load, but the torque needed to drive a damper closed also has to overcome blade-seal friction, linkage losses, and the differential pressure across the closed blade. Sizing on area alone is the most common cause of actuators that stall short of full close at design static, which shows up as a TAB failure and a string of RFIs. The submitted torque calculation must account for seal friction and applied safety factor explicitly. {note}
+
+## Spring-return (fail-safe) actuators shall be furnished on all outside-air, exhaust, and smoke-control dampers.
+
+## Damper actuator return type shall be selected for the service.
+
+```datasheet
+label: Damper Actuator Return Type
+type: radio
+options:
+ - "Spring-return (fail-safe) — required on OA, exhaust, smoke-control"
+ - "Non-spring-return (power-driven both directions)"
+default: "Spring-return (fail-safe) — required on OA, exhaust, smoke-control"
+```
+
+## Damper actuator control mode shall be selected for the application.
+
+```datasheet
+label: Damper Actuator Control Mode
+type: select
+options:
+ - "Modulating, 2-10 VDC"
+ - "Floating (tri-state, 24 VAC)"
+ - "On/off (open/close)"
+default: "Modulating, 2-10 VDC"
+```
+
+## Modulating damper actuators shall use a 2-10 VDC control signal with spring return, not 0-10 VDC.
+
+## With a 0-10 VDC actuator, a lost or broken signal reads as 0 V, which the actuator interprets as a valid full-open (or full-closed) command rather than a fault. A 2-10 VDC actuator treats 0 V as signal-loss and drives to its spring-return fail-safe position instead. Specifying a 2-10 VDC live-zero signal is what makes signal loss a safe event. {note}
+
+## Damper actuator torque rating shall be selected to satisfy the calculated requirement.
+
+```datasheet
+label: Damper Actuator Torque Rating
+type: select
+options:
+ - "35 in-lb"
+ - "70 in-lb"
+ - "90 in-lb"
+ - "180 in-lb"
+ - "300 in-lb"
+default: "70 in-lb"
+unit: in-lb
+```
+
+## Damper actuator fail-safe position on loss of power shall match the sequence of operations. [[drawing: damper fail-safe position schedule]]
+
+# Valve Actuators {toc}
+
+## Electric valve actuators for hydronic two-way and three-way control valves shall be furnished under this section.
+
+## The valve body and trim are part of the hydronic system; this section covers the electric actuator that drives it, its control signal, and its fail-safe direction. Industrial process control valves and positioners are not covered here and are governed by [[sync/control-valves-and-actuators]]. {note}
+
+## Valve actuators shall be electric type with a 24 VAC/VDC supply, unless an existing pneumatic system is being retained.
+
+```datasheet
+label: Valve Actuator Type
+type: radio
+options:
+ - "Electric, modulating"
+ - "Electric, on/off"
+ - "Pneumatic (existing pneumatic system retained)"
+default: "Electric, modulating"
+```
+
+## Modulating valve actuators shall accept a 2-10 VDC control signal.
+
+## Valve actuators shall be rated for at least 1.25 times the valve close-off differential pressure.
+
+## An actuator that can position the valve mid-stroke but cannot drive it fully closed against system differential pressure leaks flow at the closed position, defeating temperature control and wasting energy. Sizing for 1.25 times the close-off pressure gives margin for pump head variation and valve wear. {note}
+
+## Valve actuator fail-safe position on loss of power shall be coordinated with the coil it serves and matched to the actuator's spring-return direction at the time of purchase.
+
+## Fail direction is a life-and-property decision, not a default. A chilled-water coil valve should fail closed so a power loss cannot flood the coil and the space below it. A hot-water or steam coil in a freeze-prone air stream may need to fail open to keep flow through the coil and prevent a freeze burst. The spring-return direction is fixed when the actuator is bought, so the failure mode must be settled before procurement, not at startup. {note}
+
+## Valve actuator fail-safe position shall be selected per the served coil.
+
+```datasheet
+label: Valve Actuator Fail-Safe Position
+type: select
+options:
+ - "Fail closed (chilled-water coils)"
+ - "Fail open (hot-water/steam coils in freeze-prone air streams)"
+ - "Fail last (modulating, no freeze or flood risk)"
+default: "Fail closed (chilled-water coils)"
+```
+
+# Network Integration {toc}
+
+## Networked field devices shall communicate over the project's BAS network protocol per ANSI/ASHRAE 135.
+
+## BACnet MS/TP and BACnet/IP are the dominant building-controls protocols; Modbus RTU appears on some packaged equipment. The network architecture, addressing, and controller-side integration are owned by [[sync/building-automation-system]]; this section requires only that the field device speak the protocol the project has standardized on. {note}
+
+## Networked field device protocol shall be selected to match the BAS network.
