Demand Limit a chiller?

[winslowfam]

Hi...I have a client who purchased a 60 ton chiller where only a 45 ton chiller is needed. Unfortunately, the breaker panel that will be used to feed this chiller will be overloaded by this larger-than-needed chiller's amp draw based on nameplate MCA. The chiller has a control option called a demand limiter that can be set to current-limit, with password protection, the chiller power that, if set correctly, will result in the breaker panel NOT being overloaded. My first thought is that this is not good engineering nor what the code would allow but want to consider it a bit more to see if this can be done to save the client from buying a smaller chiller. Your thoughts?

 

[jusme123]

wouldnt it be cheaper to run a separate feed as opposed to purchasing a new 45 ton chiller?

 

[jusme123]

also I would not rely on the demand limiter as a way to make it work

 

[winslowfam]

Thanks for your ideas. The feeder to the breaker panel that will feed this new chiller is the wiring that will be overloaded by the increased chiller size. The breaker panel main circuit breaker will be overloaded, also. I can upsize the MCB since the panel's rating is larger than the MCB they have now, but would have to re-pull the wiring that feeds the breaker panel, too. it would be best to lower the amp draw of the new chiller somehow...without replacing it with a smaller unit.

 

[mxslick]

Well, let them install the oversize chiller, set the demand limit, wait for the password to get out, someone will soon override the demand limiter, and the feeder and MCB will fail violently after being reset a hundred times, resulting in lots of downtime, possible injuries and huge monetary losses. :roll:

The ONE and ONLY SAFE and proper course of action is to upsize the feeder, replace the MCB with the proper rating, charge the customer and be able to sleep soundly with the knowledge that you did the right thing.

The client's lack of knowledge and failure to consult with you regarding the power requirements does NOT give you or anyone else an excuse to take shortcuts to save a few bucks.

Do it right or walk away from it....life safety is more important than saving a few bucks...sheesh.

 

[winslowfam]

Thank you for confirming our initial reaction to the problem. Thanks for all your help.

 

[markstg]

Any chance it a a multistage chiller such that the stages can be mechanically/electrically defeated?

 

[mxslick]

Any chance it a a multistage chiller such that the stages can be mechanically/electrically defeated?

And to reiterate the point I made in my other post..

Sometime down the road someone WILL come along and undo any defeats/overrides.

I think the OP has made the right decision and will have a new feeder pulled and the breaker changed. It is the ONLY smart and Code compliant thing to do.

And it was said before I chimed in:

also I would not rely on the demand limiter as a way to make it work

 

[iwire]

Well, let them install the oversize chiller, set the demand limit, wait for the password to get out, someone will soon override the demand limiter, and the feeder and MCB will fail violently after being reset a hundred times, resulting in lots of downtime, possible injuries and huge monetary losses. :roll:

I respect your view but see it entirely differently.

The NEC allows breakers to be adjustable, the NEC allows fused disconnects, either one can be dangerous if the unqualified get involved.

The ONE and ONLY SAFE and proper course of action is to upsize the feeder, replace the MCB with the proper rating, charge the customer and be able to sleep soundly with the knowledge that you did the right thing.

No, that is an opinion not a fact.

Do it right or walk away from it....life safety is more important than saving a few bucks...sheesh

I do not see a safety issue.

 

[iwire]

Consider the following.

Had the person replaced the single 45 ton unit with two 45 ton units 220.60 could be used to allow them to be connected to the same feeder.

It does not even require that the two loads be interlocked only that is 'unlikely' that they will be used simultaneously.

IMO, the password protected demand limiter could be used in this instance. If it is not to be used for demand limiting what is it's intended function?