Pressure Drop Of The Solar Thermal System - Viessmann Vitosol 100-FM Technical Manual

Information regarding design and operation
2 or more collector arrays (≥ 4 m
A
With this connection, the "Relay kick" function on the Vitosolic 200
must be enabled (see chapter "Functions" in the "Solar control units"
section).
A Collector temperature sensor in the flow

13.6 Pressure drop of the solar thermal system

■ The specific flow rate for the collectors is determined by the type of
collector and the intended method of operation of the collector
array. The way the collectors are linked determines the pressure
drop of the collector array.
■ The overall flow rate for the solar thermal system results from mul-
tiplying the specific flow rate by the absorber area. The pipework
dimensions are determined assuming a required flow velocity of
between 0.4 and 0.7 m/s (see page 129).
■ Once the pipework dimensions have been determined, the pres-
sure drop for the pipework (in mbar/m) is then calculated.
■ External heat exchangers must be calculated as well and should
not exceed a pressure drop of 100 mbar/10 kP. For smooth tube
internal indirect coils, the pressure drop is much lower and can be
ignored in solar thermal systems with a collector area of up to
20 m 2 .
13
VIESMANN
126
2 )
(cont.)
■ The pressure drop of further solar circuit components can be found
in the relevant technical documentation. Include the pressure drop
of further solar circuit components in the overall calculation.
■ When calculating the pressure drop, take into account the fact that
the heat transfer medium has a different viscosity to pure water.
The hydraulic characteristics become more similar as the tempera-
ture of the media increases. At low temperatures around freezing,
the high viscosity of the heat transfer medium may result in a
pump rate some 50 % higher than for pure water. With a medium
temperature above approx. 50 °C (controlled operation of solar
thermal systems), the difference in viscosity is only minor.
VITOSOL