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McQuay Enfinity horizontal water source heat pumps
are available with a factory mounted and tested Alerton
BACnet unit controller as a special . The unit controller is
factory programmed and tested with all the logic required
to control the unit, and is designed to communicate over
a BACnet MS/TP communications network to an Alerton
BACtalk building automation system (BAS) . Each individual
controller must be programmed with a unique mac address .
Each controller must be physically addressed at the board
using dip switches . The controller operates the compressor,
fan, and reversing valve as required to maintain the space
temperature within the current setpoints . Data regarding
equipment status, water and air temperatures, and fault
conditions can be monitored by an Alerton BACtalk BAS .
Setpoints and other system preferences must be changed
remotely using an Alerton BACtalk workstation or Alerton
service tool software .
The controller makes operational data and commands
available on the Alerton BACtalk network using BACnet
objects and properties . Each heat pump controller connects
to the BACtalk network using a BACnet MS/TP LAN, which
is a simple twisted-pair communications connection that
operates at up to 76 .8 Kbps . DIP switches on the control-
ler enable the MS/TP MAC address to be set in the range
0-127 . A status LED on the unit indicates communication
activity on the MS/TP LAN .
Each BACnet-compliant unit includes discharge air and
leaving water temperature sensors, as well as all safety
sensors, signals, and switches . Wall-mounted room sen-
sors are available from Alerton to control heating and cool-
ing operation . Available sensors include tamper-resistant
stainless steel wall sensors with optional push-button for
status override; wall-mounted sensors with tenant setpoint
adjustment lever and timed-override button; wall-mounted
sensors with LED status, timed-override button, tenant set-
point adjustment buttons, password-protected field service
access to operational data, and optional humidity sensor;
and wall-mounted sensors with LCD and programmable
operation .
BACnet
®
WSHP unit controller
Each BACnet-compliant controller has the following operat-
ing features:
●
Start-up – The unit will not operate until all the inputs and
safety controls are checked for normal conditions .
●
Fan operation
– Fan operation can be customized in
software to run continuously during occupied mode, or to
cycle ON or OFF appropriately on a call for heating and
cooling .
●
Cooling mode
– On a call for cooling, the compressor
and fan start immediately . Compressor run-time is cal-
culated as a percent of full cycle time (17 minutes) using
proportional-integral control to maximize efficiency .
●
Heating mode
– On a call for heating, the compressor
and fan start immediately, and compressor run-time
is calculated as a percent of full cycle time (17 min-
utes) using proportional-integral control to maximize
efficiency .
●
Short Cycle Protection and Random Start
– A start
delay of 180 seconds plus the compressor’s MAC
address in seconds prevents short-cycling and simul-
taneous start-up . A minimum 2-minute on time and
5-minute off time for the compressor further ensures
short-cycle protection .
●
Occupied Mode
– A simple software control signal
from the building automation system or a wall-mounted
unit puts the unit into occupied mode . The unit controls
compressor and fan operation to maintain occupied
setpoints . High and low limits for occupied setpoints are
software configurable .
●
Unoccupied Mode
– A simple software control signal
from the building automation system or a wall-mounted
unit puts the unit into unoccupied mode for night set-
back operation . The unit controls compressor and fan
operation to maintain unoccupied heating and cooling
setpoints, which are also software configurable .
●
After-hours Override Mode
– A simple software control
signal from the building automation system or a wall-
mounted unit can initiate after-hours heating or cooling
in half-hour increments . Maximum override time is soft-
ware configurable up to 9 .5 hours . This feature can also
be disabled in software .
●
Reversing valve delay
– When the compressor turns
off after heating mode, the reversing valve remains
energized for 60 seconds before it returns to the normal
cooling position to eliminate swishing . The reversing
valve energizes 10 seconds before the compressor .
●
Load Shed
– Load shedding can be orchestrated by the
building automation system using the occupied/unoccu-
pied command in software .
●
Brownout Protection
– An onboard sensor measures
input voltage and suspends compressor and fan opera-
tion if the supply voltage drops below 82% of the normal
line voltage for a minimum of 10 seconds, creating an
alarm available in software . The alarm automatically
resets when the supply voltage returns to above 90% of
normal .
BACnet
®
WSHP Unit Controller