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Engineering ToolBox > Expected Loads in Sanitary Drainage Systems
The total theoretical load for a sanitary drainage system can be calculated by adding all fixtures known maximum loads. Due to the nature of intermittent use the number of fixtures will unfortunate add up to unrealistic loads for the main drainage lines to handle. Realistic loads will always be far less than the total theoretical loads.
An expected load for a sanitary drainage system can be estimated using a formula like
qet = k ( Σqn )1/2 (1)
where
qet = expected total drainage load (gpm, l/s)
k = system coefficient describing the nature of the system
Σqn = total theoretical load - all fixtures summarized (gpm, l/s)
Note that the minimum expected total load can never be less than the load from the largest fixture.
The system coefficient is used to compensate the calculation to the nature of the system. For systems typical serving large groups of people where the use is intermittent, like
the coefficient - k - should be in the range 0.5 - 0.8. Closer to 0.8 for smaller systems with few fixtures and closer to 0.5 for larger systems with many fixtures.
For more ordinary systems where consumption patterns are more continuously like
the coefficient - k - should be in the range 0.3 - 0.6. Closer to 0.3 for larger systems with many fixtures and closer to 0.6 for smaller systems with few fixtures.
If the theoretical loads from the fixtures in a smaller hospital adds up to 50 l/s, the expected load can be estimated to
qet = 0.7 ( 50 )1/2
= 4.9 l/s
Assuming this is a smaller hospital the coefficient is set to 0.7.