The Relationship Between Classroom Air Quality and Student Performance

Parents and teachers care deeply about our children’s education. Who doesn’t want them to have the most fruitful experience possible? One aspect of education that is often neglected is indoor air quality. Good air quality in schools can improve student performance significantly and it deserves as much attention as any item on a school planner’s agenda. Attendance, productivity, and other performance indicators are shaped by it. The consensus is clear — students and staff need clean air.

Indoor air contaminants are well-known causes of absences, interruptions, and lack of productivity in students, faculty, and staff.  In a poll of Chicago teachers, 25% said respiratory problems, including asthma, are the most encountered problems relating to school facility quality. Another 16% reported problems that are often caused by poor indoor air quality (IAQ), such as sinus infections.1 The EPA states that indoor air quality can help to improve test scores and attendance,10 and science have given us insight as to why that is.

The Effects of Poor Air Quality in Schools

Supporting students and faculty by providing high-quality air can make a difference. Studies have shown that student performance improves as classroom air quality improves. In such studies, the relationship between student performance and good air quality explains the positive correlation between them. Air quality has a direct impact on students but also on their teachers and others involved in their school experience.


There has been little research into asthma symptoms caused by school air quality. However, a 2013 study found that mouse allergen was significantly more abundant in schools than in students’ homes and that higher levels of mouse allergen contributed to a 27% increase in asthma symptom occurrence.6 Another study found that schools with new ventilation systems installed reported a reduction in asthma symptoms.7

Mouse allergen is not the only allergen found is schools, of course. Some of the most common asthma triggers include tobacco smoke, dust mites, mold, cockroaches, and other pests,5 all of which must be mitigated in schools.

According to the EPA, 12.8 million school days were lost due to asthma attacks in 2003.3 Though it’s unclear how many of those resulted from school air quality (versus home and outdoor air quality), absenteeism could have been reduced if indoor air triggers were not present in schools.

Teacher Substitution 

Teachers experience illness caused by poor indoor air quality just as students do. Sometimes this leads to teacher absence. The disruption caused by substituting a class’s permanent teacher cannot be fully compensated for and has a negative impact on student achievement. A study of 62 Florida schools found that students who spent four weeks or more with a substitute teacher scored 11 points lower on the reading portion of the Florida Comprehensive Assessment Test.4

Student Absenteeism

22% of absences in a study of North Carolina schools were caused by respiratory illnesses such as asthma and allergies.8 In a review of 11 studies, 7 of them found an inverse correlation between absence rate and school performance.9 That is, a student’s performance is usually poorer as the student’s absence rate increases.

Additional Concerns

Poor air quality in schools can bring on numerous health concerns that reduce student performance, ranging from nasal congestion to respiratory infection. Even school staff members who don’t regularly interact with students can have a negative impact on student performance when poor air quality has affected their health. Staff may spread contagious illness within the school facilities. Their work performance may decline as well, which can affect students in various ways. Everyone involved needs high air quality standards.

Good Indoor Air Quality is a Necessity in Schools

Many scientists and statisticians have delved into the question of what factors can affect student and faculty performance. Factors that have been researched and tested include temperature, air quality, lighting, acoustics, and class size. Many studies place a high level of importance on air quality.

A 2004 paper 2 consolidates empirical studies from the 1970s until the early 2000s to rank 31 criteria in terms of their effect on “school building adequacy.” Glen Earthman, the author, is an experienced school facility planner and former director of the Educational Resource Information Center (ERIC). Dr. Earthman found significant evidence that indoor air quality is one of the most important factors in student learning. In his prioritization, the only factor that ranks higher than air quality is “human comfort” (i.e. air temperature). Earthman describes indoor air quality as “appropriate ventilation and filtering systems, as regulated by appropriate HVAC systems.”

Bipolar Ionization Boosts Air Quality and School Performance

You may be asking what you can do to improve the air quality in your facility. One of the most effective solutions is called bipolar ionization, an air purification technology that reduces a wide range of air contaminants. Cleaning the air with a high-quality ionization device reduces and often prevents the effects of asthma, allergies, and other illnesses, including influenza A.


