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Sequences of Operation
Fan Control for Rooftop and Heat
Pump Units
A user with Password 1 can set the BACnet™ Thermostat controlled fan
to either run continuously or to start automatically on a call for cooling
or heating.
Auto – When Auto is selected, the fan runs only when there is a call
for heating or cooling. It continues to run for the period set by the fan
delay timer after the call for heating or cooling.
ON – The fan will run continuously regardless of the heat/cool modes
or occupied state.
Economizer Cooling for Rooftop and Heat
Pump Units
Some models of the BACnet Thermostat include programming for an
economizer. This programming controls an economizer outside air
damper connected to the output terminal (ECON).
NOTE:
The economizer can be enabled only if outside air
temperature and discharge air temperature sensor are
connected to the BACnet Thermostat.
The economizer mode is enabled for cooling when the outside air
temperature (OAT) is 2°F below the value of the limit set by Economizer
Enable Temperature and disabled if the OAT is 2°F above the value of
Economizer Enable Temperature.
Once enabled, the economizer outside air damper opens to the larger
value of either the minimum damper position limit (Minimum Econ
Damper) or the Discharge Air Temperature loop. The Discharge Air
Temperature loop modulates from 0% to 100% as the Discharge Air
Temperature rises above the Discharge Air Temperature setpoint.
IO-DAPPS
The Discharge Air Temperature setpoint resets between room
temperature and the limit for minimum discharge air temperature
as the cooling loop varies between 0 and 50%. If the Discharge Air
Temperature decreases below 55°F, the Outside Air Damper returns to
the minimum damper position.
Heat Pump Unit Specific Functions
The heat pump unit fan and staging is similar to the roof top unit fan
and staging principles.
Reversing Valve Action
The BACnet Thermostat reversing valve output (O/B) is energized on
a call for cooling ('O' function). The action can be changed from the
user interface to be active on a call for heating ('B' function). The 'O'
function is the default.
Auxiliary or Emergency Heat Action
The heat pump unit AUX/E output is for auxiliary or emergency heat.
Operation can be configured for one of three modes.
Compressor lockout – The AUX/E output is active only on a call for
heating when the compressors are locked out because the outside air
temperature has dropped below the value of the Compressor OAT Low
Limit. The lockout is cleared when the outside air temperature rises
2°F above the value of Compressor OAT Low Limit.
Third stage – The AUX/E output functions as the output for a third
stage of heat.
None – This function is a manual operation that can only be turned
on from the user interface. When emergency heat is turned on, the
AUX/E output is used to maintain the active heating setpoint and both
compressor outputs are locked-out.
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