One of the prime principles of a building is to provide a comfortable, healthy and productive atmosphere for the occupants. There are four key players in achieving such an environment, namely, the structure, the HVAC system, outdoor environment and occupants’ activities. The ventilation system in buildings is a component of the HVAC system. It has been reported that from the aspects of the built environment, the most influential factors on the occupants of a building are ventilation, indoor air quality, acoustics and lighting. The satisfactory quality of each of these aspects is necessary for achieving occupant satisfaction and considerations must be incorporated in the design of the building (Khaleghi et. al., 2007). In the context of this paper, focus is on the ventilation system and its impact on the occupants of the buildings.
Ventilation – Concept & Significance:
Adequate building ventilation is essential to human health and comfort. Ventilation refers to bringing in outdoor air to a space through the ventilation system, via either flow through open doors and windows, natural forces caused by wind and by temperature differences between indoor and outdoor air, and by infiltration through the building envelope or mechanical ventilation systems with fans (Seppanen & Fisk, 2001). Proper ventilation is interpreted as the building envelope as being sealed to reduce the uncontrolled air leakage (infiltration) and ensuring that all of the ventilation efforts are complementing each other, rather than negating each other’s effects. Precise air pressure and airflow aids in maintaining a balanced building temperature and better indoor air quality (Diamond, et. al., n.d.).
Ventilation basically enables the outdoor air to the occupied zone and eradicates or dilutes indoor-generated pollutants (Seppanen & Fisk, 2001). The purpose of ventilation systems is to satisfy the air quality and thermal comfort requirements in any space. In buildings, this is either achieved by supplying natural fresh air or conditioned air (Zhou & Haghighat, 2009). Ventilation systems should always be controllable, either manually or automatically, so as to maintain acceptable indoor air quality and avoid energy wastage. This leads to a comfortable environment for the residents. An effective ventilation system ensures that the pollutant levels in the occupant’s breathing zone, if not entirely eliminated, are with acceptable limits in terms of healthy requirements (The Building Regulations, 2000).
Ventilation in Building Regulation:
From the building code perspective, adequate ventilation refers to that level of ventilation that protects the health and safety of its occupants. Most countries in the world have building codes that specify ventilation levels for new buildings as well as existing buildings. In the US, such requirements may include ventilation rates (ASHRAE Standard 62-1989), and thermal comfort (ASHRAE Standard 55). Building codes typically necessitate operable, exterior window openings for certain rooms within the living space and in the spaces where operable windows may not be feasible, mechanical ventilation is necessary (Diamond, et. al., n.d.).
According to the Building Regulation Code in United Kingdom, the definition of ventilation is simply the removal of stale indoor air from a building and its replacement with fresh outside air (assuming that the outside air is of suitable quality). The code identifies the various purposes of ventilation requirement; one or more may be applicable, as provision of outside air for breathing; dilution and removal of airborne pollutants, odor inclusive; control of excess humidity, which is caused by water vapors in the indoor air; provision of air for fuel-burning appliance; and as a means to control thermal comfort. The airborne pollutants and water vapors are released from materials and products used in construction, decoration and furnishing of a building as well as from the activities of the building occupants. All of these factors have direct impact on the healthy and comfort of the residents (The Building Regulations, 2000). As per the regulation, buildings are ventilated via a blend of infiltration, which is the unmanaged air exchange between the inside and outside of the building through a wide range of air leakage paths in the structure and purpose-provided ventilation, which is the controlled air exchange through a range of natural and/or mechanical devices. The infiltration should be minimised and there should be sufficient purposed-provided ventilation (The Building Regulations, 2000).
The amount of ventilation required for specific purposes and occupancies is defined by the building codes in terms of air change per hour, or in cubic feet per minute (cfm) per person. ASHRAE standard 62-1989, Ventilation for Acceptable Indoor Air Quality, recommends 15 to 20cfm of outdoor air per person for most applications (Binggeli, 2003).
