Air Cooled Chiller Elementary School

[hotairman]

I am designing a new chilled water system for an existing elementary school. I plan on using a 130 ton, R134A, air cooled screw chiller that is remotely located on a concrete pad.

We are designing the system to '99 Ashrae 90 Energy Requirements. My building cooling loop requires a 20-25HP circulating pump and therefore requires a VFD (pumping circuits over 10HP require reduction in horsepower at part load). The existing mechanical room is centrally located within the building but the chiller is approx. 300ft away.

How do I use primary/secondary pumping when the chiller is remotely located from the Pumping station? Also, has anyone tried variable flow through an air cooled screw chiller? I wanted to keep the system simple for the school to purchase & maintain.

 

[imok2]

Rather then trying to explain this technique I refer you to this web site:

http://www.bellgossett.com/Press/2ndpump.html

 

[KenRad]

hotairman,

Should not be a problem to do variable flow through your screw chiller; it all depends on your definition of "simple." The manufacturer's data should include a range for evaporator flow, and the key is to ensure that you are always above the minimum. One method that I've used is to install 3-way valves on one or more appropriatly sized coils. Another is the use of a flowmeter and bypass valve, which begins to open as flow approaches minimum. The first method is a little more fail-safe, but warnings need to be posted on your 3-way coils to ensure that they don't get valved off. In any case, you still need either a flow switch or differential pressure switch across the evaporator, set for minimum flow, that will shutdown the chiller if something goes wrong.

---KenRad