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Effective cooling coil design: simple coil design methods that work.

Author(s) : WERNICK B.

Type of article: Article

Summary

The fin-and-tube heat exchanger is probably the most common piece of equipment found in any air-conditioning installation. These heat exchangers are typically referred to as coils and are designated by the fluids in the tube. So, a chilled water coil is a fin-and-tube heat exchanger used for cooling air where the coolant is chilled water and the direct expansion coil is a fin-and-tube evaporator found in a vapour compression cycle. These two coil types are primarily used to cool air. In most cases, the temperature of the coolant at the coil inlet is in the order of 6 °C and at typical air-conditioning temperatures, this would result in a coil surface temperature that is below the dew point of the air being cooled. The consequence of this is that there will be condensation on the coil surface and this condensate is clearly evident by the water flowing out of the drain pans of many installations. Methods to design and select heating coils are based on an overall heat transfer coefficient multiplied by the appropriate temperature difference. In cooling coils where there is condensation, the temperature difference is not the correct driving force since the latent heat of condensation is not accounted for. There have been different ways of dealing with this shortfall. These include the introduction of a sensible heat factor to modify the outside film coefficient, use of a log mean enthalpy difference and the effectiveness method based on a saturation specific heat. In this paper, the authors develop the equations and by simulation, illustrate the validity of the effectiveness method for solving wet surface cooling coils.

Details

  • Original title: Effective cooling coil design: simple coil design methods that work.
  • Record ID : 2004-2750
  • Languages: English
  • Source: RACA Journal - vol. 19 - n. 11
  • Publication date: 2004/02
  • Document available for consultation in the library of the IIR headquarters only.

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