Water Side Economizer Control Sequence 3

[joejoedancer]

Editorial Comment First: This is an awesome forum that I wish I came across long before today, and I'm looking forward to reading and contributing.

Questions: What is/are some of the more reliable and trouble free control sequence(s)and system piping configuration for automatically switching back and forth between free cooling mode(plate&frame in parallel with chiller)via the tower water, and mechanical cooling with a centrifugal chiller? It seems that invariably there are chiller head pressure problems when hitting the condenser with say 42 degree tower water. Is specing a chiller with head pressure control recommended, or is there other better alternatives to accomplish trouble free switching?

 

[absrbrtek]

Yes you need a form of head pressure control, 3 way bypass works well. Over the years I have serviced and helped install many of these systems. Its all in the control sequence.

 

[quark]

Welcome to the forums.

What is the equipment that is being cooled? You can do it with an actuated 3-way valve (ball valve is better). You can use temperature sensors that trigger 2-way isolation valves for accidental flow of cooling water into chilled water circuit and vice-versa.

 

[joejoedancer]

Thanks absrbrtek and quark, I will try to get my paws on a few example control sequences.

 

[UDP10]

I recently completed a project where we put VFD's on the condenser pumps. In normal operation, the condenser pumps are constant speed. In transitioning from water side economizer to mechanical cooling, the chiller (via the bas via the vfd)controls the speed of the pumps to maintain refrigerant head pressure until the condenser water warms up.

Sidenote - I've been putting VFDs on all pumps, even if they're constant flow. If you compare the cost of a VFD with that of a balance valve, motor starter, misc. control devices, and the time for balancing, it makes complete sense - forget the energy savings...