Friction Loss Calculation
It is of utmost importance that a calculation to be made to determine the total friction loss along
the piping network. This is to ensure that the water pump is able to deliver the required flow rate
through the system. If the friction loss is too high, the flow rate will reduce, thereby causing
improper operation of the chiller. If the friction loss is too low, the piping system may be
redesigned for cost savings and better efficiency.
The following guidelines should be followed during calculation:
1. It is necessary to have a drawing of the entire piping network, showing the lengths,
sizes, material and fittings used. Such drawing may be in 2-dimensional or 3-
dimensional (preferred).
If the system is an open type, determine the height difference between the chiller
unit and storage tank (if any).
The straight length of a pipe is measured from center-to-center of each fitting
along the pipe.
2. It is a good practice to have markings on the drawing for each branch of the pipe
network. This will help in identification of which branch is being calculated.
3. The following information must be available for calculation: water flow rate (GPM) of
each pipe branch, internal friction losses of the chiller unit / fan coil unit and water
pump head available.
These information can be obtained from the product catalogs or technical manuals.
4. Calculate for the branch which gives the highest friction loss. This usually
corresponds to the branch which have the furthest fan coil unit from the chiller.
5. It would be better to have the actual pressure drop across any of the fittings used
vs. the estimated equivalent lengths presented in the attached tables. This is
especially so for the valves (with specific C
v
values) and strainers (with different
mesh sizes).
6. Add a safety factor of 15 - 20% to the final friction loss to account for estimation
errors and actual site installation of the piping system.
7. Check the final friction loss against the pump head available. The pump head
must be higher than this calculated value if the system is to work properly.
An EXCEL spreadsheet programme has been written to help in this friction loss calculation.
Several worked examples are shown for typical installations in the following pages. The EXCEL
programme has been used in the computation.
Section 4 Page 72
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