What are Absorption Chillers and how they work?

What are Absorption Chillers and how they work?

What are Absorption Chillers and how they work?

1) Boiler’s and Refrigerator’s compressor

1.1) What is a boiler?

Simply speaking, a steam generator or a boiler is designated to a closed container in which water is heated by burning of fuel in the presence of air at a desired temperature, pressure and a preferred mass flow rate to be converted into steam.
It is an example of a heat exchanger which refers to a mechanical system especially designed and used for the exchange of heat between the hot fluid and the cold fluid.
The boiler system is made out of three different systems:
– Feed Water System: this system is designed to feed the needed amount of water to the boiler and automatically regulating its flow rate to meet the steam demand.
– Steam system: this system is responsible for collecting and controlling the steam that is produced in the boiler.
– Fuel system: the fuel system, is the combination of equipment necessary for generating Heat.

1.2) What is a Refrigerator compressor?

A refrigerator compressor is a device that plays a vital role in the refrigerating cycle:

refrigerating cycle

The refrigerating compressor is very similar to an automobile engine. In this system, the motor drives the piston to compress the refrigerant inside a cylinder. While the piston moves down into the cylinder, it sucks the refrigerant from the evaporator.

2) Introduction to absorption chillers

2.1) What is an absorption Chiller?

An absorption chiller is basically a refrigerator that uses a heat source in order to provide the energy that is needed to drive the cooling system. These chillers are growingly replacing the regular compressor refrigerators where electricity is unreliable or expensive, and where noise from the compressor can also be problematic.

Absorption Chiller

2.2) How does an absorption chiller work?

In an absorption chiller, the water vapor comes in contact with the condenser section which then turns it into a liquid.  This liquid water is transferred to a tray inside the condenser and then moves into the evaporator through a pipe. The volume flow rate of water is controlled via a fixed orifice. The evaporator is kept at a very low pressure and this low pressure causes the water to flash and drop its temperature. The water reduces temperature to around 4°C which is around 40°F. The chilled water carries all the unwanted heat of the building from the AHU’s and fan coil units etc. 

2.3) Types of Absorption Chillers

Types of absorption chillers

There are many different types of Absorption chillers some of which include the followings

  • SINGLE EFFECT HOT WATER DRIVEN ABSORPTION CHILLER:

In a single effect hot water driven absorption chiller, the water is cooled down by a refrigerant from a double tray system. The vaporized refrigerant is then absorbed into a concentrated solution coming from the generator. The concentrated solution becomes diluted in order to absorb the evaporated refrigerant. This is process is completed once the heat is absorbed by the water. The diluted solution in the absorber then flows to the generator through a Heat exchanger. The hot water which is around 95°C heats up the diluted solution and the refrigerant is finally vaporized. The vaporized refrigerant is now condensed and returned to the refrigerant circuit. 

  • DOUBLE EFFECT HOT WATER DRIVEN:

Unlike the single effect hot water driven absorption chiller, in a double effect hot water driven, the chilled water is cooled down this time twice by the refrigerant from a double tray. Coming from the 2nd generator the vaporized refrigerant is absorbed into concentrated solution. Thanks to the double tray system, the quantity of Vapor that can be absorbed is increased by double. The heat is later on absorbed into the cooling water. Through a low temperature, the diluted solution flows to the first generator.  Posed to a hot water, the diluted solution is heated up and the refrigerant is then vaporized. The absorbent solution then flows to the second generator and this time through a high temperature. The hot water then heats up the solution and more refrigerant is vaporized. The refrigerant vapors which are generated in the first generator and second one are condensed and then transferred into the evaporator. The heat in the condenser is later absorbed by a cooling water.

  • DIRECT FIRED ABSORPTION CHILLER:

Similar to the Single Lift Hot water however different in few things. In a direct fired system, the solution is heated directly by the gas flame in order to regenerate the solution and the refrigerant.

3)  Pros and Cons of using boilers for the cooling facility

3.1) Benefits of using Absorption Chillers

Using an absorption chiller has a lot of advantages such as:

  • Long service life approximately up to 20 years.
  • A Low cost of produced cold
  • Due to the lack of compressors, with electric motors, noise and vibration are significantly reduced and thus they operate quietly
  • A reduction in the initial cost of the system which makes them competitive compared to conventional systems.
  • Maximizing the energy savings during periods of peak demand due to not consuming electricity for the production of cold or heat.
  • The possibility of combining the district steam systems with an efficient refrigeration unit
  • Minimizing the overall impact on the environment as the consumption of electricity is significantly reduced.

3.2) Disadvantages of using Absorption Chillers:

There are some disadvantages and cos for using absorption chillers such as:

  • Initial capital cost: Though the running cost of the absorption chiller system is much lower than the vapor compression system, its initial capital cost is considered to be much higher.
  • Low working pressures: The working pressures of the absorption chiller cycle are very low, and this can be problematic for some facilities.

4) Conclusion

In conclusion, absorption chillers are similar to any technology new or not, they are not perfect, they have their own advantages but they also have their own share of disadvantages and drawbacks, however according to research and statistics the benefits that are provided by using absorption chillers are far greater than that of its challenges, that’s why many companies and facilities are switching from the regular and traditional compressor refrigerators to the new and advanced systems the absorption chillers.

One Comment

  1. Oliver Ray
    July 12, 2019 Reply

    I didn’t know that the double effect chiller seems to do double the job by being able to absorb more of the vapor. We are looking to get a new chiller system in our home and my wife loves it to be cold in the home. We might get a double effect chiller so we can have the home at the right icy temperature during the summer.

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