10/20
53799173-05
APPLICATION
1
To maximise performance, pipe runs should be kept as short as possible, avoiding sharp bends.
However, individual pipe runs to a maximum of 80m, including 20m lift, are permissible provided good
refrigeration practice is followed.
Published performance duties are based on 7.5m pipe runs. Correctly sized pipes for each installation,
and fitting the correct expansion orifice (restrictor) will result in no significant loss of capacity on
extended pipe runs.
a)
Pipe sizes are based on: -
Minimum of 3.8 m/s (750 fpm) suction gas velocity for horizontal or downflow.
Minimum of 7.6 m/s (1500 fpm) suction gas velocity for upflow.
Maximum of 15.2 m/s (3000 fpm) suction gas.
b)
Where vertical risers exceed 3m, oil traps must be formed in the pipe. This will help ensure that oil
returns to
the compressor. Typically fit an oil trap every 3m with a trap at the bottom of the riser.
2
Add 25 grams of polyolester (POE) oil for every 350 grams of charge added to systems with pipe runs
exceeding 25m, up to a maximum of 300 grams; preferably by slowly pumping into the suction side with
the unit running, after charging the system.
3
The maximum pipe lengths to be used for each pipe size and outdoor unit are shown in the table below.
Use of these sizes and lengths is recommended in order to achieve optimum system performance.
4
In calculating equivalent lengths of pipe runs, the effect of bends and fittings must be taken into
account. The table below covers the fittings most likely to be encountered in this type of installation.
The equivalent lengths of all the fittings in a particular pipe run must be added together and the total
added to the actual length of pipe in the run, in order to calculate the total equivalent length.
FITTING LOSSES,
in equivalent straight lengths of pipe (metres).
Pipe Size (outside diameter in inches)
Fitting
3/8
1/2
5/8
3/4
7/8
1-1/8
45° Bend
0.12
0.15 0.18 0.21 0.24 0.3
90° Bend R/d = 1
0.37
0.43 0.49 0.55 0.61 0.79
90° Bend R/d = 1.5
0.24
0.27 0.30 0.37 0.43 0.52
180° Bend C/d =
0.73
0.91 1.10 1.28 1.46 1.83
180° Bend C/d =
0.46
0.55 0.64 0.76 0.85 1.07
90° Elbow
0.67
0.85 1.04 1.25 1.46 1.89
R = Radius of bend
d = Diameter of tube
C = Centres of
5
Use the shortest possible route, avoiding sharp bends
.
6
Fully insulate
both
the suction and expansion lines, including the expansion device, since both lines
may sweat.
Heronhill - for all your Marstair requirements
Tel: 01823 665660
www.heronhill.co.uk
Fax: 01823 665807
