joule DIRECT - Page 8

unvented hot water cylinders
installation and maintenance instructions
Page 8 / 17
Examples of acceptable discharge arrangements are:
1. Ideally below the fixed grating and above the water seal in a trapped gulley.
2. Downward discharges at a low level; i.e. up to 100mm above external surfaces such as car parks, hard standings, grassed areas etc. are
acceptable providing that where children play or otherwise come into contact with discharges, a wire cage or similar guard is positioned to
prevent contact whilst maintaining visibility.
3. Discharges at a high level; e.g. in to metal hopper and metal down pipe with the end of the discharge pipe clearly visible (tundish visible or
not) or onto a roof capable of withstanding high temperature discharges of water and 3m from any plastic guttering systems that would
collect such discharges (tundish available).
4. Where a single pipe serves a number of discharges, such as in blocks of flats, the number served should be limited to not more than 6
systems so that any installation can be traced reasonably easily. The single common discharge pipe should be at least one pipe size larger than
the largest individual discharge pipe to be connected. If unvented hot water storage systems are installed where discharges from safety
devices may not be apparent, i.e. in dwellings occupied by blind, infirm or disabled people, consideration should be given to the installation of
an electronically operated device to warn when discharge takes place.
WORKED EXAMPLE
The example below is for G1/2 temperature relief valve with a discharge pipe (D2) having 4 No. elbows and length of 7m from the tundish to the point of
discharge.
From Table 1:
Maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2) from a G1/2 temperature relief valve is: 9.0m. Subtract the resistance for
4 No. 22mm elbows at 0.8m each = 3.2m. Therefore the maximum permitted length equates to: 5.8m. 5.8m is less than the actual length of 7m, therefore
calculate the next largest size.
Maximum resistance allowed for a straight length of 28mm pipe (D2) from a G1/2 temperature relief valve equates to: 14m. As the actual length is 7m, a 28mm
(D2) copper pipe will be satisfactory.
Table1 - Sizing of copper discharge pipe (D2) for a temperature relief valve with a G1/2 outlet size (as supplied).
Size of discharge
pipework
Maximum length of
straight pipe (no bends or elbows)
Deduct the figure below from the maximum length
for each bend or elbow in the discharge pipe
22mm Up to 9m 0.8m
28mm Up to 18m 1m
35mm Up to 27m 1.4m