[evlatests] Antenna 13 cooling problems

[Bob Broilo]

> 	Antenna 13's cooling problems appears to be getting worse.
> Over the weekend the outlet temperature from the air handler (into
> the racks) is oscillating up to 5 degrees C over fifteen minutes.

>From looking at the plots, this certainly looks like the economizer
valve problem, we will go out and set the system for constant mixing.
This should stabilize the temperature at the expense of efficiency.

When the economizer valve switches off, it creates a "dead branch" in
the water loop which can be hot or cold.  When this valve opens, this
slug of off-temperature water gets mixed in, which can cause the
controller to oscillate.  We thought we had cured this problem in the
winter (with obviously a cold slug of econ water) but now that it is
summer I suspect that the slug is hot.

Possible long-term solutions to the problem include
a) an orifice bypass to keep the dead branch temperature more constant
d) finer control of the chiller at low-load conditions
b) better tuning of the controller to prevent oscillation
c) a small overlap area between chiller and economizer operation

> I've attached a plot and if you would like the actual data, just let
> me know.

Doug, please send me the data.  Thanks!

-Bob.