Maintaining moisture control in buildings is essential to protecting occupants from adverse health effects and the building’s structure, its mechanical systems and its contents from physical or chemical damage. The United States Environmental Protection Agency (EPA) states that moisture control is fundamental to the proper functioning of any building.
In our previous blog (Healthy Buildings: How to Reduce the Risk of Infection in Your Buildings), we state that Americans spend approximately 90 percent of their time indoors, where concentrations of some pollutants can be 2 to 5 times higher than typical outdoor concentrations.
Outdoor weather and climate conditions, mingled with occupant behavior can also affect indoor air quality (IAQ). The EPA states that weather conditions influence whether building occupants keep windows open or closed and whether they operate air conditioners, humidifiers, or heaters, all of which can affect IAQ. Certain climatic conditions can also increase the potential for unwanted indoor moisture and mold growth if not controlled by adequate ventilation or air conditioning.
The air exchange rate with the outdoors is an important element in determining indoor air pollutant concentrations. The air exchange rate is affected by the design, construction, and operating parameters of buildings and is ultimately a function of infiltration, natural ventilation, and mechanical ventilation.
Maintaining Moisture Control in Buildings with Infiltration
Maintaining moisture control in buildings with infiltration occurs due to a natural, uncontrolled flow of air in a space through unintentional gaps and/or cracks within a building, which can affect both IAQ and building energy consumption. Infiltration can also play an important role in the heating or cooling of a building.
Vents and other openings that are part of the ventilation design of a building can be additional routes for unintentional air flow to enter spaces in a building that can be caused by weather conditions. Air filtration not only increases the amount of air that enters a building, but it can also alter the projected amount of air flow that goes within a space for good IAQ and comfort for your occupants.
The corresponding loss of air from an enclosed space is referred to as exfiltration. The rate of air infiltration is dependent on the absorption of the building’s shell and the magnitude of the natural driving forces of wind and temperature. Vents and other openings that are integrated within a building as a part of the ventilation system can also become routes for unintentional air flow when the pressures acting across unintentional openings are dominated by weather conditions, rather than intentionally induced driving forces.
You may be thinking that if your building has mechanical ventilation, infiltration will be almost nonexistent. Unfortunately, that’s not the case for the following reasons:
The pressure within a building is not consistent within each individual space and each floor, if applicable.
Wind pressures from the outside of the building are extremely different based on the shape and side of the building the wind pressure is present.
In most instances, mechanical ventilation cannot be used to attempt to offset high wind pressures, especially wind-facing exterior building walls on windy days.
ANSI/ASHRAE Standard 62.2 recognizes the standards for ventilation system designs and acceptable IAQ’s when it comes to infiltration within a building.
Maintaining Moisture Control in Buildings with Natural Ventilation
Natural ventilation is vital to maintaining moisture control in buildings. Unlike fan-forced ventilation, natural ventilation uses natural forces of wind and buoyancy in order to deliver fresh air into buildings. By allowing fresh air to flow within a building it's automatically working to alleviate odors, provide oxygen for your occupants, and increases thermal comfort.
[Video by: Hologram Digital]
There are two types of natural ventilation techniques that are most commonly used: wind-driven ventilation and stack ventilation. Whole Building Design Guide (WBDG) states that natural ventilation, unlike fan-forced ventilation, uses the natural force of wind and buoyancy in an effort to delivery fresh air into buildings.
Wind. Wind applies negative pressure on the leeward side of a building and positive pressure on the wind facing side. The fresh air from the outdoors is able to enter in any opening in the wind facing side of a building and is then able to escape through any opening on the leeward side of a building.
Buoyancy. There are two different forms of buoyancy in ventilation –temperature-induced (stack ventilation) or humidity induced (cool tower). Using both of these forms combined, the cool tower will deliver evaporatively cooled air in a space and then rely on the increased buoyancy of the humid air as it warms to exhaust air from a space through stack ventilation.
Maintaining Moisture Control in Buildings with Mechanical Ventilation
Maintaining moisture control in buildings with mechanical ventilation also plays a crucial role. Without the use of mechanical ventilation to assist in providing fresh air you risk moisture, odors and other pollutants to build up within your building. To help maintain moisture control in your building, mechanical ventilation systems help circulate fresh air that’s coming in using ducts and fans rather than relying solely on natural ventilation.
As buildings are becoming more airtight in an effort save on energy usage, there can be some unintentional effects that may arise due to an accumulation of contaminants that can cause poor IAQ. The best way to enhance IAQ is by increasing and balancing proper ventilation, and mechanical ventilation is able to help consistently year-round. As long as there’s plenty of controlled fresh air coming within a building and the stale air is pushed out, you’ll be able to achieve a better indoor environment. The American Lung Association states that proper ventilation is essential for keeping air fresh and healthy within a building or home.
If a building’s mechanical ventilation system is properly installed and maintained, there are a number of advantages by having this as one of your ventilation methods:
Reliable in delivering the right amount of air flow within a building, despite the impacts of wind and temperature outdoors
A filtration system can be installed in the mechanical ventilation system to remove microorganisms, pollutants, odors, moisture and other contaminants that can be in the air
The path of the airflow can be controlled
There are a variety of different mechanical ventilation systems that are available based on the local climate and the buildings HVAC system.
Supply Ventilation. This system uses a fan to pressurize a building by forcing outside air into the building while air leaks out of the building through small gaps and/or holes (natural infiltration). Supply ventilation allows for better control of the air that enters your building and works best in hot or mixed climates.
Exhaust Ventilation. This system works by depressurizing a building. Exhaust ventilation disperses the air from the building, changing the pressure that gets pulled in from the outside through small gaps or holes. This system is most appropriate for buildings that are located in colder climates.
Balanced Ventilation. This system, if installed and used properly, neither pressurizes nor depressurizes a building. Instead, balanced ventilation introduces and exhausts approximately equal quantities of fresh outdoor air and polluted indoor air. This ventilation method is suitable for any climate.
Energy Recovery Ventilation. This system provides a controlled option of ventilation a building while decreasing energy loss. Energy recovery ventilation reduces the cost of having to heat air in the winter by transferring heat from the warm, inside air to fresh (cold) air from outside. This ventilation can be used in mixed climates.
For More Information
Maintaining moisture control is a healthy component of healthy buildings. To schedule an assessment for HVAC controls to be installed in your building, contact Illumetek today at firstname.lastname@example.org or (800) 644-2566.