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Pre-Installation
A Class HP Installation a
nd User Instructions R02583
-6 09/15
Page
12
4.4.2 Worked Example
This example is for a G½ temperature relief
valve with a discharge pipe (D2) (as fitted on
125 to 300L cylinders) having 4 No. 22mm
elbows and length of 7m from the tundish to
the point of discharge.
From Table 2, the maximum resistance allowed
for a straight length of 22mm copper discharge
pipe
(D2) from a G½ 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, which is less than the actual
length of 7m, therefore calculate the next
largest size.
Maximum resistance allowed for a straight
length of 28mm copper discharge pipe (D2)
from a G½ temperature relief valve is: 18m
Subtract the resistance for 4 No. 28mm elbows
at 1.0m each = 4m
Therefore the maximum permitted length
equates to 14m.
As the actual length is 7m, a 28mm (D2)
copper pipe will be satisfactory.
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 (D2) to be
connected.
The discharge pipe should not be connected
to a soil discharge stack unless the soil
discharge stack is capable of safely
withstanding temperatures of the water
discharged, in which case, it should:
contain a mechanical seal, which allows
water into the branch pipe without allowing
foul air from the drain to be ventilated
through the tundish.
there should be a separate branch pipe with
no sanitary appliances connected to it.
if plastic pipes are used as branch pipes
carrying discharge from a safety device,
they should be either polybutalene (PB) or
cross-linked polyethylene (PE-X) complying
with national standards.
be continuously marked with a warning that
no sanitary appliances should be connected
to the pipe.
4.4.3 Termination of Discharge Pipe
“The discharge pipe (D2) from the tundish
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 a fixed grating and above the water
seal;
downward discharges at low level; i.e. up
to 100mm above external surfaces such as
car parks, hard standings, grassed areas
etc. are acceptable providing that a wire
cage or similar guard is positioned to
prevent contact, whilst maintaining
visibility; and,
discharges at high level: e.g. into a metal
hopper and metal downpipe 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 system that
would collect such discharges.”
Note: As the discharge would consist of
high temperature water and steam,
asphalt, roofing felt and non-metallic
rainwater goods may be damaged by such
discharges.
4.5 Limitations
The heat pump must be specified correctly,
to ensure it is compatible with the model of
cylinder installed. This is to prevent the
heat pump malfunctioning when preparing
domestic hot water.
The heat exchangers in this range of
cylinders have been specifically designed
for heat pump applications. Great care
must be taken if using these cylinders with
other heat sources, due to the heat
exchange capacity of the product.
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