80
the T56slider offset).
SSpaceTemperature reading is available.
SIf it is unoccupied and the SPT > (unoccupie d cool
setpointplus the T56 slider offset). The indoor fan will be
turned on by the staging algorithm.
SIf economizeris available and active and economizer
open> 85% and SAT> (SAT low limit+ 5_F) a nd SPT >
effectivesetpoint + 0.5_F.
OR
Economizer is available, but not active
OR
Economizer is not available
SOAT> DX Lockout temperature.
If all of the above conditions are met, the compressors
will be energized as required, otherwise they will be
de--energized.
There is a fixed 3--minute minimum on time and a
5--minute off time for each compressor output and a
3--minute minimum time delay between staging up or
down.
Any time the compressors are running the RTU--MPwill
stage downthe compressors if the SAT becomes less than
the cooling low supply air setpoint.
After a compressor is staged off,it may be started again
after a normal time--guard period and the supply air
temperature has increased above the low supply air
setpoint.
Economizer
The Economizer dampers are used to provide free cooling
and Indoor Air Quality,i f optional CO2sensoris installed,
when the outside conditions are suitable.
The following conditions must be true for economizer
operation:
SIndoor Fan has been on for at least 30 seconds.
SEnthalpy is Low if the Enthalpy input is enabled.
SSATreading is available.
SOATreading is available.
SSPTreading is available.
SOAT <= High OAT economizer lockout configuration
(default= 75).
SOAT<= SPT
If any of the mentioned conditions are not true, the
economizer will be set to its configured minimum
position. The minimum damper position can be
overridden by the IAQ routine described later in this
section.
If the above conditions are true, the Economizer Control
Master Loopwill calculate a damper position value based
on the followingcalculation:
Damper Position = minimum position + PID (SPT --econ
setpoint). Econ setpoint is half way between the effective
cool and heat setpoints. If the SAT drops below the
cooling low supply air setpoint (+ 5_F), the economizer
will ramp downto minimum position.
PowerEx haust
If RTU--MP is also controlling an exhaustfan, it can be
enabled based on damper position or by occupancy. If
configured for continuous occupied operation, it will be
energizedwhenever the controller is in the occupied mode
and disabled when in the unoccupied mode. If configured
for damperposition control, it will be energized whenever
the economizer exceeds the power exhaust setpoint and
disabled when the economizer drops below the setpoint by
a fixed hysteresis of 10%.
Heating
The heating outputs are controlled by the Heating Control
PID Loop and Heating Stages Capacityalgorithm. They
will be used to calculate the desired number of stages
needed to satisfy the space by comparingthe SPT to the
Occupied Heat Setpoint plus the T56 slider offset when
occupied and the Unoccupied Heat Setpoint plus the T56
slider offset if unoccupied. The following conditions must
be true in order for this algorithm to run:
SIndoor Fan has been ON for at least 30 seconds.
SCool mode is not active and the time guardbetween
modes equals zero.
SIf occupiedand SPT <(occupied heat setpoint plus T56
slideroffset)
SSPTreading is available
SIf it is unoccupied and the SPT < (unoccupied heat
setpoint plus T56 slider offset). The indoor fan will be
turned on by the staging algorithm.
SOAT<High OAT lockout temperature.
If all of the above conditions are met, the heatingoutputs
will be energized as required, otherwise they will be
de--energized.If the SATbegins to exceed the high supply
air setpoint, a ramping function will cause the Heat Stages
Capacity algorithm to decrease the number of stages until
the SAThas dropped below the setpoint.
There is a fixed one minute minimumon time and a one
minute off time foreach heat output. Heat staging has a 3
minute stage up and 30 second stage down delay.
IndoorAir Quality
If the optional indoor air quality sensor is installed, the
RTU--MPwill maintain indoor air quality within the space
at the user configured differential setpoint. The setpoint is
the difference between the indoor air quality and an
optional outdoor air quality sensor. If the outdoor air
quality is not present then a fixed value of 400ppm is
used. The following conditions must be true in order for
this algorithmto run:
SThe mode is occupied.
SIndoor Fan has been ON for at least 30 seconds.
SIndoor Air Qualitysensor has a valid reading
As air quality within the space changes, the minimum
position of the economizer damper will be changed thus
allowing more or less outdoor air into the space depending
on the relationship of the indoor air quality to the
differential setpoint. If all the above conditions are true,
the IAQ algorithm will run and calculates an IAQ
minimum position value using a PID loop. The IAQ
minimum damper position is then compared against the
user configured economizer minimum position and the
greatest value becomes the final minimum damper
position of the economizer output.
48TC