We are designing an integrated water-side plant to serve cold water
directly to IT racks (No air). We're projecting that at 65F water
temperature, we should get more than 65% compressor-free cooling.
The current modeling approach it to build a dedicated cooling system
(chiller, cooling tower, associated loops) with a direct load placed on
the loop. We are having difficulty in determining whether or not we can
model a water-side economizer using this approach because the water-side
economizer is specified within the air system (which we have none). The
issue in eQuest is how to introduce water-side economizer in a secondary
loop that only serves process loads and no zones? Is the correct way to
build a dummy zone and system and zero-out the fan power?
Any ideas?
Cassie Waddell
You already know how to make it work (your last recommendation about
building a dummy zone).
Build a dummy zone, include the IT room max power load (KW), create a
fan coil system for that room, and just zero out the fan energy. You'll
also need to use a free-cooling chiller in your loop.
Or, you can do it all thru the chiller - the free-cooling chiller
provides waterside economizer operation automatically for your chilled
water loop, and you don't have to specify a system if you don't want to.
However, I've never done it this way before, and I'm not sure if a loop
HAS to have a system attached, otherwise you might get no-flow errors
even with a process load?? You'd have to check this...
It would be interesting to do it both ways, and compare results.
James Hansen, PE, LEED AP
James & Cassie,
I have been able to have chilled water loops with only process loads. To avoid the zero design flow errors on loops, I often put in a tiny process load with a schedule that is only on for a single hour on the design day.
Admittedly, I have not tested this approach with all of the free cooling operations but I think it is worth trying before creating a dummy space and AHU.
Paul Riemer