Fundamentals of HVAC Control Systems

This article describes the minimum requirements for HVAC control systems consisting of sensors, indicators, actuators, final control elements, interface equipment, other apparatus, accessories, and software connected to distributed controllers operating in multi-user, multi-tasking environment on token passing network and programmed to control mechanical systems.

Control shall be electric, electronic, pneumatic, direct digital or a combination of the four.

Fundamentals of HVAC Control Systems

Document Submittals to Client by Engineers

Product data shall include manufacturer’s technical literature for each control device and indicate dimensions, capacities, performance characteristics, electrical characteristics, finishes for materials, and installation and startup instructions for each type of product indicated.

  • Shop Drawings shall include the following:

a. Bill of materials

b. Detail equipment assemblies and indicate dimensions, weights, loads, required clearances, method of field assembly, components, and location and size of each field connection.

c. Schematic flow diagrams showing fans, pumps, coils, dampers, valves, and control devices.

d. Wiring diagrams indicating power, signal and control wiring. Wiring diagrams shall differentiate between manufacturer installed and field installed wiring.

e. Details of control panel faces, including controls, instruments, and labeling f.     Schedule of dampers including size, leakage, and flow characteristics.

g. Schedule of valves including leakage and flow characteristics.

h. Trunk cable schematic showing programmable control unit locations and trunk data conductors i.     Listing of connected data points, including connected control unit and input device.

j. System graphics indicating monitored systems, data (connected and calculated) point addresses, and operator notations.

k. System configuration showing peripheral devices, batteries, power supplies, diagrams, modems, and interconnections.

l. Each control device labeled with setting or adjustable range of control.

  • Software and Firmware Operational Documentation including the following:

a. Software operating and upgrade manuals

b. Program software backup on a magnetic media or compact disc, complete with data files c.    Device address list

d. Printout of software application and graphic screens

e. Software license required by and installed for DDC workstations and control system

  • Maintenance data including the following:

a. Maintenance instructions and lists of spare parts for each type of control device

b. Interconnection wiring diagrams with identified and numbered system components and devices

c. Keyboard illustrations and step-by-step procedures indexed for each operator function

d. Inspection period, cleaning methods, cleaning materials recommended, and calibration tolerances

e. Calibration records and list of set points

Quality Assurance Points

Installer Qualifications:

An experienced installer who is an authorized representative, a certified installer or an approved installer of the automatic control system manufacturer for both installation and maintenance of units required.

Manufacturer Qualifications:

  • A firm experienced in manufacturing automatic temperature-control systems similar to those indicated for this Project and with a record of successful in-service performance.
  • Electrical components, devices, and accessories shall be listed and labeled as defined in NFPA 70, Article 100, by a testing agency acceptable to authorities having jurisdiction, and marked for intended use.
  • HVAC control system shall comply with NFPA 90A.
  • HVAC control system shall comply with ASHRAE 135 for DDC system control components.
  • Computer hardware and software shall be capable of accurately processing, providing, and receiving date data from, into, and between the twentieth and twenty-first centuries, including leap-year calculations.

DDC Equipment System Requirement

Operator station shall be a microcomputer station with dot matrix or ink jet type printer. Operator workstation shall be an IBM compatible microcomputer with minimum configuration as follows:

a. Processor shall be Intel Pentium MMX, 600 MHz.

b.    Minimum random access memory shall be 32 MB.

c.    Minimum cache memory shall be 256 kB.

d. Graphics shall be super video graphic adapter (SVGA), minimum 1280 x 1024 pixels, 0-MB EDO video memory.

e. Monitor shall be 432 mm, noninterlaced, color, with maximum 28-mm dot pitch. f.     Keyboard shall be 105 keys in ergonomic shape.

g. Floppy disk drives shall be 1.44 MB. h.    Hard disk drive shall be 4.0 GB.

i. CD ROM drive shall be 24x. j.     Mouse shall be three but

k. Modem shall be autodial, internal, minimum 56 kBaud.

l. Tape backup shall be internal, 56 kBps, external zip drive, 100 MB or internal zip drive, 100 m.   Operating system shall be Microsoft Windows 95 or later.

n. Where BACnet conformance is required, workstation shall support BACnet device and have minimum capabilities defined in PICS for the following areas:

(i)    Network

(ii)   Functional groups

(iii)  Standard application services supported

(iv)  Standard objects supported

Color, ink-jet type printers shall be as follows:

a. Print head shall be 1440 x 1440 dpi photo quality color resolution.

b.    Internal memory buffer shall be 32 kB minim

c. Paper handling shall be a minimum of 100 sheets.

d. Print speed shall be a minimum of 8 pages per minute (ppm) in black and 4 ppm in color.

