Written by craig braddick

What Is An Absorption Chiller?

Absorption chillers all work on a similar principle, when the pressure system is low the absorption fluid evaporates and the heat is removed from the water parts that are chilled and the absorption solution is then regenerated either by steam, hot water, or exhaust gas.


If it is in a waste energy plant or cogent, it will usually consist of stream fired absorption due to the cost of the steam being lower. If it is in a hybrid and/or higher cost of electricity areas it usually will use the direct fired, using natural gas units. Many users will buy absorption chillers to use as an environmental advantage since absorption chillers do not use refrigerant such as CFC and/or HCFC.

Principle & Mechanism:

As a principle, it does not sound presumptuous to use a burning flame in order to cool something down, however,that is just what is done with absorption chillers. The refrigerant is merely water that acts as a medium and it goes through a phase which causes a mechanism to change causing a cooling affect. It then takes a second fluid to make the process work and that is salt (usually in the form of lithium bromide). Next, the two fluids are then separated by the use of heat, and when the two are put back together and the water remixes with the salt at a slow pace, normally at a low temperature having a normal atmosphere pressure, which will cause water to vaporize at 212F within an absorber, the vaporizing water is cold enough to put off water as cold as 46F.

An explanation on description of structure, shapes, and/or diagram of system:

One could use electric chillers, however, they do cost a lot more to use, and if purchasing right out, they are going to be about twice as much. So, if one wanted to justify an absorption system that is base-loaded, it is going to take more than a reason like average electric costs. That is why the economy favors the hybrid systems, they have a combination that lets them use absorption chillers when the electricity is at its peak, however, it also lets it use electric chillers when it is not at its peak, or rather, during its base load of operation.

The savings effect on energy:

The energy savings is estimated to be upwards toward 50% more efficient as the conventional chillers.

The equipment cost, economically speaking:

The cost of the equipment that is chosen will depend on several different factors, which include: equipment, utility rate, equipment building type, climate, and scalar ratio.


Absorbers have a co-efficient in its performance (COP) that factors in at near 1.0, when compared to the engine driven compressors, which factor in at nearly 1.5 and the electric one at nearly 3.0.

How does an absorption chiller work?

There are various stages that coolant goes through during the cycle of a absorption chiller. Read more below to understand individual principles.

The effect of the single lift hot water driven absorption chillers:

Hot water driven for a single lift absorption chiller means that the water is chilled one time using a refrigerant in a double tray inside the evaporator. The refrigerant vaporizes and is absorbed, turning into a concentrated solution, usually, potassium bromide, a concentrated solution coming out of the generator. While this concentrated solution is being diluted it is absorbing the refrigerant (which is evaporated) and heat is being absorbed by the cooling water. Now, the absorber, with the diluted solution goes into the generator by heat exchanging. The water is at 950C and is heating up the diluted solution, causing the refrigerant to vaporize. After the refrigerant has vaporized it becomes condensed, returning to the refrigerant circuitry. It has regenerated the diluted absorbent and can recycle it.

The double driven hot water effect:

In an absorption chiller for a hot water driven with a double lift there is a primary cycle and the auxiliary cycle. Whereas, the chilled water is cooled down two times by the refrigerant of the double tray located in the evaporator, Once the refrigerant has vaporized it is turned into concentrated solution, which comes out of the second generator. The double tray system increases the amount of vapor that the absorber can absorb by the cooling water. Then the diluted solution that is in the absorber will flow into the first generator by the use of a lower temperature heat ex changer and a higher temperature ex changer, at 950C hot water will heat the diluted solution, and then it vaporizes the refrigerant. While the absorbent solution is an intermediate solution at the first generator, and it flows into the second generator through high-temperature heat ex changer. Now the intermediate solution that is in the second generator is being heated with use of the hot water, making more refrigerant vaporize in the second generator as well. Auxiliary diluted solution is being made as the vapor is being absorbed by the absorbent solution, which is already in the auxiliary absorber. Next, the auxiliary heat ex-changer uses the auxiliary generator to carry the auxiliary diluted solution, which is heated by use of the hot water that comes from the first generator, turning it into an auxiliary concentrated solution. In short, first the auxiliary concentrated solution gets carried to the auxiliary absorber by way of the auxiliary heat ex-changer. All vapors that are generated in the first generator, and also the auxiliary generator become condensed within the condenser, letting it flow to the evaporator. The cooling water then absorbs the condensers heat.

Direct-fired Absorption Chiller:

The direct-fired system is very similar to the hot water single lift series with one exception, and that is that it does not use hot water in order to generate an absorption solution, instead, the solution is regenerated by using a gas flame and heating it directly, this also regenerates the refrigerant.

Driven absorption chiller using the double effect of exhaust gas:

The water in the evaporator boils at a low temperature of 4.40C, this is due to the vacuum conditions inside the evaporator. The chilled water gets cooled down from the tubes of the evaporator by use of latent heat. Which in return lowers the temperature of the outlet to near 70C. The transfer of the heat gets help from the spraying of refrigerant or rather distilled water, through a refrigerant pump. Then the refrigerant or water vapors will flow to the absorber and the lithium bromide solution absorbs it. The lithium bromide now becomes a diluted solution as it reduces its amount of absorption.

The diluted solution now gets transferred by a solution pump to a generator and it is re-concentrated (re-concentrating takes two stages, which is the double-effect) by boiling the previous water absorbed, off. With the diluted solution then being pumped into a higher temperature generator and heat in order to re-concentrate into a medium concentration solution using exhaust heat coming out of the reciprocating engine’s exhaust gases.

Flowing from the high temperature generator is the intermediate solution and going into the lower temperature generator and it is heated, becoming a concentrate solution through high temperature water vapors being released out of the solution during the time in the high temperature generator.

Because of the low-temperature generator acting like a condenser in the high temperature generator, the applied heat energy of the high-temperature generator is being used in the low temperature generator as well. Compared to the single stage chiller it reduces the input by around 45%. The vapors that are released on the shell side in the low temperature generator goes into the condenser and cools, now it returns into a liquid form. The refrigerant (water) now goes back to the evaporator to begin another cycle.

The tubes of the absorber first get cooling water from the cooling tower to cool the chiller, and then circulate, removing heat caused from the vaporization.

Phoenix Chiller Repair & Maintenance

If you need to have chiller repair done on your chiller in the Phoenix area All Kote Lining, Inc. is here to help. We understand how to inspect, recondition, repair, and perform general maintenance on your chillers. This will get you the longest life, best efficiency, and get you the peace of mind you need when it comes to the chiller installed in your building or business. If you have questions or would like to schedule your chiller repair please call 480-966-4446.

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