Boiler Connections
36
Installation Examples
(continued)
Low-loss header (field supplied)
Low-Loss Header
–Type 80/50
Part No. 7134 230
(max. flow rate 17.6 GPM / 4 m
3
/h)
–Type 120/80
Part No. 7134 244
(max. flow rate 35.2 GPM / 8 m
3
/h)
A low-loss header offers additional benefits
not provided by a pair of closely spaced
tees. Viessmann strongly recommends and
prefers the use of a low-loss header over
closely spaced tees.
When used in conjunction with the Vitodens
100-W boiler, the low-loss header acts as
hydraulic break, decoupling boiler and
system circuits from each other (no sensor
required).
It is recommended to use the low-loss
header in applications in which the total
system flow rate exceeds the maximum (or
minimum) boiler flow rate.
For maximum boiler flow rates, see table on
page 27 in this manual.
Viessmann strongly recommends the use of
a low-loss header in cases where the
system head and flow rates are unknown.
In addition, the low-loss header helps
eliminate air and debris from the heating
system.
See figures on the right for an illustration of
the principle of operation.
The low-loss header is available in the
following sizes. Select the size based on the
maximum system flow rate of your
application.
Model No.
Max. system flow rate
Type 80/50
17.6 GPM / 4 m
3
/h
Type 120/80
35.2 GPM / 8 m
3
/h
*1
Product does not look exactly as
illustrated.
Legend
AB Air Bleed
BR Boiler Return
BS Boiler Supply
BY Bypass (with laminar flow)
D
Debris (or air if LLH is flipped)
DV Drain Valve
SR System Return
SS System Supply
TS Viessmann Temperature Sensor (not
used)
SW Sensor Well
T1 Boiler supply temperature
T2 Boiler return temperature
T3 System supply temperature
T4 System return temperature
V
primary
Boiler circuit flow rate
V
secondary
Heating circuit flow rate
V
bypass
Bypass flow rate
Q
primary
Heat supplied by boiler
Q
secondary
Heat consumed by system
V
primary
< V
secondary
T1 > T3
T2 = T4
Q
primary
= Q
secondary
T1
±
176°F / 80°C
V
secondary
=V
V
bypass
When installing a low-loss header, system
mixed supply temperature (T3) must be
calculated as follows:
T3
=
T1
×
V
primary
+
T4 V
bypass
V
secondary
5
5
8
1
7
7
5
1
.3
DV
BS
SS
SR
BR
TS
BY
AB
D
Low-loss header design
(Type 80/50 or 120/80)
SW
T1
T2
V
primary
V
secondary
T3
T4
Principle of Operation
T4
V
bypass
IMPORTANT
