News: Dehumidification
Dehumidification Guide
The Methods, Benefits and Opportunities of Dehumidification
The air we breathe contains water vapour due to evaporation of water from rivers, lakes, seas and oceans. If present in large quantities we feel uncomfortable, so we often speak of the air being humid. Moisture is a key parameter in all sectors of human activity but it is also an invisible element that can cause severe damage to processes and products.
The control of moisture reduces the growth of mould and corrosion problems, increases the reliability of electrical and electronic components, can increase feelings of well being for people with arthritis complaints, improve the comfort of the environment, eliminate odours and increase the life of food.
Methods of control
Two basic methods are used of dehumidification, desiccant type units and refrigerant cycle based equipment.
Desiccant type units work by using a chemical that is very hydroscopic and over which the air passes. Moisture in the air is absorbed by the desiccant. The desiccant is then heated to remove moisture and regenerate the material ready for another cycle. Usually, this is preformed using direct acting electric heaters. This energy is lost into the air.
Refrigerant cycle based units operate by cooling the air until it can no-longer contain the moisture which condenses into liquid and discharges. The energy removed is absorbed in the refrigerant and is then used, in combination with the electrical energy supplied to the compressor, to re-heat the air before returning it to the room. In essence, the latent heat contained by the air becomes sensible heat (moisture 595W/kg) along with the electrical energy input to drive the process.
When to use
Refrigerant type dehumidifiers are more efficient than their desiccant counterpart's. However, given the mode of operation, desiccant type dehumidifier's have been used when the dew point is below 5˚C, as the refrigerant type will need defrosting below these temperatures. However, evolution with the refrigerant type of products has resulted in the currently available machines being able to run at the dew point of -5˚C and, despite the thawing phase, maintain a constant air discharge temperature. Hidros developed these products in its range of cold room dehumidifiers for applications in industrial processes such as plastic moulding.
Temperature Control
Both methods, in their simplest form, will result in an increase in the room temperature because there is a net energy input to the system. In fact, with the desiccant type unit, relatively high temperatures are reached during regeneration. If temperature control is required it is necessary to perform another process or treat the air.
For the desiccant type the only option is to cool the air following the de-humidification process. This will require the provision of cold water.
With the refrigerant type it's possible to have an external condenser for the refrigerant gas to be diverted to if the room temperature rises above the set-point. One such application is independent and does not require additional external energy. Most Hidros products are available in this format.
Swimming Pool Climate Control, De-humidification and Energy Recovery
The most rigorous application for de-humidification is the swimming pool. By nature they are enclosed spaces that contain large amounts of warm water, maintained at high temperature and maximize the natural light with large areas of glass. For such applications both humidity and temperature must be controlled and heat recovery performed since they are excessively large users of energy. Refrigerating machines are available from Hidros to perform all these tasks and ensure complete control of climate.
Heat recovery is preformed on the exhaust air using a cross-flow plate and bringing the air-conditioning near to saturation. The air is then transferred to the evaporator where it is cooled and the moisture is removed. Cold saturated air passes through the cross-flow plate, where it's heated, before passing through the condenser where the energy is removed from the evaporator and compressor and transferred back into the air. If this not enough to meet the pools heat loss (winter for example), an LPHW coil is available for final tempering.
If, for example, the temperature leaving the condenser happens to be too high due to solar gain in the pool hall, a de-super heater unit can be installed and the energy transmitted to the pool water. Moreover, an external condenser can be used to divert energy into the atmosphere as described above.
Euro Controls UK Ltd are suppliers to the HVAC industry. We have a helpful team of consultants to help with most HVAC applications.
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Submitted by Jodie Norton on Monday 18th April 2011