-Plasma Air- 

WHO declares the new coronavirus outbreak a Public Health Emergency of International Concern

The second meeting of the Emergency Committee convened by the WHO Director-General under the International Health Regulations (IHR) (2005) regarding the outbreak of novel coronavirus 2019 in the People’s Republic of China, with exportations to other countries, took place on Thursday, 30 January 2020, from 13:30 to 18:35 Geneva time (CEST). The Committee’s role is to give advice to the Director-General, who makes the final decision on the determination of a Public Health Emergency of International Concern (PHEIC). The Committee also provides public health advice or suggests formal Temporary Recommendations as to appropriate. 

Proceedings of the meeting

Members and advisors of the Emergency Committee were convened by teleconference.

The Director-General welcomed the Committee and thanked them for their support. He turned the meeting over to the Chair, Professor Didier Houssin. 

Professor Houssin also welcomed the Committee and gave the floor to the Secretariat. 

A representative of the department of compliance, risk management, and ethics briefed the Committee members on their roles and responsibilities.

Committee members were reminded of their duty of confidentiality and their responsibility to disclose personal, financial, or professional connections that might be seen to constitute a conflict of interest. Each member who was present was surveyed and no conflicts of interest were judged to be relevant to the meeting. There were no changes from the previous meeting.  

The Chair then reviewed the agenda for the meeting and introduced the presenters. 

Representatives of the Ministry of Health of the People’s Republic of China reported on the current situation and the public health measures being taken. There are now 7711 confirmed and 12167 suspected cases throughout the country. Of the confirmed cases, 1370 are severe and 170 people have died. 124 people have recovered and been discharged from the hospital. 

The WHO Secretariat provided an overview of the situation in other countries. There are now 83 cases in 18 countries. Of these, only 7 had no history of travel in China. There has been human-to-human transmission in 3 countries outside China. One of these cases is severe and there have been no deaths. 

At its first meeting, the Committee expressed divergent views on whether this event constitutes a PHEIC or not. At that time, the advice was that the event did not constitute a PHEIC, but the committee members agreed on the urgency of the situation and suggested that the Committee should continue its meeting on the next day when it reached the same conclusion. 

This second meeting takes place in view of significant increases in numbers of cases and additional countries reporting confirmed cases. 

Conclusions and advice

The Committee welcomed the leadership and political commitment of the very highest levels of the Chinese government, their commitment to transparency, and the efforts made to investigate and contain the current outbreak. China quickly identified the virus and shared its sequence, so that other countries could diagnose it quickly and protect themselves, which has resulted in the rapid development of diagnostic tools. 

The very strong measures the country has taken include daily contact with WHO and comprehensive multi-sectoral approaches to prevent further spread. It has also taken public health measures in other cities and provinces; is conducting studies on the severity and transmissibility of the virus, and sharing data and biological material. The country has also agreed to work with other countries that need their support. The measures China has taken are good not only for that country but also for the rest of the world. 

The Committee acknowledged the leading role of WHO and its partners. 

The Committee also acknowledged that there are still many unknowns, cases have now been reported in five WHO regions in one month, and human-to-human transmission has occurred outside Wuhan and outside China. 

The Committee believes that it is still possible to interrupt virus spread, provided that countries put in place strong measures to detect disease early, isolate and treat cases, trace contacts, and promote social distancing measures commensurate with the risk. It is important to note that as the situation continues to evolve, so will the strategic goals and measures to prevent and reduce the spread of the infection. The Committee agreed that the outbreak now meets the criteria for a Public Health Emergency of International Concern and proposed the following advice to be issued as Temporary Recommendations. 

