What are the common sources of friction loss in HVAC piping?

There are several sources of friction loss in HVAC piping, including pipe roughness, bends, valves, fittings, and changes in pipe diameter. Pipe roughness, for instance, can increase friction loss by creating turbulence in the fluid flow. Similarly, bends and fittings can disrupt the flow, leading to increased resistance and energy loss. Proper design and installation of HVAC piping can help minimize these sources of friction loss.