Designing mechanical and plumbing systems for industrial and commercial applications requires evaluation of several factors, including wastewater planning. Any discussion of plumbing installations or retrofits must include some consideration of wastewater, since wastewater is a regular output from the system. It must also factor into design planning for hydronic and mechanical systems, as they often generate wastewater in condensation or other forms.  

With this guide, professionals can understand how wastewater planning affects the efficiency, reliability, maintenance needs and compliance of plumbing and mechanical system design. 

Pipe Sizing 

Pipe sizing is a critical element of plumbing and mechanical system efficiency and reliability. The pipe’s size determines how quickly wastewater can drain through the stack. System designers must evaluate the wastewater flow rate to determine if the pipe size is sufficient to permit regular drainage, without risking pooling or backflow. Pipe flow at peak capacity is an important consideration, as exceeding flow rates can cause significant fluctuations in pressure.  

In general, recommended pipe sizing depends on the number of fixture units, such as toilets or sinks, served by that particular pipeline. Building codes dictate the maximum amount of fixture units allowed by pipe dimension, requiring engineers to select the appropriate size for compliance. 

Drainage Capacity 

While pipe sizing and drainage capacity often go hand in hand, they have important distinctions. Pipe sizing dictates how fast water can flow once it enters the system, while drainage capacity describes the maximum flow rate that the drain line can handle without overwhelming the system. 

Drainage capacity is measured through assessments of factors such as the pipe’s slope or the type of system used for drainage (e.g., gravity or siphonic). This information accompanies the anticipated maximum flow of wastewater through the drain line, so designers can select the drainage capacity that meets efficiency goals and compliance standards. 

Treatment Requirements 

Industrial facilities must generally treat or filter their wastewater before it reaches the municipal sewer line. Organizations may need to address treatment requirements from the local water authority, as well as the National Pollutant Discharge Elimination System (NPDES). 

For the design of plumbing, hydronic and mechanical systems, engineers should consider the limitations of the pipeline as well as the treatment requirements.  

To meet NPDES guidelines, the facility may need to engage in mechanical or chemical filtration prior to releasing wastewater into public waters. It should select pipe materials and designs that can accommodate the range of possible contaminants prior to filtration and treatment, to help ensure that the pipes will not corrode or leak as a result. 

Maintenance Access 

The design of plumbing, hydronic or mechanical systems in new or existing buildings requires analysis of maintenance needs and limitations. Maintenance access often looks like the integration of corridors and access panels for quick entry that is minimally invasive. For example, hotel bathrooms often feature access panels from interior closets to allow maintenance crews to access plumbing efficiently and effectively. 

Access planning is often a last-minute consideration, but it should be a priority from the early design stages. Maintenance for these systems is non-negotiable, even with sensors and automated tracking systems. Advanced development of maintenance protocols decreases downtime, which can boost overall efficiency and long-term reliability. 

Leak Management 

In any conversation about designing lines that involve water, potential for leaks must be a high priority. At an industrial or commercial scale, leak management is a matter of public health and safety. In these facilities, wastewater planning often includes accommodating large volumes of water moving at high speeds, which can increase wear and risk to the drain lines. 

These days, effective leak management involves the use of sensors to track wastewater movement and identify leaks. Sensors can isolate pipe weaknesses or abnormalities for maintenance teams to inspect. They can also pinpoint the location of existing leaks for prompt repair, which improves system reliability and efficiency. 

Compliance Challenges 

Mechanical and plumbing systems always have building code requirements, but compliance may create challenges for designers and engineers to overcome. Retrofits tend to present a number of compliance obstacles, for multiple reasons. 

First, existing buildings may not have been built according to modern building codes, which means that the pipe sizing or drainage capacity may not suit the wastewater production of the anticipated plumbing or mechanical system.  

Second, retrofits may make it more difficult to install new drain lines, since they require vents and other features. Design teams must identify compliance limitations before progressing through the design cycle. 

Engineering and Design Team Collaboration 

For a new building or significant remodel of an existing facility, multiple teams may be working at the same time to develop an appropriate design for individual systems. They should collaborate to better ensure that the systems will work together as intended.  

For example, a facility manager may hire a contractor to install a new HVAC system. Since HVAC often involves the production and drainage of condensation, the new drain line must also work with the plumbing system. Coordinating environmental engineering firms with design teams can help identify and overcome challenges related to divergent needs. 

Infrastructure Coordination 

Coordinating with in-house design teams and outside engineering firms is critical, but facility managers must also integrate input and requirements from the local water jurisdiction. Water authorities dictate limitations on acceptable water quality, as well as required flow limits and drainage capacity. They can also identify structural bottlenecks, such as the existence of limited sewer line capacity in rural or underdeveloped areas. 

Although facility managers may already be deep into design development before they request permits and information from the municipality or local water jurisdiction, they should aim to start much earlier. Gaining practical information about the limits of the existing system provides time to consider alternatives and find a design that complies with regulations and meets efficiency goals. 

Wastewater planning is a critical element of the design of plumbing, mechanical and hydronic systems. These systems depend on effective drainage to protect the function of the facility, as well as the health and safety of its occupants.  

Integrating these wastewater considerations into design plans can help facilities improve efficiency, increase system reliability, streamline maintenance needs and aid regulatory compliance. 

Joseph M. Heaney, III, P.E., is a Principal at Walden Environmental Engineering, a firm providing environmental and engineering consulting services across multiple industries. With more than 30 years of experience, he provides strategic direction for the company's technical operations and oversees complex engineering projects. Heaney is known for delivering practical, decisive solutions to challenging environmental and engineering issues and is a licensed Professional Engineer in New York, New Jersey, Connecticut, and Pennsylvania.