Resistance created by
each elbow or bend
Maximum resistance al-
lowed, expressed as a
lenght of straight pipe
(i.e. no elbows or bends)
Minimum size of dis-
charge pipefromtundish
Minimum size of dis-
charge pipe
Valve outlet size
0.8 mmup to 9 m22 mm15 mmG1/2
1.0 mmup to 18 m28 mm15 mmG1/2
1.4 mmup to 27 m35 mm15 mmG1/2
1.0 mmup to 9 m28 mm22 mm<G3>/4
1.4 mmup to 18 m35 mm22 mm<G3>/4
1.7 mmup to 27 m42 mm22 mm<G3>/4
1.4 mmup to 9 m35 mm28 mmG1
1.7 mmup to 18 m42 mm28 mmG1
2.3 mmup to 27 m54 mm28 mmG1
Table sizing of copper discharge pipe for common temperature relief valve outlet sizes.
HARD WATER AREAS
Normally, there should not normally be any problem installing
S735 in hard water areas, as the operating temperature is
50–60°C.
CLEANING THE CLIMATE SYSTEM
When the water heater and the climate system have been
filled with water, S735 must operate at maximum normal
temperature for at least one hour. Thereafter the system
must be drained of water and refilled.
Before installing the heat pump in an existing system, it is
important that the system is properly flushed through.
Even if the heat pump is to be installed in a new system, the
heat pump and system should be flushed.
NOTE
Ensure that cleaning agent has been removed from
the entire system before adding inhibitor.
After flushing an inhibitor should be used for long-term anti-
corrosion protection.
NIBE Energy Systems Limited recommends water treatments
(supplied by e.g. Fernox and Sentinel) specifically designed
for heat pumps.
SYSTEM VOLUME
S735 is equipped with an expansion
vessel (CM1).
The volume of the expansion vessel
is 10 litres and it is pre-pressurised as
standard to 0.5 bar. As a result, the
maximum permitted height "H"
between the expansion vessel and the
highest installed radiator is 5 m, see
figure.
If the pre-pressure is not high enough,
it can be increased by filling with air
via the valve in the expansion vessel. Any change in the pre-
pressure affects the ability of the expansion vessel to handle
the expansion of the water.
The maximum system volume, excluding S735, is 285 litres
at the above-mentioned pre-pressure.
15Chapter 4 | Pipe and ventilation connectionsNIBE S735
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