Dot matrix type printers shall be as follows:

a. Print head shall be 24 pin, 360 x 360 dpi resoluti

b. Carriage shall be wide, 132 characters per line of paper.

c. Paper handling shall be fan fold paper, with 2 cartons containing minimum of 2500 sheets each.

d.    Print speed shall be a minimum of 120 characters per second.

Application software shall include the following:

a. Input/output capability from operator station

b. Operator system access levels via software password

c.    Database creation and support

d. Dynamic color graphic displays

e.    Alarm processing

f. Event processing

g. Automatic restart of field equipment on restoration of power

h.    Data collection

i. Graphic development on workstation

j.     Maintenance management

Control units shall be modular, comprising processor board with programmable, nonvolatile, random-access memory; local operator access and display panel; integral interface equipment; and backup power source.

a. Units shall monitor or control each input/output point; process information; execute commands from other control units, devices, and operator stations; and download from or upload to operator statio

b. Stand alone mode control functions shall operate regardless of network status. Functions shall include the following:

(i)    Global communications

(ii)   Discrete/digital, analog, and pulse input/output

(iii)  Monitoring, controlling, or addressing data points

(iv)  Units shall have the ability to test and develop control algorithms without disrupting field hardware and controlled environment

c. Local operator interface shall provide for download from or upload to mobile operator stati

d. Where BACnet conformance is required, units shall reside on BACnet LAN in Ethernet IEEE 802.3, Class 3, minimum, with routers between LAN and other panels, with at least one communication port, and have minimum capabilities defined in PICS for the following areas.

Local control units shall be modular, comprising of a processor board with electronically programmable, nonvolatile, read-only memory; and backup power source.

a. Units shall monitor or control each input/output point; process information; and download from or upload to operator stati

b. Stand alone mode control functions shall operate regardless of network status. Functions shall include the following:

(i)    Global communications

(ii)   Discrete/digital, analog, and pulse input/output

(iii)  Monitoring, controlling, or addressing data points

c. Local operator interface shall provide for download from or upload to mobile operator stati

d. Where BACnet conformance is required, unit shall reside on BACnet LAN using MS/TP, Class 2, minimum, with at least one communication port, and have minimum capabilities defined in PICS for the following areas:

(i)    Network

(ii)   Functional groups

(iii)  Standard application services supported

(iv)  Standard objects supported

Software shall be updated to latest version of software at Project completion. The following capabilities shall be included and implemented as applicable from the control units:

  1. Units of measure shall be inch-pound and SI (metric).
  2. Load control programs shall be demand limiting, duty cycling, automatic time scheduling, start/stop time optimization, night setback/setup, DDC with fine tuning, and trend logging.
  3. HVAC control programs shall be optimal run time, supply air reset, and enthalpy switchover.
  4. Chiller control programs shall control function of chilled water reset and equipment sequencing. e.    Programming application features shall include trend point, alarm messages, weekly scheduling, and interlocking.

Control Panels for HVAC Control Sytem

Central (master) control panels shall be fully enclosed, steel rack type cabinet with locking doors or locking removable backs. Finish of panels shall be matched and provide multicolor graphic displays, schematically showing system being controlled.

Local control panels shall be unitized cabinet with suitable brackets for wall or floor mounting, located adjacent to each system under automatic control. Common keying shall be provided for panels.

    1. Panels shall be fabricated of 1.5 mm thick, furniture-quality steel, or extruded-aluminum alloy, totally enclosed, with hinged doors and keyed lock and with manufacturer’s standard shop-painted finish.
    2. Panel mounted equipment shall include temperature and humidity controllers, relays, and automatic switches; except safety devices. Devices shall be mounted with adjustments accessible through front of panel.
    3. Door mounted equipment shall be flush mount (on hinged door) manual switches, including, as applicable, damper positioning switches, changeover switches, thermometers, and gages.
    4. Graphics shall be color coded graphics, laminated plastic displays on doors, schematically showing system being controlled, with protective, clear plastic sheet bonded to entire door.

