HUMIDIFICATION ABSORPTION DISTANCES
Four reasons why humidity control is important
Humidification is a vital part of environmental control. While humidification is simply the addition of water to air, the wrong humidity levels can cause discomfort for people and can lead to damage in plant and equipment.
Health and comfort
nothing if the if humidifier is incorrectly installed on site. Too often absorption distances are compromised by contractors installing a humidifier where it is easiest to fit, rather than placing it in its optimum location. However, with the system designed correctly and the humidifier properly installed, a comfortable, healthy, humidified environment awaits. CJ
ANDIE CHESUN is national sales manager at HygroMatik, which is a member of the HEVAC Humidity Group. The group is committed to the correct provision of humidification across all applications. Visit: www.feta.
co.uk/humidity for more details.
People are most comfortable when relative humidity is between 35% and 55%. Low levels of humidity are more likely to occur in winter, when outside moisture levels are lower. In this drier air, below about 40% RH, moisture evaporates more quickly from the skin and tissues lining the nose, mouth and lungs; it can also dry the eyes, which can be a particular problem for contact lens wearers. Dry air encourages the transmission of airborne viruses through the evaporation of droplets released by people coughing and sneezing. Conversely, high levels of humidity above 70% can lead to the growth of mould. According to the CIBSE Knowledge Series publication, KS19, CIBSE recommend maintaining a normal maximum of 60% for air-conditioned spaces.
Controlling static electricity Voltages accumulate on surfaces so that when a surface at a higher voltage approaches one at the lower voltage, a discharge occurs. Voltage spikes can be particularly damaging to the electronic chips at the heart of most electronic devices.
Shocks due to static electricity are unlikely to occur if humidity levels are maintained over 40%. Above this level the air will have lower electrical resistance and a film of moisture can form on surfaces conducting charges to the ground. Where there are high levels of organic dust or petrol vapour that could be explosive, CIBSE recommends a minimum humidity level of 65% to reduce the risk of a static electricity discharge.
Stability of materials
Dry air can cause serious production problems for hygroscopic materials such as paper, leather, textiles and wood. Humidity is likely to have more of an impact on the rate of expansion of materials so stability is the key to minimising any production problems. However, if humidity levels are too high, the hygroscopic nature of these materials makes them susceptible to mould. Impermeable materials such as metals benefit from low levels of humidity.
Food storage
Humidity is critical for food storage in maintaining freshness and to minimise product weight loss. Refrigerating food will cause it to lose a significant amount of moisture, unless high levels of humidity are maintained. If humidification is used in conjunction with effective defrosting systems, the problem of icing up will be minimised.
www.cibsejournal.com
February 2013 CIBSE Journal 47
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