The Committee emphasized that the declaration of a PHEIC should be seen in the spirit of support and appreciation for China, its people, and the actions China has taken on the frontlines of this outbreak, with transparency, and, it is to be hoped, with success. In line with the need for global solidarity, the Committee felt that a global coordinated effort is needed to enhance preparedness in other regions of the world that may need additional support for that. 

Advice to WHO

The Committee welcomed a forthcoming WHO multidisciplinary technical mission to China, including national and local experts. The mission should review and support efforts to investigate the animal source of the outbreak, the clinical spectrum of the disease and its severity, the extent of human-to-human transmission in the community and in healthcare facilities, and efforts to control the outbreak. This mission will provide information to the international community to aid in understanding the situation and its impact and enable the sharing of experience and successful measures.

The Committee wished to re-emphasize the importance of studying the possible source, to rule out hidden transmission and to inform risk management measures

The Committee also emphasized the need for enhanced surveillance in regions outside Hubei, including pathogen genomic sequencing, to understand whether local cycles of transmission are occurring.

WHO should continue to use its networks of technical experts to assess how best this outbreak can be contained globally. 

WHO should provide intensified support for preparation and response, especially in vulnerable countries and regions.

Measures to ensure rapid development and access to potential vaccines, diagnostics, antiviral medicines and other therapeutics for low- and middle-income countries should be developed. 

WHO should continue to provide all necessary technical and operational support to respond to this outbreak, including with its extensive networks of partners and collaborating institutions, to implement a comprehensive risk communication strategy, and to allow for the advancement of research and scientific developments in relation to this novel coronavirus. 

WHO should continue to explore the advisability of creating an intermediate level of alert between the binary possibilities of PHEIC or no PHEIC, in a way that does not require reopening negotiations on the text of the IHR (2005).

WHO should timely review the situation with transparency and update its evidence-based recommendations.

The Committee does not recommend any travel or trade restriction based on the current information available. 

The Director-General declared that the outbreak of 2019-nCoV constitutes a PHEIC and accepted the Committee’s advice and issued this advice as Temporary Recommendations under the IHR. 

To the People’s Republic of China

Continue to:

• Implement a comprehensive risk communication strategy to regularly inform the population on the evolution of the outbreak, the prevention and protection measures for the population, and the response measures taken for its containment.  

• Enhance public health measures for containment of the current outbreak.

• Ensure the resilience of the health system and protect the health workforce. 

• Enhance surveillance and active case finding across China.

• Collaborate with WHO and partners to conduct investigations to understand the epidemiology and the evolution of this outbreak and measures to contain it.

• Share relevant data on human cases.

• Continue to identify the zoonotic source of the outbreak, and particularly the potential for circulation with WHO as soon as it becomes available.

• Conduct exit screening at international airports and ports, with the aim of early detection of symptomatic travelers for further evaluation and treatment, while minimizing interference with international traffic.  

To all countries

It is expected that further international exportation of cases may appear in any country. Thus, all countries should be prepared for containment, including active surveillance, early detection, isolation and case management, contact tracing and prevention of the onward spread of 2019-nCoVinfection, and to share full data with WHO. 

Countries are reminded that they are legally required to share information with WHO under the IHR. 

Any detection of 2019-nCoV in an animal (including information about the species, diagnostic tests, and relevant epidemiological information) should be reported to the World Organization for Animal Health (OIE) as an emerging disease.

Countries should place particular emphasis on reducing human infection, prevention of secondary transmission and international spread, and contributing to the international response though multi-sectoral communication and collaboration and active participation in increasing knowledge on the virus and the disease, as well as advancing research.  

The Committee does not recommend any travel or trade restriction based on the current information available.  

Countries must inform WHO about any travel measures taken, as required by the IHR. Countries are cautioned against actions that promote stigma or discrimination, in line with the principles of Article 3 of the IHR. 

The Committee asked the Director-General to provide further advice on these matters and, if necessary, to make new case-by-case recommendations, in view of this rapidly evolving situation. 