For stand alone analog alarm systems, alarm panels shall be an indicating light for each alarm point, single horn, acknowledge switch, and test switch, mounted in hinged cover enclosure.

a. Alarm condition shall be indicated with light flashes and horn sound

b. Acknowledge switch shall silence horn is silent and indicating light remains steady. c.    Second alarm shall sound horn and indicating light remains steady.

d. Alarm condition cleared shall reset system and indicating light shall be extinguished.

e. Contacts in alarm panel shall allow remote monitoring by independent alarm company if requir

Analog Controllers

  • Step controllers shall be 6 or 10 stage type, with heavy duty switching rated to handle loads and operated by electric motor.
  • Electric, outdoor reset controllers shall be remote bulb or bimetal rod and tube type, proportioning action with adjustable throttling range, adjustable set point, scale range minus minus 23 to plus 21° C, and single or double pole contacts.
  • Electronic controllers shall be wheatstone bridge amplifier type, in steel enclosure with provision for remote resistance readjustment. Adjustments on controllers shall be identified, including proportional band and authority. Single controllers may be integral with control motor if provided with accessible control readjustment potentiometer.
  • Fan speed controllers shall be a solid state model providing field adjustable proportional control of motor speed from maximum to minimum of 55 percent and on-off action below minimum fan speed. Controller shall briefly apply full voltage, when motor is started, to rapidly bring motor up to minimum speed. Controller shall be equipped with a filtered circuit to eliminate radio interference.
  • Receiver controllers shall be single or multiple input models with control point adjustment, direct or reverse acting with mechanical set point adjustment with locking device, proportional band adjustment, authority adjustment, and proportional control mode.

a. Remote control point adjustment shall be plus or minus 20 percent of sensor span, input signal of 21 to 90 kPa.

b. Proportional band shall extend from 2 to 20 percent for 34 kP c.    Authority shall be 20 to 200 percent.

d. Air supply pressure of 124 kPa, input signal of 21 to 103 kPa and output signal 0 to supply pressur

e. Gages shall be 38 mm, 64 mm or 89 mm in diameter, 5 percent wide scale accuracy, and range to match transmitter input or output pressure.

Electronic Sensors

Electronic sensors shall be vibration and corrosion resistant; for wall, immersion, or duct mounting as required. Thermistor temperature sensors shall be as follows:

a. Accuracy shall be plus or minus 0.3° C or 2° C at calibration point.

b.    Wire shall be twisted, shielded pair cable.

c. Insertion elements in ducts shall be single point, 20 cm or 46 cm long and used where not affected by temperature stratification or where ducts are smaller than 1 sq. m.

d. Averaging elements in ducts shall be 91 cm or 183 cm long, flexible; or 46 cm long, rigid and used where prone to temperature stratification or where ducts are larger than 1 sq. m.

e. Insertion elements for liquids shall be brass socket with minimum insertion length of 64 mm.

f. Room sensors shall match room thermostats, with locking cover.

g. Outside air sensors shall be a watertight inlet fitting, shielded from direct sunlight.

h. Room security sensors shall be with a stainless steel cover plate with insulated back and security screws.

Platinum resistance temperature detectors shall be as follows:

    1. Accuracy shall be plus or minus 0.2 percent at calibration point.
    2. Wire shall be twisted, shielded pair cable.
    3. Insertion elements in ducts shall be single point, 20 cm or 46 cm long and used where not affected by temperature stratification or where ducts are smaller than 1 m².
    4. Averaging elements in ducts shall be 91 cm or 183 cm long, flexible; or 46 cm long, rigid and used where prone to temperature stratification or where ducts are larger than 1 m².
    5. Insertion elements for liquids shall be brass socket with minimum insertion length of 64 mm.
    6. Room sensors shall match room thermostats, with locking cover.
    7. Outside air sensors shall be a watertight inlet fitting, shielded from direct sunlight.
    8. Room security sensors shall be with a stainless steel cover plate with insulated back and security screws.

