Section 1 focuses on the relationship between Indoor Air Quality and HVACs. It starts with a definition of HVAC systems and takes a look at some of the types of systems in use. This section then draws attention to the effects of HVAC systems on indoor air quality. Greater focus has been given to the negative effects as these ones can be dangerous to workers’ health.
Section 2 focuses on filters and their effect on indoor air quality. A description of filters is then followed by an examination of some of the common types of filters. This is followed by an explanation of the effects of filters on indoor air quality. After section 2, an examination of how maintenance affects indoor air quality has been done. This has been followed by a comprehensive examination of the case studies done on HVACs and indoor air quality. A chapter summary on both sections has been provided.
HVAC and indoor air quality
An HVAC system works by drawing in fresh air from the external environment and mixing it with air in the internal environment. The mixture of air is then cooled or heated and then filtered before circulating it into the workplace. It is assumed that when HVAC systems are put in place, they replace the polluted indoor air through dilution (Wargocki, & Jukanovic 2005). There are three major functions that the HVAC serves. It prevents exposure of people to sources of pollutants by the placement of physical barriers and use of pressure-air relationships. It also eliminates contaminants through dilution using ventilation mechanisms. Third, it focuses on cleaning air pollutants through filtration. Certain components are present in HVACs and these include the supply fan, the water chiller, the cooling tower, the boiler, the control, the self-contained cooling or heating unit, the exhaust fans and air outlets, the return air system, the terminal device, and the ducts.
There are a number of things that must be considered when operating an HVAC system. The ventilation system design is an important aspect because the ability to deliver a certain capacity of air is dependent on the number of people that were estimated to occupy that building. A storage room that becomes an office space will necessitate corresponding changes in the HVAC system. Outdoor air supplies are another important concern in HVAC operations too. The system requires a sufficient supply of outdoor air to dilute the pollutants that may have been released from office equipment, people, products, and furnishings (Bako-Biro et al 2004). Ventilation air distribution is vital in according these occupants a certain degree of comfort. Outdoor air quality must also be considered when operating an HVAC system. If there is dust, pollen, carbon monoxide or any other source of contaminant, then this could find its want into the ventilation system. HVACs that have the right filters are designed to trap such particles from the outdoor supply. However, to control gaseous pollutants, one may require highly specialized equipment that cannot be accorded by the HVAC.
For HAVC systems to work, considerations need to be given to the degree of space planning. For example, if a computer or another heat-generating device is placed directly under the HVAC’s thermostat, the system will assume that the building is warm and will keep delivering too much cool air. Conversely, the use of certain partitions in a work area may block airflow and this minimizes the indoor air quality of the system (Zhu et al 2006).
Types of HVAC
There are various types of HVAC systems. One such type is the single zone HVAC. It has only one air handling unit. Although it has the ability to serve more than one area, the other areas need to have similar cooling, ventilation and heating requirements. All areas that have the same control or thermostats are called zones and some accountability needs to be done for those cooling and heating load differences.
The second type of air filter is known as the multiple-zone. Such a system has the capacity to cater to several zones. It provides different temperatures to different zones by cooling and heating airstreams in those areas. Sometimes, these kinds of HVAC systems may deliver air through constant temperature but may vary the airflow volume. Alternatively, they may moderate room temperature through a supplementary system such as perimeter hot water piping.
A constant volume HVAC is also another classification. This one works by delivering a constant volume of airflow to particular spaces. The alterations in the temperature are handled by switching the air handling unit off or on. They are also done through heating or cooling the air.
The fourth type is the variable air volume system. This one works by changing the volume of the air delivered rather than changing the temperature of that air. It is only on a seasonal basis that variable air volume system temperatures can be reset. Adjustments are also made depending on the loads under consideration since overcooling or overheating can occur. Variable air volume HVACs tend to have many cases of under ventilations once a minimum quantity of outdoor air has not been set.
