Raypak MVB 1104A, Installation & Operating Manual

Page: 17 / 64

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Mode 2 (Type H Units Only)
This mode selection is for hydronic heating systems
with single or multiple boilers (Maximum 4 boilers) in
primary/secondary piping configuration with or without
Outdoor Air Reset (S4) with indirect DHW on the sys-
tem loop (with or without priority). The system
temperature is controlled by the System sensor (S3).
The Indirect DHW sensor (S5) determines the indirect
call/tank setpoint. The system temperature is boosted
to Target Max when using the Indirect DHW sensor
(S5) during an indirect call for heat. Priority mode tog-
gles off the System Pump (P2) when an indirect call for
heat is present. The Boiler Pump (P1) runs during any
call for heat. The Indirect DHW Pump (P3) runs during
an indirect call for heat with no “off” delay. The Boiler
Pump (P1) and System Pump (P2) delay “off” as user
defined in the ADJUST menu. The System Pump (P2)
runs whenever the system is enabled for heating and
the outdoor air temperature is lower than the WWSD
temperature setting (if utilized) unless an indirect call
for heat is present with priority.
Mode 3 (Type H Units Only)
This mode selection is for hydronic heating systems
with single or multiple boilers (Maximum 4 boilers) in
primary/secondary piping configuration with or without
Outdoor Air Reset (S4) with indirect DHW on the boil-
er loop (with priority). The system temperature is
controlled by the Supply sensor (S3) whenever the
indirect call for heat is not active . The DHW Supply
sensor (S5) determines the indirect call/tank setpoint.
During an indirect call for heat the boiler firing rate is
determined by the water temperature at the Indirect
Supply sensor (S6) and the Target Max setting when
using the Indirect DHW sensor (S5). The Boiler Pump
(P1) runs during all heat calls regardless of priority.
The Indirect DHW Pump (P3) runs during an indirect
call for heat with no “off” delay. The Boiler Pump (P1)
and System Pump (P2) delay “off” as user defined in
the ADJUST menu. The system pump (P2) runs
whenever the system is enabled for heating and the
outdoor air temperature is lower than the WWSD tem-
perature setting (if utilized) unless an indirect call for
heat is present.
Fig. 15: MODE 2 - Single Boiler with Indirect
on System Loop
Fig. 16: MODE 3 - Single Boiler with Indirect
on Boiler Loop
NOTE: A Tank Aquastat can be used in lieu of the
Indirect DHW Sensor (S5). See the Versa IC manu-
al for additional details.
NOTE: MODE 1 can also be used for process heat-
ing applications in conjunction with a buffer/storage
tank when operating temperatures above 160 ° F are
required. Care must be given to ensure water hard-
ness is no more than 15 grains per gallon for scale
free operation.
Domestic Hot Water
When designing the water piping system for domestic
hot water applications, water hardness should be con-
sidered. Table G indicates the suggested flow rates for
soft, medium and hard water. Water hardness is ex-
pressed in grains per gallon.