Ventilation in Buildings:
In the recent times, the numbers of apartment and office buildings are rapidly increasing due to urbanization and high population density in many regions. Apartment buildings are becoming most common type of residences, especially in the cities and office buildings concentrated in the urban center of the cities are considered hub of economical activities (Lee & Kim, 2008). Ventilation design suited for buildings is more complicated and complex as oppose to single-family houses. The reason lies in the fact that in apartments, there is a limitation of exposure of walls and windows to the outside environment. In addition, the natural physical forces that move air are more distinct in taller buildings, such as infiltration and exfiltration – the uncontrollable flow of air through cracks and leaks in the envelope of building (Diamond, et al., n.d.).
Low rise buildings, which are of three stories and under, often prefer to use natural ventilation, relying on the supply of air through operable windows. High rise buildings, which are above three stories, mostly use mechanical ventilation systems in the form of fans, air-inlets, ducts and registers. Often high rise buildings, especially residential, provide for both types of ventilation systems (Diamond, et. al., n.d.). There has been an increase focus of residents in enhancing the quality of life, thus, there has been a shift in focus of construction activities in improving the housing quality. Among the various concerns, there is a particular apprehension over indoor air quality of houses and buildings (Lee & Kim, 2008).
Types of Ventilation System:
Prior to understanding the impact that ventilation systems have on residents of buildings, it is essential to comprehend the various types of ventilation systems. There are two main types of ventilation system available in the buildings, namely the natural ventilation system and mechanical ventilation system. Natural ventilation system is defined as a system that permits constant ventilation as a result of the differences in pressure between indoor and outdoor air, except for conventional openings such as windows and door. Mechanical ventilation system is a forced ventilation system that utilises motorised fans. The choice of the ventilation system depends on the type and size of the building (Lee & Kim, 2008).
Mechanical ventilation systems can be classified into four main types: self-adjustable mechanical ventilation, controlled relative humidity mechanical ventilation, mechanical ventilation with heat recovery and mechanical ventilation with local exhaust fans (Dept. of Building & Housing, 2006) The mechanical ventilation system has been reported to potentially lower the indoor concentration of contaminants by swapping polluted indoor air and fresh outdoor air, hence protecting the residents from the harmful effects of the pollutants and ensuring a healthy environment. The mechanical ventilation systems offer more control and reliability as oppose to the natural ventilation systems (Lee & Kim, 2008).
The comparison of the common ventilation systems in context of their advantages and disadvantages is as follows: There are three typical types of natural ventilation systems; the structure installation type, which is slotted in and installed at the wall punching section, the window frame insertion type, which is inserted and installed after grooving the window (common in European countries), and the window insertion type. The natural ventilation has the capacity to solve the condensation problems on the balcony of the buildings during winter times (Lee & Kim, 2008).
In the most of the old residential buildings, there is a lack of extensive and well equipped ventilation system. The components of ventilation system found were exhaust fans in bathrooms and kitchens and window and door openings. In the last decade, however, there has been a change in the trend and a variety of ventilation systems are being employed in the newly built buildings. The major focus is on using mechanical ventilation systems and there are many companies manufacturing and supplying mechanical ventilation system, like duct type systems, exterior-wall-attached ductless systems, etc. There are, however, natural ventilation devices being developed which can be installed on window glasses (Lee & Kim, 2008).
There has been a recent addition to the types of ventilation systems called hybrid ventilation system. Various research projects have been conducted lately through the cooperation of ventilation manufacturers in the development of hybrid ventilation system. The objective of this type of system is to achieve ventilation requirements as well as energy conservation and sustainability by utilising mechanical and natural ventilation systems. It is basically a two mode system, which is different from a conventional ventilation system due to its automatic control between natural and mechanical mode to conserve energy as well as maintain a satisfactory indoor environment (Lee & Kim, 2008; Heinonen &, Kosonen, 2000).
Effects of Ventilation Systems on Building Occupants:
The major impact that the presence or lack of ventilation systems has is on the comfort level of the residents as well as the quality of indoor air in the building. Studies have shown that occupants’ behaviour related to ventilation is often largely dictated by their desire to improve the comfort of the environment (Diamond et al., 1986).
