replacing the air cooled to centrifugal chiller.

[motoguy128]

That's a matter of opinion.

That's a matter of water treatment. With good water treatment, I've heard of units going year without beign brushed.

Cooling towers in many climates need to be cleaned as often as condenser coils.

[dlove]

I don't understand how the pay back can be the same for both systems. I also, would not bet on the ROI to be 3 years. If they agree to get payed over the the time period they say it will take to get your ROI then they would have a vested interest in making sure they were right. (don't hold your breath) Every time i hear 3 year ROI i double it. I would forecast the next 5 years of water cost and electrical cost. if cost of water, and electrical goes up this would effect the ROI period. Unless you already added in the increases. DO you pay for sewage waste?

Also, are there any other buildings in your area that has water cooled and are about the same size as yours? If so i would talk with them and get their input. Not sure of the water chemistry but, depending on the type of water you have towers can be the bane of your life.

Personally i would stay with what you have and make repairs. I would imagine the capital cost comes out of your bottom line. Do repairs come out of common charges? if so why would you dump all that money in a new system? Just wondering, I would think if you took that money and properly invested it, the return would be greater than what you make on the savings over the next three years. -just saying. The ROI will always be there, whether you do it now or later. Unless they are making you a deal you cant refuse.




anyway not to get to far off track. Overall not knowing all the little details. Unless the entire systems is failing i would make repairs. If you have the money and just want to save money and they really believe they can get you a 3 year ROI, Then that's great, all new equipment today will save money, much has changed over the last 10 years. But again, Who can support for the equipment your will buy. If there is no local support for this new equipment or there are only a few who can work on it, i would shy away.

[supertek65]

i will be the idiot here!

what is an MHI chiller?????

[Dallas Duster]

i will be the idiot here!

what is an MHI chiller?????

ok I think it's the panel on the chiller.

[flange]

If I were bidding this, I would look at a third solution. With the amount of runtime they get over there verses our traditional cooling season, payback can occur more quickly. we have less degree days for cooling, I would think by a lot. At any rate, if I had the infrastructure in place for RTAA's, I would look at a repalcement using either screws or turbocore, using evap condensing, with all pumps, evaporater, tower etc, all bundled neatly into one package, and set it in place of those rtaa's. you will see similiar kw/ton performance, and less initial cost, but thats just me. payback would be sooner, with less water treatment involved.

[flange]

but what do I know?

[KnewYork]

what is an MHI chiller?????

It's a chiller made by Mitsubishi. The MHI stands for Mitsubishi Heavy Industries.

@flange I would not consider Turbocor compressors in a desert environment. I think they would not spend much time in their sweet spot and quite frankly the numbers I have seen tell me they suck at full load conditions. There are many very large central plants in Dubai many of which are district cooling facilities.

[supertek65]

wow!!!!!!
they have come a long way since the zeros bombed pearl harbor!!!!!!!!!!!!!

i hope there arent any af those in any army bases!!!!!!!!! LOL

It's a chiller made by Mitsubishi. The MHI stands for Mitsubishi Heavy Industries.

[dlove]

If I were bidding this, I would look at a third solution. With the amount of runtime they get over there verses our traditional cooling season, payback can occur more quickly. we have less degree days for cooling, I would think by a lot. At any rate, if I had the infrastructure in place for RTAA's, I would look at a repalcement using either screws or turbocore, using evap condensing, with all pumps, evaporater, tower etc, all bundled neatly into one package, and set it in place of those rtaa's. you will see similiar kw/ton performance, and less initial cost, but thats just me. payback would be sooner, with less water treatment involved.

I like your thinking

[Screwit]

It's a chiller made by Mitsubishi. The MHI stands for Mitsubishi Heavy Industries.

@flange I would not consider Turbocor compressors in a desert environment. I think they would not spend much time in their sweet spot and quite frankly the numbers I have seen tell me they suck at full load conditions. There are many very large central plants in Dubai many of which are district cooling facilities.

Dubai has a design wet bulb of 89 degrees so agree the Turbocor performance would suck, but agree with Flange, given the lack of available wet bulb relief, worth investigating a VSD screw option.


For information on the Mutsuibishi Centrifugal http://www.mhi.co.jp/en/products/cat...l_chiller.html

[flange]

Didnt know it was that high. Yup, I would be all over me some screws, copeland, bristol, whatever they are called these days. I like those pumps.

[Tech Rob]

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

[flange]

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.

[flange]

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.

[rscamaro]

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

[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.

[KnewYork]

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.

[Southern Mech]

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.

[motoguy128]

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.

[R123]

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