Brochure

Operating principle
The thermostatic sensor, completely immersed in the medium, controls the
movement of a shutter that regulates the bypass flow from the boiler and
toward the system. At boiler startup, the boiler protection recirculation and
distribution unit recirculates the bypass flow from the boiler to bring the
boiler up to temperature as quickly as possible (fig. 1). When the bypass
flow from the boiler Tf exceeds the setting of the fixed thermostatic sensor
Tset, the unit’s return from the system port starts opening to produce the
water mixing Tmix: in this phase the system loading begins (fig. 2).
When the mixed flow to the boiler temperature Tmix is greater than the
set point of the boiler protection recirculation and distribution unit by
approximately 18°F (10°C), the bypass flow from the boiler port closes
and water returns to the boiler at the same temperature as the return
flow from the system (fig. 3).
When power is out and the circulation pump stops running, the flapper
check valve, which is closed during normal operation, opens with a slight
pressure differential resulting from the effects of heated water in the
boiler and cooler water in the distribution syste, a natural thermosyphon
flow. This prevents a excessive heat buildup which eventually would
cause the pressure relief valve to open (fig. 4).
Tf = By-pass flow from boiler temperature, Tset = Boiler protection valve set point temperature,
Tmix = Mixed water temperature, Tr = Return from system temperature
Tf
NON-
CONDENSING
BOILER
By-pass from boiler
Mixed
to boiler
Return
from system
Tf
Tmix
Ts e t
Tr
by-pass open
system return
closed
1 1
TF ≤ Tset BOILER START UP
TF ≤ Tset, Tmix = Tf
TF ≤ Tset BOILER START UP
t by-pass open
t system return closed
TF ≤ Tset, Tmix = Tf
Tf
Tr
Tmix
Ts e t
-NON-
CONDENSING
BOILER
By-pass from boiler
Mixed
to boiler
Return
from system
Tf
Tmix
Ts e t
Tr
by-pass open
system return
closed
44
Pump OFF
Natural circulation flapper check valve open
Natural circulation of the medium
Pump OFF
Natural circulation flapper check valve open
Natural circulation of the medium
Tf
NON-
CONDENSING
BOILER
By-pass from boiler
Mixed
to boiler
Return
from system
Tr
Tmix
Ts e t
Tf
by-pass closed
system return
open
3 3
Tmix > Tset + 18°F SYSTEM LOADED
t by-pass closed
t system return open
TF > Tmix > Tset +18°F, Tmix = Tr
Tmix > Tset + 18°F SYSTEM LOADED
TF > Tmix > Tset +18°F, Tmix = Tr
Tf
NON-
CONDENSING
BOILER
Tf
Tmix
Ts e t
Tr
By-pass from boiler
Mixed
to boiler
Return
from system
by-pass open
system return
open
22
TF > Tset START OF SYSTEM LOADING
t by-pass open
t system return open
TF ≤ Tset, Tmix = Tf
TF > Tset START OF SYSTEM LOADING
TF ≤ Tset, Tmix = Tf