Modern ventilations systems try to create a subtle indoor climate control, however, more often than not, survey results reveal the complaints of the residents as the atmosphere being either too hot or too cold, simultaneously. Due to the energy crisis in the early 1970s, according to which high cost of associated with energy consumption in the residential and commercial buildings, more emphasis have been dedicated to energy efficiency. The building design has shifted towards high level of insulation, air tightness and minimal ventilation rate, especially in the office buildings. The result of this trend is the deterioration of indoor air quality and elevated problem of sick building syndrome (Zhou & Haghighat, 2009). Research has shown that the risk of sick building syndrome and other sickness is strongly related to ventilation systems in the buildings (Pejtersen et al., 1999; Wargocki, et al. 2000). There has always been trade-offs between the energy usage for ventilation and the advantages of ventilation to occupant’s comfort and health (Zhou & Haghighat, 2009).
ASHRAE mandates that if the building falls below a certain criteria for measuring indoor air quality, then it must be mechanically ventilated. In the multi-storey building, as aforementioned, there is a sharing of at least one common wall with another dwelling, hence, leading to indoor air quality issues. This results in the available number of portals for fresh air coming directly into the units from outside (Hayes & Baruch, 1994). There was a survey conducted in the New York City buildings. In the bathrooms and kitchens of most of the buildings, there were operable windows and no mechanical exhausts were present. Corridors in the tenement buildings were not mechanically provided with supply air rather, had ventilation openings at the top of the stairwell, usually in a skylight. There were mere four percent of the surveyed buildings, where supply air was provided mechanically. This was the case primarily in larger buildings where the fresh air was provided from a single fan into the corridor on each floor. Most of the upstate New York buildings surveyed (96%) had some type of mechanical exhaust. It usually comprised of tenant-controlled small exhaust fans in bathrooms and kitchens. Supply of fresh air was provided mechanically in 36% of buildings (Hayes & Baruch, 1994).
In the buildings surveyed, it was found that one of every four fans was turned off, noise complaints, or comfort complaints being one of the key reasons for the action. When the airflow on a number of fans in the buildings was measured with a balometer (flow hood) and was compared to the design values, the result showed actual airflows ranged from 6%-254% of rated airflow, averaging 68% (almost one-third less than required). The cause was usually dirty registers which were heavily caked with dirt; however, these were not the chief reason of airflow obstruction, as most systems did not have filters. There was unusual airflow obstructions such as tape or paper placed over registers, insulation in the ductwork, etc., all results of the associated noise complaints of the ventilation system (Hayes & Baruch, 1994).
Tenant surveys exposed that mechanical ventilation was linked with complaints about drafts. From the eight buildings which were equipped with supply fans, three of them had serious comfort complaints in the corridors, two of them were turned off, and two were severely under-ventilated. This problem is not only limited to multifamily buildings but, can also be seen in commercial buildings. The ventilation resulting from tenant control of exhaust fans was seen to be adequate to manage temporary odors in the kitchen or bath. It was not used to draw in fresh air for the entire building, or to address other sources of poor indoor air quality. When audits were conducted, auditors recognized significant ventilation-interactive issues such as health and safety, comfort, indoor air quality and building condition. A high correlation was found between the level of ventilation and the level of air-quality complaints (Hayes & Baruch, 1994).
It has been reported in previous unpublished UBC studies that with the forced-air HVAC systems or mechanical HVAC systems, the resultant ventilation quality and noise levels are inversely related. Rooms with adequate ventilation are often noisy and the occupants have to deal be constant noise which may disturb their peace and quiet, especially during sleeping and resting hours. Quiet rooms, on the other hand, may lead to inadequate ventilation, which may lead to problems like suffocation, uncomfortable temperature levels, etc. In additional to that, it has also been found that if noise-control measures are introduced, that also adversely affect both the ventilation quality and indoor air quality (Khaleghi et. al., 2007).
