Specifications

62
High Cool cannot occur until there has been a minimum of
8 minutes of Low Cool operation. High Cool cannot occur as
long as the Low Cool mode is causing a reduction in the space
temperature trend. If the space temperature trend stops improv-
ing but the demand still exceeds 2.0 F, then High Cool mode
goes into effect.
HEATING MODES EXAMPLE
LH.ON = 1.5 F
LH.OF = 0.5 F
HH.ON = 2.0
• Heating Demand = (set point) – Space Temp.
• Low Heat begins when a 1.5 F demand exists (SPT = 68.5
[70.0-1.5]).
• Low Heat ends when the demand returns to 0.5 F (SPT = 69
[68.5 +0.5]).
• High Heat begins when the demand exceeds 2.0 F (SPT =
66.5 [68.5-2.0]).
• High Heat ends when the demand returns to LH.OF/2 (SPT =
68.75 [68.5+0.5/2]).
High Heat cannot occur until there has been a minimum of
8 minutes of Low Heat operation. High Heat cannot occur as
long as the Low Heat Mode is causing an increase in the space
temperature trend. If the space temperature trend stops improv-
ing but the demand still exceeds 2.0 F, then High Heat goes
into effect.
The routine can operate with either 2 stages or multiple
stage of cooling based on the unit control type (CTL.T) located
in the CONFIGURATION-UNIT submenu.
HVAC_VAV ROUTINE (VAVRAT AND VAVSPT) —
This routine is used for the heating, cooling or ventilating con-
trol of VAV configured units. The heating, cooling, or ventila-
tion mode will be controlled and configured using the cooling
and heating set points. To configure when cooling is enabled or
disabled, use the configurable VAV Cool On Set Point
(V.C.ON) which can be configured in the SETPOINT-COOL
submenu and the VAV Occupied Cool Off Delta (V.C.OFF)
which can be configured in the SETPOINT-COOL submenu.
Both VAVRAT and VAVSPT routines start a mode and end a
mode based on return-air temperature. The only difference is
that when the unit is in unoccupied mode, the determination to
bringonthesupplyfanandsamplethereturnairstreambefore
starting a mode will be based on space temperature or return air
temperature.
When in occupied mode, the control will first determine if
heating or cooling is to be used. If the return-air temperature
(RAT) is above the VAV occupied cooling on set point
(VC.ON), then the control will entering normal cooling mode
and control to the leaving air temperature set point. The control
will use the economizer if possible and then turn on compres-
sors to meet the demand. Cooling will be turned off when the
return air temperature goes below the VAV cool off delta set
point (V.C.OFF).
If the return-air temperature falls below the Heating set
point (OH.SP) then the control will use the logic from the
HVACSPT2 Routine. When in heating, the HIR will be closed
to indicate to the terminal controls that they must be open to the
minimum unit CFM heating airflow. If the HIR is not installed,
then the heating capacity could be limited by tripping of the
heat limit switches.
When the unit is in the unoccupied mode, both cooling and
heating modes (if enabled) will use the HVACSPT2 routine
and the unoccupied set points.
TheVAVRATlogicalsohasaspecialfeaturethatisactive
during the unoccupied period. The logic will sample the return
air temperature to determine whether or not a mode is neces-
sary. An unnecessary mode can occur when the sensor(s) read
the temperature with the supply fan off and the duct airflow
stagnant. In addition, there is a configuration parameter
(SAMP), which can reschedule a re-sampling of the airstream.
This feature will result in the supply fan turning on during un-
occupied periods.
The temperatures and configuration items that are used are
listed below.
Temperatures
• Space Sensor Temperature (SPT) — This is the temperature
measured by the T55 sensor. It is used in the unoccupied
mode to initiate operation. This can be read in the
TEMPERATURE-UNIT submenu.
• Evaporator Discharge Tmp (EDT) — This is the tempera-
ture of the air leaving the evaporator coil and is used for
control of cooling and economizer control. This can be read
in the TEMPERATURE-UNIT submenu.
• Return-Air Temperature (RAT) — This is the temperature
of the return duct air temperature. This can be read in the
TEMPERATURE-UNIT submenu.
• Mixed-Air Temperature (MAT) — This is the temperature
of the air after the economizer and before the evaporator
coil. This is a calculated value. The control routinely
calibrates the economizer to develop an equation to
calculate the MAT based on the OAT and RAT. This can be
read in the TEMPERATURE-UNIT submenu.
• Outside-Air Temperature (OAT) — This is the temperature
of the outside air temperature entering the economizer hood.
This can be read in the TEMPERATURE-UNIT submenu.
Set Point
• Supply Air Set Point (SA.SP) — This is the supply air set
point that is used during cooling with the economizer and
compressor. It can be set using the SETPOINTS-SA.SP
submenu.
• Supply Air Heating Set Point (SA.SH) — This is the supply
air temperature set point used for staged gas heating.
Configurations
• Estimate MAT? — This is used to enable the mixed air esti-
mation routine. It is located in the CONFIGURATION-
UNIT submenu. If there is a need to reset the self learning
table, use the Reset Mixed air temperature table (R.MAT)
configuration.
• VAVUnocc.FanRetryTime(SAMP)—Thisisusedinthe
unoccupied mode to allow for sampling of the space
temperature using the return air temperature.
• VAV Occupied Cool On Set Point (V.C.ON) — This is the
temperature set point at which a VAV unit in the occupied
mode will begin to attempt to maintain the Supply Air
Set Point (SASP). It is configured in SETPOINTS-COOL
submenu.
• VAV Occupied Cool Off Delta (V.C.OF) — This is the delta
temperature below the VAV Occupied Cool On Set point
(V.C.ON) at which a VAV unit in the occupied mode will
stop attempting to maintain the Supply Air Set point
(SASP). When the temperature is below this set point,
the unit will be in the Vent mode. It is configured in
SETPOINTS-COOL submenu.
VENTING MODE — For all units, the venting mode is used
between heating and cooling modes, when outside air is used
for ventilation and IAQ control. In this mode, cooling is not ac-
tive and the damper will be at the minimum position. If
equipped with an IAQ sensor, the damper will modulate closed
as determined by the indoor IAQ CO
2
levels.
If the unit is operating in vent mode and the resulting
supply-air temperature is too cold, then tempering of the supply
air will be enabled. The air is heated with gas or electric heat to
meet the Tempering Vent Set points (T.VO and T.VU).
Tempering can also be used in cooling when the economizer is
at the minimum effective damper position but the supply-air
temperature is below the appropriate Tempering in Cool Set
point. (T.CL).