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GPM * ∆T/24 = actual capacity

So, if you have a machine rated at 250 tons and is flowing 600 GPM @ 7 degrees ∆T, its real time capacity is 175 tons. This would be ~87% of its nominal capacity. If the entering condenser water temp is below the nominal, say <85ºF ECWT, when this same chiller is producing 175 tons, the % RLA will be lower than it would be if the entering condenser water temp was 85ºF. This has to do with the pressure differential between condenser and cooler, and how much work the compressor must do to overcome that difference.

Originally Posted by R123

Don't get % RLA confused with % capacity. There 2 differant things.

Yep.

Dears,

York engineers visited the site, they would submit the proposals and their advice in this regards.
As I get the comments from York, I would update you.

Moideen-DIRE

nope. anudder company that makes semi custom stuff and refrigidation stuff, lol.

Sometimes you have to go with where you can get the best service and support. In my area, Trane is pretty much it at the industrial level. Even at the commercial level, they are doing most of the support for all makes.

Originally Posted by flange

...there are other thingsa ut there than a trane rtac.

i know...i only had access to trane equipment specs and he had 2 trane rtaa's already.

well i would be curious to find out what direction they went. it would be nice to hear back from those who posted once in a while..

Originally Posted by flange

my response was actually leaning toward a single package, evap condensing machine, with multiple screws that can do the 500 tons. Single evaporater, no series flow or isolation valves to shut one down on low load, just simple, straight forward chiller package. Yes it exists, and yes it can include pumps, vfd's etc all in one platform. total plant kw would be in the .8kw/ton range, and be rigged to the roof in one shot. there are other thingsa ut there than a trane rtac.

You thinking Epak or Chillpak?

my response was actually leaning toward a single package, evap condensing machine, with multiple screws that can do the 500 tons. Single evaporater, no series flow or isolation valves to shut one down on low load, just simple, straight forward chiller package. Yes it exists, and yes it can include pumps, vfd's etc all in one platform. total plant kw would be in the .8kw/ton range, and be rigged to the roof in one shot. there are other thingsa ut there than a trane rtac.

Originally Posted by R123

Don't get % RLA confused with % capacity. There 2 differant things.

was i working on my post so long that you beat me to it??? man, i have got to shorten my answers. probably won't happen though!

let's keep in mind the difference between RLA and Tonnage. despite what every BAS guy on the planet thinks, they are not the same thing nor is there a 1 to 1 correlation...not even at '100%'.

as for a multi-compressor system versus a single compressor system, sure a multi-compressor system is going to have a better turn down ratio than a single compressor system, but there are many other factors to consider as well, such as barrel heat transfer rates...the air cooled compressor barrels (that just about every manufacturer uses) have very poor heat transfer compared to just about everybodys centrifugal evaporators...with this factored in, the turn down ratio may not be nearly as significant as it at first seems.

other things to think about are the 2 unit (or more) arrangement. at first this system seems to favor a 2 unit (6 compressors total, RTAC-250, 50 Hz) system, however, this brings up how the unit is piped.

piped in parallel, the maximum flow rate is 1,243 GPM per unit (2,486 GPM total). When the load is low, you will be cycling 2 compressors ON and OFF instead of 1 compressor ON and OFF with a sinlge package unit (centrifugal or air cooled screw)...not nearly as much turn-down-ratio as one would think.

with the chillers piped in series, you have the limitation of 1,243 GPM...less cycling but less range of total flow rate...minimum is 339 GPM per chiller.

lots to think about.

Don't get % RLA confused with % capacity. There 2 differant things.

Sorry, I'm probably confusing our air cooled unit with 3 compressors that can run down to 10-12% RLA, but that would still be 30% on one compressor.

I still remember from training I had on Trane centrifugals and rotary that the rotary would go quite a bit lower. Centrifugals seem more "sensitive" and we walked into one out our chillers rooms and it was getting noisy and RLA was only 60% without any apparent issues. But these are lower temp machines. IN another area, a pair of similar centrfugals were running happily at 48-50%. Who knows, maybe the IGV's need looking at on that one. The approach might have been starting to creep up a little too.

I guess from my limited experience with Trane units, you can run the screws lower loads than the seemly more sensitive centrifugals that find themselves near the edge of surging at times.

I thought it was something to factor in. A mutili compressor RTAA will defnitely run a much wider range of loads. SO in this case his 456 ton nominal system with two RTAA's could probably run down to almost 5-8% system capacity. A single centrifugal won't even come close and would need a large storage tank to prevent short cycles whe hte building is under low load, at night, during low occupancy periods.

Originally Posted by motoguy128

One more thing I'm not sure I saw mentioned? How greatly do the loads vary? Centrifugals often have minim capacities around 30-50% load. Screws can run down to 10-15% RLA in many cases. I felt that in many cases, centrifugals were best installed in pairs, on a system with a minimum load, or used as base load chillers together with a screw machine.

What scrrw will run to10/15 % capacity?, thats not even posible with a screw. I think you have your statement backwards.

Originally Posted by motoguy128

Centrifugals often have minim capacities around 30-50% load.

Centrifugals are capable of turning down to 10% load and if equipped with VSD do so quite nicely. Even w/o VSD they can certainly turn down well below 30%. Can't imagine where you are receiving your information.

One more thing I'm not sure I saw mentioned? How greatly do the loads vary? Centrifugals often have minim capacities around 30-50% load. Screws can run down to 10-15% RLA in many cases. I felt that in many cases, centrifugals were best installed in pairs, on a system with a minimum load, or used as base load chillers together with a screw machine.

Yes, Yes it do suck. Don't recommend it for anyone. The 2nd. to last time I used rods was to get a whole bunch of fill from a tower out of a 1,500 ton absorber bundle. Suck doesn't even start to describe what kind of work that was.

...Ron

not to mention here in the states, it is a different type of leverage on the building, potentially creating tax saving opportunity over central plant.

obviosuly that is preferred for ease of maintenance, however, thinking slightly outside of the proverbial box, there are reasons why my plan might make some sense. first, it offers a quicker payback than a central plant. second, it doesnt generally require any more footprint or a dedicated mechanical room inside a building, which brings on a whole new set of problems such as refirgerant monitoring, ventilaltion, etc.. it is better than an air cooled solution, and can be designed to run very close to or better than total plant kw for a central plant, depending upon the style of centrifigual chosen.

I'll take tube-brushing over coil-cleaning any day!