Velocity Shadow Series, Installation And Operating Instructions Manual

Page: 68 / 104

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CAUTION
Radiant heating systems generally require much lower boiler supply temperatures than those
required for a DHW demand. Such systems can be damaged by excessive water temperatures. When
such damage is possible, use an external control, such as a thermostatic mixing valve to limit the
temperature of the water entering the heating system.
C. Pump Control and DHW Priority
Pump operation in response to different demands is shown in Table 12.5. This behavior cannot be changed.
Like all boilers, this one is capable of regulating only one target boiler water temperature at any given time. This means that
priority must be given to either the CH or DHW target temperature. For this reason, the boiler gives priority to the DHW demand
for the first 60 minutes during which both calls for CH and DHW continuously exist. If there are still simultaneous calls for DHW
and CH at the end of this time, the boiler will continue to use the DHW target temperature, but will also operate the system pump
in an attempt to satisfy the call for heat. The boiler will once again use the CH target temperature when the call for DHW ends.
D. Frost Protection
Frost Protection starts the boiler and system pump, and fires the boiler, when low supply water temperatures and/or extremely low
outside air temperatures are sensed. The control does this as shown in Table 12.6.
TABLE 12.5: Summary of Target Temp and Pump Behavior
Status of:
Demands
None CH Only DHW Only
CH + DHW
(<60min)
CH + DHW
(>60min)
Boiler Pump OFF ON ON ON ON
DHW Pump OFF OFF ON ON ON
System Pump OFF ON OFF OFF ON
Target Temp NONE CH DHW DHW DHW
TABLE 12.6: Frost Protection Behavior
Device Started When Stopped When
Boiler & System Pump
Outdoor Sensor less than 0F
OR
Boiler Supply Sensor less than 45F
Outdoor Sensor greater than 2F
OR
Boiler Supply Sensor greater than 45F
Burner Boiler Supply Sensor less than 38F Boiler Supply Sensor greater than 50F
CAUTION
The boiler control helps provide freeze protection for the boiler water . Boiler flue gas condensate
drain is not protected from freezing. Since the Control only controls the system and boiler circulators
individual zones are not necessarily protected. It is recommended that the boiler be installed in a
location that is not exposed to freezing temperatures.