HVAC effect on indoor air quality
There are a number of challenges that emanate from HVAC systems. First, there’s an inadequate amount of fresh external air that actually comes into the workplace. A large number of HVAC systems only allow 20% external air to mix with 80% of re-circulated internal air. This compromises the indoor air quality that workers are subjected to. However, the number of HVAC systems that re-circulate air is dependent on the geographical region of the office building. Bell & Standish (2005) have shown that fifty percent of all office buildings in Europe re-circulate air. This contrasts sharply with about ninety percent of office buildings in the United States. The average number however is 80%.
The HVAC systems in use also have limited mechanisms for controlling contaminants. Consequently, continued use of HVAC systems will lead to the accumulation of many contaminants in the workplace environment. The contaminants may sometimes come from molds or microbial growth in the HVAC system. Alternatively, it may be high humidity or the presence of water near the cooling, humidifying, and dehumidifying components of the HVAC. Sometimes, oil residues may have been left behind during the manufacturing process. The systems may also have sound and insulation materials that eventually contaminate them (Burroughs 2005). For contaminant sources, HVAC systems are not effective in controlling these exposure levels because the contaminant is not directly ventilated. It has been noted that sometimes the quantity of air needed to remove contaminants is large; an HVAC system cannot cope with the air exchange volume. What’s more, a number of HVAC systems do not have provisions that allow worker control of ventilation rates as most of them have fixed settings.
HVAC systems often start operating prior to workers’ entry into the premises and may shut down before they leave. Some HVACs have exhaust and intake vents that have been placed too close together. This makes workers susceptible to poor ventilation rates (Lee & Chan 2004).
Sometimes HVAC systems may be located in outdoor environments that are dangerous to workers. For instance, they may be found in busy streets, near loading docks or standing water and this would definitely minimise the ventilation rate in that concerned building (Zhao et al 2006).
Sometimes there could be problems with the design or installation of the HVAC system. For instance, if a drain pan was constructed poorly, then it can lead to the accumulation of standing water. Alternatively, it may be the installation of that drain pipe that could cause the development of standing water. If a drain has not been properly dimensioned, then this could also lead to problems in the indoor air quality of the system. If the selection of equipment is poorly done, then this may create a number of problems. First, air filters may not fit well into the handling units. This may lead to the passage of unfiltered air in the workplace (Johnson et al 2009). Alternatively, it could be the roof top handling equipment that has a problem. In this regard, the equipment may be too close to the exhaust steam and this may lead to the re-entrapment of pollutants. If there are air leaks in heat exchangers, then this could cause pollutants to be transferred from the exhaust stream to the supply air stream.
The above mentioned problems are associated with the improper selection of certain equipments. Sometimes, HVAC challenges could be linked to their designs. If the HVAC has been made in a way that allows snow and rain to get into the system through the inlet louvers, then this could ruin the indoor air quality (Simoni et al 2010). If the equipment has been designed in a manner that does not offer access to it for maintenance, then this may eventually prevent one from rectifying problems inside it. When fans or duct systems have been poorly designed, this may lead to the poor distribution of outside air inside the office. If ventilation rates have been poorly specified, then a HVAC system may create low ventilation rates in the workplace. In certain circumstances, this may be accompanied by high levels of recirculation. Pollutant transfer may also be necessitated if the exhaust air is designed to have a higher pressure than the supply air in the heat recovery system (Maynard & Kuempel 2005).
Poor installation can also create a number of challenges for users of HVAC systems. Once dust and debris from construction are left in the system, then this can be regarded as a pollution source that affects the indoor air quality. Alternatively, the improper balance of air flows at the installation process may cause leakages, blocking, thermal discomfort and poor ventilation. If a duct has been disconnected from a duct system, this could lead to ventilation and thermal challenges.
The operation of the HVAC system may also hamper its success. In certain circumstances, there could be improper set points which lead to indoor temperature that falls outside the thermal comfort levels of workers (Jensen et al 2005). Alternatively, it may be the excessive humidity that emanates from high temperature, which may prevalent at the cooling coils. If the HVAC system does not operate well, then this could lead to the development of microbial contaminants and high humidity if the office facility is located in a humid region.
