Keeping cool with low moisture – John Barker

The problems that can be caused by icing up of evaporator coils in cold rooms are well understood, as are the benefits of using dehumidification to prevent this from happening. However, with several options available it’s important to select the dehumidification solution that best meets each project’s requirements.

The key issue is that moisture in the air will condense onto the evaporator coil and freeze, resulting in reduced efficiency of the refrigeration plant. There can also be problems of ice formation in other areas, potentially creating hazards and almost certainly resulting in downtime for defrosting.

Using a dehumidifier to remove the moisture from the air will therefore prevent or minimise condensation and help to maintain the efficiency of the system.

The most effective form of dehumidification for cold room applications is generally accepted as being the use of desiccants to adsorb the moisture from the air. In these systems there is a constant and simultaneous flow of two airflows through a desiccant rotor in opposite directions. One airflow is for drying (process air) and the other is for rotor reactivation (wet air).

After filtering, the process air enters the desiccant rotor, and relinquishes most of its water vapour content. It is then extracted from the dehumidifier as dry air, ideally using an EC fan for optimum efficiency, and returned to the cold room.

Desiccant rotor systems can reduce moisture levels at temperatures as low as -70°C and are typically housed in antechambers with air locks to reduce the infiltration of humidity. Correct sizing involves quantifying the level of humidity infiltration and determining the required dew point.

One concern that some cold store operators have expressed is that the returning air is at a higher temperature than the air in the cold store, so that the refrigeration plant needs to consume more energy to reduce that temperature.

One option that has recently been introduced to the market is to combine the process described above with a heat recovery process which effectively works in reverse to the heat recovery used in other applications.

To read the full article see the latest September edition of EiBI.