If nomodeiscurrentlyactive,theLinkageCooMinatorwill
determinethemodebyfirstcomparingtheAHDandtheACD.
Ifonlyonedemandisgreaterthanthestartdemand(HeatSt_ut
Avg.DemandorCoolStartAvg.DemandintheMaster[Link-
ageCoordinator]ServiceConfigurationtable),thesystemwill
stCu'tinthatmode.If bothaveragedemandsalegreaterthanthe
configuredminimumaveragedemandrequiredto begina
mode,thenthemodewiththegreatestdemandwillbeselected.
If bothheatingandcoolingaveragedemandareexactlythe
samethenthemodewiththegreatestindividualzonedemand
willdeterminethesystemmode.
Oncethemodeisselected,theinfommtioniscommunicat-
edtoitsairsourceviatheLinkageCoordinatorsothattheair
sourcemayrespondtotherequestedmode.TheLinkageCoor-
dinatoralsohasthecapabilityoflockingoutthemodebasedon
theoutsideairtemperature(OAT).If theOAThasexceededthe
lockoutsetpointforthatmode,thentheLinkageCoordinator
willnotrequestthatmodefromtheairsource.Thereisafixed
3° Fhysteresisontheheatingandcoolingsetpointsbeforea
modeisre-enabled.
Onceamodehasbegun,thesystemmodereselecttimeris
stmledtomonitortheelapsedtimeoftheoperatingmode.A
modewillendwhentheaveragedemandforthatmodediops
belowtheaveragedemandhystelesisforthemode(HeatMode
HysteresisorCoolModeHysteresisintheMaster[Linkage
Coordinatorl Service Configuration table). If a system mode is
currently active and the average demand for the opposite mode
becomes greater than the current mode average demand, and
the opposite mode demand is also greater than the mode Stmt
Avg. Demand for that mode, then the system mode may
change but only after the system mode reselect time of the cur-
rent mode exceeds the configmed System Mode Reselect timer
v_flue. If these me all true, the system will begin the change to
the opposite system mode. This is accomplished by sending in-
formation to the air source that ends the cunent mode. The
Linkage Coordinator then waits for the supply-air temperature
(SAT) to fall within the ventilation temperature range of 65 to
75 IF.Once that occurs, the opposite mode is started.
If the mode is dropped due to the reselection criteria
above, the algorithm will not permit the original mode to be
re-established unless there is sufficient average demand to start
the new mode. This is true even if the old mode has once again
become the more dominant requirement.
Linkage- Linkage is the process used to communicate
between the air source (HVAC equipment) and the zone termi-
rods to form a coordinated HVAC system. Linkage allows the
air source to be controlled by the demands of the zones and
allows the zones to properly respond to the changes in the air
source operating modes. Linkage operation in air sources that
have Carrier communicating network controls such as
48/50HG. 48/50A, and 48/50Z Product Integrated Controls
(PIC) series rooftop units, PremierLink TM control or Universal
Controller is supported. Existing air sources that do not have
Cmrier communicating network controls may be retrofitted
with PremierLink or a Universal Controller depending on the
equipment type. The designated Linkage Coordinator of each
system will be the Linkage Coordinator between the air source
and its associated zones.
AIR SOURCES THAT SUPPORT LINKAGE -- Air sourc-
es with PICs or PremierLink controls do not require tiny
configuration settings to establish linkage with the Linkage
Coordinatol: This is done automatically when the air source
bus and element address are configured in the Linkage Coordi-
nator's LINKAGE configuration table. The linkage informa-
tion that is supplied to file air source by the Linkage Coordina-
tor is as follows:
• Reference zone temperature
• Reference zone occupied biased heating and cooling
setpoints
• Average unoccupied heating and cooling set points of all
zones serviced by the air source
• Composite occupancy mode
The air source will control the equipment based on this
information and in return will provide the Linkage Coordinator
with the following data:
• Operating mode -- Cooling, Heating, Free Cool, Pres-
sure, Evacuation or Off
• Supply-air temperature
This synchronization of data optimizes the efficiency of the
air source and the zones to operate at peak system performance
at all times. This information can be seen in linkage mainte-
nance tables of the Linkage Coordinator and the air source and
is updated at approximately 1-minute interv_ds.
The reference zone temperature that is sent by the Linkage
Coordinator will vary depending on the current demand. At
times this will be a calculated value instead of an actual v_due
to allow file air source to turn off heating or cooling after the
current mode is satisfied or as it makes a transition to a mode.
Table 24 defines when these values will be sent and how they
are determined.
Table 24 -- Occupied Reference Zone Value
SYSTEM OCCUPIED REFERENCE SYSTEM MODE CONDITION
DESIRED MODE ZONE TEMPERATURE (OZT)
COOLING OZT = RZSPT ACD >= Avg CooI Start Demand and system is in Cooling
OZT = RZHSP Heating mode has just satisfied (AHD < (Avg Heat Start Demand - Heat Mode
Hysteresis)). Fan will continue to run if configured for continuous fan operation
HEATING OZT = RZSPT AHD >= Avg Heat Start Demand and system is in Heating
NONE OZT = RZCSP Cooling mode has just satisfied (ACD < (Avg Cool Start Demand - Cool Mode
Hysteresis)). Fan will continue to run if configured for continuous fan operation
OZT = (RZCSP - RZHSP) + RZCSP RZSPT is less then RZCSP and greater than RZHSP No demand for heat or cool.
OZT = 0 1) System in unoccupied modes.
2) System is occupied, there is no demand for heat or cool and fan operation
is configured for intermittent.
3) System is occupied and bypass pressure sensor calibration is in progress.
CFLUSH, OZT = (RZCSP - RZHSP) + RZCSP System Mode Reselect is in effect and has timed out.
H_FLUSH The previous mode has ended and system is transitioning to the opposite mode.
LEGEND
ACD -- Average Cool Demand
AHD -- Average Heat Demand
RZSPT -- Reference Zone Space Temperature (actual)
RZCSP -- Reference Zone Cool Set Point
RZI-ISP -- Reference Zone Heat Set Point
52
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