To the global community

As this is a new coronavirus, and it has been previously shown that similar coronaviruses required substantial efforts to enable regular information sharing and research, the global community should continue to demonstrate solidarity and cooperation, in compliance with Article 44 of the IHR (2005), in supporting each other on the identification of the source of this new virus, its full potential for human-to-human transmission, preparedness for potential importation of cases, and research for developing necessary treatment.

Provide support to low- and middle-income countries to enable their response to this event, as well as to facilitate access to diagnostics, potential vaccines, and therapeutics. 

Under Article 43 of the IHR, States Parties implementing additional health measures that significantly interfere with international traffic (refusal of entry or departure of international travelers, baggage, cargo, containers, conveyances, goods, and the like, or their delay, for more than 24 hours) are obliged to send to WHO the public health rationale and justification within 48 hours of their implementation. WHO will review the justification and may request countries to reconsider their measures. WHO is required to share with other States Parties the information about measures and the justification received.  

The Emergency Committee will be reconvened within three months or earlier, at the discretion of the Director-General. 



Coronaviruses (CoV) are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS-CoV). A novel coronavirus (nCoV) is a new strain that has not been previously identified in humans.  

Coronaviruses are zoonotic, meaning they are transmitted between animals and people.  Detailed investigations found that SARS-CoV was transmitted from civet cats to humans and MERS-CoV from dromedary camels to humans. Several known coronaviruses are circulating in animals that have not yet infected humans. 

Common signs of infection include respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. In more severe cases, the infection can cause pneumonia, severe acute respiratory syndrome, kidney failure, and even death. 

Standard recommendations to prevent infection spread include regular hand washing, covering mouth and nose when coughing and sneezing, thoroughly cooking meat and eggs. Avoid close contact with anyone showing symptoms of respiratory illness such as coughing and sneezing.


The new corona virus: What we do

A rapidly evolving health story broke in late December when a novel illness originating in Wuhan, China made the news. Reports of the number of infected people swiftly rose, and isolated cases of this new coronavirus — dubbed 2019-nCoV by scientists — have appeared in several countries due to international travel. At this writing, almost 1,300 confirmed cases and over 40 deaths have occurred in China, according to an article in the New York Times.

Fortunately, public health officials in many countries, have put measures in place to help prevent further spread of the virus. 

With information changing so quickly and every news report about the virus seeming to raise the stakes, you may be wondering how worried you should be. Here’s a primer on what we do — and don’t — know about this virus and what it may mean for you. While there is much we don’t yet understand about the virus, public health officials, medical experts, and scientists are working in collaboration to learn more.

What is a coronavirus?

Coronaviruses are an extremely common cause of colds and other upper respiratory infections. These viruses are zoonoses, which means they can infect certain animals and spread from one animal to another. A coronavirus can potentially spread to humans, particularly if certain mutations in the virus occur.

Chinese health authorities reported a group of cases of viral pneumonia to the World Health Organization (WHO) in late December 2019. Many of the ill people had contact with a seafood and animal market in Wuhan, a large city in eastern China, though it has since become clear that the virus can spread from person to person.

What are the symptoms of this coronavirus?

The symptoms can include a cough, possibly with a fever and shortness of breath. There are some early reports of non-respiratory symptoms, such as nausea, vomiting, or diarrhea. Many people recover within a few days. However, some people — especially the very young, elderly, or people who have a weakened immune system — may develop a more serious infection, such as bronchitis or pneumonia.

How is it treated?

Scientists are working hard to understand the virus, and Chinese health authorities have posted its full genome in international databases. Currently, there are no approved antivirals for this particular coronavirus, so treatment is supportive. For the sickest patients with this illness, specialized, aggressive care in an intensive care unit (ICU) can be lifesaving.

Should you worry about catching this virus?

Unless you’ve been in close contact with someone who has the coronavirus — which right now, typically means a traveler from Wuhan, China who actually has the virus — you’re likely to be safe. In the US, for example, only two cases of the virus have been confirmed so far, although this is likely to change.

