HUMIDITY CONTROL
are highly effective in cooler conditions, or when a low dew point is required. Since liquid water is not produced by the process, it can be used at sub-zero temperatures.
At the heart of a desiccant system is a rotating wheel made from alternating layers of flat and corrugated sheets, impregnated with a highly hygroscopic chemical. This presents an array of parallel air channels through which the humid air stream is drawn. As it passes through, water vapour is transferred to the desiccant, in the process releasing energy.
Rotors are often compartmentalised into two separate zones, each dedicated to either moisture removal or regeneration. As the rotor is rotated by a motor, air is drawn into the active adsorbing section. Energy generated by the moisture adsorption process is transferred to the air, leaving the system dry and warm (see picture). At the same time, on the regeneration side of the rotor a heated air stream is pulled through the rotor’s reactivation zone, driving out moisture adsorbed from the process air. The air, now warm and wet, is normally exhausted to outside. These parallel processes proceed in a continuous cycle, enabling highly effective and sustained dehumidification. The moisture removal
capacity of the system can be controlled by varying the degree of heating to the regeneration side of the rotor.
Energy efficiency can be significantly increased by using a heat recovery system on the regeneration side, harnessing the heat generated within the system itself to augment electrical inputs.
This can involve the use of a third zone within
the rotor, in which incoming reactivation air is pre-warmed by adiabatically generated heat from the rotor, before moving on to the regeneration heater. In liquid desiccant systems, the air stream is passed through a spray of desiccant solution (often lithium chloride), in the process removing moisture. Varying the concentration of lithium- chloride and air stream speed determines the rate of moisture removal.
An additional benefit of this approach is that the desiccant solution disinfects the airstream, which may be desirable for certain applications, such as in food manufacture and pharmaceuticals. The desiccant solution is regenerated by heating, whereupon it gives up its moisture and is then reintroduced as spray into the air stream, and the hot, moist waste air is exhausted from the unit.
As mentioned, the best system for a particular application will depend on the precise conditions, and the scale and rate of moisture removal required. Watkins offers both refrigerant-based and desiccant dehumidifiers, and following recent investment operates one of the largest fleets of specialist dehumidifiers in the UK.
Our specialist humidity control team provides comprehensive support for building owners and industrial end users, with access to humidity control equipment for hire from our network across the UK and Ireland.
Equipment is capable of treating between100m3 to 8000m3
of air per hour, and removing between 29ltr/24hr based on 60% RH at 20°C, and 71 ltr/ hr based upon 80% RH at 20°C. As part of a strategic growth plan in this important and growing sector of environmental control, we recently invested in a new fleet of state-of-the-art desiccant dehumidifiers, based on the KwikDRY system.
Equipment is deployed across the country at manufacturing sites, ship yards, sports halls, commercial buildings, restoration projects following flood or water leakage, storage facilities, food processing, and floor laying on construction sites.
Heronhill For all your humidification requirements
www.acr-news.com www.heronhill.co.uk
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