KMC Controls BAC-4000 series, Installation, Operation, And Application Manual

Page: 75 / 128

Economizer cooling
for roof top and
heat pump units
Some models of the AppStat include programming for an economizer. This
programing controls an economizer outside air damper connected to the
output terminal (ECON).
Note:
The optional economizer can be enabled only if outside air temperature
and
discharge air temperature sensors are connected to the AppStat.
The optional 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 PID loop
modulates from 0% to 100% as the Discharge Air Temperature rises above the
Discharge Air Temperature setpoint. 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 fan and staging sequences for heat pump units are similar to the roof top
unit fan and staging sequences. See the topics
Staged heating and cooling for for
roof top and heat pump units on page 74 and Fan control for roof top and heat
pump units on page 74
.
Reversing valve action
The AppStat reversing valve output, terminal 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 terminal is active only on a call
for heating when the compressors are locked out. The compressors are locked
out when the outside air temperature drops 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.
Installation, Operation, and Application Guide for AppStat Section 5: Sequences of operation
Revision G 75