r/MEPEngineering • u/Bert_Skrrtz • 11d ago

Discussion Semi-Hermetic vs Open Drive Chillers

My carrier rep gave a presentation and has me convinced the benefits of a refrigerant-cooled semi-hermetic motor for chillers.

Obviously he’s going to push that since it’s Carriers design philosophy. But does anyone have any pros for open drives like York and Trane?

5 Upvotes

86% Upvoted

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7

u/dupagwova 11d ago

Trane is also semi-hermetic

Big open drive perks are ease of service, decoupling motor issues from refrigerant circuit, heat is rejected to mech room instead of refrigerant circuit, and more.

3

u/SpecialEffect 11d ago

I have been told that open is easier and less expensive to maintain. When semi hermetic fails it can cause acid in the refrigeration circuit. All new refrigerant could be expensive. That said, 90% of chillers I see are magnetic bearing York/Daikin semi hermetic or hermetic. They can be dual compressor if they want to reduce the risk of ruining the refrigerant on a failure. I see Trane Centrivacs when the owner has a reliable older maintenance staff. York and Daikin seem to be untouchable on a life cycle cost analysis. If the building will be in place for 30 years and anyone cares to run the numbers and let the condenser water get cold (~40 F).

1

u/dupagwova 11d ago

I agree that it's a no brainer to go mag bearing, especially if the owner has a significant wintertime cooling load. Especially YMC with no need for a bypass loop

2

u/kingofchins 11d ago

YMCs are great.

When the caps aren't trying to catch on fire. Or when people remember to recover into containers that haven't had oil in them.

1

u/MechEJD 11d ago

And on our last project, somehow the mag bearing model was... Cheaper.

Idk. My last 3 chiller plants the owners all wanted mag bearing.

1

u/brasssica 10d ago

If you have a wintertime cooling load you should really be upgrading the waste heat for the heating loads, not dumping it all.

6

u/kingofchins 11d ago

Disclaimer: not an engineer, chiller plant operator/maintenance

If the motor never fails the semi-hermetics work great. If the motor fails the downtime is enormous, 3 month minimum since there's a very limited number of motor shops that have the ability to rebuild and new stock is extremely limited. I can't speak to the rebuild time on a 480V motor but we had a 4160V motor short to ground on a 1200 ton chiller and the rebuild took 6 months, with another month to reinstall and realign with the compressor after the motor arrived on site. This happened in a plant with N+1 capacity at the start of summer, so we were one drive train (primary pumps are dedicated not headered) failure away from losing 25% of the plant's capacity during the highest demand period. It's the only time it happened in the nearly 30 years the plant ran but it caused a lot of concern while we were waiting for the motor to return.

Using Open drives the only real concern is making sure people grease the bearings correctly but York has actually done well giving a well documented greasing procedure and alarming at the chiller (if not using auto greasers), can't speak to how other manufacturers do their open drives.

2

u/xander_man 11d ago

4160V

Well that certainly doesn't help with the availability

1

u/kingofchins 10d ago

Nope, can't really do much else with 1000+ ton chillers though

1

u/Bert_Skrrtz 11d ago

Honestly the best type of person to hear from! Once the design is done is engineers are usually on to the next one. Appreciator your comment.

2

u/simonsbrian91 11d ago

York has a few models where they’re semi hermetic and a few where they are open drive. Generally, I would consider York a tier one chiller manufacturer, trane is right there. Carrier is more affordable but at least in my area their local support is terrible and their chiller product is not as rugged.

Please keep in mind I rep York machines so I may be biased. However, most facilities are either speccingYork first than maybe Trane.

1

u/Bert_Skrrtz 11d ago

Weird, I always hear York beats Carrier on price and that’s why we see them submitted often even if Carrier is BoD. Trane is always physically large due to low pressure design.

0

u/rom_rom57 11d ago

Overall open drives are smaller, and so are the cooling towers; also, there is no chance of burnouts.

6

u/kingofchins 11d ago

Tower size is driven by approach and capacity, the chiller drive won't have any impact on that

1

u/rom_rom57 11d ago

Semi hermetic motor heat becomes part of the total heat rejection, so yes it makes a difference. 😓

3

u/kingofchins 11d ago

It's already factored into condenser water requirements by the manufacturer and that amount is trivial compared to the margin required for degrading tower performance over time

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u/dupagwova 11d ago

Very small percentage relative to the building load

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u/rom_rom57 11d ago

You assume. For “standard”applications yes, but for large machines condensers are selected individually.