33
6
Drain
Piping
6.1
Design
Considerations
Drain
piping
design
should
take
account
of
the
following
considerations:
Indoor
unit
condensate
drain
piping
needs
to
be
of
sufficient
diameter
to
carry
the
volume
of
condensate
produced
at
the
indoor
units
and
installed
at
a
slope
sufficient
to
allow
drainage.
Discharge
as
close
as
possible
to
the
indoor
units
is
usually
preferable.
To
prevent
the
drain
piping
becoming
excessively
long,
consideration
should
be
given
to
installing
multiple
drain
piping
systems,
with
each
system
having
its
own
drainage
point
and
providing
drainage
for
a
subset
of
the
overall
set
of
indoor
units.
The
routing
of
drain
piping
should
take
into
consideration
the
need
to
maintain
sufficient
slope
for
drainage
whilst
avoiding
obstacles
such
as
beams
and
ducting.
The
drain
piping
slope
should
be
at
least
1:100
away
from
indoor
units.
Refer
to
Figure
3
‐
6.1.
Figure
3
‐
6.1:
Drain
piping
minimum
slope
requirement
a b o v e 1 / 1 0 0
︵1 c m / 1 m ︶
To
avoid
backflow
and
other
potential
complications,
two
horizontal
drain
pipes
should
not
meet
at
the
same
level.
Refer
to
the
Figure
3
‐
6.2
for
suitable
connection
arrangements.
Such
arrangements
also
allow
the
slope
of
the
two
horizontal
pipes
to
be
selected
independently.
Figure
3
‐
6.2:
Drain
piping
joints
–
correct
and
incorrect
configurations
Drain pipe
Tee joint
Tee joint
Drain pipe
Tee joint
Branch
drain
piping
should
join
main
drain
piping
from
the
top,
as
shown
in
Figure
3
‐
6.3.
Recommended
support/hanger
spacing
is
0.8
–
1.0m
for
horizontal
piping
and
1.5
–
2.0m
for
vertical
piping.
Each
vertical
section
should
be
fitted
with
at
least
two
supports.
For
horizontal
piping,
spacings
greater
than
those
recommended
leads
to
sagging
and
deformation
of
the
pipe
profile
at
the
supports
which
impedes
water
flow
and
should
therefore
be
avoided.
Air
vents
should
be
fitted
at
the
highest
point
of
each
drain
piping
system
to
ensure
that
condensation
is
discharged
smoothly.
U
‐
bends
or
elbow
joints
should
be
used
such
that
the
vents
face
downwards,
to
prevent
dust
entering
the
Figure
3
‐
6.3:
Branch
drain
piping
joining
main
drain
piping
Figure
3
‐
6.4:
Effect
of
insufficient
drain
piping
support
g a s b a g
g a p t o o b i g
45°
