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Humidity can compromise building occupants comfort and health

Wael Ayoub

General Manager – i2i

We are all too familiar with that sensation of stepping out into the extreme searing heat and atmospheric humidity during the summer months, leaving our chilled air-conditioned bubbles behind, but what is humidity and why does it have such an impact on our indoor environment? 

Humidity is a broad term with three main measurements: absolute, relative and specific. Relative Humidity is defined as a percentage of the amount of moisture in the air compared to the highest temperature. When the air cannot hold all the moisture, then it condenses as dew.

Excess humidity affects the indoor air quality, particularly in the summer months, where the high temperatures increase the amount of moisture the air can hold, resulting in excessively warm and uncomfortable indoor environments.  An effective air-conditioning system has a major influence over the indoor environment by removing the humidity from the air.

So how are we increasing the indoor humidity levels? There are many causes of high relative humidity, such as cooking, laundry and even breathing.  An individual exhale approximately 200 milliliters of water vapor per hour whilst awake and 20 milliliters whilst asleep.  The building too has a critical part to play in the high indoor humidity levels, such things as untreated air infiltrations to the building envelope through floor joints, wiring holes, plumbing vents, open slabs and gaps between door or window frames can contribute to the humidity levels. But the most important contributor is an ineffective HVAC (Heating, Ventilation and Air Conditioning) system.  An ineffective HVAC system will pull in the hot outdoor moisture from the buildings vents, gaps and untreated air infiltrations, resulting in uncontrolled indoor humidity.  

The health effects of excessive indoor humidity range from microbial growth, dehydration, Fatigue, Muscle Cramps and even heat stroke.   ASHRAE Standard 62.1-2016 recommends the Relative Humidity in occupied spaces to be controlled to less than 65%, to reduce the likelihood of developing health conditions related to humidity.

High humidity levels should not be overlooked, as it can take its toll on a buildings structure.  The building can start to deteriorate from the inside. Insulation and walls can rot and lose their ability to resist temperature change, mold can form on insulations, wood and drywall where it destroys the strength of the component and presents many health risks.  Not to mention that high humidity levels make the air-conditioning systems less effective, due to dense air, the systems are forced to run longer and harder in the effort to reduce the temperate, almost always without the desired results.

How does the HVAC system help to prevent high humidity whilst providing comfortable indoor temperatures?  A HVAC system consists of Air Handling Units (AHU’s) and fans, the main purpose of which is to achieve optimal cooling and ventilation simultaneously.  HVAC design engineers regulate the required air flow rate for supply and exhaust of air flow at every location within the building by obtaining the appropriate Air Change Rate per Hour (ACH). ACH varies depending on the type of building and room usage, in other word ACH for a kitchen is different than that of a living room or dining room.

It is important to maintain extra fresh air within the building, approximately 10% to 15%(depending on ACH) more than what’s being exhausted by the ventilation and air conditioning system to ensure positive pressure of at least 10 Pascal (unit used to quantify air pressure) is retained which will lead to preventing infiltration of warm air that causing uncontrolled indoor humidity as shown in the diagram below.

Additionally, if air conditioning units are not achieving the cooling requirements this may impact the conditioned air circulating the indoor area, and there is a possibility for the air to contain high Relative Humidity since the return air is mixed with fresh air.

High level humidity is commonly observed in the region due to harsh weather conditions.  In many scenarios we observe poor balancing of HVAC systems is failing to identify the presence of humidity within the building, or reasons that may lead to it at a later stage. i2i performs testing and balancing with complete professionalism and integrity in line with international standards, our engineers take all necessary measures to thoroughly assess HVAC systems, at all levels, in the effort to identify causes contributing to humidity conditions such as HVAC system design and installation. i2i goes the extra mile in supporting our customers with solution based recommendations related to HVAC system installation.