Fan Mode; Plenum Warmup/Purge; Fan Proof Failure; System Shutdown - Emerson Site Supervisor User Manual
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- Quick setup manual (9 pages)
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5.6.9
Fan Mode
The fan can be designated as Continuous, Auto, or
Summer On/Winter Auto. There are separate fan mode
settings for occupied heating, unoccupied heating,
occupied cooling and unoccupied cooling. When the fan
mode is set to "Auto", the fan only turns on if there is an
active stage of heating/cooling or if economization is
enabled. When the fan mode is set to "Continuous", the
fan runs continuously in the selected heating or cooling
mode, regardless of whether any stages of heating or
cooling are currently active. When the fan mode is set to
"Sum ON/Win Auto", the fan runs continuously during the
summer season, and runs in Auto mode during the winter
season.
5.6.10 Plenum Warmup/Purge
The application supports a plenum warmup/cooldown
delay on startup and a purge delay when turning off. There
are separate delays for both heating and cooling modes,
and these are only used when the fan is in Auto mode. The
warmup/cooldown delays allow the plenum to reach a
target temperature before turning on the fan to prevent
undesirable supply air from reaching the building
occupants. The purge delays are used to extract the
remaining heat/cold from the plenum after the heating/
cooling has turned off.
5.6.11 Fan Proof Failure
When Fan Prf Fail En is enabled and a fan proof failure
is detected, heating and cooling loads are shut down until
the proof failure goes away or the fan proof alarm is reset
or cleared. If the fan is configured to shut down on a fan
proof failure, the system is restarted by setting the FAN
FAIL RST input to ON or clearing the fan proof failure
from the advisory log.
5.6.12 System Shutdown
If the SHUTDOWN input is turned ON, the
application goes into a shutdown mode that turns off the
fan. The fan remains OFF as long as the SHUTDOWN
input is ON.
5.6.13 Economization (Damper)
Control
HVAC economizers can save energy in buildings by
using cool outside air as source of cooling the indoor
space. When the temperature of the outside air is less than
the temperature of the re-circulated air, conditioning the
outside air is more energy efficient than conditioning re-
circulated air. When the outside air is both sufficiently
cool and sufficiently dry (depending on the climate), the
amount of enthalpy in the air is acceptable and no
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Site Supervisor Controller User Guide 2.0
additional conditioning of it is needed; this portion of the
air-side economizer control scheme is called free cooling.
The AHU economizer control operation depends on
whether a two-position or variable position damper control
is used. The user may also select "None" as the
economizer damper type if no economization is desired.
The Two Basic Operations of the Economizer
Algorithm are Divided into:
1.
Determine if economization should occur:
• Is the outdoor air suitable for economizing?
• Is the AHU in heat mode?
• Is there a failure in the AHU?
• Does the control temperature require cooling from
economization?
• Is the supply temperature too low?
2.
Determine the analog damper position:
Steps to Determine if Economization Should Activate
The algorithm begins with determining whether
economization should occur. This is determined by five
inputs:
1.
Is the outdoor air suitable for economizing?
2.
Is the AHU in heat mode?
3.
Is there a failure in the AHU?
4.
Does the control temperature require cooling
from economization?
5.
Is the supply temperature too low?
Outdoor Air Suitability
The economizer outdoor air suitability algorithm
determines whether outdoor air conditions are suitable for
the algorithm to enable economization. The result of the
algorithm is an "Econ OK" signal. The suitability is
determined by comparing the outdoor air temperature to
the control temperature. If the outside air temperature is
cooler, then the Econ OK signal is set to ON.
In addition to the outdoor air temperature, there is a
user-defined maximum outdoor air humidity setpoint
(Max OA Hum) above which outdoor air is not used for
economization. In this case, the Econ OK signal is set to
OFF.
Heat Mode
If the AHU is in heating mode, economization is
disabled. Economization is a cooling function and would
therefore be counterproductive to heating.
Failure Lockout
If the AHU application has detected a failure,
economization is disabled. Failures that can lock out
economization are:
026-1800 Rev 3 02-AUG-2016
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