Pide cascade hot water coil

kirk

Lifetime Supporting Member
Join Date
Jul 2003
Location
Houston
Posts
71
So I have an application controlling the temperature by means of a hot water coil.

The coil holds lots of energy even after the flow stops, creating an overrrun control / tuning nightmare.

The way I understand it, this is the type of application designed for a PIDE with CASCADE function.

Do any of you have any good videos or papers recommendations describing the theory and programing using a PIDE block (studio 5000)?

The videos I found, were either based around standard PIDE function or the presenter had an accent that I couldn't process (that's TOTALLY on me, but it is, what it is)
 
Can you provide a sketch of the system? Is there temperature measurement of fluid entering coil? Is there a pump on the coil?
 
Cascade control will work if you have control of the hot water coils. I bet dead time is a major issue. The comment about the hot water coils holding heat is a giveaway. What is being heated? It is also possible that the inner loop, the heating coils, have a longer time constant and dead time than what heating coils are heating. If so, this will be a problem.
 
I have done cascade control on large air handler coils before, however, we had designed the plumbing to allow this to happen. We had a pump that pumps a constant flow of water through the coil. We had temperature measurement on the fluid entering and exiting the coil. The control valve would be opened/closed to let more or less fresh fluid into the loop (hot for heating coil and cold for cooling coil). The outer loop of discharge air temp would set the target to the inner loop of coil entering fluid temp. This works extremely well, however, the system has to have the mechanics/plumbing in place first.
 

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