Heatrae Sadia PremierPlus PES170D Installation And User Manual page 8

INSTALLATION - DISCHARGE
It is a requirement of Building Regulation G3 that any discharge from an unvented system is conveyed to where it
is visible, but will not cause danger to persons in or about the building. The tundish and discharge pipes should be
fitted in accordance with the requirements and guidance notes of Building Regulation G3. The G3 Requirements and
Guidance section 3.50 - 3.63 are reproduced in the following sections of this manual. For discharge pipe arrangements
not covered by G3 Guidance advice should be sought from your local Building Control Officer. Any discharge pipe
connected to the pressure relief devices (Expansion Valve and Temperature/Pressure Relief Valve) must be installed in
a continuously downward direction and in a frost free environment.
Water may drip from the discharge pipe of the pressure relief device. This pipe must be left open to the atmosphere.
The pressure relief device is to be operated regularly to remove lime deposits and to verify that it is not blocked.
G3 REQUIREMENT
"...there shall be precautions...to ensure that the hot water discharged from safety devices is safely conveyed to where
it is visible but will not cause danger to persons in or about the building."
Notes:
Discharge pipe-work D2 can now be a plastic pipe but only pipes that have been tested to a minimum 110°C must
be used.
Discharge pipe D2 can now be plumbed into the soil stack but only soil stacks that can handle temperatures of 99°C
or greater should be used.
The following extract is taken from the latest G3 Regulations
Discharge pipe D1
3.50 Safety devices such as temperature relief valves or combined temperature and pressure and pressure relief
valves (see paragraphs 3.13 or 3.18) should discharge either directly or by way of a manifold via a short
length of metal pipe (D1) to a tundish.
3.51 The diameter of discharge pipe (D1) should be not less than the nominal outlet size of the temperature relief
valve.
3.52 Where a manifold is used it should be sized to accept and discharge the total discharge form the discharge
pipes connected to it.
3.53 Where valves other than the temperature and pressure relief valve from a single unvented hot water system
dischargeby way of the same manifold that is used by the safety devices, the manifold should be factory fitted
as part of the hot water storage system unit or package.
Tundish
3.54 The tundish should be vertical, located in the same space as the unvented hot water storage system and be
fitted as close as possible to, and lower than, the valve, with no more than 600mm of pipe between the valve
outlet and the tundish (Fig. 5 & Table 3, page 10).
Note: To comply with the Water Supply (Water Fittings) Regulations, the tundish should incorporate a suitable air
gap.
3.55 Any discharge should be visible at the tundish. In addition, where discharges from safety devices may not be
apparent, e.g. in dwellings occupied by people with impaired vision or mobility, consideration should be
given to the installation of a suitable safety device to warn when discharge takes place, e.g. electronically
operated.
Discharge pipe D2
3.56 The discharge pipe (D2) from the tundish should:
(a) have a vertical section of pipe at least 300mm long below the tundish before any elbows or bends in the
pipework (see Diagram 1, G3), (Fig. 5, page 10); and
(b) be installed with a continuous fall thereafter of at least 1 in 200.
3.57 The discharge pipe (D2) should be made of:
(a) metal; or
(b) other material that has been demonstrated to be capable of safely withstanding temperatures of the water
discharged and is clearly and permanently marked to identify the product and performance standard (e.g. as
specified in the relevant part of BS 7291).
3.58 The discharge pipe (D2) should be at least one pipe size larger than the nominal outlet size of the safety
device unless its total equivalent hydraulic resistance exceeds that of a straight pipe 9m long, i.e. for
discharge pipes between 9m and 18m the equivalent resistance length should be at least two sizes larger
than the nominal outlet size of the safety device; between 18 and 27m at least 3 sizes larger,
bends must be taken into account in calculating the flow resistance. (See Diagram 1, Table 1, G3), (Fig. 5 &
Table 3, page 10) and the worked example.
Note: An alternative approach for sizing discharge pipes would be to follow Annex D, section D.2 of BS 6700:2006
Specification for design, installation, testing and maintenance of services supplying water for domestic use within buildings
and their curtilages.
3.59 Where a single common discharge pipe serves more than one system, it should be at least one pipe size larger than
the largest individual discharge pipe
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and so on;