Start-up
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Microprocessor control system
Zehnder Rittling Horizontal Heat Pumps feature a
microprocessor-based control system. The control
system is specifically designed to protect the unit
against abnormal building system conditions including
high voltage spikes and brown-out situations, EMI,
and RFI interference. The control system interfaces
with a heat pump-type thermostat or a digitally
communicating thermostat.
Features
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Rapid system refrigerant pressure equalization to
prevent hard compressor starts
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Anti-short cycle time for compressor operation
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Random start on power up mode
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Low/high voltage protection
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Unit shutdown on high or low refrigerant pressures
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Unit shutdown on low water/air temperature
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Solid-state condensate overflow protection
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Option to reset unit at thermostat or disconnect
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If a fault occurs 3 times sequentially without
thermostat meeting temperature, then lockout
requiring manual reset will occur
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Time delay override for servicing
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Light emitting diodes (LEDs) on circuit board to
indicate high or low pressure, high or low voltage,
low water/air temperature, condensate overflow,
control voltage status, temperature sensor failure
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The low-pressure switch shall not be monitored
for the first 60 seconds after a compressor start
command to prevent nuisance safety trips
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24V output to cycle a motorized water valve or other
device with compressor contactor.
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Water coil low temperature sensing (dip switch
selectable for water or anti-freeze)
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Two speed fan control of cooling and heating modes
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Removable thermostat connector
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Two dry contact accessory relays that can be
cycled with the compressor or the fan
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Ability to work with heat pump thermostats using O
or B reversing valve control
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Emergency shutdown contacts
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Relay to operate an external damper
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Ability to automatically change fan speed from
multistage thermostat
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24V relay to start system pump
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50VA control transformer - with load side short
circuit and overload protection via a built in circuit
breaker
Digital communicating thermostat
The microprocessor control system communicates
with the thermostat to display (at the thermostat) the
unit status, fault status, and specific fault condition.
The digital communicating thermostat has an infrared
remote control unit for operation of the temperature
set point, mode and fan.
RS-485 communication port
The microprocessor shall have an RS-485 serial
communication port that will allow connection of a
PC. This port will allow read and write access
to the microprocessor with proprietary software
for maintenance and servicing functions. The
RS-485 serial communication port shall also allow
connections of BACnet and LonWorks application
cards for connection to BAS systems.