+
+```datasheet
+label: Networked Device Protocol
+type: select
+options:
+ - "BACnet MS/TP"
+ - "BACnet/IP"
+ - "Modbus RTU"
+default: "BACnet MS/TP"
+```
+
+## Wireless field sensors shall be used only where a wired run is impractical.
+
+## Wireless field sensors shall provide a minimum 5-year battery life.
+
+## Wireless mesh sensors are a retrofit tool for places a wire cannot reasonably reach, not a default. ASHRAE Guideline 13 sets a 5-year minimum battery life so a ceiling full of sensors does not become an annual ladder-and-battery maintenance burden. Mechanical rooms are RF-hostile and may need wired repeaters that must be accounted for in the BAS scope, not discovered at startup. {note}
+
+## Wireless sensor battery replacement access shall be provided without removing finished ceiling or equipment.
+
+```datasheet
+label: Field Sensor Wiring Method
+type: radio
+options:
+ - "Wired"
+ - "Wireless mesh (retrofit, ≥5-year battery, wire run impractical)"
+default: "Wired"
+```
+
+# Installation {toc}
+
+## Devices shall be installed in accordance with the manufacturer's published instructions and the approved shop drawings.
+
+## Sensor and actuator locations shall be coordinated with [[sync/mechanical-insulation]] so that pipe-mounted sensors and flow stations are excluded from the insulation scope or provided with serviceable insulation jackets.
+
+## A pipe temperature tap or flow station buried under continuous insulation is unreadable and unserviceable. Coordinating the insulation scope at submittal keeps the sensing points accessible and the insulation continuous everywhere else. {note}
+
+## Wiring terminations shall be made to the field controller per the approved wiring diagrams and classified per NFPA 70 Article 725.
+
+## Immersion sensors shall be installed with the element tip in the flowing stream and the thermowell oriented against the flow where required by the manufacturer.
+
+## Outdoor sensors shall be installed in their radiation shields, away from exhaust discharges, condensing-unit airflow, and wall-reflected solar load.
+
+## Each installed device shall be labeled with its ISA-5.1 tag number matching the device schedule.
+
+# Testing {toc}
+
+## Each device shall be point-to-point verified from the sensing element or actuator to the controller input/output before TAB and commissioning.
+
+## Point-to-point verification confirms that the device wired to a given controller terminal is the device the drawings say is there and that it reads or strokes correctly. It is a device-level check; integrated functional performance testing of the assembled system is owned by [[sync/commissioning]], and instrument-calibrated flow measurement is owned by [[sync/testing-adjusting-and-balancing]]. {note}
+
+## Each sensor shall be field-calibrated against a reference instrument and verified to within 1.5 times its rated accuracy.
+
+## Each modulating actuator shall be stroked through its full range and verified to reach commanded position at 0%, 50%, and 100%.
+
+## Each spring-return actuator shall be verified to drive to its fail-safe position on loss of power and loss of signal.
+
+## A signed field calibration and verification report shall be submitted for every device before TAB begins.
+
+# Delivery, Storage, and Handling {toc}
+
+## Devices shall be delivered in the manufacturer's original packaging with calibration certificates enclosed.
+
+## Devices shall be stored indoors in a clean, dry, temperature-controlled environment until installation.
+
+## CO2 and humidity sensors shall be protected from construction dust.
+
+## CO2 and humidity sensors shall not be energized or exposed during dusty construction activities.
+
+## Construction dust coats optical CO2 windows and contaminates humidity elements, shifting calibration before the device ever sees service. Keeping these sensors sealed until the space is clean preserves the factory calibration the project paid for. {note}
+
+# Warranty {toc}
+
+## Devices shall be warranted against defects in materials and workmanship for a minimum of one year from substantial completion.
+
+## CO2 sensors shall carry a manufacturer's calibration-stability warranty of not less than five years.
+
+## A long calibration-stability warranty is the manufacturer's commitment that the device will not drift out of tolerance over its service life, which is the property that actually matters for a DCV sensor. A one-year defects warranty says nothing about drift. {note}
+
+# Spare Parts {toc}
+
+## The Contractor shall furnish the following spare parts and consumables:
+- Two of each space temperature sensor type installed.
+- One of each transmitter type installed.
+- Replacement CO2 sensor elements or modules where the sensor uses a field-replaceable element, in the quantity scheduled.
+
+```datasheet
+label: Spare Parts Furnished
+type: checkbox
+options:
+ - Space temperature sensors (2 of each type)
+ - Transmitters (1 of each type)
+ - Replaceable CO2 elements/modules (as scheduled)
+default:
+ - Space temperature sensors (2 of each type)
+ - Transmitters (1 of each type)
+```