Humidity sensors

a. Humidity sensors shall be bulk polymer sensor element.

b.  Accuracy shall be 5 percent full range with linear output.

c. Room sensors shall come with a locking cover matching room thermostats with a span of 25 to 90 percent relative humidity.

d. Duct and outside air sensors shall come with an element guard and mounting plate with a range of 0 to 100 percent relative humidity.

Static Pressure Transmitter

a. Static pressure transmitter shall be a non-directional sensor with suitable range for expected input, and temperature compensated.

b. Accuracy shall be 2 percent of full scale with repeatability of 0.5 perce c.    Output shall be 4 to 20 mA.

d. Building static pressure range shall be 0 to 62 Pa. e.    Duct static pressure range shall be 0 to 1243 Pa.

Pressure Transmitter

Pressure transmitters shall be direct acting for gas, liquid, or steam service; range suitable for system; proportional output 4 to 20 mA.

Pneumatic Transmitters

Pneumatic transmitters shall be vibration and corrosion resistant.

Space Temperature Sensors

Space temperature sensors shall be linear output type, 10 to 38° C range, with blank locking covers matching room thermostats.

Room Temperature Sensors

Room return air temperature sensors shall be linear output type with bimetal sensing element and corrosion proof construction, 10 to 38° C range, designed to be mounted in light troffers.

Duct Mounted or Immersion Type Temperature Sensors

Duct mounted or immersion type temperature sensors shall have a range as required for 21 to 103 kPa output signal.

Temperature Transmitters

Temperature transmitters shall be rigid stem type with bimetal sensing elements, unless averaging is required, 21 to 103 kPa output signal.

    1. Averaging element sensors shall be single or multiple unit capillary elements.
    2. Tamperproof sensors shall be corrosion resistant construction, suitable for mounting on vibrating surface with exposed capillary protected with temperature compensated armor or protective tubi
    3. Pipe mounted temperature sensing elements shall be rod and tube type, with separable wells filled with heat-conductive compound, mounting brack
    4. Outdoor sensors shall be provided with a bulb shield with mounting brack

Space and Duct Humidity Transmitters

a. Space and duct humidity transmitters shall be one pipe, directly proportional, with minimum sensing span of 20 to 80 percent relative humidity for 21 to 103 kPa output signal, corrosion resistant and temperature compensated, and with factory-calibrated adjustment.

b. Space mounted transmitters shall come with covers to match thermostats.

Differential Pressure Transmitters

Differential pressure transmitters shall be one pipe, direct acting for gas, liquid, or steam service; pressure sensor and transmitter of linear output type; with range of 0 to 344 kPa, and 21 to 103 kPa output signal.

Differential Air Pressure Transmitters

a. Differential air pressure transmitters shall be one pipe, direct acting, double bell, unidirectional with suitable range for expected input, and temperature compensa

b. Accuracy shall be 5 percent of full range and 2 percent of full scale at midra c.    Output signal shall be 21 to 103 kPa.

Equipment Operation Sensors

    • Status inputs for fans shall be a differential pressure switch with adjustable range of 0 to 1243 Pa.
    • Status inputs for pumps shall be differential pressure switch piped across pump with adjustable pressure-differential range of 55 to 414 kPa.
    • Status inputs for electric motors shall be a current sensing relay with current transformers, adjustable and set to 175 percent of rated motor current.

Digital to Pneumatic Transducers

Digital to pneumatic transducers shall convert plus or minus 12 V dc pulse width modulation outputs, or continuous proportional current or voltage to 0 to 138 kPa.

Pneumatic Valve / Damper Position Indication

Pneumatic valve/damper position indication shall be a potentiometer mounted in enclosure with adjustable crank arm assembly connected to damper to transmit 0 to 100 percent valve/damper travel.

Electronic Valve / Damper Position Indication

Electronic valve/damper position indication shall have a visual scale indicating percent of travel and 2 to 10 V dc, feedback signal.

Water Flow Switches

Water flow switches shall be pressure flow switches of bellows actuated mercury or snap acting type, with appropriate scale range and differential adjustment, with stainless steel or bronze paddle. For chilled water applications, vapor-proof type shall be provided.

