MultiStack or AirStack chillers

[greg r]

Hello all.
Our department at Oregon State Univ. is embarking on a project to replace a chiller in one of our science buildings.

The present 160 tonTrane absorption unit is being replaced with an electric chiller. The chiller is in the mechanical room with the building supply fan unit, and the chill water system is relatively small. The chill water circuits to the chiller and the fan unit less than 20 feet away, and uses 6" pipe.

An engineering firm is doing design considerations for the replacement chiller. So far they are favoring MultiStack or an Airstack chiller plant with 3 50 ton units and one 20 ton unit connected together. They also want to incorporate a large chill water tank for thermal mass to reduce chiller short cycling.

I haven't any experience with these units. We have one small MultiStack in the campus's boiler plant. It's about a year old, no calls for repairs to it yet. But, it looks like a serviceman's nightmare. Not easy to replace components or service without a lot of disassembly.

I need some field experiences. Please share with me some war stories from those who have worked on them.

Thank you much,

Greg

[brahern]

I can say from personal experience that multistacks are horrible. Just wait till you have to clean the heat exchangers, you have to take the entire header apart. And don't think cleaning it in the spring will last. We cleaned the exchangers 3 times in one season. Brand new building, nice 2 cell evapco cooling tower, spot on water treatment, doesn't matter. In addition to the cleaning we had thrust bearings go on 2 of the 5 screw compressors. I would imagine your chiller would use scroll compressors so that probably is not an issue for you.

As far as modular goes, I've looked at ClimaCool's line of products and they seem to have taken a design similar to multistack, but have corrected most of the problems associated with MS. You can isolate each chiller circuit to clean the heat exchangers, which you cannot do on MS. It also looks like each chiller circuit has its own independent power supply, not the bus bar system multistack has. So you can completely mechanically and electrically isolate each module. Sounds good to me. I have no actual experience with ClimaCool though, so I cannot say how much better they are, if at all.

Hope this helps.

[flange]

engineers have a way of specifying that equipment which their salesman at the local rep agency helps them specify. it may or may not be the best solution. for my money, multistack is not what i would buy, unless there were no other viable option due to space, rigging restraints, or availabiltiy.

[greg r]

Thanks guys, keep 'em coming. I seem to recall awhile back some people I talked to mentioned control problems. I would think these modular units have to talk to each other in some fashion, and that seemed to be the weak link in that problem or trouble codes couldn't be quickly isolated to the point or source of failure.

[flange]

thats the least of your worries. maintenance and repair tops the list unless they have made great strides recently.

[jiffypop]

Take a look at Thermalcare with the Turbocor, very nice unit you can also utilize an aircooled condensor if you want to get rid of the tower. I started 6 of these up last year all were on tower's.

[HVAC Teacher]

The modular idea is sound for certain applications.

Don't expect the longevity you had with that absorber.

[drivewizard]

Do a search on this site for Multi stack and see what you come up with.

They are very heavy on maint. But, hey thats what we get paid to do right?

Sounds like job security to me.
Our office sells a lot of them, we had to hire extra guys to handle all the service calls. It's a win win. Well,,, for the contractors anyway.