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Technical information Chillers ABSORPTION CHILLERS


About 92% of refrigerating systems used for HVAC applications in the United States, the electric drive of the vapor compression cycle systems. However, in some areas, mainly in the large cities and in some universities and hospital complexes, large steam distribution systems. In past years, this pair is often cheaper than electricity and was used to provide cooling, the use of absorption refrigeration cycle. As a rule, is not so little or no new absorption cooling is used, except when the waste heat source, for example, cogeneration or some industrial processes or where the use of absorption cooling during peak cooling periods can reduce the seasonal electric demand charges (see 2.3 Sec).

Absorption refrigeration cycle relatively old technology. The concept of date from the late 1700s, and the first absorption cooling machine was built in the 1850s. However, by the beginning of World War I, the technology and use of reciprocating compressors have reached a point where the interest in the development absorption cooling in fact, frozen, until the 1950s.

During this period, in two phases of absorption cooling machine was developed in the United States, while the direct fired concept was tested in Japan and other Pacific-rim countries.

Fundamental single absorption cycle is presented on Fig. 1.8. Evaporator consists of a heat exchanger, held under low pressure, with a separate refrigerant (usually water) pump. Pump sprays of the refrigerant through the tubes with chilled water, it absorbs the heat of the water evaporates as low-pressure gas. Low pressure gas streams absorber, due to the differential pressure. Absorber at a lower pressure than in the evaporator is because the focus of absorbent solution (usually lithium bromide) has a molecular attraction for the refrigerant. The absorbent solution is sprayed into contact with refrigerant vapor. Condensation of refrigerant, because the heat is absorbed by the absorbent. Absorbent, then cooled condenser water.

Absorbent now consists of the diluted solution, because of its absorbing water vapour refrigerant. The diluted solution is pumped to the beneficiation plant, where heat is applied for re-evaporation of the coolant. A concentrated solution of the absorbent is then returned to the absorber. Refrigerant steam enters the condenser, where it is condensed in the condenser water. To increase the efficiency of the heat is used for heating of the diluted solution, with the heat contained in a concentrated solution of the absorbent.

Air leakage allow you to log in refrigerant, representing the non-condensable gases. These gases must be removed or obliterated, to prevent pressure in the absorber is increasing to the point where the flow of refrigerant vapour at the outlet of the evaporator will stop. The solution at the bottom of the absorber is relatively quiet, and these gases tend to accumulate at this moment. They can be removed by use of a vacuum pump, which is usually called clean the pump

Absorption chillers are defined as indirect fired or direct-fired and can be a one-stage or two-stage (research on the three-stage cooler now), as follows:

  1. Indirect-fired single-machine uses low and medium pressure steam (5-40 psig) to provide heat in the absorption process. This type of cooler requires about 18 500 BTU/HR per ton of cooling effect, resulting in the chiller COP on 0.67.
  2. Indirect-fired two stages cooler uses high-pressure steam (not less than 100 pounds per square inch) or high temperature hot water (400F or higher) and requires approximately 12,000 Btu/hour per ton of cooling effect, resulting in the chiller COP 1.0.
  3. Direct heated hmm, as its name implies, do not use steam, but uses a natural gas and/or liquid fuel, burners, systems of heat supply. These refrigerators two stages of the machine, resulting in an overall efficiency of 1.0-1.1.

Indirect-fired units, the total COP should be reduced for accounting for losses in the production of steam in boilers. With a typical boiler efficiency shooting 80-85%, which reduces the overall COP for single-stage systems about 0.54 and about 0.80 for the two-stage system.

Because absorption cooling COP has only 0.54-1.1, this is bad competes with the electric drive of rotary compressor chillers, as shown in Табл.1.5.

Other factors that must be considered for absorption chillers include the following:

  1. Absorption chillers require approximately 50% more floor space than the equivalent electric drive (vapor compression cycle) hmm. In addition, because of their height, mechanical equipment of the rooms must be 6-10 feet taller than the rooms of the building of the electric drive of chillers. Finally, because the liquid solution contained in the long, shallow trays within absorption chiller, the floor should be as close as possible to the absolute level as possible.
  2. Absorption chillers weight will be at least twice the equivalent electric drive hmm.
  3. Because of their size, absorption chillers, sometimes comes in several areas requiring the field of welding for final Assembly.
  4. While the majority of electrical chillers are shipped from the factory with their refrigerant installation of refrigerant and absorbent (including additives) should be the installation of absorption chillers.
  5. While the noise and vibration are real problems for electric drive chillers (see C. 6.1), absorption chillers (if not a direct-fired) silently and, in fact, without vibration.
  6. Due to the potential for crystallization of lithium bromide in cooler if it gets too cool the condenser water temperature must not exceed 75 -80F.
  7. Emergency power supply may be required if a lengthy power outages are common. Without electricity and heat, hmm begins to cool and lithium bromide solution may crystallize. However, since the absorption chiller has a very small electrical load requirement (usually less than 10 kW), a dedicated backup generator is not a major element.
  8. Heat rejection from the condenser at 20-50% more than the equivalent electric drive hmm, requiring higher consumption of water in the condenser and more, cooling towers and condenser water pumps.
  9. Finally, indirect-fired absorption chiller will be at least 50% more expensive than buying an equivalent electric drive hmm. Direct fired absorption chillers would cost almost twice as electrical machine, and were added costs associated with the provision of combustion air and ventilation (stack).
Direct fired absorption cycle chillers, should be carefully checked at any time the engine-drive vapor compression cycle hmm considered. Even if the cost of energy for the absorption chiller can be higher, the increase in expenses on the maintenance motor drive systems may make absorption more cost effective..
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