While we don’t yet understand the particulars of how this virus spreads, coronaviruses usually spread through droplets containing large particles that typically can only be suspended in the air for three to six feet before dissipating. By contrast, measles or varicella (chickenpox) spread through smaller droplets over much greater distances. Some coronaviruses also have been found in the stool of certain individuals.

So it’s likely that coughs or sneezes from an infected person may spread the virus. It’s too early to say whether another route of transmission, fecal-oral contact, might also spread this particular virus.

Basic infectious disease principles are key to curbing the spread of this virus. Wash your hands regularly. Cover coughs and sneezes with your inner elbow. Avoid touching your eyes, nose, or mouth with your hands. Stay home from work or school if you have a fever. Stay away from people who have signs of a respiratory tract infection, such as runny nose, coughing, and sneezing.

In the US, the average person is at extremely low risk of catching this novel coronavirus. This winter, in fact, we are much more likely to get influenza B — the flu — than any other virus: one in 10 people have influenza each flu season. It’s still not too late to get a flu shot, an easy step toward avoiding the flu. If you do get the flu despite having gotten the vaccine, studies show that severe illness, hospitalization, ICU admission, and death are less likely to occur.

Source -  Harvard Health Blog 

How your house is making you sick?

Did you know that bad air quality can give you sleepless nights? Poor air quality in your home can negatively impact your sleep, energy levels, and cause irritation in your nose, sinuses and the back of your throat.

Yes, it is true; the bad air quality in your home can cause insomnia and many other psychological disorders. The bad air quality is something we are all victims of, and the worst part is that we do not even know about it. Most of us feel that pollution is an outdoor phenomenon so you got to take precautions when you are outside but indoors it is your home after all, where everything is neatly decked up so no need to worry about anything, least of all the air quality.

Just consider these facts to get more clarity about the impact of the bad air in your home:

  • We take 20,000 breaths each day and unless we have a problem, we don’t think about what we’re breathing in, and how that air might affect our bodies.
  • The air indoors is 2 to 5 times worse than outdoors (EPA)
  • Air quality is the single biggest environmental hazard in the world (WHO)
  • 72% of toxic chemicals are indoors (UL)

Indoor air quality can deteriorate due to various reasons like cooking, stored cleaning agents, pets, cracks in the walls, poor ventilation, flooring, etc. Furnaces and other wood-fueled heaters are also a major reason behind the poor air quality in our homes.

Mechanical Ventilation

What is Mechanical Ventilation?

By light definition, mechanical ventilation is the process of actively supplying air to and removing it from areas inside the home with the usage of powered equipment. There are two main types of mechanical ventilation systems—spot ventilation (exhaust fans in bathrooms and above kitchen ranges, for example), which is designed to remove the pollutant from the source, and whole-house ventilation. Whole-house ventilation utilizes multiple fans and duct systems, and there are multiple different types of setups to choose from.

  • Exhaust:

This whole-house mechanical ventilation system primarily places home in a depressurized (negative pressure) state. Exhaust systems are inexpensive to install and work well in cold climates.

  • Supply:

This whole-house mechanical ventilation system puts a home in a pressurized (positive pressure) state. Supply systems are relatively inexpensive to install and work best in hot and humid climates.

  • Balanced:

This whole-house mechanical ventilation system functions by bringing in fresh outdoor air to replace polluted indoor air (in equal amounts). Due to it’s a more moderate approach to air ventilation, a balanced system works well in any climate. The cost to install however is greater than that of a simple exhaust or supply system.  

  • Energy Recovery & Heat Recovery Ventilators:

These whole-house mechanical ventilation systems regulate the exchange of indoor and outdoor air while simultaneously using existing heated or cooled air. This allows comfortable air to flow through your home without using a ton of energy. Energy recovery and heat recovery systems reduce energy costs and work well for homes in naturally humid climates. The cost of installation for these devices, however, is quite high when compared to that of other systems.

How does air pollution hit kids’ growth?

