Condensing units vs dry coolers?
What's the difference and why is one designed over the other?
what exactly do you mean? i have not seen dry coolers installed where a chiller is not used...so do you have a job where there are dry coolers and not a chiller?
Originally Posted by Grawburg
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You see both, alot, with server rooms. With a drycooler, you can use the glycol/water to be the first stage of cooling, during low ambients, reducing energy used by mechanical cooling. Also, your refrigerant charge is in a packaged unit, less refrigerant to deal with. Not to mention, you always know how much to weigh in, if need be.
Only disadvantage I see, is the glycol pumps. If a mech. seal goes bad, there is no make-up. The compressors trip on high head and your dead in the water. Liebert gives you two pumps for redundancy, for this vary reason. However, someone still has to isolate the leaking pump and add glycol/water (usually 40/60) back into the system, before he can reset the compressors and get cooling going again.
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To answer the basic question, and prevent a fight over terminology, I'll mention the condensor first. If you're talking about what I call a fan coil, that being a large unit with only fans and a coil which is physically seperate from the rest of the system but connected to it by pipes carrying refrigerant. Doing the same job it would if it were part of any air cooled refrigerant system, just not in the same box.
Drycooler is the same thing but is running water instead of refrigerant, as is the case of the Lieberts mentioned by Whec. The water is pumped through heat exchangers in the indoor unit, so the heat is transfered from refrigerant to water. The water takes it outside and transfers it to air by the drycooler. When you see plate exchangers mentioned it is one type used for this setup.
And it should be installed with a backflow preventor, treatment tank, and pressure regulator in a makeup water line. To prevent the kind of shutdown described. Then only some water treatment is lost, without unit shutdown. A bit cleaner, but not as efficient as a water tower, and usually chosen when the smaller tonnage equipment won't justify using a tower.
Dry coolers are more practical in multi story buildings, pumping glycol 10 stories works better than moving refrigerant. The self contained units are easier to service in one space and also with proper sizing multiple units can utilize one dry cooler. There are still the same maintenance issues plus water treatment and containment.
Ditto to Franks post, but I don't see a large difference in the maintanence between dry-coolers and remote condensers.
Don't buy a Lee-Temp condenser if all you really need is a P66 fan control.
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Ok, maybe the better question is why would you use a drycooler instead of a cooling tower. If both options are for cooling indoor condensers, what's the advantage of one over the other?
Like everything else in the buis, the answer depends on the situation. If you want lighter weight, less maintenance, dryer area around it, less hassle to purchase (manufacturers usually offer them as an option) and possibly lower up front cost. And don't mind higher a electric bill, have room for it, replacing the odd fan motor occasionally, and are running under 75 tons. A drycooler is probably better.
However if when the tonnage is 40 or above, anytime space is restricted (a 200 ton tower takes up approx. the same sq. ft. as a 40 ton cooler, not counting height), weight isn't a problem, efficiency is, then towers become the best option. Then theres always a situation that blows everything said up to this point to hell.
I may not have all the facts, or covered all the reasons, being just a silly service tech. But this is what I've seen in my area. No bodies bothered to ask me to choose, just to fix whatever is keeping it from doing what they thought it would when it was installed.
Last edited by Coolmaniac; 06-28-2008 at 04:11 PM.
has anyone done/seen the replacement of a tower with a dry cooler due to terribly hard water conditions for the tower...i.e. scaling over of the heat exchanger in the tower.....the towers i work on are in a city that the water is terrible, they went for approx three seasons with a crappy Dolphin treatment system and it trashed the towers, i have 1/8 inch of scale built up on the exchanger.....when i took over the building, i had a chem company come in and try to remove the scale to no avail.....dry cooler just comes to mind just want to see if anybody has retrofitted a tower over to a cooler
have had 2 coolings towers removed and they have put in two drycoolers, the work well lot less maintenance, cheaper to run because of less dosing of chemicals, we had a few little teathing problems but now i dont have any trouble with it.
clean them out which is easy and wash the evap pads every 6 months
I know a lot of cooling towers have been replaced with these
We use alot of dry coolers p here in AK. Condensers work in the cold but not as well as we like. The dry coolers here use glycol and are the main source of cooling in the winter. With temps below zero a good part of the winter, the incoming glycol is plenty cold for cooling and in many cases the compressors wont run for 2 or 3 months depending on heat load and situation. Except for the pump being the weak link in the chain they work good.
We recently installed a drycooler (glycol) to serve a computer room Liebert unit. Prior to that the Liebert was cooled by the central plant condenser loop, which worked fine as long as the main condenser pumps & cooling towers were running. Problem was that after the chiller plant shut down in the evening the mickey mouse system they had to pump cond water out to the towers was constantly losing prime & shutting down the unit. It works much better now.
Just another example of a drycooler in action.