Carbon Monoxide Detectors

Carbon monoxide detectors shall be single or multi-channel, dual level detectors, using solid state sensors with 3 year minimum life, maximum 15 minute sensor replacement, suitable over a temperature range of minus 5 to plus 55° C, calibrated for 50 and 100 ppm, with maximum 120 second response time to 100 ppm carbon monoxide.

Carbon Dioxide Sensor and Transmitter

Carbon dioxide sensor and transmitter shall be single detectors, using solid state infrared sensors, suitable over a temperature range of minus 5 to plus 55° C, calibrated for 0 to 2 percent, with continuous or averaged reading, 4 to 20 mA output, and wall mounted.

Oxygen Sensor and Transmitter

Oxygen sensor and transmitter shall be single detectors, using solid state zircon cell sensing, suitable over a temperature range of 0 to 593° C, calibrated for 0 to 5 percent, with continuous or averaged reading, 4 to 20 mA output, and wall mounted.

Refrigerant Detectors

Refrigerant detectors shall be dual level detectors, using solid state sensors, with alarm preset for 300 ppm, alarm indicator light, alarm silence light and button, alarm test light and button, and trouble light. Auxiliary relay preset for 150 ppm shall be provided.

Thermostats for HVAC Control Sytem

Combination Thermostat and Fan Switches

  1. Combination thermostat and fan switches shall be line voltage thermostats with two, three, or four position, push button or lever-operated fan switch.
  2. Switches shall be labeled “FAN ON-OFF,” “FAN HIGH-LOW-OFF,” “FAN HIGH-MED-LOW-OFF.” Unit shall be provided for mounting on two-gang switch box.

Electric Solid State, Microcomputer Based Room Thermostat with Remote Sensor.

Electric solid-state, microcomputer-based room thermostat with remote sensor shall be as follows:

  • Automatic switching from heating to cooling
  • Preferential rate control to minimize overshoot and deviation from set point c.    Set up for four separate temperatures per day
  • Instant override of set point for continuous or timed period from 1 hour to 31 days e.    Short-cycle protection
  • Programming based on every day of week
  • Features including ° F or ° C display, 12- or 24-hour clock, keyboard disable, remote sensor, fan on-auto
  • Battery replacement without program loss
  • Thermostat display features include the following:

(i)    Time of day

(ii)   Actual room temperature

(iii)  Programmed temperature

(iv)  Programmed time

(v)   Duration of timed override

(vi)  Day of week

(vii) System mode indications include heating, off, fan auto, and fan on

Low Voltage, On-Off Thermostats

Low voltage, on-off thermostats shall be NEMA DC 3, 24-V, bimetal operated, mercury switch type, with adjustable or fixed anticipation heater.

Line-Voltage, On-Off Thermostats

a. Line voltage, on-off thermostats shall be bimetal actuated, open contact or bellows actuated, enclosed, snap switch type, or equivalent solid state type, with heat anticipator, integral manual on-off-auto selector switch.

b. Thermostats which control electric heating loads directly, shall be equipped with off position on dial wired to break ungrounded conductors.

c. Dead band shall be maximum 1° C.

Remote Bulb Thermostats

a. Remote bulb thermostats shall be on-off or modulating type, liquid filled to compensate for changes in ambient temperature, with copper capillary and bulb, unless otherwise indicated.

b. Bulbs in water lines with separate wells shall be of the same material as bu c.    Bulbs in air ducts shall be with flanges and shields.

d. Averaging elements shall be copper tubing with either single or multiple unit elements, extended to cover full width of duct or unit, adequately supported.

e. Scale settings and differential settings shall be clearly visible and adjustable from front of instrument.

On-off thermostats shall be with precision snap switches, with electrical ratings required by application.

g. Modulating thermostats shall be constructed so complete potentiometer coil and wiper assembly is removable for inspection or replacement without disturbing calibration of instrument.

