Control Valve Flow Coefficient (Cv) Sizing for HW/CHW Systems
Control Valve Flow Coefficient (Cv) Sizing for HW/CHW Systems
(OP)
ASHRAE Systems and Equipment Handbook indicates that control valves should be sized for a pressure drop of 25 to 50 percent of the pump head in order to obtain good control. I have seen many projects where all the valves are sized for a 5 psig pressure drop. I this "rule of thumb" method for sizing control valves valid? Where does the 5 psig come from?





RE: Control Valve Flow Coefficient (Cv) Sizing for HW/CHW Systems
RE: Control Valve Flow Coefficient (Cv) Sizing for HW/CHW Systems
RE: Control Valve Flow Coefficient (Cv) Sizing for HW/CHW Systems
http://www.documentation.frco.com/groups/public/documents/book/cvh99.pdf
free download - 295 pages in PDF format - Emerson Process Management - The Control Valve Handbook has been a primary reference for more than 30 years.
This third edition is a complete revision and update that includes vital information on
control valve performance and the latest technologies.
Good luck !
RE: Control Valve Flow Coefficient (Cv) Sizing for HW/CHW Systems
Control valve authority is the simple equation of control valve pressure drop/controlled system pressure drop (Including the control valve)
i.e. if you are controlling a heater battery using a diverting valve and you want a valve authority of 0.5 (Typically 0.3 to 0.5 are acceptable for good control)
and if we have a heater battery pressure drop of 20kPA,
then 0.5 = VPd/20+Vpd
in this case Vpd is also 20 since 20/20+20=0.5
If the value is lower than 0.3 then the control is poor
higher values are simply wasteful of energy
(If I knew how to send you a sketch I would)
Regards