Bosch UT-L 12 - Boiler Circuit Pump as Primary Circuit Pump

System examples | 55
6 720 807 794 (2013/04)UNIMAT
9.3.2 Boiler circuit pump as primary circuit pump
Fig. 36 Sample hydraulic circuit for a 2-boiler system with boiler circuit pump as primary circuit pump
FVS Strategy flow temperature sensor
FR Return temperature sensor
PK Boiler circuit pump
RK Boiler return
SR Actuator for return temperature raising facility
SV Safety valve
VK Boiler flow
VSL Safety flow
Boiler circuit pump flow rate V
PK
In systems with primary circuit pumps (e.g. with
hydraulic balancing lines or depressurised distributors),
we recommend installing the boiler circuit pump in the
heating return.
F. 6 Formula with sizing factor for estimating the flow
rate of the boiler circuit pump in a single boiler
system
V
HK
Flow rate of the heating circuits in l/h
V
Kges
Total boiler circuit flow rate in l/h
F. 7 Formula with sizing factor for estimating the flow
rate of the boiler circuit pump in a 2-boiler system
V
HK
Flow rate of the heating circuits in l/h
V
Kges
Total boiler circuit flow rate in l/h
In 2-boiler systems, distribute the pump rates of the
boiler circuit pumps according to the boiler outputs. If
several heating circuits are constantly operated with
high flow temperatures and the maximum flow rate, the
flow rate of every boiler circuit pump should correspond
to the flow rate of the heating circuit pumps. For
systems with gas condensing boilers, there are special
requirements to be followed, e.g. maintaining as low a
return temperature as possible. The pump rate of the
boiler circuit pump may then need to be matched to the
pump rate of the heating circuits.
Sizing the 3-way valve
Size the 3-way valve for the flow rate that has been
calculated. When doing so, observe the pressure loss
when the valve is fully open, as the control quality is
influenced by the proportional pressure loss.
Head of the primary circuit pump
The head of the boiler circuit pump is the result of:
• The pressure loss of the boiler at the selected flow
rate V
PK
• The pressure loss in the pipework and
• All individual pressure loss levels in the boiler circuit
(path: A–D–E–H,  Fig. 36).
Example
Given
• Heat demand of the heating circuits ΣQ
HK
= 4000 kW
• Heating system flow temperature ϑ
V
=90°C
• Heating system return temperature ϑ
R
=70°C
• Total flow rate with selected sizing factor
( formula 7) V
Kges
= V
HK
×1.3
Result
• V
HK
= 172000 l/h ( formula 4)
• V
Kges
= 223600 l/h
(paths: C–D and E–F,  Fig. 36)
Divide the total flow rate calculated for the boiler circuit
side according to the rated outputs (here 50/50 %):
• V
PK
= 111800 l/h
(paths: A–C, B–G and F–H,  Fig. 36)
VK RK VK RK
AA
HH
C
D
F
BG
BG
E
90 °C
70 °C
FVS
SR1SR2
PK2
PK1
FR2 FR1
V
HK
V
PK1
V
PK2
6 720 642 347-48.1il
SV
VSL
SV
VSL
V
Kges, 1
V
HK
1,0...1,2()×=
V
Kges, 1
V
HK
1,2...1,5()×=