Medics will tell you that adults breathe an average of 14-16 times per minute whereas newborn babies breathe up to 30-60 times per minute. That sounds harmless enough. Unless you are breathing in polluted air – in which case infants and kids can find that ruinous for their development and future well-being.

The statistics are shocking. Globally, two billion kids – 90% of the total– are exposed to air pollution at and above the World Health Organization (WHO) environmental guidelines. In fact, a recent UNICEF study found that a staggering 17 million infants worldwide are breathing polluted air. More than two-thirds of the affected infants – over 12 million – live in South Asia and are exposed to pollution six times higher than recommended limits. And research also shows that polluted air poses risks to the health of the unborn and could lead to impaired brain (intellect) development.

Kids’ brains vulnerable to air pollution

The damaging effect of air pollution on the brains of babies and young kids is perhaps the most shocking discovery of the latest research. During development, young brains are especially vulnerable to even small doses of toxic chemicals. This is exacerbated by the increased breathing rate of infants that we alluded to earlier.

“The brains of babies and young children are constructed by a complex interplay of rapid neural connections that begin before birth,” says Pia Rebello Britto, the UNICEF chief of early childhood development. “These neural connections shape a child’s optimal thinking, learning, health, memory, linguistic and motor skills.”Exposure to polluted air makes children more vulnerable to developmental problems. This may prevent the full growth of their brains. Recent research has also shown that air pollution can stunt growth, impact intelligence and memory, and cause psychological issues such as anxiety, depression and attention-deficit hyperactivity disorder. Obviously, all these conditions will adversely affect a child’s performance in school and limit their social potential.

The air inhaled by infants and children during their first eight years is critical to build their immunity and ward off potential allergies. Exposure to air pollution during this crucial time adversely affects the functioning of kids’ lungs, causing colds, flu, bronchitis, asthma, and pneumonia. Sadly, the lungs of growing children are more permeable to air pollutants because their defense system is not adequately evolved.

How To Improve Indoor Air Quality In Your Home?

sometimes the danger that can be seen and realized is not that harmful than the one lurking in the dark for which you are not even aware. Well, we are not talking about the suspicious guy in your home, We are talking about a far more dangerous element in your home – the air you breathe! That’s right your home air could be far more dangerous than the pollution outside. At least the outside pollution is visible – the dust from construction site, smoke from vehicles, etc. and so one can at least avoid it or take some remedial measures but inside your home, there are so many things which make your home highly polluted and toxic which can give you and your family members a number of deadly diseases. The culprits could be the lead in your wall paint, radon gas creeping from your ground, your pet’s dander, VOC from stored cleaning agents, the kitchen smoke and so on the list goes on. These can be detrimental to human health and cause respiratory diseases, kidney ailments, and even cancer.

So, what to do is the million-dollar question, quite literally as you may end up spending your hard-earned money on the treatment. First of all, do a mental audit of your home. Just think of any peculiar smell that makes you uncomfortable, the cracks in your ground from where radon leaks in, stored cleaning agents and so on. 

If the air quality of your home is in danger zone, then it would be a good idea to buy an indoor air purifier for your home. Apart from that, you could take a number of steps. To begin with, improving the ventilation in your home; how often your windows open and do you allow smoking in your home are some important questions you must ask yourself. Do you store huge quantities of cleaning agents because it makes sense to buy them in bulk? Don’t save on that, if you must store it in open area like your rooftop, balcony, etc. The next thing to do is to improve the performance of your kitchen smoking outlet.

Even after these precautions, your indoor quality does not improve then it is highly recommended that you buy an air purifier that can take care of you, especially if you have old people or children at home.

Smoking should be avoided at all times indoors. Plugin the leaks in the ground and walls and maintain 30 to 50% humidity in your home, too little or too much moisture is certainly not good for your health.

Air pollution kills an estimated seven million people worldwide every year

Air pollution kills an estimated seven million people worldwide every year. WHO data shows that 9 out of 10 people breathe air containing high levels of pollutants. Sirocco Air Technologies working to improve air quality. 

