Building HVAC (Equipment w/Factory-Installed Controls)
50 Series Vertical Pack
Vertical Pack - Sequence of Operation
Indoor Packaged Water-cooled Variable Air Volume Cooling Unit
With Carrier Comfort Network (CCN) Controls
Size Range: 60 to 100 Tons, Nominal Cooling
Carrier Model Number: 50XJ
Note: The following is a sample of a typical sequence of operation that may be adapted for a
particular project. This is provided as a suggestion on how to write a sequence of operation for a
specific project. Consult your Carrier representative if the sample sequence requires alterations.
4.2.12 Indoor Packaged Water-cooled Variable Air w/ Factory Communicating Controls
4.2.12.1 System Description
Indoor, water-cooled, vertical discharge, microprocessor controlled Variable Air Volume (VAV),
cooling and heating unit utilizing scroll type compressors for cooling duty. Units shall discharge
supply air vertically upward or horizontally through an acoustic discharge plenum as shown on
the contract drawings. Package Unit communicates with and sends alarms to, the building
automation network and alarm printer
4.2.12.2 Controls, Safeties and Diagnostics
A. Controls:
Control shall be accomplished through the use of a factory-installed, microprocessor based control
system and associated electronic and electrical hardware. Control system shall determine control
sequences through monitoring the following operational variables:
1. Day and time
2. Schedule (Unoccupied/Occupied)
3. Setpoints (Unoccupied/Occupied, Economizer, Duct Pressure, others)
4. Space temperature
5. Outdoor air temperature
6. Unit supply air temperature
7. Unit return air temperature
8. Supply air fan status
9. Economizer position
10. Accessory and/or field-supplied sensors, function switches and/or signals.
B. Controls shall be capable of performing the following functions:
1. Capacity control based on discharge air temperature and compensated by rate of change of return
air temperature (VAV [variable air volume]). Capacity control shall be accomplished through the
use of compressor staging.
2. Perform a quick test to check the status of all input and output signals to the control system using
diagnostic display module.
3. Control of integrated economizer operation, based on unit supply air temperature.
4. Supply fan volume control shall control output from a Variable Frequency Drive to maintain duct
static pressure at user configured setpoint.
5. Heating control shall provide space temperature control for unoccupied period heating, morning
warm-up sequence and occupied period heating (when configured).
6. Adaptive optimal start shall determine the time unit will commence cooling, heating or heating for
morning warm-up during the unoccupied mode to ensure occupied space reaches the setpoint in
time for occupied mode.
7. Alerts and Alarms:
Control shall continuously monitor all sensor inputs and control outputs to ensure safe and proper
system operation. Alerts shall be generated whenever sensor conditions have gone outside userconfigured criteria for acceptability. Alarms shall be initiated when unit control detects that a
sensor input value is outside its valid range (indicating a defective device or connection that
prevents full unit operation), that an output has not functioned as expected, or that a safety device
has tripped. Twelve alerts and 40 alarms shall be available. Current alarms shall be maintained in
STATUS function; up to 9 (current or reset) shall be stored in HISTORY function for recall.
8. Timed override function shall permit a system in Unoccupied mode to be returned to Occupied
mode for a user configured period of 1, 2, 3 or 4 hours by pressing the override button on the front
of the space temperature sensor.
9. Nighttime Free Cooling (NTFC) shall start the supply fan and open the economizer on cool nights
to precool the building structure mass using only outdoor air. Function shall be restricted to
operation above a user-configured low lockout temperature setpoint.
10. Modulating power exhaust control shall modulate capacity of exhaust fan system in response to
building static pressure at user-configured setpoint. Power exhaust fan operation shall be
interlocked with supply fan status.
11. Smoke Control Functions:
Control shall initiate any of four separate smoke control functions in response to closure of field
switches. Functions shall include, Pressurization, Evacuation, Smoke Purge and Fire Shutdown.
Should two or more switches be closed simultaneously, Fire Shutdown shall be initiated.
12. Indoor Air Quality (IAQ) mode shall admit fresh outdoor air into the space whenever space air
quality sensors detect unsuitable space conditions, by overriding economizer minimum damper
position. The IAQ mode shall be permitted only during occupied periods. Control shall permit user
to configure for three priority levels: sense and alert but no ventilation action; ventilate only when
comfort conditions are satisfied; ventilate immediately upon demand. IAQ mode shall also provide
control for reheat via auxiliary heating coil during ventilation (when configured).
13. IAQ pre-occupancy purge function shall provide complete exchange of indoor air with fresh air
during unoccupied periods, when outdoor conditions permit. Function shall energize supply fan
and open economizer two hours before next occupied period; duration of purge shall be userconfigured (5 to 60 min).
14. Outdoor Air Control (OAC) function shall maintain a minimum quantity of outdoor airflow into an
occupied space. The OAC mode shall be available only during an occupied period.
