Vapour trails

With heavy rain a normality and summers gett ing hott er each year in the UK, high humidity is likely to be an issue that will continue to present itself.

For building engineers, moisture doesn’t just make working conditions on-site uncomfortable. It can also spell disaster for building materials and the fi nished product if not properly mitigated. As the UK is oft en struck by cold, rainy weather, many tradespeople believe winter months present the only periods of high humidity levels, whereas summer is drier so the problem is reduced. This is a key misconception. During the summer months, the warmer weather expands the air, allowing it to have a larger humidity capacity. This means the relative humidity may show a lower percentage, yet the physical volume of moisture is still the same as under cooler conditions. It is, therefore, vital to understand that humidity is a yearround challenge for building professionals.

When it comes to relative humidity – the percentage of water within an air particle – it averages at 76% in the UK’s largest cities. Considering that the comfortably dry range for relative humidity falls between 40% and 60%, it is clear that moisture in the air is a signifi cant issue.

Free moisture can be the surface water or water that has been absorbed into a material, or water that is chemically bound into the cells of materials in the room. There are several sources that are found on construction sites. The following are the most common: water vapour diff usion – water vapour from outside a building can permeate into the space through cracks or by being absorbed into materials.

The moisture coming from outside to within the room does so through this water vapour diff usion water evaporation – any water that is introduced into a space for cleaning or mixing with building materials can evaporate and contribute to moisture in the room evaporation from materials – building materials that have been brought on-site can release water absorbed in their cells into the space intended ventilation – ventilation systems that have been installed may not be able to keep up with high moisture levels in a space, so humidity in the room remains high unintended ventilation – leaving windows and doors open on a construction site can allow moisture-fi lled air from outside to permeate a room through unintended ventilation human-derived emissions – those working on-site release moisture from breath and perspiration plant and machinery emissions – any equipment used in a space on-site can produce moisture from its exhausts, particularly in enclosed, poorly ventilated spaces.

Premature deterioration of building materials is something any building engineer wants to avoid. In particular, poor humidity can aff ect things such as electrical components – the moisture can fi nd its way into the smallest areas and spaces. This, in turn, can leave behind corrosive deposits that continue to cause damage aft er drying, not to mention prolonged time for paintwork, adhesives and cement to dry or cure.

Improper drying and moisture control can also exacerbate such problems while creating new ones, which could lead to further damage and potentially higher costs. In particular, building engineers working

With airfl ow capacities up to 7,000m3/hour, Aggreko’s industrial dehumidifi ers are capable of drying out very large areas

on high-value projects such as luxury apartments or historic buildings should be aware of the potential costs that could mount up.

When it comes to building works, there are a number of common misconceptions that can lead to more time-consuming work, or even further damage. The main one relates to the diff erentiation between heating and dehumidifi cation. While many believe that vigorously heating a space on-site is the best way to dry moisture, this method doesn’t actually remove the problem. By heating the space, the atmosphere is expanded, drawing the moisture from the materials into the air. Once the heat is removed, it only takes around 48 hours for moisture equilibrium to be restored, as it returns “Moisture can spell disaster from the air back into the building’s fabric. for building Eff ective removal The drying process materials and the fi nished of any space relies on three key factors that must work in product if harmony to ensure that moisture is drawn not properly out of the structure mitigated” and is removed – heat, air movement and moisture removal. By following this process and controlling it carefully, building engineers can ensure that the problem is solved permanently.

Firstly, add heat into space to excite the molecules of water within materials. It is at this point that they are drawn into the expanded atmosphere and out of the building structure. In hot summer months, heat can already be present in the atmosphere, so additional heaters may not be required as they would be in winter. Once the water molecules are excited and moving throughout the space, the air must be circulated using fans to aid the removal of moisture. Finally, this is the point where a dehumidifi er is used to remove the energised water molecules and, therefore, any moisture from the environment.

Dehumidifi cation removes water vapours from the air completely by drawing air from the environment over a coil and reducing to a very low temperature via a refrigeration system. This essentially cools the air below the dew point temperature so that it condenses and drains away. With airfl ow capacities up to 7,000m3/hour, Aggreko’s industrial dehumidifi ers are capable of drying out very large areas.

Humidity is clearly an issue for UK building engineers. The air is full of moisture in both the summer and winter months, so careful temperature and moisture control is required all year round. Temperature and moisture control should be a gradual process during building works, with each stage of the process being independently assessed and optimised.