0 10 20 30 40 50 60 70 80 90 100 Chilling Capacity (%)

0 10 20 30 40 50 60 70 80 90 100 Chilling Capacity (%)

Fig. 38-17 Large-Capacity, Direct-Fired LiBr Absorption Chiller/Heater. Source: Carrier Corp.

chiller/heaters. Figure 38-17 shows a large-capacity system and Figure 38-18 shows a small-capacity system housed inside a cabinet.

Operation of double-effect direct-fired LiBr absorption machines designed for simultaneous heating and cooling basically follows the normal cooling cycle, with the exception that some of the refrigerant vapor produced in the firststage generator is bled off into a hot water heat exchanger to meet heating load requirements. Because the vapor bypasses the second-stage generator, less cooling capacity is

Fig. 38-18 Small-Capacity, Direct-Fired LiBr Absorption Chiller/Heater Inside Cabinet. Source: American Yazaki Corp.

Fig. 38-19 Simultaneous Heating Capacity vs. Cooling Capacity. Source: York International available during simultaneous heating and cooling. Temperature controllers modulate the flow of refrigerant to maintain hot water and chilled water temperature set points. Either cooling or heating can be given priority, in case of unbalanced loads. Figure 38-19 shows how cooling capacity varies during simultaneous heating/cooling operation.

Heat Recovery Systems

Heat recovery or exhaust gas-fired chillers and chiller/heaters are double-effect machines that can be powered from a source providing clean, hot exhaust gases, such as a gas turbine or reciprocating engine. Direct coupling to a combustion engine can reduce installation cost and space requirements because a separate heat recovery boiler is not needed. They will, however, carry the premium cost associated with custom design.

A 2,000 kWe reciprocating engine-generator set can produce between 500 and 700 tons (1,760 to 2,460 kWr) of absorption cooling under standard ARI conditions in a typical application, while a gas turbine of the same capacity can produce between 1,000 and 1,500 tons (3,500 to 5,200 kWr) of cooling. Figures 38-20 and 38-21 show the available cooling and heating capacity, respectively, based on engine exhaust flow and temperature.

Triple-Effect Absorption Cycles

LiBr absorption machines using what is termed a triple-effect absorption cycle have been in prototype development for several years. These triple-effect absorption chillers will be direct-fired designs and are expected to provide nearly a 50% thermal efficiency improvement over existing double-effect units. Units currently under development are expected to have full-load COPs in

Available Cooling Capacity (tons)


J1 ri* ri* ck A

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