Tom,

In the equest/DOE new features manual, there's a section on "water
economizer chillers"

Basically, to run a cooling tower in water economizer mode, you have to
define a (virtual) water economizer chiller and attach a cooling tower &
condenser water loop to it. You'll need to set up the water econ chiller,
water econ condenser loop, and water econ cooling tower as *completely*
separate entities from any other chillers & cooling towers that you run and
have them attached to the primary chilled water loop in parallel with the
other chillers.

You also may need to use schedules, equipment controls, and load management
of the chillers and circulation loops depending on your exact plant
configuration.

For the water econ info, look under help/DOE2 help/Volume 6: New
Features/Chiller Water Economizer

Hope this helps,

Steven Savich, LEED AP