Mitsubishi Electric ecodan ECOSLIM150L-PP-MEUK Installation Manual page 30

Discharge Arrangement
21
The discharge pipe (D2) from the tundish should be of metal or other material that has been demonstrated to be
capable of withstanding temperatures of the water discharged.
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. discharge pipes between
9m and 18m 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, and so on. Bends must be taken into account in
calculating the flow resistance. Refer to diagram 1, Table 1 and the worked example. An alternative approach for
sizing discharge pipes would be to follow BS6700 Specification for design installation, testing and maintenance of
services supplying water for domestic use within buildings and their curtilages.
The discharge pipe (D2) should terminate in a safe place where there is no risk to persons in the vicinity of the
discharge. Examples of acceptable discharge arrangements are:
• To a trapped gully with the end of the pipe below the fixed grating and above the water seal.
• 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.
• Discharges at a high level; e.g. in to metal hopper and metal down pipe with the end of the discharge pipe
clearly visible or onto a roof capable of withstanding high temperature discharges of water and 3m from any
plastic guttering systems that would collect such discharges.
• Device to warn when discharge takes place.
WORKED EXAMPLE
The example below is for a 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.
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.
Sizing of copper discharge pipe 'D2' for a temperature relief valve with a G1/2 outlet (as supplied)
Size of discharge
pipework
22mm
28mm
35mm
Pre-Plumbed Slimline Cylinder Installation Manual
30
Maximum length of straight
pipe (no bends or elbows)
Up to 9m
Up to 18m
Up to 27m
(continued)
Deduct the figure below from the maximum length
for each bend or elbow in the discharge pipe
0.8m
1m
1.4m