What is ventilation?
Chances are you live and work in a building of some type and are not outside for the majority of your modern life. That means the air you are surrounded by for most of your time needs to be recycled and changed in order to be free from pollutants and undesired particles. How does this happen? What do we rely on in order to remain healthy and free from harmful substances in the air we breathe?
Ventilation is the act of moving outdoor air into a building or a room and distributing the air within the building or room. The purpose of ventilation in buildings is to provide healthy air for breathing by diluting the pollutants in the building and then removing the pollutants from it. It helps alleviate issues from stuffy bedrooms to the Sick Building Syndrome in commercial spaces. It adds the right amount of fresh air from outside to your indoor air.
Without ventilation, you will likely have comfort and, eventually health issues, plague you. In a best-case scenario, you will not have fresh air in your space and it will become stagnant and uncomfortable and very worst case, your air will have trapped toxins and contaminants that make people sick.
Older buildings are more susceptible to outside air due to leaky ducts and poorly insulated walls, windows and doors. This is a positive due to the fresh air but negative because of the lost energy efficiency when your air conditioner works harder in summer and heater works harder in the winter.
Building ventilation has three basic elements – ventilation rate, airflow direction and air distribution or airflow pattern.
There are three methods that may be used to ventilate a building – natural, mechanical and hybrid ventilation.
Natural forces drive outdoor air through purpose-built, building openings, including windows, doors, solar chimneys, wind towers and trickle ventilators. This natural ventilation of buildings depends on climate, building design and human behaviour.
Fans are the source of mechanical ventilation. Fans can be installed directly in windows or walls, or installed in air ducts for supplying air into, or exhausting air from, a room. It also provides more control over how much outside air is added and the source of the air.
Mechanical ventilation prevents the buildup of odors, excess moisture and pollutants in your living and work spaces. They can be expelled from areas which is important for your homes in your kitchens and living rooms, but also in public spaces such as restaurant kitchens, gyms, locker rooms and restrooms. In business terms, excess moisture and odors can cost you money and lead to worse problems, such as mold and damage to furnishings and equipment.
Hybrid ventilation depends on natural forces to provide the desired flow rate. It uses mechanical ventilation when the natural ventilation flow rate is too low.
When natural ventilation alone is not enough, exhaust fans can be installed. However, this simple type of ventilation needs to be used with care. The fans should be installed where room air can be exhausted directly to the outdoor environment through either a wall or the roof. The size and number of exhaust fans depends on the desired ventilation rate and must be measured and tested before use.
Problems associated with the use of exhaust fans include installation difficulties, noise, increased or decreased temperature in the room and the requirement for non-stop electricity supply. If the environment in the room causes thermal discomfort, spot cooling or heating systems and ceiling fans may need to be added.
Ventilation performance in buildings can be evaluated based on the following questions:
• Does the system provide sufficient ventilation rate as required?
• Is the overall airflow direction in a building from clean to dirty zones?
• How efficient is the system in delivering the outdoor air to each location in the room?
• How efficient is the system in removing the airborne pollutants from each location in the room?
Two overall performance indices are often used. The air exchange efficiency indicates how efficiently the fresh air is being distributed in the room, while the ventilation effectiveness indicates how efficiently the airborne pollutant is being removed from the room. The ventilation flow rate can be measured by measuring how quickly injected tracer gas is decayed in a room, or by measuring the air velocity through ventilation openings or air ducts, as well as the flow area. The airflow direction may be visualized by smoke.
If well designed, installed and maintained, there are a number of advantages to a mechanical system. Mechanical ventilation systems are considered to be reliable in delivering the designed flow rate. As mechanical ventilation can be integrated easily into air-conditioning, the indoor air temperature and humidity can also be controlled. Filtration systems can be installed in mechanical ventilation so that harmful microorganisms, particulates, gases, odours and vapours can be removed. Mechanical ventilation can work everywhere electricity is available.
