BSEE
Ryan Stanley, Moisture Control Sales & Product Manager Northern Europe at Aggreko explains why humidity is unwanted on construcon sites, and how best to remove it without comming common errors associated with this process.
likely to be an issue that will become increasingly prominent in the future. For building engineers, this in-air moisture doesn’t just make working conditions onsite uncomfortable – it can also spell disaster for building materials and the finished product if not remedied.
W A constant concern
The UK is known for its cold, rainy weather, so many tradespeople believe only the winter months present periods of high humidity, in contrast to summer, where the hotter temperatures leads to drier air. As a result, some building professionals may believe in-air moisture does not require a year-long, ongoing strategy to alleviate. This, however, is a misconception, as summer’s warmer weather causes the air to expand, giving it a greater capacity for humidity. As a result, while relative humidity may be at a lower percentage in these months, the air still contains the same physical volume of moisture as it does in winter, when temperatures drop. Consequently, it is vital that building professionals treat humidity as a constant concern and maintain strategies to remedy it past the winter. When we also consider that data from World Weather Online suggests relative humidity – the percentage of water within an air particle – averages at around 76% in our nation’s largest cities, there is further cause for concern for building professionals. Because this figure exceeds the comfortably dry range for relative humidity, which falls between 40% and 60%, this data further highlights problems moisture present in on-site air could cause.
Moisture sources
Moisture can be found on-site as water that is chemically bound into the cells of material in the room, or as free moisture – water that has either been absorbed into a material or is present as surface water. There are multiple sources of moisture present on a construction site.
ith heavy rain a normality and summers getting hotter each year in the UK, high humidity is
FOCUS: HEATING & VENTILATION How to tackle humidity on construction sites
The building materials themselves, for instance, can impact overall site humidity. Water introduced to these materials for cleaning or mixing purposes can raise the moisture levels within a room as it evaporates, and these materials may also release water previously absorbed into its cells in hotter site conditions. Furthermore, water vapour from outside the building can permeate into the space via cracks or absorption into these materials, increasing moisture levels in the air. This process is known as water vapour diffusion.
Machinery and ventilation systems may also contribute to higher humidity, as if plant equipment is operated in poorly ventilated or enclosed spaces, moisture present within this space will rise. Similarly, ventilation systems installed on-site may not be equipped to reduce increased moisture levels, meaning humidity in the room will remain high. Outside of materials and machinery, even site workers can contribute to humidity levels. Whether by leaving windows and doors open that allow moisture-filled air from outside to permeate a room through unintended ventilation, or by simply breathing and perspiring, on-site personnel should also be regarded as a factor when considering humidity.
Deterioraon and damage
Rising humidity levels can cause the premature deterioration of building materials, and present situations construction professionals would seek to steer clear of. As moisture can find its way into even the smallest areas and spaces, electrical components are particularly vulnerable to its effects. This moisture can leave behind corrosive deposits that can continue to damage building materials and systems after drying, and prolong time taken for adhesives, cement and paintwork to dry and cure.
While these are clearly
circumstances building professionals would wish to avoid, improper drying and moisture control strategies could end up making the problem worse,
24 BUILDING SERVICES & ENVIRONMENTAL ENGINEER JANUARY 2021
and even create new ones. Indeed, carrying out incorrect actions could lead to rising costs, longer builds, and, by extension, reputational damage, especially on high-value projects such as historic buildings and luxury apartments.
The extreme cost of heating
When tackling humidity on construction sites, there are multiple areas in which misconceptions exist, and these misconceptions can lead to further damage or additional, unnecessary time spent on-site. The overarching issue relates to the difference between heating and dehumidification, and specifically, the belief that vigorously heating a space is the best strategy to dry moisture.
However, this course of action does not solve the problem. Instead, the added heat expands the atmosphere, drawing moisture from materials into the air. When the heat is removed, water previously drawn into the air returns into the material, restoring moisture equilibrium in a process that only takes around 48 hours.
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 differentiation between heating and dehumidification. While many believe that vigorously heating a space onsite 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 from the air back into the building’s fabric.
Effective moisture removal strategy
To ensure moisture is removed effectively from any space as part of the drying process, three factors
need to work in harmony – moisture removal, heat and air movement. If building engineers follow and control this process carefully, humidity concerns can be permanently resolved.
The first step in this strategy involves the addition of heat into space. This heat excites water molecules, so they are drawn out of the building structure and into the expanded atmosphere. Though this step may have already occurred to an extent in the warmer summer months, additional heaters may be required in winter to encourage this process. With the water molecules now excited and moving throughout the space, fans can be introduced to circulate the air, aiding the removal of moisture and avoiding leaving. Once this has occurred, a dehumidifier should then be used, removing energized water molecules from the environment, in turn reducing moisture levels.
Dehumidificaon
Essentially, dehumidification 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 airflow capacities up to 7,000 m3/hr, Aggreko’s industrial dehumidifiers are capable of drying out very large areas.
In conclusion, humidity presents year-round problems for building engineers, so remediating it should not be a seasonal concern. The air remains full of moisture in both colder and warmer months, and ongoing strategies are required in order to alleviate issues it can cause, such as impaired electrical components, material deterioration, and longer on-site processes. Temperature and moisture control should therefore be a gradual process during building works, with all parts of this process being independently assessed and optimised.
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