Heating And Cooling Control; Control Logic; Heat/Cool Lockout Based On Outside Air Temperature; System Shutdown - Emerson Site Supervisor User Manual

can be a single space temperature, a combination of two
space temperatures, or the return air temperature.
The Controlled By parameter specifies which sensor
is used as the control temperature.
NOTE: Either Space or Return may be
selected.
The Num Space Temps parameter specifies the
number of space temperature inputs that will be used. Note
that either one or two may be selected.
The Temp Comb Meth parameter specifies how two
space temperature sensors are combined. The possible
selections are:
• Average - The control temperature is the average
value of all sensors.
• Min - The lowest temperature value is used as the
control value.
• Max - The highest temperature value is used as the
control value.
5.6.4

Heating and Cooling Control

The AHU application supports up to four stages of
heating and four stages of cooling. Additionally, the
application supports up to two heat pump stages.
5.6.5

Control Logic

The application will control heat and cool stages using
a T-Stat strategy. This strategy utilizes a deadband to
determine when heating or cooling stages should be
switched on or off.
Deadband
T-Stat Deadband specifies the range of temperatures
around the heat and cool setpoints within which the
temperature is considered acceptable. When the control
temperature is between the current setpoint plus 1/2 the T-
Stat Deadband and the current setpoint minus 1/2 the T-
Stat Deadband, the AHU will keep all stages in their
current states and will not activate or deactivate any
stages.
Multiple Stage Support
Multiple Stage Support is activated based on a stage delay
in conjunction with the T-Stat Deadband parameter when
multiple heating or cooling stages are defined.
The Two Delay Parameters are the Following:
• Cool Stage Delay - The delay between cool stage
activations or deactivations. After a cool stage is
activated, the AHU waits an amount of time equal
HVAC Control
to the Cool Stage Delay. If the temperature is still
above the cool setpoint (plus one-half the
deadband) it activates the next stage of cooling.
Similarly, after a cool stage is deactivated, the AHU
waits until the Cool Stage Delay has elapsed, and if
the temperature is still below setpoint (minus one-
half the deadband) it deactivates the next cool
stage.
• Heat Stage Delay - The delay between heat stage
activations or deactivations. After a heat stage is
activated, the AHU waits an amount of time equal
to the Heat Stage Delay. If the temperature is still
below the heat setpoint (minus one-half the
deadband) it activates the next stage of heating.
Similarly, after a stage is deactivated, the AHU
waits until the Heat Stage Delay has elapsed, and if
the temperature is still above setpoint (plus one-half
the deadband) it deactivates the next heat stage.
5.6.6 Heat/Cool Lockout Based on
Outside Air Temperature
The heating and cooling functions can be disabled if
the outside air temperature is outside of a specified range.
Cooling can be configured for OAT lockout by setting
the "Cool Lockout En" parameter to Yes. When enabled, if
the outside air temperature falls below the value specified
by "COOL OAT LO, C", all cooling functions are
disabled. When the outside air temperature rises above this
setpoint, cooling is enabled.
Heating can be configured for OAT lockout by setting
the "Heat Lockout En" parameter to Yes. When enabled, if
the outside air temperature rises above the value specified
by "HEAT OAT LOC", all heating functions are disabled.
When the outside air temperature falls below this setpoint,
heating is enabled.
5.6.7

System Shutdown

If the SHUTDOWN input is turned ON, the
application goes into a shutdown mode that immediately
turns off any heating or cooling stages presently on. The
heating and cooling stages remain OFF as long as the
SHUTDOWN input is ON.
5.6.8

Fan Control

The AHU application supports a single-speed indoor
fan.
NOTE: The variable speed fan support may be
incorporated into this application in a later
phase of the product.
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