Pneumatic Room Thermostats

a. Pneumatic room thermostats shall be one, two or three pipe(s), fully proportional with adjustable throttling range and tamperproof locking settings, direct or reverse acting as required. Thermostats shall be factory calibrated at 12 kPa/deg C.

b. Range shall be 7.2 to 29.4°

c. Sensitivity adjustment range shall be 7 to 27.6 kPa/deg C.

d. Dual temperature thermostats shall be automatic changeover from normal setting to lower unoccupied setting, with manual reset lever to permit return to normal temperatures during unoccupied cycles, with automatic reset to normal during next cycle of operation.

e. Limits shall be field adjustable, to limit setting cooling set point below 24° C, and heating set point above 24° C.

Room Thermostat Cover Construction

a. Room thermostat cover shall be manufacturer’s standard locking covers.

b.    Set point adjustment shall be concealed or exposed.

c. Set point indication shall be concealed, keyed or exposed.

d. Thermometer shall be concealed, exposed, red reading glass or spiral bimetal.

e. Orientation shall be horizontal or vertical.

Immersion Thermostat

Immersion thermostats shall be remote bulb or bimetal rod and tube type, proportioning action with adjustable throttling range and adjustable set point.

Airstream Thermostats

Airstream thermostats shall be two pipe, fully proportional, single temperature type, with adjustable set point in middle of range and adjustable throttling range, plug in test fitting or permanent pressure gage, remote bulb, bimetal rod and tube, or averaging element.

Electric Low Limit Duct Thermostat

    1. Electric low limit duct thermostats shall be snap acting, single pole, single throw, manual or automatic reset switch that trips if temperature sensed across any 300 mm of bulb length is equal to or below set point.
    2. Bulb length shall be minimum 6 m.
    3. One thermostat shall be provided for every 2 s m of coil surface.

Electric High Limit Duct Thermostat

    1. Electric high limit duct thermostat shall be snap acting, single pole, single throw, manual or automatic reset switch that trips if temperature sensed across any 300 mm of bulb length is equal to or above set point.
    2. Bulb length shall be minimum 6 m.
    3. One thermostat shall be provided for every 2 m2 of coil surface.

Heating / Cooling Valve Top Thermostats

Heating/cooling valve top thermostats shall be proportional acting for proportional flow, molded rubber diaphragm, remote bulb liquid filled element, direct and reverse acting at minimum shutoff pressure of 172 kPa, and cast housing with position indicator and adjusting knob.

HVAC Humidistats

Pneumatic Room Humidistats

Pneumatic room humidistats shall be wall mounted, proportioning type with adjustable throttling range, 20 to 90, 55 to 95 or 25 to 65 percent operating range, cover matching room thermostat cover.

Duct Mounted Humidistats

Duct mounted humidistats shall be electric insertion, 2 position type with adjustable 2 percent throttling range, 20 to 80 percent operating range, single or double pole contacts.

Pneumatic Duct Mounted Humidistats

Pneumatic duct mounted humidistats shall be proportioning type with adjustable throttling range, 20 to 90, 55 to 95 or 25 to 65 percent operating range, in galvanized steel duct box.

Actuators Used in HVAC Control Sytem

Electric motors shall be sized to operate with sufficient reserve power to provide smooth modulating action or two position action.

  1. Permanent split capacitor or shaded pole type shall have gear trains completely oil immersed and sealed. Spring return motors shall be equipped with integral spiral spring mechanism in housings designed for easy removal for service or adjustment of limit switches, auxiliary switches, or feedback potentiometer.
  2. Non-spring return motors for valves larger than NPS 2-1/2 shall be sized for running torque of 16.9 N x m and breakaway torque of 33.9 N x m.
  3. Spring return motors for valves larger than NPS 2-1/2 shall be sized for running and breakaway torque of 19 N x m.
  4. Non-spring return motors for dampers larger than 3 m2 shall be sized for running torque of 16.9 N x m and breakaway torque of 33.9 N x m.
  5. Spring return motors for dampers larger than m2 shall be sized for running and breakaway torque of 16.9 N x m.

Electronic Damper and Large Valve Actuators

a. Electronic damper and large valve actuators shall be direct coupled type designed for minimum 60,000 full-stroke cycles at rated torque.

b. Valve actuators shall be sized for torque required for valve close-off at maximum pump differential pressure.

c. Damper actuators shall be sized for running torque calculated as follows:

(i)    Parallel blade damper with edge deals shall be sized for 86.8 kg-cm/ m2 of damper. (ii)   Opposed blade damper with edge seals shall be sized for 62 kg-cm/ m2 of damper.

