Pipe friction loss describes the pressure decrease caused by friction between flowing fluid and the interior pipe surface, a function of pipe roughness, fluid velocity, and Reynolds number. This loss increases with velocity and pipe length, making it the primary component of system pressure drop.
Factors Affecting Loss
Friction loss depends on absolute roughness values specific to each pipe material: copper at 0.000005 feet, steel at 0.00015 feet, and PVC at 0.000005 feet. Reynolds number determines flow regime and friction factor, with values above 4000 indicating turbulent flow where friction loss increases significantly. Laminar flow below 2300 creates lower friction but rarely occurs in HVAC systems.
System Performance
Friction loss directly determines pump power requirements and operating costs. A system with 50 feet of equivalent length carrying 20 gallons per minute water experiences friction losses of approximately 10-15 psi. Regular maintenance, including strainer cleaning and corrosion prevention, reduces friction by maintaining smooth pipe surfaces and preventing scale buildup that increases roughness.