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Comparison of frost and defrost performance between microchannel coil and fin-and-tube coil for heat pump systems.

Author(s) : PADHMANABHAN S., CREMASCHI L., FISHER D., et al.

Summary

This paper presents a comparison of frost and defrost cycling performance between a microchannel heat exchanger with louvered fin and a fin-and-tube heat exchanger with straight fins employed as outdoor coils of a 4-ton (48 000 Btu/hour) heat pump system. In addition to temperature, pressure, and flow rate measurements taken at various locations of the systems, the fin-base and tube wall surface temperature were also recorded by using fine-gauge precalibrated thermocouples on the coils. Further, load cells were used to measure the mass of frost accumulation during heating tests. Data showed that the frosting time of the microchannel heat exchanger is more than 50% shorter than for the fin-and-tube heat exchanger, which is chosen as the baseline system. The average heating capacity and system performance are also lower for the system with microchannel heat exchangers. Higher frost growth rate in microchannel heat exchangers are due to residual water in the coil after defrost, augmented temperature difference between air and the surface of the heat exchanger, and preferential frost nucleation sites on the louvered fins and microchannel tubes. Blowing nitrogen on the microchannel coil after defrost removed any visible water retained in the coil after the defrost cycle but the cycle time increased only by 4% with respect to wet and frost conditions. The cycle time of the same microchannel starting with dry condition was about 60% longer than the cycle time in wet and frost conditions.

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Details

  • Original title: Comparison of frost and defrost performance between microchannel coil and fin-and-tube coil for heat pump systems.
  • Record ID : 2009-1646
  • Languages: English
  • Source: 2008 Purdue Conferences. 19th International Compressor Engineering Conference at Purdue & 12th International Refrigeration and Air-Conditioning Conference at Purdue [CD-ROM].
  • Publication date: 2008/07/14

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