(iii)  Parallel blade damper without edge seals shall be sized for 49.6 kg-cm/ m2 of damper. (iv)  Opposed blade damper without edge seals shall be sized for 37.2 kg-cm/ m2 of damper.

(v)   Dampers with 500 to 750 Pa of pressure drop or face velocities of 5 to 13 m/s shall be sized by multiplying the minimum full stroke cycles above by 1.5.

(vi)  Dampers with 750 to 1000 Pa of pressure drop or face velocities of 13 to 15 m/s shall be sized by multiplying the minimum full stroke cycles above by 2.0.

d. Coupling shall be V bolt and V shaped, toothed cradle.

e. Overload protection shall be electronic overload or digital rotation sensing circuitry.

Fail safe operation shall be mechanical, spring return mechanism. External, manual gear release shall be provided on non-spring return actuators.

g. Power requirements (two position spring return) shall be 24, 120 or 230 V ac.

h. Power requirements (modulating) shall be a maximum 10 VA at 24 V ac or 8 W at 24 V dc.

Proportional signal shall be 2 to 10 V dc or 4 to 20 mA, and 2 to 10 V dc position feedback signal.

j.     Temperature rating shall be minus 30 to plus 50° C or 4 to 40° C.

Pneumatic Valve Operators

Pneumatic valve operators shall be rolling diaphragm, spring loaded, piston type with spring range as required and start point adjustment, positioning relay or both. Operator shall maintain full shutoff at maximum pump differential pressure.

Pneumatic Damper Operators

a. Pneumatic damper operators shall be rolling diaphragm, piston type with adjustable stops and spring return, sized to operate with sufficient reserve power to provide smooth modulating action or two-position actio Where actuators operate in sequence, pilot positioners shall be provided.

HVAC Control Valves

Control valves shall be factory fabricated, of type, body material, and pressure class based on maximum pressure and temperature rating of piping system, unless otherwise indicated.

Globe Valves

a. Globe valves NPS 2 and smaller shall be bronze body, bronze trim, rising stem, renewable composition disc, and screwed ends with backseating capacity repackable under pressure.

b. Globe valves NPS 2-1/2 and larger shall be iron body, bronze trim, rising stem, plug type disc, flanged ends, and renewable seat and disc.

c. Hydronic system control globe valves shall have the following characteristics:

(i)    Rating shall be Class 125 for service at 862 kPa and 121° C operating conditions.

(ii)   Internal construction shall be replaceable plugs and seats of stainless steel or brass.

(iii)  Single seated valves cage trim shall provide seating and guiding surfaces for plug on top and bottom of guided plugs.

(iv)  Double seated valves shall be balanced plug; cage trim shall provide seating and guiding surfaces for plugs on top and bottom of guided plugs.

(v)   Sizing shall be 21 kPa maximum pressure drop at design flow rate.

(vi)  Two-way valves shall have equal percentage characteristics; three-way valves shall have linear characteristics. Operators shall close valves against pump shutoff head.

Butterfly Valves

    1. Butterfly control valves shall be 1380 kPa, 1035 kPa maximum pressure differential, ASTM A 126 cast iron or ASTM A 536 ductile iron body and bonnet, extended neck, stainless-steel stem, field-replaceable EPDM or Buna N sleeve and stem seals.
    2. Body style shall be wafer, lug or grooved.
    3. Disc type shall be nickel plated ductile iron or aluminum bronze.
    4. Butterfly control valves shall be sized for 7 kPa maximum pressure drop at design flow rate.

Terminal Unit Control Valves

    1. Terminal unit control valves shall be bronze body, bronze trim, two or three port as indicated, replaceable plugs and seats, union and threaded ends.
    2. Rating shall be Class 125 for service at 862 kPa and 121° C operating conditions.
    3. Terminal unit control valves shall be sized for a 21 kPa maximum pressure drop at design flow rate, to close against pump shutoff hea
    4. Flow characteristics for two way valves shall be equal percentage characteristics; three-way valves shall have linear characteristics.