However, mechanical ventilation systems also have problems. Mechanical ventilation systems may not work as expected, and normal operation may be interrupted for numerous reasons, such as equipment failure, utility service interruption, poor design, poor maintenance or incorrect management. If there is a need for continuous operation, all the equipment may have to be backed up — which can be expensive and unsustainable. Installation and maintenance costs for the operation of a mechanical ventilation system may be very high. If a mechanical system cannot be properly installed or maintained due to shortage of funds, its performance will be compromised.
There are several advantages of a natural ventilation system, compared with mechanical ventilation systems: natural ventilation can generally provide a high ventilation rate more economically, due to the use of natural forces and large openings; natural ventilation can be more energy efficient, especially if heating is not required; well-designed natural ventilation could be used to access higher levels of daylight.
If properly designed, natural ventilation can be reliable, particularly when combined with a mechanical system using the hybrid (mixed-mode) ventilation principle, although some of these modern natural ventilation systems may be more expensive to construct and design than mechanical systems.
In general, the advantage of natural ventilation is its ability to provide a very high air-change rate at low cost using a very simple system. Although the air-change rate can vary significantly, buildings with modern natural ventilation systems (that are designed and operated properly) can achieve very high air-change rates by natural forces, which can greatly exceed minimum ventilation requirements.
Unfortunately, there are a number of drawbacks to a natural ventilation system though. Natural ventilation is variable and depends on outside conditions relative to the indoor environment. The two driving forces that generate the airflow rate (i.e. wind and temperature difference) vary randomly, therefore natural ventilation may be difficult to control, with airflow being uncomfortably high in some locations and stagnant in others.
There is also a possibility of having a low air-change rate during certain unfavourable climate conditions. Natural ventilation precludes the use of particulate filters. Climate, security and cultural criteria may dictate that windows and vents remain closed; in these circumstances, ventilation rates may be much lower. Natural ventilation only works when natural forces are available; when a high ventilation rate is required, the requirement for the availability of natural forces is also correspondingly high. Natural ventilation systems often do not work as expected, and normal operation may be interrupted for numerous reasons, including windows or doors not open, equipment failure (if it is a high-tech system), utility service interruption (if it is a high-tech system), poor design, poor maintenance or incorrect management. Although the maintenance cost of simple natural ventilation systems can be very low, if a natural ventilation system cannot be installed properly or maintained due to a shortage of funds, its performance can be compromised, causing an increase in the risk of the transmission of airborne pathogens.
These difficulties can be overcome, for example, by using a better design or hybrid (mixed-mode) ventilation. Other possible drawbacks, such as noise, air pollution, insect vectors and security, also need to be considered.
Historically, the use of outdoor air for natural ventilation, combined with natural cooling techniques and the use of daylight, have been essential elements of architecture. Classical architecture with H, L, T or U-shaped floor plans was used with open courts, limited plan depth and maximum windows sizes to exploit natural ventilation and daylight. In current times, natural ventilation has been largely replaced by mechanical ventilation systems in high- and middle-income countries. At first, full mechanical heating, ventilation and air-conditioning systems appeared to be able to solve all the practical problems of natural ventilation for year-round control of indoor environmental conditions.
However, mechanical ventilation also requires careful design, strict equipment maintenance, rigorous standards, and design guidelines that take into consideration all aspects of indoor environmental quality and energy efficiency.
The same is also true for high-tech natural ventilation and it is not without its problems, particularly for facilities in countries where winters are cold. More work is needed to design low-cost and reliable ventilation systems for rooms that encourage, rather than prevent, the flow of air and yet allow internal temperature control.
Natural and mechanical ventilation systems can, in practice, be equally effective for infection control. However, natural ventilation only works when natural forces are available, for example, winds or breezes, and when inlet and exhaust apertures are kept open. On the other hand, the difficulties involved in properly installing and maintaining a mechanical ventilation system may lead to a high concentration of infectious droplet nuclei and ultimately result in an increased risk of disease transmission.
There is a lot to consider with your ventilation system requirements and decisions. Modern structures generally require a mechanical ventilation system in order to properly adjust to the changing external conditions to meet internal requirements. Choosing what is right for your building, business and most importantly, your health, are serious considerations. The experts at Superfoil can work with you to meet your individual needs and requirements to achieve the best outcomes for comfort and health with your ventilation system.