Difference of the DX and CW system.

[steven86]

Anybody who can tell me what is the difference of DX system and chilled water system ? When we need to use DX system and when we need to use CW system ?
DX system is more energy saving than the CW system?

[moideen]

Anybody who can tell me what is the difference of DX system and chilled water system ? When we need to use DX system and when we need to use CW system ?
DX system is more energy saving than the CW system?

The air from the space to be air conditioned is circulated over the cooling in which the low pressure liquid is boiling. The latent heat of vaporization for the liquid refrigerant is taken from the air being circulated over the cooling coil. So this is known as the Direct-Expansion (DX) system.

In the indirect system, chilled water or brine from the refrigeration plant is circulated through the cooling coil located in the air handling unit to cool and dehumidify the room air. This type system is known as chilled water (CW) system. chilled water system more power per unit of refrigeration (Kw/tonne) compare to DX system.

Moideen-Dubai

[icecube51]

whit the DX system you need more refrigerant than for CW systems for the same amount of refrig tons. also the distance between indoor and outdoor units can be greater for CW tan for DX. incase of a leak on CW systems, anybody can do the repairs, a plumber or handy man. for DX you have to be a certified technician, and most of all, now what you are doing.

Ice

[steven86]

The air from the space to be air conditioned is circulated over the cooling in which the low pressure liquid is boiling. The latent heat of vaporization for the liquid refrigerant is taken from the air being circulated over the cooling coil. So this is known as the Direct-Expansion (DX) system.

In the indirect system, chilled water or brine from the refrigeration plant is circulated through the cooling coil located in the air handling unit to cool and dehumidify the room air. This type system is known as chilled water (CW) system. chilled water system more power per unit of refrigeration (Kw/tonne) compare to DX system.

Moideen-Dubai

Tat mean CW system is more energy saving then the DX system ?

[frank]

Tat mean CW system is more energy saving then the DX system ?

Consider that you have a large chiller in the basement or rear of the building that provides chilled water to 150 indoor fan coils.

If only 1 indoor fan coil calls for cooling because all of the other 149 are at thermostat off condition, the large chiller has to come on line and cool the entire chilled water loop before that 1 fan coil can be served.

Doesn't seem that 'energy efficient' to me

[dougheret0]

You asked two questions initially – what is the difference between the two types of system, and when should you use one or the other. The answers are complex, involved not only with the technology of the systems, but with the architecture of the project and the experience and judgment of the designer – usually an engineer, but often a skilled technician.

The best way to find the answer to both questions is with the ASHRAE handbooks – Equipment and Systems, and Applications. New editions of each are published every four years. The most recent Equipment and Systems is dated 2007, and previous editions will be dated 2003, 1999, etc. Likewise, the most recent edition of Applications is 2008, with earlier editions at four year intervals. Any edition since 1987 (or 1988) would be useful, and used versions of such earlier editions can often be found either in hardcopy or CD form (recommended) on E-bay.


As pointed out by Frank, the more modular or distributed a system, the more efficient. Ideally, every cooling zone should have its own compressor, but this may not be practical given the architecture of a particular project. Water cooled DX systems can approach this goal, but so can multiple chillers, or chillers with large turndown ratios. On small projects, multiple air cooled DX systems may be the most cost effective and efficient solution.

[Sridhar1312]

chilled water is energy efficient to the extent as you produce chilled water and circulate to all end use Air handling units. The air handling units may not operate at peak load and there will be diversity on the load compared to estimated load. This diversity can be 60% to 80 % and hence you need chiller capacity at 60% of the toatl load .whereas the DX system this advantage is not to that extent

[anna.savvy]

That was very helpful...ultimately i understand the difference.