All these problems may subject workers to a diminished level of oxygen and an increased level of carbon dioxide. Poor humidity and temperature control may also come about once the HVAC system develops excessive cooling or heating capacities. Additionally, biological and chemical contaminant may keep building up to the point of compromising the indoor air quality. Poorly maintained HVACs also lead to extreme temperature which may distract workers from their respective tasks. They may report excessive levels of discomfort and will keep on being fatigued when they are at their work premises (Breyssea et al 2005). The HVACs described earlier can also cause irritating workplace odours. Dirt and dust may keep accumulating in the affected office building. Perhaps a worrying trend is the development of Sick building syndrome, which is characterised by fatigue, eye irritations, colds and flu, headaches and irritations in the noise (Bräuner et al 2008). These symptoms tend to reduce once workers have left the building. Godwin & Batterman (2006) explained that this was the case because of low ventilation rates. When ventilation rates go below 10 Ls-1 per person, then chances are that the person will develop SBS. Low ventilation rates are found to be very common in office buildings that have mechanical ventilation. In Sweden, Bordass & Leaman (2004) explain that forty eight percent of the buildings had ventilation rates that were less than the mandatory code values in mechanically ventilated systems. Among the buildings analysed, it was also found that twenty five percent of all the mechanically ventilated systems that possess heat recovery had these low ventilation rates
There is increasing evidence to show that multiple chemical sensitivity (MCS) tends to develop when individuals are exposed to chemicals or a number of chemicals. Such persons will report symptoms such as skin rashes (Ramachandran et al 2005). Throat irritations, nose and eye irritations, problems in the central nervous systems are other symptoms that are linked to MCS.
Filters and IAQ
Filters are used to take out particles from air. When proper filtration exists, chances are that the rest of the HVAC may be protected. Furthermore, filters contribute towards maintenance of good indoor air quality in office buildings. All air filters need to be maintained and selected in order to offer maximum filtration. This implies that the supply fan should not be overtaxed. The supply fan can blow out when no air filter exists (Yoon et al 2008).
Types of filters
Filter designs normally determine the kind of energy that is required to push air through them. Low efficiency filters only have the ability to prevent dust and lint from clogging the cooling or heating coils (Qi et al 2008). Medium efficiency filters have the ability to tackle smaller particles. High efficiency particles can filter very small particles. The only problem is that they tend to clog quite quickly (Clausen 2004).
Alternatively, filters may be classified on the basis of their design. Here, one may have the roll filter which has a set of rolls on it. There is the bag filter, the panel filter and the pleated filter as well. Pleated medium efficiency filters are preferable in the workplace as they do not require regular maintenance; they do not clog easily and protect both the indoor environment as well as the rest of the HVAC system (Kennedy et al 2007).
Filters effect on IAQ
Filters need to be properly selected. If this is not done well, then unfiltered air will be allowed to pass through the filters and this could damage the indoor air quality. Additionally, low efficiency filters can lead to the prevalence of a high level of indoor concentration of particles. Sometimes, the problem may stem from missing filters, which may have been lost in the operational process. This can lead to the entrance of polluted air in the workplace owing to the presence of unfiltered air.
Filters need to be cleaned and maintained regularly (Zhang & Zhong 2009). As a filter continues to load up with particles, it tends to become more efficient at removal of particles, but keeps reducing the pressure drop in the system. This eventually minimises air flow. When the filters are excessively loaded, they may blow out of their filter racks. This can cause clogging of coils, it may make ducts to block and will seriously compromise the indoor air quality (Moritz et al 2004).
Sometimes filters can be the source of volatile organic compounds (VOCs), in a study carried out by Bernstein et al (2007), it was found that air filters in VOCs are a significant source of VOCs, which lead to Sick Building Syndrome (Kuo-Pin et al 2006). The analysis involved unused and used air filters. These were taken in a test chamber and incubated there for some time. It was found that the test chamber that had used filters reported excessive levels of acetone and formaldehyde. A parallel test was also done in order to determine whether the continued use of filters led to accumulation of VOCs. In other words, tests were done before and after use of air filters. It was found that acetone and formaldehyde concentrations were much higher after use of those air filters than before, the tests also revealed that microorganisms tend to survive in air filters. These creatures are the ones that emit acetone and formaldehyde (McHugh et al 2007).
