Minimizing TEWI by Charge Reduction in a Compact Chiller

MINIMIZING TEWI BY CHARGE REDUCTION IN A COMPACT CHILLER A simulation model was developed to investigate strategies for reducing total equivalent warming impact (TEWI) in compact water chillers. The focus was on minimizing R-410A refrigerant charge while increasing efficiency. Compact flat plate heat exchangers with refrigerant channels similar in scale to microchannels (Dh= 0.7 mm and 0.8 mm for the condenser and evaporator, respectively) appear capable of reducing total system charge about 80% compared to conventional air-air split systems. Results are also compared to those obtained for highly efficient air-to-air unitary systems, in which minimum-TEWI design strategies require larger heat exchangers having greater charge. Overall the two approaches achieve comparable reductions in global warming impacts; the chiller depends more on reducing direct emissions, compared to unitary systems' dependence on reducing indirect emissions through use of flat mUlti-port tubes with folded fins. These results are tentative, because the simulations did not include detailed analysis of possible opportunities for improving the chiller technology by optimizing the air and water pumping requirements in the secondary loop. The primary benefit of the chiller technology, relative to air-air unitary, appears to lie in its compatibility with the use of toxic or flammable refrigerants.