CW Loop Wet-Bulb Reset?

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I was almost sure that eQUEST/DOE-2.2 had a built-in control mode to
reset the tower-leaving condenser-water setpoint relative to outdoor
wet-bulb temperature. After puzzling over why I couldn't find it in the
GUI, I eventually realized that I was thinking of EnergyPro/DOE-2.1e.
This is a fairly common control strategy for open towers, so I was
wondering why this feature disappeared between DOE-2 releases and what
others are doing to simulate this control mode using eQUEST.

Of course, COOL-SETPT-CTRL = OA-RESET is based on dry-bulb. So you
could assume a constant wet-bulb depression and use a SUPPLY-LO greater
than SUPPLY-HI (this is allowed, right?), but this is very crude.

I guess you could use COOL-SETPT-CTRL = SCHEDULED, parse the hourly
wet-bulb temps out of the weather file, add the tower design approach to
everything, and dump those values into a COOL-SETPT-SCH (hopefully using
a perl script or something). However, SCHEDULEs are limited to 12
WEEK-SCHEDULEs, so it's not really possible to define a schedule of 8760
arbitrary values. But even if you could, it seems to me that there's a
reason the weather file has hourly wet-bulb data in it, and one of them
is to avoid having to do stuff like this...

I had thought of using user expressions, but I think eQUEST evaluates
these when it generates the BDL, so they wouldn't be evaluated during
the simulation for each hour. I'm pretty sure there's no user variable
for current outdoor wet-bulb temp anyway, because this isn't something
that can be evaluated ahead of time. Is this something that can be done
with DOE-2 subroutines/functions (I haven't played with those yet)?
Something like:



The idea is that MAGIC-EXPRESSION would be evaluated every time DOE-2
references the value of TWR-SETPT-SCH for the current hour.

Should I put this on the list of ECMs where I have to tell people that I
can't really model that, or is there hope after all?


Jeff Saretsky

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Joined: 2011-09-30
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