From smog hanging over cities to smoke inside the home, air pollution poses a major threat to health and climate. The combined effects of ambient (outdoor) and household air pollution cause about seven million premature deaths every year, largely as a result of increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections.

More than 80% of people living in urban areas that monitor air pollution are exposed to air quality levels that exceed WHO guideline limits, with low- and middle-income countries suffering from the highest exposures, both indoors and outdoors.


Fashion maker in ventilation

Now the most exacting bathrooms will be satisfied with an exclusive interior. The new ultramodern fans came to change the old-fashion fan models. The Sirocco has presented a series of design fans to Sri Lanka. For example, model “Vents X” with the original design in the form of “butterfly” or model “Vents P” in ultramodern design, etc.

The majority of models are available in a form when the whole front cover of the fan is closed with the polished aluminum plate. This design allows the fan not only to enter the modern interior organically but also to make it a significant element of this interior.

Fans are intended for small and average accommodations, for ceiling and wall installation.

Fans of this series are equipped with movement sensors, timers, and other electronic devices that allow programming work of the fan in a wide range of modes.

Types of Ventilation Systems

Exhaust Ventilation Systems

Exhaust ventilation systems work by depressurizing the building. By reducing the inside air pressure below the outdoor air pressure, they extract indoor air from a house while make-up air infiltrates through leaks in the building shell and through intentional, passive vents. Exhaust ventilation systems are most applicable in cold climates. In climates with warm, humid summers, depressurization can draw moist air into building wall cavities, where it may condense and cause moisture damage. Exhaust ventilation systems are relatively simple and inexpensive to install. Typically, an exhaust ventilation system is composed of a single fan connected to a centrally located, single exhaust point in the house.

A preferable option is to connect the fan to ducts from several rooms (especially rooms where pollutants tend to be generated, such as bathrooms). Adjustable, passive vents through windows or walls can be installed to introduce fresh air rather than rely on leaks in the building envelope. However, passive vents may be ineffective because larger pressure differences than those induced by the ventilation fan may be needed for them to work properly.

Spot ventilation exhaust fans installed in the bathroom but operated continuously represent an exhaust ventilation system in its simplest form.

One concern with exhaust ventilation systems is that they may draw pollutants, along with fresh air, into the house. For example, in addition to drawing in fresh outdoor air, they may draw in the following:                                                     Radon and molds from a crawlspace
• Dust from an attic
• Fumes from an attached garage
• Flue gases from a fireplace or fossil-fuel-fired water heater and furnace.

This can especially be of concern when bath fans, range fans, and clothes dryers (which also depressurize the home while they operate) are run when an exhaust ventilation system is also operating. Exhaust ventilation systems can also contribute to higher heating and cooling costs compared with energy recovery ventilation systems because exhaust systems do not temper or remove moisture from the make-up air before it enters the house.

Supply Ventilation Systems

Supply ventilation systems work by pressurizing the building. They use a fan to force outside air into the building while air leaks out of the building through holes in the shell, bath- and range-fan ducts, and intentional vents. As with exhaust ventilation systems, supply ventilation systems are relatively simple and inexpensive to install. A typical system has a fan and duct system that introduces fresh air into usually one—but preferably several—rooms that residents occupy most (for example, bedrooms, living room, kitchen). This system may include an adjustable window or wall vents in other rooms.

Supply ventilation systems allow better control of the air that enters the house than do exhaust ventilation systems. By pressurizing the house, these systems discourage the entry of pollutants from outside and prevent back-drafting of combustion gases from fireplaces and appliances. They also allow air introduced into the house to be filtered to remove pollen and dust or to be dehumidified.

Supply ventilation systems work best in hot or mixed climates. Because they pressurize the house, they have the potential to cause moisture problems in cold climates.

In winter, the supply ventilation system causes warm interior air to leak through random openings in the exterior wall and ceiling. If the interior air is humid enough, some moisture may condense in the attic or parts of the exterior wall, where it can promote mold, mildew, and decay.

