Sanitary Drainage Loads

Overview

Engineering reference data for Sanitary Drainage Loads in sanitary drainage.

Key Formulas

Manning's Equation

$Q = \frac{1}{n} A R_h^{2/3} S^{1/2}$

Open channel flow.

Slope

$S = \frac{\Delta h}{L}$

Hydraulic gradient.

Variables

Expected Total Load Estimation

For sanitary drainage systems, the expected total load (q_et) is significantly lower than the theoretical total load (Σq_n) due to intermittent fixture usage. It is estimated using the following empirical equation:

$q_{et} = k \sqrt{\Sigma q_n}$

Where:

• q_et = expected total drainage load (gpm or l/s)
• k = system coefficient (dimensionless)
• Σq_n = total theoretical load from all fixtures (gpm or l/s)

Important Constraint: The expected total load can never be less than the load from the largest single fixture in the system.

System Coefficient (k) Values

The system coefficient k accounts for the usage pattern of the building and varies with system size.

Intermittent Use Systems (e.g., large groups of people)

These systems have peaks and valleys in usage. A smaller k value is used for larger systems with many fixtures.

• k Range: 0.5 - 0.8
• Building Types: Hotels, hospitals, schools, theaters, wardrobes in factories.
• Selection Guidance: Use closer to 0.8 for smaller systems (fewer fixtures) and closer to 0.5 for larger systems (many fixtures).

Continuous Use Systems (e.g., consistent consumption)

These systems have more predictable, sustained usage patterns.

• k Range: 0.3 - 0.6
• Building Types: Homes, offices, nursing homes.
• Selection Guidance: Use closer to 0.6 for smaller systems (fewer fixtures) and closer to 0.3 for larger systems (many fixtures).

Example: Sanitary Drainage System for a Hospital

A smaller hospital has a calculated theoretical total fixture load (Σq_n) of 50 l/s. Using a system coefficient k = 0.7 for a smaller intermittent-use system, the expected total load is calculated as:

$q_{et} = 0.7 \times \sqrt{50 \text{ l/s}} = 4.9 \text{ l/s}$

References

• Original Source