It has been estimated that ventilation deficiency can lead to high concentration levels of volatile organic compounds. Lack of proper ventilation can lead to the problem of Sick House Syndrome and Multi Chemical Sensitivity, as the petrochemical building materials and furniture give out volatile organic compounds, which get suspended in the enclosed rooms and spaces. Proper ventilation systems are essential to avoid Sick Building Syndrome and other issues related to the lack of fresh air supply (Lee & Kim, 2008).
The sick building syndrome (SBS) include symptoms such as eye, nose, throat, and skin irritation; nasal congestion (stuffy, blocked nose); nasal excretions (runny nose); cough; wheeze; tight chest; mental fatigue; headache; nausea and dizziness. Mostly the sick building syndrome is associated with commercial buildings, however, it is seen in residential buildings as well. According to the studies, the occurrence of sick building syndrome is influenced by the characteristics of buildings and ventilation systems. The method of heating of building, ventilation system and air conditioning are important factors in determining the indoor air quality of the building, which in turn significantly affects the healthy and comfort of the occupants (Seppanen & Fisk, 2001).
According to the studies conducted in the 1990’s by Mendell & Smith, buildings were categorized according to their HVAC systems into five groups: natural ventilation, simple mechanical ventilation, air-conditioning without humidification, air-conditioning with steam humidification, and air-conditioning with water-based humidification. It was observed that the symptoms of sick building symptoms were significantly higher in the air-conditioned building than in naturally ventilated buildings. Air-conditioning systems which were equipped with steam humidification did not exhibit higher prevalence of symptoms in comparison to the systems without humidification. Air-conditioning systems with liquid-water-based humidification, however, did show association with an elevated prevalence of some of the sick building symptoms as oppose to systems without humidification. Simple mechanical systems, with mechanical supply and exhaust but no air conditioning, were not found to be consistently linked with a higher prevalence of symptoms than natural ventilation. The authors, however, emphasized that fact that these results were based on buildings in the United Kingdom and Denmark, and should be carefully generalized for other countries, due the difference in climate, building type, HVAC system designs and operational procedures. It is noteworthy, that the ventilation systems do not directly influence heath symptoms; rather it may be a surrogate for one or more exposures that affect symptom prevalence (Seppanen & Fisk, 2001).
The probable risk factors associated with the poor indoor air quality associated with HVAC types and feature is as follows:
From the point of view of the occupants, adequate ventilation may be defined as the amount of air needed to remove odors and to maintain a healthy and comfortable environment. Ventilation is also particularly significant in reducing odorless pollutants such as moisture or carbon monoxide, which have negative impacts on the health and comfort. The residents who are responsible for their heating and or cooling bill, the energy cost associated with ventilation is an important factor which affects them. In the existing mechanical ventilation systems, there are associated issues like noise from connected fans, drafts produced by high air velocities, the location of registers, or discomfort from ventilation temperature, they may turn off, or otherwise undermine the operation of their systems (Diamond, et. al., n.d.).
A satisfactory ventilation system, which avoid negative impacts on the occupants of the building, supplies air with minimal impurities or pollutants, comfortable temperatures and low flow rate and reduced noise. There are cases, when occupants to relieve their discomfort, block the ventilation on purpose, by taping over registers and vents, by putting blankets or towels against a door having undercut for providing ventilation. This behaviour is motivated by the discomfort caused by the cold drafts. There are other reasons as well for sealing the ventilation supply routes such as to shut out noise, light, insects, or odor. People, at times, experience discomfort from the movement of air depending on the temperature and velocity of the air. Movement of air with a temperature below 70 oF can be experienced as discomfort. These are few uncomfortable impacts of ventilation systems in buildings (Diamond, et. al., n.d.).
To sum up, research shows that with the mechanical ventilation system providing occupants with better indoor air quality, the associated noise levels are higher. Natural ventilation systems provide occupants with unsatisfactory ventilation quality but acceptable noise levels with windows closed, and satisfactory ventilation quality but unacceptable noise levels with windows opened (Khaleghi et. al., 2007). There are many shortcomings, relating to both indoor air quality and energy use associated with the ventilation system, which lead to health and comfort issues for the building occupants. With adequate ventilation system for the building, the result is a comfortable and healthy environment for the residents.