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). See Fig. 9. The
system temperature is controlled by the System sen-
sor (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 toggles off the System Pump (P2) when an indi-
rect 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) is delayed “off” as user defined
in the
BOILER
menu, and System Pump (P2) is 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
17
Fig. 11: MODE 3 - Single Boiler with Indirect
on Boiler Loop
Fig. 12: WH Units - Single Water Heater with Tank
H Units - Single Boiler with Process Tank
NOTE:
WH units will operate to a maximum tank
temperature of 150F. For temperatures required
above 150F an “H” model boiler must be used and
great care must be given to ensuring water hardness
is less than 5 grains per gallon to ensure scale free
operation. MODE 1 should be used and configured
for setpoint operation for process heating applica-
tions using a Manual Differential set for between 3
and 5ºF.
(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)
is delayed “off” as user defined in the
BOILER
menu,
and System Pump (P2) is 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.
WH – Direct DHW Configuration
When the unit is ordered as a “WH” configuration the
only application available to it is direct DHW with sin-
gle or multiple heaters (Maximum 4 heaters). The tank
temperature is controlled by the System sensor (S3).
The Boiler Pump (P1) runs during any call for heat.
The System Pump (P2) output is active whenever the
system is enabled. The Boiler Pump is delayed “off”
after the Tank Target temperature is achieved and as
user defined in the
BOILER
menu.
Maximum distance not to exceed 4 pipe
diameters or 12” whichever is less
NOTE:
A Tank Aquastat can be used in lieu of the
Indirect DHW Sensor (S5). See the VERSA IC
Applications Guide for additional details.
NOTE:
Indirect DHW pump contacts are not active
in this configuration.
