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[EnergyPlus_Support] Supply air temperature control

I am having problems with my program not keeping the supply air temperature 
at the appropriate setpoint.  I have used purchase chilled water and have 
more than enough capacity.  My cooling coil has water supplied at 3°C 
and  a delta T of 9°C.  The supply air temperature is set at 12°C.  The 
trend I have been seeing is that when the cooling coil has the maximum flow 
rate of water through it, it can not meet the supply air 
setpoint.  However, when the max flow rate is present, the temperature rise 
of the water is only 1-2°C.  When the setpoint is actually met, the flow 
rate through the coil is usually small and the temperature rise of the 
water is often large.  Many times the temperature rise is about 12-15°C 
which is more than the design value of 9°C.  Also, there seems to be a 
large gap in flow rates between the maximum and the flow rates at the times 
where the setpoint temperature is met.  My cooling coil UA is about 2000 
W/delK which has been on autosize.  I have tried to increase the UA 
manually and this has not solved the problem.  I have also adjusted the 
chilled water capacity with no luck.  The delta T of the cooling water has 
also been adjusted.  Any suggestions of what might be happening?

Mike McCarty
Graduate Student, Mechanical Engineering
Iowa State University
2043 Black Engineering
Ames, IA 50010

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