HVAC Dampers

  • Control dampers shall be AMCA rated, parallel or opposed blade design, 2.8 mm minimum, galvanized-steel frames with holes for duct mounting; damper blades shall not be less than 1.6 mm galvanized steel with maximum blade width of 203 mm.
  • Blades shall be secured to 13 mm diameter, zinc plated axles using zinc plated hardware, with nylon blade bearings, blade linkage hardware of zinc plated steel and brass, ends sealed against spring stainless steel blade bearings, and thrust bearings at each end of every blade.
  • Operating temperature range shall be from minus 40 to plus 93° C.
  • For standard applications, closed-cell neoprene edging shall be included.
  • For low leakage applications, parallel or opposed blade dampers shall be designed with inflatable seal blade edging, or replaceable rubber seals, rated for leakage at less than 51 L/s per sq. m of damper area, at differential pressure of 995 Pa when damper is being held by torque of 5.6 N x m; when tested according to AMCA 500.

HVAC Air Supply

Control and Instrumentation Tubing

Control and instrumentation tubing shall be one of the following:

a. Type K, seamless copper tubing complying with ASTM B 88 (ASTM B 88M) or Type ACR, copper tubing complying with ASTM B 280.

(i)    Fittings shall be cast bronze solder fittings complying with ASME B16.18; or wrought copper solder fittings complying with ASME B16.22, except forged brass compression type fittings at connections to equipment.

(ii)   Joining method shall be soldered or brazed.

b. Virgin polyethylene, flame retardant, nonmetallic tubing complying with ASTM D 2737 with flame retardant harness for multiple tubing.

(i)    Fittings shall be compression or push on polyethylene fittings.

Where required by system requirements, the following shall be provided:

a. Air filter rated for 97 percent efficiency at rated airflow, and combination filter/pressure reducing station or separate filter and pressure-reducing statio

b. Refrigerated air dryers shall be self-contained, refrigerated air dryer complete with heat exchangers, moisture separator, internal wiring and piping, and with manual bypass valv

(i)    Heat exchangers shall be air to refrigerant coils with centrifugal type moisture separator and automatic trap assembly.

(ii)   Refrigeration units shall be hermetically sealed, operating to maintain dew point of minus 11° C at 138 kPa, housed in steel cabinet with access door and panel.

(iii)  Refrigerated air dry accessories, where required, shall include air inlet temperature gage, air inlet pressure gage, on-off switch, high temperature light, power on light, refrigerant gage on back, air outlet temperature gage, air outlet pressure gage, and with contacts for remote indication of power status and high temperature alarm.

c. Desiccant dryers shall obtain dew point in pneumatic air piping between compressor and tank at least minus 9° C below inlet air dew point at design conditions.

d. Pressure gages shall be black letters on white background, 64 mm diameter, flush or surface mounted, with front calibration screw to match sensor, in appropriate units.

e. Instrument pressure gages shall have black letters on white background, 38 mm diameter, stem mounted, with suitable dial range.

Diaphragm control and instrument valves shall be 6 mm forged-brass body with reinforced polytetrafluoroethylene diaphragm, stainless steel spring, and color coded phenolic handle.

g. Gage cocks shall be tee or level handle, bronze, rated for 862 kPa.

h. Relays for summing, reversing, amplifying, highest or lowest pressure selection, with adjustable input/output ratio.

i. Switches shall be with indicating plates, accessible adjustment, calibrated and marked.

j. Pressure regulators shall be zinc or aluminum castings with elastomeric diaphragm, balanced construction to automatically prevent pressure build up, and producing flat reduced pressure curve.

k. Particle filters shall be zinc or aluminum castings with 97 percent filtration efficiency at rated airflow, quick disconnect service devices, and aluminum or plastic bowl with metal guard and manual drain cock.

l. Combination filter/regulators shall be zinc or aluminum castings with elastomeric diaphragm, balanced construction to automatically prevent pressure build-up, and producing flat reduced-pressure curve; with threaded pipe connections, quick-disconnect service devices, and aluminum or plastic bowl with metal guard and manual drain cock.

Take More Reference from this Book of HVAC Control Operation and Maintenance.

HVAC Controls – Operation and Maintenance 3rd ed – Guy W. Gupton, Jr. (Fairmont Press, 2002)

 

 

Leave a Reply