McQuay IM 660-3
9
Description of Operation
Holding Mode
If the unit comes out of the heating or cooling modes into the
holding mode, the compressor de-energizes after the 2-minute
timer expires. The unit must stay in the holding mode with the
compressor off for 30 seconds before it is allowed to go into
the heating or cooling states. During this time, the reversing
valve is not allowed to switch states.
Tenant Override Mode
A wall-mounted tenant override switch is available for use
with all MicroTech 2000 WSHP unit controllers. Pressing and
holding the tenant override button for 1.0 to 6.0 seconds puts
the unit into tenant override mode for a set time period (default
= 60 minutes). Press the tenant override button again for 1.0 to
6.0 seconds and the unit returns to unoccupied mode by
default. A separate configuration property is available that
allows users to extend the tenant override period up to 60
minutes with a second button press. Except for the fact that it
is temporary, the Tenant Override operating mode is identical
to the Occupied operating mode.
L
ON
W
ORKS
only:
Pressing and holding the tenant override
button for at least 6.0 seconds but not more than 10 seconds
activates the network “query address” mode, indicating the
unit address in question at the MicroTech gateway panel.
L
ON
W
ORKS
only:
Pressing and holding the tenant override
button more than 10 seconds activates the network
“self-configure” mode, requesting the assignment of the next
sequential address from the MicroTech gateway panel.
L
ON
M
ARK
only:
Similar to pressing the service pin, pressing
and holding the tenant override button for more than 10
seconds causes the Neuron chip to broadcast a message over
the Lon network containing its unique 48-bit Neuron ID. This
is useful during network commissioning.
Load Shed Mode (L
ON
W
ORKS
only)
When the network load shed level is less than or equal to the
load shed threshold setting in the unit, load shedding is
activated. The amount the controller adjusts the set points
depends upon the network threshold level and the step value.
Optimal Start (L
ON
W
ORKS
only)
Whether heating or cooling, every start is an optimal start if
the optimal start window is greater than zero. The unit
controller optimal start logic examines past data to calculate
the optimal time to change the heat pump from unoccupied to
occupied operation. During optimal start, load shed and tenant
override are ignored.
If this option is selected, two hours (adjustable) prior to
scheduled time of occupancy, the unit begins calculating the
time required to bring the space temperature to occupied set
point. At the appropriate moment, the unit energizes and
begins heating or cooling as necessary. The unit notes actual
time to reach occupied set point and compares it to calculated
time. If the difference exceeds 15 minutes, the unit adjusts its
factors to adapt to actual room conditions.
Faults
The WSHP controller examines fault conditions in the order of
ascending priority. Higher priority faults do not override lower
priority faults. A higher priority fault must be manually
cleared before the WSHP controller can indicate a second,
lower priority fault. If the unit has only one compressor, faults
on the second circuit are ignored. For units with two
compressors, second circuit faults are lower priority than first
circuit faults. In a dual circuit unit, a second circuit fault
indication does not disable the unit unless the first circuit also
fails.