Engineers Look at Multiple Factors When Designing Plumbing Systems

By David Shreve

Senior Consultant

An engineer considers multiple factors and variables when designing a plumbing system. The process begins with assessing the available water pressure, which is crucial for designing the water distribution system.

Considerations When Designing Systems

Factors such as pressure losses from valves, fittings, and piping friction must be balanced against the available water pressure. If the pressure is too low, a pump may be necessary, while excessively high pressure may require a pressure reducing valve.

Flow rates for individual fixtures are specified in the plumbing code, but determining the combined peak demand of all building plumbing fixtures is more complex. Statistical tools assist engineers in figuring out the peak building demand, as fixtures are typically not operated simultaneously. Based on these calculations, the design water-supply flow-rate and pipe sizes are verified.

Hot-Water Systems

When designing the hot-water system, engineers perform a similar demand load analysis as the main water supply. Additionally, engineers must consider how to control the temperature of the hot water. Factors such as peak and minimum demand loads, available fuel or electrical power options, space availability, initial investment cost, energy efficiency, and maintenance and operating costs influence the selection of the water heating system.

Sanitary-Waste Systems

Engineers determine the sanitary-waste system load and pipe size based on drainage fixture units specified by the plumbing code for various fixture types. Pipe sizes are calculated based on the total number of fixture units connected to a pipe section. Statistical data assists engineers in figuring out the building demand, which is usually less than the sum of the peak fixture demand.

Storm Drainage Systems

An engineered storm drainage system includes roof drains and piping designed to effectively carry rainwater from the roof and away from the building. Engineers figure out the appropriate roof drain types and quantities, as well as pipe sizes, by looking at the roof area and maximum expected hourly rainfall.

Specialized Systems

Plumbing systems also encompass natural gas and specialized systems for medical, laboratory and manufacturing facilities. Designing these systems requires analyzing connected appliances, high-tech equipment and the pressure and flow requirements.

In summary, plumbing codes establish minimum requirements for public health and safety. Good plumbing design not only meets these requirements, but also satisfies the performance objectives of the project, ensuring optimal functionality and surpassing the prescribed plumbing code standards, when necessary.