optimum control of air handlers 2

[Herman2]

We are rebuilding some large (20,000 cfm)industrial air handing units that use chilled water for cooling. We have control of individual dampers and can also modulate the chilled water valve and fan speeds. We plan to optimize the AHU controls for minimum energy.

We also plan to modify the controls at our central chiller plant to do some optimization.

Question - Should we... #1) optimize the AHU controls assuming constant chilled water temperature, or #2) try to somehow integrate the chiller plant optimization with AHU controls and arrive at an even better solution.

In my view, it's a matter of complexity versus the likely benefits. Any experience out there? Thanks...

 

[quark]

As far as my experience is concerned, even with variable speed controlled centrifugal chillers couldn't maintain constant chilled water temperature. Moreover a switch is the best energy conserving device. (I would rather say reduction in energy wastage to energy conservation) So answer to your first question is a "No".

If you already have control valves in your system try for variable speed pumping system for secondary circuit. As chillers have their own temperature controllers energy at chiller can be taken care of. As far as cooling towers are concerned I strongly think no variable speed for pump or fan and a temperature controlled on/off switch for fan could be ok.

 

[VEEKRISH]

Herman2,
I presume your system is a water-cooled system. For this, would suggest the following -
Have a primary-secondary system.
Flow through AHU is controlled by a two way valve, which in turn will be hooked up to a Variable Speed Drive for the secondary pumps.
In case you are using a VFD for the Fan, ensure that minimum ventilation rates are maintained.
Chiller will cycle off based on set LWT. This will provide best optimization.
For Cooling Tower, no point in controlling flow, as this will meerly raise discharge pressure. Better to reduce fan power consumption during favorable ambients. Try cycling off the fans with a ambient themostat.
You may also consider using evaporative cooled condensers. This will yield better efficeincy.