CHW temp and cooling coil leaving temp

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HI,
I am trying to model a VAV system for cooling and heating. On the cooling side, I specify a 52F CHW loop temperature and a "Zone Entering Min Supply Temp" of 55F. When I run the simulation I get an error that states "cooling coil leaving temperature must be at least 6F higher than entering water temp". I played with adjusting the "Zone Entering Min Supply Temp" to see what minimum value would work without errors and the lucky number was 61F. I am trying to figure out why this is the minimum temperature eQuest accepts without errors. The 61F is 9F higher than the entering water temperature and not 6F like the error states. Any ideas what is going on? Thanks so much for your help and insight.

Josh Doherty

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Josh,

You need to consider fan heat. If it's a draw-through coil, then eQUEST
knows that the SAT leaving the coil needs to be lower than the zone entering
temperature. So in your case, when you enter 55F for zone entering
temperature, then the coil leaving temperature is 55F minus the fan delta T.

-Erik Kolderup

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Josh,

I think the program picks up fan heat. So depending on how you have defined your fans, that will change the miminium temp equest accepts without errors.

Linda Lam, LEED?? AP

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