Adsorption and Absorption Cooling System

Adsorption Cooling

The pores of activated carbon, silica-gel and zeolite materials absorb large amounts of gas.Adsorption cooling systems have been developed by utilizing these properties of such solid materials. In such systems, silica-gel / H2O, Zeolite / H2O and silica-gel-NH3 pairs are generally used. Silica-gel / H2O and Zeolite / H2O are used in water cooling groups, silica-gel and zeolite absorbent, water serves as refrigerant. Silica-gel / NH3 is used for cooling applications and silica-gel absorbing ammonia is a refrigerant.

The system for cooling applications consists of a boiler (also absorber) condenser and a vaporizer. Electric heaters and cooling coils are installed in the boiler. By heating the boiler, the silica gel heats up and the absorbed ammonia evaporates and separates from the silica gel.When it reaches a certain pressure, it opens the outlet valve and goes to the condenser. Here, ammonia, which becomes liquid by heating the environment, flows into the evaporator. After a while, the float in the evaporator rises and closes the electric heater circuit. It opens the coolant valve and the heater starts to cool. The ammonia that evaporates by pulling heat from the environment begins to be absorbed by the silica gel in the boiler that serves as the absorber when the electric heater is turned off. Thanks to the pressure drop in the cooling boiler, the evaporation of the ammonia will be easier. The resulting ammonia vapor opens the suction valve and returns to the absorbent. After a while the liquid level in the evaporator drops and the float closes the coolant valve and activates the heater. In this way circulation continues.

Adsorbed systems are used as water cooling groups. Adsorption water cooling groups are machines that use solid solution materials instead of liquid solutions. In daily applications, water, refrigerant and silica gel are used as absorbents. In recent years, some producers have begun to use zeolite instead of silica-gel as absorbent. There are two different applications; Silica-gel / H2O and Zeolite / H2O.

As can be seen in the following, the system consists of two absorbent sections, one being the evaporator and the other being the condenser. The absorber in the first section adsorbs the water vapor from the absorbent evaporator in the second compartment while being separated by the hot water from the external heat source (e.g. waste energy, solar energy). To ensure continuous adsorption , the second part should be cooled with cooling water from the cooling tower. The fluid which evaporates from the evaporator due to the low pressure conditions, allows the water entering the evaporator to cool.

Adsorption water cooling circuit diagram

Today, there are very few adsorbent water coolers in Asia and Europe. Despite being the oldest producer in Japan, nowadays the producers in Germany have started to take place in the sector.Under normal operating conditions, the hot water inlet temperature is 80 ° C and the EER value in these conditions is about 0.6. But hot water inlet temperature can work up to 60 ° C. The water cooling capacity range is between 5.5-500 kW.

The construction is simple and robust. There is no risk of crystallization. There is no need for a solution pump and electricity consumption is low enough to be tried. Their volume and weight are too high. Production costs are high because there is not too much production. As the heat exchanger design evolves, the volume and weight of the adsorption water cooling groups will decrease.

Absorption Cooling

Absorption refrigeration systems are basically similar to mechanical compression refrigeration systems as a working principle. In absorbing refrigeration systems, steam generators and absorbers are used instead of mechanical compressors, which provide fluid circulation in steam compression mechanical cooling systems and consume the most electrical energy. Two different fluids circulate in the absorption cooling systems. The first of these fluids is the refrigerant and the other is the absorber. Ammonia (NH3) -Su and Water-Lithium Bromide (LiBr) pairs are used in practice in recent years, although there are too many fluid pairs.

Ammonia-Water Pair: Ammonia is used as refrigerant and water is used as absorbent. Since ammonia is used as a refrigerant, such absorbent cooling systems are used in cooling systems and low temperature applications. The champion of the ammonia-water cooling machine was taken in 1859 by French Ferinand Carre. At the beginning, these machines were used to make ice and cool food. The following is an absorption cooling system using ammonia / water.

Absorption cooling system (Ammonia / water)

In low-temperature, low-temperature applications (up to -40 ° C), the ammonia-couple is used. In applications where the cooling capacity is small, air-cooled condensers are usually used. In large-scale applications, water-cooled condensers working with water cooling towers are used as in water-LiBr applications. The ammonia vaporized in the generator with the energy from the steam source or other energy source is passed through the heat exchanger and the water mixed in the ammonia is returned to the generator. The ammonia is made liquid in the condenser, the pressure is reduced by passing through the expansion valve. In the expansion valve, ammonia which is reduced in pressure is evaporated in the evaporator and cooling is performed. Evaporator evaporates in the evaporator. Here, the mixture comes back into solution with the water coming from the generator and the cooling water coming from the condenser. The liquid mixture is sent back to the generator via the pump and the process continues in this way.

There is also a small-capacity ammonia-water-absorbing cooling system used especially in areas where there is no electricity or in campsites. In such applications, the carrier duty is to replace the pump with a third fluid, hydrogen. Propane is usually used as the heat source.

Water-Lithium Bromide (LiBr) Dual: Water is used as the refrigerant, Lithium Bromide (LiBr) is used as the absorber. As water is used as a refrigerant, reaching 0 ° C is very difficult. In such systems the water in the evaporator is usually evaporated under vacuum at 4 ° C and the water to be cooled can be cooled to a temperature of 6-7 ° C according to the application requirement.Such absorbent cooling systems produce cold water for industrial processes and central air conditioning systems. There are generally four types of applications.

• Single effect absorptive chiller
• Double acting absorption chiller
• Three effective absorptive chillers
• Direct burned absorptive chiller

Single effect absorptive chiller: Such systems are particularly suited for businesses with waste steam, flue gas and hot water energy. Geothermal and solar energy etc. It is appropriate to use absorbent chillers in countries with energy sources such as It is also advantageous to use direct burned absorption systems in countries where natural gas is very cheap. Due to the high cost of electricity in recent years, large shopping malls and industrial facilities have begun to set up natural gas power plants to meet their electricity needs. With this waste heat, in winter heating or process heating water, in summer, the process cooling water or cold water needs for central air conditioning are met. These systems, which are becoming more widely used today, are expressed as “trigeneration” applications. Trigeneration applications can meet electricity generation, heating and cooling needs. The following is a schematic representation of trigeneration. “Quattro-generation” applications can also be applied for businesses that require drying.

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