Premisys MP - Page 22

22
Packaged and Split Rooftop Ventilator
© 2021 Mitsubishi Electric US, Inc.
PremiSys
Optional Component Operation
Electronically Commutated (EC) Condenser
Fans with Standard Scroll or Digital Scroll
Compressors
The EC condenser fan(s) will modulate up and down
to maintain the optimal liquid line pressure using built
in control sequences within the factory controller. One
pressure transducer is provided with each refrigeration
circuit for monitoring and the factory controller will ramp
condenser fan(s) up or down based on the condenser
set point.
Economizer Fault Detection Diagnostics
Provides the status and faults of the air economizer
to indicate proper economizer sequence operation.
This assures the benets of free cooling when outdoor
conditions are suitable for economizer functions. The
fault detection diagnostics system will indicate when
free cooling is available and if the outside air damper
and recirculation damper are reacting properly. If the
dampers are not functioning correctly an alarm will be
generated.
Air-Source Heat Pump
Operating Conditions and Limitations
To operate in Cooling mode, the following conditions
must be true:
1. Supply air temperature above minimum low supply
temperature limit (35°F)
2. Outside air temperature above the cooling ambient
lockout (55°F, adj.)
To operate in Heating mode, the following conditions
must be true:
1. Supply air temperature below maximum high supply
temperature limit (120°F)
2. Supply air temperature above 35°F
3. Outside air temperature above the low ambient
lockout (10°F, adj.)
For more information on air-source heat pump operation,
reference the supplemental Reference Guide for
Microprocessor Controller.
Airow Monitor
A factory-wired, mounted, and powered airow
monitoring system is provided in the outdoor, supply,
and/or exhaust air streams. The airow control system
displays outdoor, supply, and/or exhaust air in actual
cubic feet per minute (CFM) at factory controller or
can be read by a building management system if
communication is established.
Operation
Outdoor airow monitoring is accomplished using two
thermal dispersion sensors that accurately measure
airow velocity down to zero feet per minute (fpm). The
airow controller takes the average measurement for
two sensor congurations, and determines the outdoor
airow rate based on the e󰀨ective intake area. Field
calibration of the outdoor airow monitoring device
determines the e󰀨ective intake area of the unit. For
additional information on how to navigate through the
outdoor airow controller menus, refer to technical
manuals from GreenTrol® Automation Inc. at www.
greentrol.com.
Supply and/or exhaust airow monitoring is
accomplished by measuring the pressure drop across
the fan inlet venture. The airow is then calculated by the
factory controller based on the measured pressure drop
and a K-Factor specic for each fan size.
Hot Gas Reheat Valve
Units equipped with a reheat coil use a three-way
valve with actuator to control the supply air discharge
temperature of the unit during dehumidication mode.
The unit controller provides a 0-10 VDC signal to control
the amount of reheat to meet the supply temperature set
point.
Controls by Others
The reheat coil needs to be purged to ensure adequate
oil return. It is recommended that every six hours of
reheat compressor run time should initiate a six minute
purge cycle. During the purge cycle, the reheat valve
should be modulated to 100% open to the reheat coil.
IMPORTANT
Air-source heat pumps are equipped with a defrost
cycle to remove ice from the outdoor coil. During
defrost cycles, melted water may drip from the bottom
of the refrigeration section under the outdoor coil. In
cold climates, proper drainage/heat tape must be
installed under the outdoor coil to prevent the buildup
of ice on the roof.
IMPORTANT
Melted water from snow accumulation on the unit
roof can be sucked into outdoor fans, resulting in ice
formation on fan blades under certain conditions.
Remove snow accumulation from the unit roof and
outdoor coil section after snow storms.
IMPORTANT
For the outdoor airflow monitoring device to perform
as intended, field calibration is required. Calibration of
the airflow monitoring device requires an independent
measurement of airflow and should be performed
when the system undergoes test and balance.