Three Way mixing valves
Three Way mixing valves
(OP)
Is better to use a diverting valve or mixing valve at the AHU on a chilled water system?
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RE: Three Way mixing valves
Three-way valves by their nature bypass supply chilled water into the return line, causing chilled water return temperatures lower than design. This exacerbates low delta -T problem. Therefor you want to use a minimum of three-way valves in variable flow system. Two-position bypass valves across supply and return lines, strategically situated and controlled properly is preferred to ensure minimum flow.
RE: Three Way mixing valves
RE: Three Way mixing valves
RE: Three Way mixing valves
RE: Three Way mixing valves
To reiterate the predominance of 3-way maixing valves, it's the reason you see two-way valves traditionally placed on the return side of coils (where the mixing valve would go as opposed to the diverting valve).
Ifc09: Don't forget, when using the 3-way mixing valve, you need a balance valve in the bypass line which matches the pressure drop of the coil so that a fluid "short circuit" won't occur.