The primary component in an outside air conditioning unit is the cooling coil. The conditions in the region (hot and humid) determine that the primary purpose of this cooling coil is to offset the ventilation moisture load.

In temperate and dry climates the cooling coil's primary role is to provide the space cooling for all air systems or pretreated air in air-water systems.

In this scenario moisture condensed on the cooling coil is largely incidental and not a critical requirement in maintaining space humidity at comfortable levels. This is in contrast to hot and humid climates where the cooling coil is tasked with offsetting the high moisture load and sensible cooling is now the incidental role.

A cooling coil simultaneously transfers heat and mass from the airstream; the ratio of sensible to latent heat transfer is a function of the chilled water temperature, air temperature and humidity along with the design of the cooling coil. While techniques exist for modifying the cooling coil performance to suit the nature of the load these are strictly limited in their effectiveness; typically a change in the fin density to modify the coil bypass factor.

The SHR of a conventional cooling coil (ratio of sensible to total cooling achieved) will lie in the region of 70 to 100%. These values are considerably higher than the required process SHR for a humid region and result in additional, energy consumptive, processes being required to produce properly conditioned supply air.

The paper looks into the technology now available for closely matching the cooling coil SHR to the required process SHR and the energy savings associated with this. The paper is based around the theory and practice surrounding the incorporation of passive heat pipes within the fin block on the entering and leaving face of the primary coil assembly. Other technologies will also be discussed.