Chilled Water Heat Exchanger Flow and Return Connections

[micksouth]

Hello All,
Do the connections of flow and return make any noticeable difference when connecting a heat exchanger for a CHW system. It has been suggested that the flow on the primary side muat be next to the secondary flow, as opposed to the primary flow next to the secondary return.
Apologies I am an electrical engineer.
Thanks for your advice.

 

[MatthewL]

micksouth,

What type of heat exchanger are you using? If it is a single pass style, you need to use a counter flow setup, otherwise you are limited in efficiency.

Think of it this way: if you have the primary (hot, say at 150 F) and secondary (cold, say at 50 F) flowing in the same direction (parallel flow), with the same mass flow rate and same heat capacity (I know, not realistic, but work with me), using a 10 degree minimum approach temperature, the lowest you can get on the hot side would be 105 F, with a cold side out of 95 F.

With the same setup, running counter flow, your hot side out would reach 60 F, with a cold side out of 140 F. Big difference!

Of course, increasing cold side flow, decreasing hot side flow, baffles, plate and frame HX, multiple passes, etc. all would allow a closer approach temperature on a parallel flow, but at a loss in system efficiency. Check out a heat transfer text if you have access, or contact a heat exchanger manufacturer for design information and how flow pattern affects efficiency.

Hope this helps!

Matt

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