Cooling tower - Upgrading Single 60 ton Chiller to double 40 Chillers 1

[Designer_82]

I'm working on a project where they want to upgrade an old 60 ton chiller to dual 40 ton chillers. 2 questions:

1)will the cooling towers need to be replaced/upgraded?
2)will the water coils in the supplied AHU need replaced/upgraded?

This building doesn't have a capacity problem, just upgrading old equipment.

 

[nuuvox000]

The more you can upgrade the better off you will be, it just comes down to budget obviously. Newer equipment and coils means less maintenance issues of course and they have to weigh that against their budget. Just curious why they want two 40 ton chillers instead of two 30 ton if they don't have a capacity problem?
How old is the chiller/tower/coils?

 

[RossABQ]

Your peak condenser water flow (both new chillers on) is going to go up by 33%, which is something the tower(s) are not going to like. Even the CW piping may be undersized for that flow.

 

[LittleInch]

1) Don't know as we have no idea of their capacity
2)Probably not if there is no capacity issues

Are these new chillers modulating?

was the 60 ton unit running well or did it short cycle?

Without knowing how your system works or what the duty cycles are and whether or not the units actually run float out or not it's all impossible to say.

But it is likely that if you have 80 tons of chiller operating that the cooling towers designed for 60 tons will be a little undersized.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Designer_82]

Thank you for your feedback.

So after an actual site visit, I discovered the situation is a bit different which leads me to a new set of questions.

It is actually an air cooled chiller (60ton) and there are no cooling towers. It is a split type of chiller, with the condenser outside and evaporator inside. The reason they are changing to two 40 ton is because they want redundancy and also the one 60 ton chiller cannot maintain water temperature in the summer. (they said they normally need 38deg water to maintain cooling and in the summer it gets up to 44deg). So the cooling coil in the air handler won't need to change.

1) The spaces this system serves are three communication rooms. The air handler is actually called a MUAU and they said it supplies 100% outside air. Why would they supply 100% OA to a communications room? Seems inefficient to me.
2)They said the existing 60ton must remain in service until the two new 40ton are up and running to not disrupt. How can this be accomplished?
3)There was a Johnson Controls panel in the mech room where the chilled water supply piping entered the building and also one in the penthouse where the air handler was. I would love to learn more about how chillers are controlled, is there a good starting place for this?


Thanks

 

[RossABQ]

What are your ambient conditions? Makes no sense to have 100% OSA. Even switching to 50% OSA might eliminate the shortfall in cooling.

 

[itsmoked]

2) At some point valved tees have to be installed. Then you install the new chillers and plumb them to the tees. Then some low temp time (after 6pm winter/spring?) you switch in a new chiller and commission it. Then the other. At which time you can valve off the old chiller drain and decommission.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BronYrAur]

Something is missing here. If you are supplying 100% outside air, you must be exhausting it somewhere. Trying to get to the bottom of why you have 100% OA units. As RossABQ said, introducing return air will substantially cut down on your load. You might be able to install two 30 ton units instead of 40. etc.

 

[EnergyProfessional]

I have to ask, what role do you have in this? Are you the designer?

You didn't research anything about the project and the first thing you do is asking here? You asked about keeping the old cooling tower and had specific cooling tower capacity numbers, even if there is none?

I hope the owner that hired you doesn't get the idea they could ask the same questions here for free.

 

[LittleInch]

Are you sure that the Make Up Air unit is the ONLY AHU there?

Or is it the only one they showed you?

First you need proper drawings and an understanding of the flows, temperatures etc of the existing system. If there are none then you need to make them.

Only then can you figure out a way to add some valves tees or other connections during a short shutdown or how you can feed the AHUS by some hoses while you attach the new piping.

To figure out the controls you do need the original documents or drawings or you might be able to get something from the vendor, but don't hold your breath.

This is a decent sized unit and I guess a power supply of >100kW. It isn't a small domestic system here and if it goes wrong it will be costly to fix.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Designer_82]

Great catch LittleInch, this MUAU is not the only air handler. They also have other air handlers dispersed throughout which are fed by other equip. (not the chiller). The chiller is the only one supplying this MUAU. This MUAU serves a communications room which must be kept to within 2 degrees or something like that.

I know the other Air handlers have return air but I believe this MUAU is 100% OA.

 

[kikal]

The refrigeration circuit is changing to water cooled. So check compressor ratings for new conditions. Your shut down activity involves pump down, flushing, vacuum, leak test gas charging... Big job, plan shutdown accordingly.