Types of Water Chillers

Types of Water Chillers

Types of Water Chillers

Packaged Air-Cooled Chiller:

Packaged or Split Components

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Packaged or Split Components

Water-cooled chillers are rarely installed with separable components. Air-cooled chillers, however, offer the flexibility of separating the components in differentphysical locations. This flexibility allows the system design engineer to place
the components where they best serve the available space, acoustic, andmaintenance requirements of the customer.
A packaged air-cooled chiller has all of the refrigeration components(compressor, condenser, expansion device, and evaporator) located outdoors.
A major advantage of this configuration is factory assembly and testing of allchiller components, including the wiring, refrigerant piping, and controls.
This eliminates field labor and often results in faster installation and improvedsystem reliability. Additionally, all noise-generating components (compressors
and condenser fans) are located outdoors, easing indoor noise concerns.Finally, indoor equipment-room space requirements are minimized.

Remote Evaporator Barrel:

Remote Evaporator Barre

An alternative to the packaged air-cooled chiller is to use a packaged condensing unit (condenser and compressor) located outdoors, with a remote
evaporator barrel located in the indoor equipment room. The two componentsare connected with field-installed refrigerant piping. This configuration locates
the part of the system that is susceptible to freezing (evaporator) indoors andthe noise-generating components (compressors and condenser fans) outdoors.
This usually eliminates any requirement to protect the chilled-water loop fromfreezing during cold weather.
This configuration is particularly popular in schools and other institutionalapplications, primarily due to reduced seasonal maintenance for freeze
protection. A drawback of splitting the components is the requirement forfield-installed refrigerant piping. The possibility of system contamination
and leaks increases when field-installed piping and brazing are required.Additionally, longer design time is generally required for the proper selection,
sizing, and installation of this split system.

Remote Air-Cooled Condenser:

Remote Air-Cooled Condenser

Another popular configuration is to use an outdoor air-cooled condenserconnected to a packaged compressor and evaporator unit (also called acondenserless chiller) that is located in the indoor equipment room. Again,the components are connected with field-installed refrigerant piping.The primary advantage of this configuration is that the compressors are locatedindoors, which makes maintenance easier during inclement weather andvirtually eliminates the concern of refrigerant migrating to the compressorsduring cold weather.

Indoor Air-Cooled Condenser:

Indoor Air-Cooled Condenser

The final configuration includes a packaged compressor-and-evaporator unitthat is located in an indoor equipment room and connected to an indoor,air-cooled condenser. The air used for condensing is ducted from outdoors,through the condenser coil, and rejected either outdoors or inside the building
as a means for heat recovery. Indoor condensers typically use a centrifugal fanto overcome the duct static-pressure losses, rather than the propeller fans usedin conventional outdoor air-cooled condensers. Again, the components areconnected with field-installed refrigerant piping.This configuration is typically used where an outdoor condenser isarchitecturally undesirable, where the system is located on a middle floor of amultistory building, or where vandalism to exterior equipment is a problem.
A disadvantage of this configuration is that it typically increases condenser fanenergy within compared to a conventional outdoor air-cooled condenser.Similarly, a packaged cooling tower in a water-cooled system can also belocated indoors. This configuration also requires outdoor air to be ducted to
and from the cooling tower, and again, typically requires the use of a centrifugalfan. Centrifugal fans use about twice as much energy as a propeller fan, but canovercome the static-pressure losses due to the ductwork. Alternatively, the tower sump can be located indoors, making freeze protection easier.

Absorption Refrigeration Cycle:

Absorption Refrigeration Cycle

Absorption Water Chillers
So far, we have discussed water chillers that use the vapor-compression refrigeration cycle. Absorption water chillers are a proven alternative to vaporcompression chillers. The absorption refrigeration cycle uses heat energy as the primary driving force. The heat may be supplied either in the form of steam or
hot water (indirect-fired), or by burning oil or natural gas (direct-fired).
There are two fundamental differences between the absorption refrigerationcycle and the vapor-compression refrigeration cycle. The first is that thecompressor is replaced by an absorber, pump, and generator. The second is that, in addition to the refrigerant, the absorption refrigeration cycle uses a
secondary fluid called the absorbent. The condenser, expansion device, and
evaporator sections, however, are similar.
Warm, high-pressure liquid refrigerant (D) passes through the expansiondevice and enters the evaporator in the form of a cool, low-pressure mixture ofliquid and vapor (A). Heat is transferred from the relatively-warm system waterto the refrigerant, causing the liquid refrigerant to boil. Using an analogy of thevapor-compression cycle, the absorber acts like the suction side of thecompressor—it draws in the refrigerant vapor (B) to mix with the absorbent.
The pump acts like the compression process itself—it pushes the mixture ofrefrigerant and absorbent up to the high-pressure side of the system. Thegenerator acts like the discharge of the compressor—it delivers the refrigerantvapor (C) to the rest of the system.
The refrigerant vapor (C) leaving the generator enters the condenser, whereheat is transferred to cooling-tower water at a lower temperature, causing the refrigerant vapor to condense into a liquid. This high-pressure liquid refrigerant(D) then flows to the expansion device, which creates a pressure drop thatreduces the pressure of the refrigerant to that of the evaporator, repeating
the cycle.
The absorption refrigeration cycle is discussed in more detail in the AbsorptionWater Chillers Air Conditioning Clinic.


 
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