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Humidity control - Can you afford to ignore it?
In maintaining acceptable comfort conditions in workplaces, humidity control shouldn’t be an add-on that’s only included when budgets permit, it should be a standard requirement, says John Barker
An Airtec high pressure humidifier from Humidity Solutions in situ
John Barker
HUMIDITY CONTROL in the UK has something of a chequered history, with specifiers often choosing not to include it in their original designs or allowing it to be ‘value engineered’ out at a later stage. However, research consistently shows that humidity is an essential ingredient in the recipe for thermal comfort and wellbeing. To understand this, it’s worth reviewing what we mean by ‘thermal comfort’. BS EN ISO 7730 (1) defines it as: ‘that condi- tion of mind which expresses sat- isfaction with the thermal envi- ronment.’ Thus is described each person’s relationship with their environment – often expressed as feeling too hot or too cold. The fact that this perception varies from one individual to
10 | May 2016 | HVR
another means it’s quite difficult to quantify but in designing the environment correctly building services engineers can minimise the impact of personal factors. In this respect the environmental variables identified in HSE Guidance note 194 (4) – in rela- tion to maintaining workplace health, safety and welfare – are air temperature, mean radiant temperature, ventilation, humidi- ty, air velocity, climatic and sea- sonal variations in outdoor tem- peratures and solar intensity. Humidity is one that has often been ignored, but BSRIA Applications Guide AG10/94.1; Efficient Humidification in Buildings (5), concluded that rel- ative humidity (RH) is an impor- tant variable for thermal comfort and the well-being of humans.
Indeed, as buildings have become more airtight the need to control humidity in support of good indoor air quality (IAQ) has increased as it is no longer possi- ble to rely on a building’s natural ‘leakiness’ to control humidity. Good humidity control will keep the RH between 40% and 60%, as problems can arise if the RH is consistently either side of this range. Low humidity (<40%) can lead to skin and eye irrita- tions and also increase the spread rate of pathogens such as the influenza virus. The survival rate of this virus is at its lowest at 40- 60% RH at a temperature of 21°C Low RH also makes occupants feel colder, so they turn the heat- ing up to compensate, which increases energy consumption and costs. Raising the tempera-
ture also reduces the RH even further, exacerbating the prob- lem. Conversely, RH at the upper end of the acceptable range will make the space feel 2-3°C warmer so that heating can be turned down.
If the RH is allowed to rise too high, though, it can lead to respi- ratory ailments, thermal discom- fort, condensation and mould growth problems, resulting in potential damage to the build- ing’s fittings and fabric.
Poor RH control has also been linked with Sick Building Syndrome and the intensity of chemical pollution caused by gases from materials used inside the buildings. This is because the RH affects the distribution rate of these gases and there may also be reactions between these
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