Like exhaust ventilation systems, supply ventilation systems do not temper or remove moisture from the air before it enters the house. Thus, they may contribute to higher heating and cooling costs compared with energy recovery ventilation systems. Because air is introduced in the house at discrete locations, outdoor air may need to be mixed with indoor air before delivery to avoid cold air drafts in winter. An in-line duct heater is another option, but it will increase operating costs.

Balanced Ventilation Systems

Balanced ventilation systems, if properly designed and installed, neither pressurize nor depressurize a house. Rather, they introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air, respectively. A balanced ventilation system usually has two fans and two duct systems. It facilitates the good distribution of fresh air by placing supply and exhaust vents in inappropriate places.  the typical balanced ventilation system is designed to supply fresh air to bedrooms and common rooms where people spend the most time. It also exhausts air from rooms where moisture and pollutants are most often generated, such as the kitchen, bathrooms, and the laundry room.

Like both supply and exhaust systems, balanced ventilation systems do not temper or remove moisture from the air before it enters the house.

They do, however, use filters to remove dust and pollen from the outside air before introducing it into the house.

Also, like supply ventilation systems, outdoor air may need to be mixed with indoor air before delivery to avoid cold air drafts in the winter. This may contribute to higher heating and cooling costs.

Balanced ventilation systems are appropriate for all climates; however, because they require two duct and fan systems, they are usually more expensive to install and operate than supply or exhaust systems.

Energy Recovery Systems

Energy recovery ventilation systems usually cost more to install than other ventilation systems. In general, simplicity is key to a cost-effective installation. To save on installation costs, many systems share existing ductwork.
Complex systems are not only more expensive to install, but often they are also more maintenance-intensive and consume more electric power. For most houses, attempting to recover all of the energy in the exhaust air will probably not be worth the additional cost. Also, these types of ventilation systems are still not very common. Only some HVAC contractors have enough technical expertise and experience to install them.
In general, you want to have a supply and return duct for each bedroom and for each common living area. Duct runs should be as short and straight as possible. The correct size duct is necessary to minimize pressure drops in the system and thus improve performance. Insulate ducts located in unheated spaces, and seal all joints with duct mastic.
Also, energy recovery ventilation systems operated in cold climates must-have devices to help prevent freezing and frost formation. The very cold supply air can cause frost formation in the heat exchanger, which can damage it. Frost buildup also reduces ventilation effectiveness.
In addition, energy recovery ventilation systems need to be cleaned regularly to prevent deterioration of ventilation rates and heat recovery, and to prevent mold and bacteria from forming on heat exchanger surfaces.

What is the different between Air purifiers & Air Filters?

Air Filters (Air Cleaners)

A typical home or business has a forced-air and heating and cooling system that blows air through the ductwork and air vents, which are located throughout the building. These systems have air filters that are designed to keep the HVAC unit clean inside. In doing so, they make the HVAC system more efficient. Air filters also reduce airborne particulate like dust and dander from being recirculated throughout the home. The key thing to note here is that air filters work by effectively trapping contaminants.                                                                                                                                                                                   There are many different types of air filters; not all filters are able to remove the same types of contaminants from the air. HEPA air filters, for example, are widely acknowledged to be the most powerful types of air filters on the market because they are capable of capturing 99.97% of contaminants in the air that are as small as 0.3 microns in size.                                                                                                Many different industries require custom made filters for their equipment. Examples include various dental equipment and the food and beverage industry. Custom made filters provide superior filtration and have a better performance and filter life over standard filters that can be bought over the shelf. 

Air Purifiers

There is a range of air purifiers on the market. Some are standalone systems; others are installed in the ductwork. Air purifiers are designed to kill bacteria, molds, and fungus. Air purifiers accomplish this by using UV germicidal lamps (instead of using a filter), which means that some air purifiers can only destroy these organisms when they are in close contact with them.

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