13
The expansion vessel should be connected to the pressure-neutral
point of the system, preferably on the return pipe. Selecting membrane
expansion vessel in closed systems user should take into account
manufacturer’s recommendations, possibly take into account the below
hint.
Hint!
Control of operation of expansion vessel should be carried
out once per year.
In pipe connecting with heating system, user should install emptying
and closing device which is protected against accidental closing e.g.
dome valve protected with a wire and seal. It is required for control the
initial pressure at least once per year within the scope of maintenance
works without emptying the system.
Size of the expansion vessel depends on the total amount of water in
the heating system. Selecting an expansion vessel user should take into
account the
recommendation of the vessel’s manufacturer or use the
below hint to calculate its size.
Hint!
Example of expansion vessel capacity calculations for boiler
of power 15 kW /tables 7-9/.
Table 7. Water expansion.
Water expansion in %
Water temperature
50
60
70
80
90
100
110
Expansion in %
1.29
1.71
2.22
2.81
3.47
4.21
5.03
Table 8. Exemplary values of pressure coefficient.
Pressure coefficient Df
Wa
te
r g
au
ge
m
In
iti
al
pr
es
su
re
b
ar
Valve opening pressure bar
1.5
2.0
2.5
4
0.7
3.6
2.5
2.1
6
0.9
5.2
3.1
2.4
8
1.1
9.4
4.0
2.8
12
1.5
9.3
4.3
Table 9. Exemplary selection of membrane expansion vessel
Exemplary selection of membrane expansion vessel
System height
4 m
Max. temperature in system
90 °C
Boiler power
15 kW
Safety valve opening pressure bar
1.5 bar
Total amount of water in the system: e.g. boiler
(50 l), heating system 100 l)
150 l
Water expansion coefficient 3.47
Initial pressure (4/10)+0.3=0.7 bar
Valve opening pressure = 1.5 bar
Working capacity Vu
6.2 l
Minimum size of membrane expansion vessel Vu*Df
~23 l
Ad.5. Safety valve or protection fittings (safety group)
Heat source in a closed system must be protected with a safety
valve. A manometer intended for pressure measurements should be
installed besides the valve.
Manometer should have a range bigger by 50% than max. operating
pressure. The main task of the safety valve is a protection of the heating
system and heat sources against exceeding allowable working pressure
(set in the factory to 1.5 bar, marked with a red hood).
A safety valve should be installed on the heat source or near the
source on the conduit supplying the system, in an easily accessible
location and should prevent exceeding maximum working pressure by not
more than 10%.
In case of exceeding of pressure set, water outflows through the
discharge conduit what results in a decrease of pressure in the system.
Water and steam outflowing from the valve should be discharged in a
safe way.
Hint!
It is recommended to use safety fittings, a so-called safety unit,
which consists of a safety valve, manometer and vent.
Note!
Direct discharge of hot water from boiler cooling is forbidden.
It may cause damage to the drainage waste and vent system.
7.4.4.
DIAGRAM FOR CONNECTING BOILER TO HEATING SYSTEM.
The following conditions are to be met to connect the boiler to the
heating system correctly:
1)
connect supply pipe using threaded couplings (pic. 2, pos. 8) and
return pipe (pic. 2 pos. 9) with the heating system in the intended location
for this purpose,
2)
Connect pipes of safety system according to the regulations obligatory
in the country of installation,
3)
fill the central heating system with water,
4)
check the condition of the heat filter insulation of the safety system,
5) to improve the
boiler’s
life, it is recommended to use mixing systems to
obtain a temperature in the
boiler equal to 80°C while in case of return
water this temperature should be not smaller than 55°C.
7) boiler should be connected to the heating system using screwed or
flanged joints.
To connect the boiler correctly with the heating system the following
conditions should be maintained: temperature on boilers should not be
less than
65°C,
while water temperature on return not less than
55°C.
This is connected with water vapour condensation on cold walls of the
boiler (so called boiler's sweating), which leads to decrease in boiler's life.
To prevent this phenomenon, the boiler's water should be set for higher
temperature and temperature in particular rooms should be adjusted by
means of thermostatic valves or, alternatively, mixing systems can be
used.
A qualified technician should choose devices for a given heating
system.
Hint!
Ensure the
minimum temperature on return not lower than 55°C.
Hint!
Use of a mixing valve reduces fuel consumption, facilitates
operation and significantly lengthens the life of the boiler.
Hint!
Installation of the boiler by welding results in loss of
warranty!!!
Hint!
Boiler installation should be carried out by a person or
company with suitable qualifications and authorizations.
It is in the
user’s interest to look after that boiler installation is
made in accordance with the regulations in force and that
installing company gives a warranty for correctness and good
quality of workmanship which should be confirmed by a
stamp and sign on the warranty card of the boiler.
Hint!
A qualified technician should choose devices for a given
heating system.