15. Dehumidification: Dehumidification function shall override comfort condition setpoints to deliver
cooler air into the space and satisfy a user-configured humidity setpoint at the space or return air
humidity sensor.
16. Supply Air Temperature Setpoint Reset: Control shall automatically reset the unit supply air
temperature setpoint on VAV models from space temperature, at user-configured rate and limit.
Control shall also reset supply air temperature setpoint via external 2 to 10 VDC signal
representing 0° to 20°F (0° to 11°C) range of reset. Control shall respond to higher of either reset
if both are active.
17. Space Temperature Offset function shall permit occupants to adjust space temperature setpoint
by ±5°F (±2.8°C) using T-56 space sensor (equipped with sliding scale adjuster).
18. Lead-lag function shall distribute starts between the two refrigeration circuits in an effort to
equalize the running time on the two circuits.
19. Condenser-head pressure control shall maintain correct head pressure down to -40 F.
20. Refrigeration system pressures and temperatures (superheat) shall be monitored via pressure
transducers and thermistors. Alarms for low pressure, high pressure, low superheat and high
superheat will be permitted.
21. Timed Discrete Output function shall control an external function or device via user-configured
activity schedule. This schedule shall be separate and different from the unit’s
occupied/unoccupied time schedule.
22. Hydronic heating coil control shall modulate a control valve in a stream or hydronic heat system
to maintain space temperature at user-configured setpoints. Analog output shall be 4 to 20 mA
signal.
23. Single-step demand limit control (when used in conjunction with the Carrier Comfort Network).
24. Display in Metric units: Display may be configured to display data in Metric or English (Imperial)
units of measure.
25. Keypad/Display Module (HSIO):
Module shall provide hardware necessary for human interface with the unit integrated system
controls. Module shall contain a keypad and display for interactive communication. Display shall
be two-line, backlit alphanumeric liquid crystal display (LCD). Each line of the LCD shall display up
to 24-character (with expanded scrolling display capability). Keypad shall contain 12 numeric, 6
function keys, and 4 operative keys.
Module shall contain RJ-14 data cable connection for simple installation and to facilitate remote
location installation. Module shall be powered by unit’s 24 V control circuit.
C. Safeties:
Unit components shall be equipped with the following protections:
1. Compressors:
A. Overcurrent using internal or external compressor overload modules (shuts down individual
compressor)
B. Crankcase heaters
C. High-pressure switch (shuts down individual compressor, automatic reset type)
D. Low-pressure switch (shuts down individual compressor, automatic reset type)
E. Check filter switch
F. High duct static switch.
D. Diagnostics:
1. Diagnostic display module shall be capable of indicating a safety lockout condition (alarm) through
an expandable scrolling display.
2. Diagnostic display module shall also be capable of indicating an alert condition which does not lock
out the unit, but informs the system monitor of a condition which could be detrimental to either the
unit or the comfort of the occupants if allowed to continue.
3. Diagnostic module must also be capable of displaying outputs of microprocessor controlled “quick
test” to verify operation of every thermistor, actuator motor, fan and compressor before unit is
started.
4.2.12.3 Operating Characteristics
A. Unit shall be capable of starting and running at 115°F (46°C) entering condenser water temperature
maximum load criteria of ARI Standard 340/360.
B. Unit shall be capable of mechanical cooling operation down to 50°F entering condenser water
temperature without head pressure control and down to 40°F with head pressure control
C. Provides multi-stage cooling capability.
4.2.12.4 Supply Fan Capacity Control/Variable Frequency Drive
Variable Frequency Drive (VFD) shall include:
A. Factory-installed VFD motor control device, provided with a NEMA Type 1 enclosure, and factorymounted, -wired and -tested. The VFD shall control motor speed to maintain setpoint static
pressure at the supply duct sensor location.
B. Digital display keyboard module, mounted on unit control panel.
C. Factory-mounted duct pressure sensing controller:
D. Differential Pressure Transducer, 2 to 10 VDC output to unit control module, with adjustable
setpoint range (0.0 to 5.0in. wg. [0 to 1246 Pa]), adjust via unit control keypad.
E. Low-pressure reference tube factory installed.
4.2.12.5 Special Features
A. Waterside Integrated Economizer
B. Airside Integrated Economizer:
Air economizer shall consist of a mixing box section with low leakage outdoor and return air
dampers and factory-mounted control system compatible with unit controller.
C. Bypass switch for VFD
D. Water Flow Switch
E. Space Temperature Sensor (T-56):
The T-56 space temperature sensor (for CV applications) shall monitor space temperature. Device
shall be suited for wall mounting in the occupied space.The T-56 sensor shall incorporate a frontpanel located slider switch to effect a remote change in setpoint of ±5°F (±2.8°C). The T-56 sensor
shall also include a button used to initiate Unoccupied Override function.
F. Fire and Smoke Control
G. Extended Filter Status