OM 1239
11 www.DaikinApplied.com
General use and information
The Microtech III unit controller is a water source heat
pump control platform used to control the heat pump in
all modes of operation, two compressors, loop pumps,
economizers, reversing valves, and all components used
to control conditioned space temperature and humidity.
By adding communications cards, (
L
on
W
orks
or BACnet)
network integration is possible. The controller can be used
with thermostat control or wall sensor control.
All MicroTech III unit controller inputs must be operated
by dry contacts powered by the control board’s power
terminals. No solid state devices (Triacs) may be used
to operate MicroTech III unit controller inputs. No outside
power sources may be used to operate MicroTech III.
All units must be properly grounded per local code
requirements. See the Installation and Maintenance
bulletin specific to your Water Source Heat Pump.
Sequence of operations
Assumes cycle fan operation - not continuous fan
operation:
■
Cooling
•
Cooling (mechanical) operation
– On an initial
call for stage 1 cooling, the fan will energize and
the 45 second flow timer will start. When the
compressor minimum off, and random startup
timers are expired, the unit will start in stage
1 cooling. If additional capacity is needed, the
unit wilili initiate stage 2 cooling. When the room
setpoint conditions are satisfied, the stage 2
compressor will shut off first followed by the stage
1 compressor. If fan cycling is enabled, the fan
will turn off once room setpoint conditions are
satisfied.
•
Secondary cooling operation - waterside
economizer
– This mode requires the optional
factory-installed waterside economizer. A
hydronic economizer coil, 3-way water valve and
temperature sensor are added to the unit. The
purpose of this mode is to satisfy some or all of
the cooling demand by using the loop water, which
is often reduced to 50°F or less via the cooling
tower to achieve sufficient cooling performance.
When a call for 1st stage cooling is engaged, with
the entering loop water below the economizer
changeover temperature, the H8 output on
the MicroTech III board is activated to open
the motorized valve allowing water flow to the
equipment. The compressor is locked out, the
3-way water valve opens to allow cool loop water
to flow through the economizer coil. The fan starts
after 30 seconds (unless it is already on thru
activation of the G terminal by the thermostat fan
switch “on”). On a further demand for cooling,
stage 2; the 1st compressor will start in the
cooling mode. On a further demand for cooling the
second compressor will energize. The waterside
economizer mode will not be activated if the
entering water temperature is below 35°F and an
alarm (fault) signal will be generated.
When the room setpoint conditions are satisfied,
the compressor will shut off, the 3-way valve will
close and the fan will either shut off (fan switch
”auto”) or continue to run (fan switch “on”). The
minimum off timer of 360 seconds starts. If the
loop temperature increases above the changeover
temperature, waterside economizer mode will
be suspended and the unit will resume normal
mechanical cooling mode with stage 1 of the
thermostat now starting the compressor.
■
Heating
•
Heating (mechanical) operation
– On an initial
call for stage 1 heating, the fan will energize, the
pump request will energize, the 45 second flow
timer will start. After the flow, compressor minimum
off, and random startup timers are expired, the
lead compressor will start, the reversing valve shall
energize 5 seconds after the lead compressor turns
on. If the stage 2 heating setpoint is reached, the lag
compressor will operate. When the room setpoint
conditions are satisfied, the compressors will shut
off. If fan cycling is enabled, the fan will turn off, once
room setpoint conditions are satisfied.
■
Secondary heating modes (field-installed)
•
Boilerless electric heat
– When the entering
water temperature is below setpoint, the
compressors will not be allowed to operate. On
an initial call for heating, the fan and electric heat
will start. When the room setpoint conditions
are satisfied, electric heat will be de-energized
and the fan will continue to operate at its “fan
only” setting when enabled, for continuous fan
operation. If fan cycling is enabled, the fan will
turn off after 30 seconds once room setpoint
conditions are satisfied.
•
Supplemental electric heat
– On an initial call for
stage #1 heating, the fan will energize, the pump
request will energize, the 45 second flow timer
will start. After the flow, compressor minimum off,
and random startup timers are expired, the lead
compressor will start, the reversing valve shall
energize 5 seconds after the compressor turns
on. If stage 2 heating settings are reached the
lag compressor will start. If stage #3 setpoint is
reached electric heat will start. When the room
setpoint conditions are satisfied, electric heat will
be de-energized and compressors will stop.
M
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