Engineering information and sizing the heat source
6 720 645 817
(2010/09)
36
5
Engineering information and sizing the heat source
5.1
Operating conditions
Tab. 18 provides an overview of the conditions that must be observed, subject to the application and the local
system-specific circumstances.
5.2
Water quality
As there is no pure water for the heat transfer, observe
the water quality. Unsuitable water quality can damage
heating systems due to scaling and corrosion.
Fill the system with clean mains water only that meets
the requirements below.
To protect the appliance from scale damage throughout
its service life and ensure trouble-free, economical
operation, the overall quantity of hardness constituents
in the fill and top-up water of the heating circuit must be
limited.
To check the permitted amounts of water subject to the
fill water quality, either perform the following
calculations or consult the graphs.
Checking the maximum amounts of fill water subject to
water quality
The fill and top-up water has to meet certain
requirements depending on the total boiler output and
the resulting water volume of a heating system.
Use the following formula to calculate the maximum
amount of water that may be introduced without
treatment:
Form. 1 Calculation of the maximum amount of water that
may be introduced without treatment
Ca(HCO
3
)
2
Concentration calcium hydrogen carbonatein mol/m
3
Q
Boiler output in kW
V
max
Maximum fill and top-up water over the entire service
life of the boiler in m
3
Information about the calcium hydrogen carbonate
(Ca(HCO
3
)
2
) concentration of the mains water can be
obtained from your water supply utility. If these details
are not included in the water analysis, the concentration
of calcium hydrogen carbonate can be calculated as
follows from carbonate hardness and calcium hardness.
Example
Calculation of the maximum permissible amount of fill
and top-up water V
max
for a heating system with a total
boiler output of 560 kW. The analysis values for
carbonate hardness and calcium hardness are quoted in
the older unit °dH.
Carbonate hardness: 15.7 °dH
Calcium hardness: 11.9 °dH
The following results from the carbonate hardness:
Ca(HCO
3
)
2
= 15.7 °dH × 0.179 = 2.8 mol/m
3
The following results from the calcium hardness:
Ca(HCO
3
)
2
= 11.9 °dH × 0.179 = 2.13 mol/m
3
The lower of the two values calculated from calcium and
carbonate hardness is decisive for calculating the
maximum permissible water volume V
max
.
Form. 2
Δϑ
max
Minimum
boiler water
flow rate
Max. water
flow rate
Minimum
boiler water
temperature
Operating
interruption
Heating circuit
control unit with
heating mixer
Minimum return
temperature
Full load = 30 K
Partial load = 40 K
No requirements
Results from
Δ
T = 8 K
No requirements
To transfer the
max. output
Δ
T must be < 30 K
Tab. 18 Suprapur operating conditions
V
max
0.0235
Q
Ca HCO
3
(
)
2
--------------------------------
×
=
.
V
max
0.0235
560 kW
2.13 mol/m
3
--------------------------------
×
6.2 m
3
=
=
