Rotor Applications

Rotor Application

A Proflute rotor is a cylinder filled with alternately flat and wave-shaped thin walls of a desiccant, usually silica gel or molecular sieve, forming a matrix of narrow channels through the length of the cylinder. The desiccant can attract and adsorb the water vapor so the air that pass into those channels at one end of the cylinder will exit as dry air at the opposite side.

Proflute rotor Dehumidification

In most desiccant dehumidifiers, the rotor rotates slowly between a large sector for the process air and a smaller sector for reactivation air. Reactivation air is a hot airstream that releases the water from the desiccant, and carries it out from the rotor. The two airstreams are kept apart by seals against the flat ends of the rotor cylinder and ducting inside and outside of the dehumidifier. The dry air is blown into the area to be dehumidified and wet reactivation air is exhausted to the outside. By the rotation of the rotor, the process is continuous, so dry air is always produced.

The reactivation air is passing through a heater, powered by electricity, hot steam or gas.
Before entering the rotor, the air is typically 80 to 140 °C (170 – 280 F). After leaving the rotor, it has cooled down but picked up the moisture adsorbed by the desiccant from the process air.

Active dehumidification is used, for instance in manufacturing of electronics, pharmaceuticals, food and candy, laminated glass, plastic bottles and lithium batteries. It is also applied for protection of several products in storage like steel, explosives, textile and leather. Most ice-rinks use active dehumidification to avoid fog, condensation and frost like domestic houses in certain areas to protect the crawl-space from mold and mildew.
Temporary need for active dehumidification is commonly used at building-sites, water damage and fires.

Low dew point dehumidification

By special design of dehumidifiers using Proflute rotors, very low dew points can be achieved. This is often required in advanced manufacturing processes, where even a little moisture in the environment can destroy the product and stop the whole production.

The rotor needs to be deeper than normal and sometimes it has to consist of a combination of different desiccants in order to both bring the humidity down to ordinary dry condition, and also down to the extraordinary condition required. The demand of reactivation energy is higher than usual and seals against the moving rotor surfaces have to be selected specially.

When the rotor rotates out from the reactivation sector it is hot. At such high temperature it has limited capability to adsorb moisture and would therefore let a portion of the process air pass more or less un-dehumidified. This cannot be accepted in a low dew point application. The solution is to build a third sector for an airstream that cools the rotor down before exposed to the process air.
In one similar solution, the reactivation air first passes a cooling sector before entering the heater
and the rotor. This will reduce the energy consumption in the reactivation heater and at the same time cool the rotor down to usable temperature.

To handle the most extreme dry air requirements, it may be necessary to first dehumidify the air that
shall reactivate the rotor. The best way to do this is often to “steal” some of the dry air produced by the rotor and lead it to the heater and into the rotor.

Examples of applications that require low dew points are lithium battery manufacturing, PET bottle production, certain laboratory compartments and test-rooms for products to be used in tough climates.

Passive dehumidification

The Proflute rotor can be used to reduce the moisture content in supply air to areas subject to air conditioning. When this is accomplished without adding any energy for reactivation it is called passive dehumidification.

The rotor is placed after the cooling coil in the AC-system, picking up moisture from the almost saturated fresh- or return air before it is blown into the area. To reactivate the rotor, the warmer exhaust air from the same area, passes the other sector of the rotor, which rotates slowly between the two sectors. Both airflows are of nearly the same size and blown through each half of the desiccant rotor.

Passive dehumidification will lower the necessary power of the AC-system, and less post-heating will be needed to make the supply air blown into the area comfortable. As a result, both the running cost and the investment for the AC-system, will be reduced.

Passive dehumidification is often incorporated in AC-systems for office buildings, hotels, schools, hospitals, and storage rooms. It is also used in HVAC-systems serving rooms where so called chilled beams have been built in.

Application Examples:
Dry air storage
Office buildings
Hospital operating rooms
Chilled beam HVAC systems

Proflute rotors in Air Conditioning and Desiccant Cooling

Air Conditioning (AC) systems, can besides reducing the temperature, also bring down the water vapor content in the air treated as a result of condensation on the cooling coil. However, some applications ask for more dehumidification than what is practically and economically justified using a standard AC-system. A common solution is to add a desiccant rotor after the cooling coil and reactivate the rotor with air heated by the evaporator in an AC-unit or some other source for low cost energy. The Proflute rotor show excellent performance in such installations.

Supermarkets use this solution in the areas where food is exposed in refrigerators and freezers to minimize condensation and build up of frost. Besides saving energy in the freezers and refrigerators, the food presentation is improved. Other applications are offices and hotels in tropical climate for improvement of indoor air quality and to avoid bad smell.

Cooling of air can be made without the use of AC-systems, that normally need heavy electrical supply and refrigerants, that may be harmful to the environment and the human health.
A Proflute desiccant rotor in combination with a heat-recovery rotor and so called evaporative coolers can, in certain climate, reduce the temperature of the fresh air blown into a building by 10 – 14 °C (18 – 25 F). Such a system is called a Desiccant Cooling system. It works according to the natural phenomena of heat being taken from air when water evaporates. The additional energy needed to reactivate the desiccant rotor can come from any moderate temperature source available, like waste heat in industry or heat from evaporators in other AC-systems. Also district-heat, which is cheap in the warm season when the heating demand otherwise is low, can be used.