Carrier Aquazone 50PSW025-420 Installation Instructions Manual page 35

Configuring Multiple W2W WSHP for 
MS/TP Operation
On installations having multiple Water-to-Water Source Heat
Pumps serving a common load, the heat pumps may be controlled
as a singular heating or cooling source utilizing the Multi-unit
MS/TP Operating Mode.
For these installations, the modules are networked together over
the BACnet MS/TP bus. One of the installed Water-to-Water
Source Heat Pumps operates as a Primary control, with the
remaining modules operating as Secondary. Configured thus, the
number of stages required to meet load conditions are determined
by the Primary control. Secondary modules will receive the num-
ber of stages required from the Primary, and will energize their
compressor outputs appropriately in sequence.
In this fashion, a Multi-unit MS/TP system can provide for up to
eight total stages of control. A Multi-unit MS/TP system will
provide coordinated heat pump operation with the same feature set
and sequences of operation as that provided by a Single Unit
configuration.
In this configuration, an independent leaving load water
temperature safety check at each unit is included to verify that
sufficient load water flow is provided. Should the leaving load
water temperature fall below the configured "Chilled Water
Setpoint" in cooling or the "Hot Water Setpoint" in heating, the
compressor stages for any unit (primary or secondary) will be re-
duced as needed without reducing the system staging
requirements.
NOTE: Before configuring the units as a Multi-unit Primary
systems, be sure to verify configuration for each secondary unit
for standalone operation as a fail-safe. Many individual configura-
tion parameters that are not required or used during secondary op-
eration such as the chilled water and hot water setpoints are hidden
(see screen captions below for hidden points) once the secondary
is linked to a primary unit. See Fig. 23-25 for visual representa-
tions of configuration.
W2W PRIMARY CONFIGURATION PARAMETERS
The following configuration parameters can be accessed in the
following figures. (See Fig. 23-25.) Properties Control Pro-
gramConfigurationService Configuration
Operation Type
Multi-unit MS/TP (default value is Single/Secondary Unit)
Total Controlled Stages
1 - 8 (this variable is the total number of stages of all W2W units
to be linked into one single system)
Control Mode Selection
For two pipe systems Manual Heat or Manual/Cool, four pipe
systems SPT, OAT, or System T1Temp
Refrigerant Circuits
Configure for the correct number of refrigerant circuits in the unit
Compressor Stages
1 - 4 (this variable is how many stages the Primary unit is capable
of using) Default value is 2
W2W SECONDARY CONFIGURATION
The following configuration parameter can be accessed in the
following table. Properties Network Points.
1. Total Req Sys Comp Stgs = bacnet://<device instance of
primary>/av:88001.
NOTE: This parameter needs to be configured first because
configuration parameters for steps #3, #5, #6 below are hidden
until the Secondary and Primary units are linked together through
Total Req Sys Comp Stgs.
The following configuration parameters can be accessed in the
following table. PropertiesControl
tionService Configuration.
2. Operation Type - Single/Secondary unit.
3. System Stage # Assigned to Y1 - This value defines when
each secondary unit will start its first stage Y1output of con-
trol for system staging.
4. Compressor Stages - Total number of compressor stages for
each individual unit.
5. Stage Number of 2
Compressor Stages = > 2) - On each unit with Compressor
Stages set to 2 or more, will be used to identify which output
stage (if any) will be used to verify feedback of the second
compressor, using the second stage feedback input. This is
always a one to one relationship unless unloaders are present.
6. Stage Number of 3
Compressor Stages = > 3) - On each unit with Compressor
Stages set to 3 or more, used to identify which output stage (if
any) will be used to verify feedback of the third compressor,
using the third stage feedback input. This is always a one to
one relationship unless unloaders are present.
Below is an example screen shot of the Service Configuration of a
Secondary Unit that has bound to a Primary W2W unit. The Sec-
ondary unit has 2 stages of compression and will be the third stage
in the system.
35
ProgramConfigura-
nd Compressor - (Option available when
Compressor - (Option available when
rd