Hello All,
Has anyone had any luck modeling a closed loop cooling tower that is only
attached to the chilled water loop? I would like to have the chilled water
loop have a closed loop CT that runs in series with the chiller with a
bypass valve when it allows. On the condenser loop would then be an open
loop CT for heat rejection from the chiller.
This closed loop CT will essentially act as "free cooler" when the wet bulb
is low enough and bypass the chiller, otherwise the chiller will make up the
rest of the cooling when the wet bulb is too high.
Any help would be great.
--
Patrick J Keeney
Hi Patrick,
I would suggest modeling your free cooler as a stand-alone condenser loop and link it to your air system through the water-side economizer coil option, creating two cooling loops essentially.
First, on the water side, create a new condenser loop and attach your dedicated cooling tower. Make sure to add a pump. Adjust the loop control temperature to a low setpoint to allow for free cooling, something like 40F maybe with a load-reset control to allow this to float.
Second, on your air-side system, there is a tab under cooling for an Economizer. Turning this option from no to yes and select a condenser water loop. On the air-side, the air stream is now pre-cooled and can act as an integrated-water-side economizer, effectively. There are some parameters for the fan penalty of the additional coil it adds on this screen that you may wish to set to zero so effectively, the coil does not modify your fan power calc.
[cid:image002.jpg at 01CC25FE.7223A000]
Adding this coil will make your stand alone condenser water loop look like the image below.
[cid:image003.png at 01CC25FC.8D778B70]
This setup will also give you more control of the waterside-economizer setpoint temperature since the condenser loop will be independent of your primary chilled water loop. This may be good, may be bad, depending on how you wish to control the loop setpoints.
I tried this out with a working 90.1 model I have and the new condenser loop shows a cooling load when I look at the PS-H reports. I would suggest playing around with the setup and then run hourly outputs to verify that it is operating in tandem with your chilled water loop as you expect.
Best of luck,
Neil Bulger
Thanks for the help Neil, I've been successful in setting the system up, and
think I am seeing the savings I am looking for.
Now I'd like to check to make sure plants are running when they should and
shouldn't be. Are there ways to:
1. Specify that a chiller runs at a certain schedule based on the
outdoor temperure. ie: I would like the chiller to run when the wet bulb is
above 57 degress F, and likewise, I would like the Water-Side Economizer
Loop (remember it is a condenser loop) to be the primary cooler when the wet
bulb is below 57 deg F.
2. Set the simulation results to report the hours of operation and
corresponding outdoor temperatures for the cooling towers and chillers.
Thanks All.