Copyright © D 361 -
03/09
9 of 20
Section C2: Boiler Sensor Placement
BOILER SENSOR ON THE SUPPLY (
Boiler Sensor
DIP switch
= Supply
)
The boiler sensor can be located on the boiler supply if the 361 is the only control that is
operating the boiler. When in the supply mode, the 361 determines the required operating
temperature of the boiler using
Boiler Load Reset. With Boiler Load Reset, the 361 operates
the boiler at the lowest possible supply temperature that is sufficient to satisfy the
requirements of the variable speed injection pump. If this mode of operation is selected,
the boiler pump should either operate continuously, or be operated in parallel with the
system pump contact (
Sys Pmp).
Note:
The boiler pump should not be operated by the boiler’s aquastat, as this may lead to
improper cycling of the boiler because of inconsistent flow past the boiler supply sensor.
BOILER DIFFERENTIAL (BOIL DIFF)
An on / off heat source such as a boiler must be operated with a
differential in order to prevent short cycling. When the boiler supply
temperature drops below the bottom rail of the differential, the 361 closes
the
Boiler contact to fire the boiler. When the boiler supply temperature
rises above the top rail of the differential, the 361 opens the
Boiler contact
to turn off the boiler. With the 361, either a fixed or automatic differential
setting is selected. If automatic differential (
Ad
) is selected, the 361
automatically adjusts the boiler differential under the current load condi-
tions to avoid short cycling.
BOILER SENSOR ON THE RETURN (
Boiler Sensor
DIP switch
= Return
)
The boiler sensor should be located on the boiler return if the 361 is one of many controls
that can call for boiler operation. When in the return mode, the 361 provides a boiler
enable as described in the BOILER ENABLE section. The 361 no longer tries to control
the boiler supply water temperature directly, but allows the boiler to operate at its operating
aquastat setting when required. If this mode of operation is selected, the boiler pump
should either operate continuously, or be operated in parallel with the system pump contact
(
Sys Pmp).
Note
: The boiler pump should not be operated by the boiler’s aquastat, as this may lead to
improper cycling of the boiler because of inconsistent flow past the boiler sensor.
NO BOILER SENSOR
The 361 is capable of operating without a boiler sensor if desired. Without a boiler sensor,
the 361 provides a boiler enable as described in the BOILER ENABLE section, but is
unable to provide boiler protection. This type of application is typical if the 361 is drawing
heat from a heat source that already incorporates some form of boiler protection.
BOILER ENABLE (
30% Enable / 10% Enable
)
The 361 has a DIP switch that allows for the selection between a 30% boiler enable and a 10% boiler enable. This switch is only
functional when the
Boiler Sensor DIP switch is set to Return.
In the 30% position, the 361 closes the
Boiler contact when the variable speed output exceeds 30%. The Boiler contact remains
closed until the variable speed output reduces below 15%. This setting would normally be chosen for low mass boilers (copper fin-
tube, etc.), or systems with low thermal mass in the loop between the boiler and the variable speed injection pump.
In the 10% position, the 361 closes the
Boiler contact when the variable speed output exceeds 10%. The Boiler contact remains
closed until the variable speed output reduces below 5%. This setting is normally chosen for high mass boilers (cast iron, steel fire-
tube, etc.), or systems with large thermal mass in the loop between the boiler and the variable speed injection pump.
In order to prevent short cycling, the
Boiler contact has a minimum on time, and a minimum off time.
Boiler supply
sensor
Boiler return
sensor
No boiler
sensor
Supply W
ater
T
emperature
Time
Differential = 10
°
F (5
°
C)
165
°
F(74
°
C)
B
o
ile
r
o
ff
B
o
ile
r
o
n
155
°
F (68
°
C)
160
°
F (71
°
C)
B
o
ile
r
o
ff
B
o
ile
r
o
n
