Original message
| anisaamm
 |  "Direct Expansion & air cooled Liquid chillers"
, posted Thu 15 Dec 11:38  
hi guys, i am new in havc, still learning the basics, would u please explain what is a direct expansion chiller and what an air cooled chiller is?
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Replies:
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| fitter597
| "Re(1):Direct Expansion & air cooled Liquid ch" , posted Sat 17 Dec 01:12
Direct expansion is a term to define a coil, we call it a DX coil, meaning that it runs refrigerant thru it instead of water, has nothing to do with chilled water.
An air cooled chiller is a system that uses air to cool the refrigerant, like in a trane RTAC screw machine chiller, or a Carrier flowtronic system, it still chills water but is normally located outside, roof, back of building, etc.
An water cooled chiller uses water thru a bundle to cool the refrigerant, Like a Centrifugal Trane CVHE Centravac system, usually located inside a building, uses a cooling tower for condenser water and chilled water for cooling.
Go to this website and read up, lot's of manuals you can download for different chillers you'll like it.
http://www.trane.com/commercial/equipment/pdf_list.aspx
"We Do It Right The First Time"
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| | chiller guy
| "Re(2):Direct Expansion & air cooled Liquid ch" , posted Wed 21 Dec 16:21
Direct Expansion refers to a type of evaporator used. You have two basic types "DX and Flooded". The derive their names from their method of evaporating the refrigerant.
DX meters the refrig. directly into the evaporator tubes where it boils as heat is picked up. The tubes can be surrounded by water (chiller) or air (home AC). It is still DX in both cases.
Flooded evaps are a big tub of liquid refrigerant with tubes laying in them. Water is pumped through the tubes and heat is transfered to the cold refrigerant. This style evap is generally used in larger tonnage equipment.
Now that we have picked up some heat we need to reject it somehow. Our choices are generally directly to the surrounding air mass or to a transfer material to get it to the air mass. Your home unit is "air cooled" as is much of the equipment you will see. Often though the unit picking up the heat is buried in the bowels of a building and getting sufficient amounts of air is impratcial. Then we use a transfer fluid to pick up the heat and move it to the outside (cooling tower) where it is then cooled and sent back for more heat.
Hope this basic discription helps! If you have more questions ASK!! The only dumb question is the one that goes un asked.
Good Luck!
All refrigerants are safe - All refrigerant are dangerous. The difference is YOU !!!
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| | anisaamm
| "Re(3):Direct Expansion & air cooled Liquid ch" , posted Wed 21 Dec 18:15
thanks for your help guys, the both explanations are helpful,
the answer i was looking for is confirmed by CHILLER GUY, i have a further question; (strictly talking chillers) is it true that some time in DX system double expansion valves are used, and that means double evaporater colis? and how one can tell which chiller is DX or Flooded. As in both systems, i think the evaporaters are enclosed in a cylender are rube. Also is true that DX system is relatively new in Chillers?
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| | chiller guy
| "Re(4):Direct Expansion & air cooled Liquid ch" , posted Thu 22 Dec 10:16
Lets see if I can keep this straight for you (and me).
1. By double expansion valves you mean more than one valve on the unit - correct? How do you feel about 4 expansion valves on a unit (air or water evap). A 400 ton, air cooled chiller will probably consist of 2 - 200 ton refrigeration circuits (completely seperate). Each circuit will have 2-100 ton TXV's (Or EXV's)
Within the evap shell are two seperate evap's. Each capable of doing 200 T. The system water is common to both evaps and how much heat is transfered depends on how much of the circuits are being used at a given time.
Evap's are generally well insulated and look the same at first glance. The difference is determined by where the system water is introduced into the evap. If the water flows into the shell side and the refrig lines in the ends, it's a DX system (refrig inside the tubes).
If it's flooded the water will be flowing into the tubes and the refrig on the shell side.
On some equipment you may have to study the unit a bit to determine which you have. As time goes on you will develope the ability to pick them up quickly.
Are DX systems new on chillers? Define new! DX chillers have been around a looooong time as have flooded evaps. I can vouch for 40 yrs.
All refrigerants are safe - All refrigerant are dangerous. The difference is YOU !!!
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