ISHED – Intelligent System for Heat Exchanger Design
for optimizing refrigerant circuitry in finned-tube heat exchangers

Finned-tube evaporators are the predominant type of heat exchangers used in comfort cooling and commercial refrigeration applications. Their performance is affected by refrigerant circuitry, i.e., by the sequence in which tubes are connected and form the refrigerant flow path through the coil. Chwalowski et al., (1989) measured as much as 30 percent evaporator capacity degradation due to a non-uniform air velocity profile. System’s capacity and efficiency degradation due to maldistributed air can be substantially avoided with an optimized refrigerant flow design.

The figure presents a schematic of a one-slab finned-tube evaporator operating with one-dimensionally maldistributed air. During the coil design process, the design engineer needs to specify the tube connections. Designing a proper refrigerant circuitry is particularly difficult if the airflow is not uniformly distributed over the coil surface.

The recent developments in machine learning – as incorporated in ISHED – allow improving the refrigerant circuitry design through an automated optimization process (Domanski et al., 2004). Up till now, ISHED was evaluated analytically (e.g., Domanski et al., 2005). In every case examined, ISHED proved capable of generating refrigerant circuitry architectures for finned evaporators that were as good as, or better than those generated by humans, particularly for operation with non-uniform inlet air velocity profiles. The goal of current research is experiment validation of ISHED’s optimization capabilities through testing four evaporators designed by humans and then optimized by ISHED. Upon experimental validation, ISHED will be incorporated into the EVAP-COND simulation package as an optimization option.

References

• Chwalowski, M., Didion, D.A., and Domanski, P.A., 1989. “Verification of Evaporator Computer Models and Analysis of Performance of an Evaporator Coil”, ASHRAE Transactions, Paper No. CH-89-23-1, Vol. 95, Part 1.
• Domanski, P.A., Yashar, D., Kaufman, K.A., and Michalski, R.S., (2004), “Optimized Design of Finned-Tube Evaporators Using Learnable Evolution Methods”, Int. J. of HVAC&R Research, Vol. 10, No. 2, pp. 201-212.
• Domanski, P.A., Yashar, D., Kim, M., 2005, “Performance of a finned-tube evaporator optimized for different refrigerants and its effect on system efficiency”, Int. J. Refrig., Vol. 28, No. 6. pp. 820-827.

Piotr A. Domanski, Leader
HVAC&R Equipment Performance Group
(301) 975-5877
piotr.domanski@nist.gov