Ferroli PREXTHERM RSH 100N Instructions D'utilisation, D'installation Et De Montage page 36

5.5 Hydraulic connections
5.5.1 Supply water
The chemical characteristics of the system and top-up water are fundamental for the correct operation and safety of the boiler. The water
must be treated using suitable systems. The values shown in the table below can be used as a reference.
TOTAL HARDNESS ppm 10
ALKALINITY mg/l CaCO3 750
PH 8÷9
SILICA ppm 100
CHLORIDES ppm 3500
The water used in the heating system absolutely must be treated in the following cases:
- Very large systems
- Very hard water
- Frequent addition of water to top up the system
If it becomes necessary to partially or completely empty the system, it should be refilled with treated water. To control the volume of water
refilled, a meter should be installed on the pipe. The most common issues arising in heating systems are:
- Lime scale deposits
Lime scale accumulates at the points where the wall temperature is highest. Due to their low heat conductivity, lime scale deposits cause
a reduction in heat exchange. Even if they're only a few millimeters thick, the heat exchange between the flue gas and the water is limited,
which increases the temperature of the parts exposed to the flame and causes cracks in the tube plate.
- Corrosion on the water side
Corrosion of the metal surfaces on the water side of the boiler is caused by the dissolution of iron into its ions. The presence of dissolved
gases, particularly oxygen and carbon dioxide, plays an important role in this process. Softened and/or demineralized water provides pro-
tection against deposits, but not against corrosion. The water must therefore be treated with corrosion inhibitors.
5.5.2 System feed/return pipes
The dimensions of the feed and return pipes for each boiler model are indicated on the DIMENSIONS table. Make sure the system has a
sufficient number of vent openings.
The boiler fittings must not support the weight of the connection pipes to the system. Appropriate supports must be installed for this purpose.
5.5.3 System fi ll/drain pipe
For filling and draining the boiler, a cock can be connected to fitting T4 on the back (see DIMENSIONS, Fig. 3).
5.5.4 Pipes, expansion vessel and safety valves
PREXTHERM RSH N boilers are suitable for operation with forced water circulation, with the expansion vessel open or closed. An expan-
sion vessel is always required to compensate for the increase in water volume due to heating. In the first case, the height of the hydrostatic
column must be at least 3 meters above the boiler body. Its capacity must be sufficient to contain the increase in volume of all water in the
system, between the surface of the water in the vessel and the overflow pipe. Tall, narrow vessels are preferable, as they ensure minimum
contact between the water surface and the air, thus reducing evaporation. In the second case, the capacity of the closed expansion vessel
must be calculated considering:
- the total volume of water contained in the system
- the maximum operating pressure of the system
- the maximum operating pressure of the expansion vessel
- the initial pre-charge pressure of the expansion vessel
- the boiler's maximum operating temperature (the maximum temperature on the thermostat fitted on the panel is 90ºC; use 100ºC to
perform this calculation).
The expansion pipe connects the expansion vessel to the system. This pipe will start at the T3 fitting (see the Dimensions table), and must
not be fitted with on-off valves. At fitting T3, or within 0.5 m of the first flange on the outlet pipe, install a safety valve suitable for the capacity
of the boiler and in compliance with current local standards. No type of shut-off device may be installed between the boiler and the safety
valves, and these valves should be set to operate when the maximum permitted operating pressure is exceeded.
36 EN
PREXTHERM RSH N
A73020821