View Full Version : Chilled Water System not Cooling
07-31-2006, 08:22 PM
I have a building with 6 air handlers with chilled water coils. The only unit that appears to be cooling properly is the unit that is farthest from the chiller plant. The other units are only pushing out around 72*F supply air. The chilled water coils are around 44*F with a 4*F delta T across the coils. All coils have been cleaned and we are getting plenty of air flow. The strainers have been cleaned. The water has not been treated in at least two years. What should I do to get the supply air lower?
• Reduce or Increase the chilled water flow?
• Any suggestions?
07-31-2006, 08:33 PM
4 degree split is low! Are you sure you don't have a ball valve or gate valve closed on the return side??
07-31-2006, 08:43 PM
There is a control valve but it appears to be wide open.
07-31-2006, 09:00 PM
if your on a chiller loop setup to the AHUs shut all but the nearest and work your way back to see the DA as you start to open them all and see the changes in entering pressures as you go...what is the pressure is in/out on the running one use that as a benchmark!
07-31-2006, 09:05 PM
A chilled water system has a design PD that if met will have the design water flow available for your cooling coils.
A rule of thumb for chilled water temp rise thru a coil is 10 degrees (44 in/54 out). If you check the chilled water temps in and out and have wider delta T, I would suspect low flow.
To begin, check pressure drop at the coil. Make sure that you take your readings at the coil and not upstream of a control valve.
Have you checked for air trapped in the chilled water coils?
Low chilled water flow = high delta T of water thru coil
High chilled water flow = low delta T of water thru coil
Low chilled water delta T thru coil = high airside delta T
High chilled water delta T thru coil = low airside delta T
07-31-2006, 09:50 PM
Is this system mixed air return or 100% outside air.
Do the dampers operate correctly? That kind of split looks like plenty of flow.
What is the return air temp?
08-07-2006, 09:48 PM
Hmmm, Face and bypass maybe?
08-07-2006, 11:26 PM
I have to comment on this because I just found a AHU where the heating and cooling coils had about a 2" gap between them that was never sealed during installation.
08-08-2006, 12:27 AM
I've chased myself around in a circle more than once, only to find the ddc troops have the valve configured backwards.
Or maybe it's busted.
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