Sizing a water piping system for a commercial space requires consideration of a number of factors, including water pressure, friction losses, and number of fixtures. In addition, the pipe material itself plays a role.
While CTS (copper tube size) PEX, CPVC, and copper all have the same outside diameters, the materials themselves require different wall thicknesses to meet standardized pressure ratings, with copper the thinnest, PEX the thickest, and CPVC in between. Therefore, for the same amount of water flowing, the velocity and pressure loss will be greatest with a PEX system due to its smaller internal diameter; a larger pipe size might be required to maintain the necessary residual pressure at the farthest fixture.
The flexibility of PEX may reduce the number of fittings versus CPVC, but the pressure drop through a CPVC fitting is less than a comparable PEX fitting. While CPVC and copper fittings surround the exterior of the pipe, PEX fittings are inserts, which creates orifices in the piping systems and restricts flow.
Copper can also experience some pressure drop over time, as it corrodes and the surface becomes rougher. This is calculated using the Hazen Williams C factor, which is a constant that applies to the pipe related to smoothness. Under the C factor, the higher the number, the smoother the pipe. At their origin, steel has a C factor of 120, and PEX, CPVC, and copper 150. However, copper’s number will decrease over time as the material scales and corrodes; CPVC’s number remains constant.
No matter the material or the project type, consult with your pipe manufacturer for special considerations and installation/engineering requirements.
The Corzan sizing tool, which helps optimize the design of piping systems for water supply applications as well as the implementation of expansion loops. The fixture unit conversions completed in this tool are based on the Uniform Plumbing Code 2010.