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Outdoor Design
The Outdoor Design temperature must be set to OFF.
Mixing Target
The Mixing Target temperature is set to the desired operating temperature of the system.
Delta T Max
The Delta T Max temperature is set to the maximum temperature difference that is desired between the system return temperature
and the system supply temperature. In order to adjust this setting, a system return sensor must be connected to the control.
Setpoint and Delta T Settings
150
140
130
120
110
100
90
80
70
60
Supply Temperature (F)
Mix Supply = Mix Target
Setpoint
Time
Heat Source Operation
The VSMC operates the heat source in two basic modes of operation. The VSMC can either “Control” the heat source or “Enable” the
heat source. The mode of operation is determined by the Heat Source Sensor location. The heat source sensor location is determined
using the DIP switch on the back of the circuit board. If the DIP switch is set to ON, the heat source sensor is to be located on the heat
source supply. If the DIP switch is set to OFF, the heat source sensor is to be located on the heat source return.
• If the DIP switch is set to On, the VSMC will “Control“ the heat source (sensor on supply).
• If the DIP switch is set to Off, the VSMC will “Enable” the heat source (sensor on return).
• If the Heat Source Sensor has not been installed, the VSMC will “Enable” the heat source.
HEAT SOURCE CONTROL
When the VSMC controls the heat source, the VSMC opens and closes the heat source contact in order to control the temperature of
the heat source supply water temperature. When the VSMC is controlling the heat source temperature, the VSMC will determine the
heat source supply water temperature that is required to satisfy the demands of the system. The VSMC will also determine a differen-
tial that is sufficient to minimize short cycling of the heat source. The VSMC will then cycle the heat source using these parameters.
Differential
An on / off heat source must be operated with a differential in order to prevent short cycling. When the supply water temperature
drops
1
/
2
of the differential below the required heat source supply temperature, the heat source is turned on. The heat source is then
Com Heat
Dem
Boil Out
Unpowered
Demand
Switch
Unpowered Demand
The VSMC recognizes an Unpowered Demand signal when a switch is closed between
the Com and Heat Dem terminals (relay type thermostat or end switch on zone control).
SYSTEM PUMP OPERATION
The VSMC has an internal system pump contact. This contact turns on when the VSMC
has a mixing demand. The system pump as well as an external heat source pump may be
controlled by this relay. By providing proper flow in the heat source loop, the heat source
temperature can be accurately controlled based on the mixing load.
Start
Time
120
110
100
90
80
70
60
50
40
30F
Supply Temperature (F)
Mix Target
Delta T Maximum
Mix Supply
Mix Return
Maximum Delta T
Variable Speed Mixing Control
ONOFF
1
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