Notes for operating a heating system | 3
B1650222_en | Operating instructions PE1e Pellet
17
3.3 Pressure maintenance systems
Pressure maintenance systems in hot-water heating systems keep the required
pressure within predefined limits and balance out volume variations caused by
changes in the hot-water temperature. Two main systems are used:
Compressor-controlled pressure maintenance
In compressor-controlled pressure maintenance units, a variable air cushion in the
expansion tank is responsible for volume compensation and pressure maintenance. If
the pressure is too low, the compressor pumps air into the tank. If the pressure is too
high, air is released by means of a solenoid valve. The systems are built solely with
closed-diaphragm expansion tanks to prevent the damaging introduction of oxygen
into the heating water.
Pump-controlled pressure maintenance
A pump-controlled pressure maintenance unit essentially consists of a pressure-
maintenance pump, relief valve and an unpressurised receiving tank. The valve
releases hot water into the receiving tank if the pressure is too high. If the pressure
drops below a preset value, the pump draws water from the receiving tank and feeds it
back into the heating system. Pump-controlled pressure maintenance systems with
open expansion tanks
(e.g. without a diaphragm) introduce ambient oxygen via the
surface of the water, exposing the connected system components to the risk of
corrosion. These systems offer no oxygen removal for the purposes of corrosion
control as required by VDI 2035 and
in the interests of corrosion protection should
not be used
.
3.4 Storage tank
NOTICE
In principle it is not necessary to use a storage tank for the system to run smoothly.
However we recommend that you use the system with a storage tank, as this ensures
a continuous supply of fuel in the ideal output range of the boiler.
For the correct dimensions of the storage tank and the line insulation (in accordance
with ÖNORM M 7510 or guideline UZ37) please consult your installer or Fröling.
Additional requirements for Switzerland in accordance with LRV Appendix 3, section 523
Automatic boilers for wood pellets with a rated thermal output of more than 70 kW
must be equipped with a heat accumulator of a volume of at least 25 litres per kW
rated thermal output. These dimensioning specifications apply up to 500 kW nominal
heat output.
