4 Planning and installation – Connections
40
R
ETURN
TEMPERATURE
CONTROL
Operating temperatures which are too low significantly shorten the
service life of the boiler. Water vapour contained in the flue gas could
be released in the form of condensation if the temperature drops
below the dew point (approx. 50 - 55 °C), especially in the area
around the water-cooled heat-exchanger surfaces. This condensa-
tion, in combination with combustion residue, can lead to corrosion.
For these reasons, a return temperature control
must
be installed for
the HDG Compact 99 - 200 heating system. The return temperature
control causes the water from the boiler return line to be mixed with
the water from the boiler supply line until the minimum return tem-
perature has been reached.
✎
The minimum return temperature is listed in chapter “3 Mode of
operation”, section “3.3 Technical data”.
The return temperature is regulated by the HDG control unit.
The return temperature control consists of a 3-way mixing valve with
a 230 V servo drive (running time 120-140 s) and a circulation pump
from energy efficiency class A. We recommend for the
•
HDG Compact 99/100/105/115: Wilo 30/1-8, 3-way mixer DN 40
(or comparable)
•
HDG Compact 150/194/199/200: Wilo 50/1-9, 3-way mixer DN 65
(flange) (or comparable)
The hydraulic system must be installed in accordance with specific
technical principles of the heating construction industry. Take into
account the stop cocks required for maintenance work and repairs.
The return temperature control must be installed according to the
specifications of HDG Bavaria.
The pipe dimensions must be adapted to meet the requirements at
the site. Take the water-side connections of the boiler for the supply
and return into account.
✎
See the chapter entitled “3 Mode of operation”, section
“3.3 Technical data”.
The use of a gravity brake is not intended for the return tempera-
ture control and should therefore not be installed.