Panel filters that are made of cellulose fibres enclosed in a frame are the common types of filters used in HVACs. Most of them can rarely remove particles that are less than 5 micrometres in diameter. This means that microbes such as fungi cannot be removed by this method. Living and dead fungi can pass through the HVAC system of an office building and may result in extra sensitivities or infections among workers (Sublett et al 2010). Dampened filters can also harbour the growth of fungi in the HVAC. Moisture in these air filters normally comes from cooling coils. The condensate from that area can dampen filters and thus minimise its safety. Once the fungi have grown to a sufficient level, they can be released to the workplace environment and eventually cause diseases.
How maintenance affects IAQ
Some HVAC system may be blocked due to excessive dust in the air vents. Alternatively, renovations may have been done in a particular building, but the HVAC system may have been left intact. As a result, it may end up having the wrong structure for the new building. Even office planning can affect the degree of satisfaction with the HVAC system. Air flow can be reduced by the placement of different kinds of materials in the vicinity of the supply vents. Maintenance may be necessary to correct this poor planning (Bluyssen 2009). Placement of heat generating equipment like photocopiers can be altered in order to reduce excessive cooling of the workplace.
HVAC problems are usually multifaceted. These are normally related to their design, operation and equipment. For example, presence of standing water in a cooling coil within a HVAC system may lead to the growth of microorganisms which may cause diseases like SBS. Failure to properly maintain such a system can indeed lead to these problems. Therefore, poor drainage can occur when one does not fully maintain one’s HVAC system (Huizenga et al 2006).
If maintenance is not done frequently, then air filters may not be replaced as frequently as they ought to be, this makes the building susceptible to odours, and even reduces the level of airflows within (Zampoli et al 2004). The cooling coils, drain pans,, and other parts of the HVAC system ought to be inspected from time to time. This would ensure that any blockage is easily detected or any microbial contaminants can be cleaned. Failure to inspect and calibrate temperature controls or other controls in the HVAC system has contributed towards low ventilation rates, and problems with temperature and humidity in the indoor environment (Sundell 2004). Sometimes, failure to inspect the areas near the humidification system can lead to accumulation of microbes. From time to time, an organisation needs to do a thorough check of the cooling tower water. In this process, there should be treatment of that water with biocides (Chase et al 2004). If this is not done, then microbial contamination can occur. Furthermore, that same water needs to have corrosion inhibitors or scale inhibitors so that HVAC system performance is not compromised. If the pumps, chillers, fans, compressors are not checked frequently, then a company may not be in a position to detect their failures. This may lead to poor ventilation rates, thermal and humidification malfunctions.
Maintenance of the systems needs to be done through frequent operational checks. It also needs to be carried out through proper training of operators. There are maintenance system procedures that have been outlined in various codes. For the US, ASHRAE 2004 is applicable; they can also use PECI (ASHRAE 2005, ASHRAE 2004a, ASHRAE 2004b). In Europe, these have been outline in the EN 2000. Once those procedures are used, then an organisation can easily avoid all the elementary challenges that stem from HVAC systems. It has been shown that the need to constantly cut costs, the prevalence of inadequate training, and ignorance has led to poor maintenance of HVAC systems.
Aside from regular maintenance procedures that directly affect the HVAC system, there ought to be certain maintenance problems that span across the entire building. For instance, if indoor space has been divided, the newly created rooms may not be adequately served by the HVAC system. Also, if a building is expanded without alteration of the HVAC capacity, then ventilation and thermal problems may arise. If a certain work area has added air supply ducts without considering the pressure imbalances and air distribution system then this could reduce the degree of distribution of the same.
On the other hand, the HVAC system or building may have remained the same, but occupancy levels could have been changed. When this occurs, there will be alterations in the internal thermal loads and this could overwhelm the HVAC system. Replacement of such a system will therefore be necessary. These changes in numbers may sometimes introduce an unexpected pollutant source that could increase the level of pollutant concentrations (Pope & Dockery 2006). If the HVAC system was properly maintained, then the need to alter ventilation rates would have been detected and implemented.
Maintenance also involves correction of other external environments that directly contribute to the air supply in the HVAC system. This can be done through the cleaning up of water spills and drainage of stagnant water near the outdoor air supply (Wang et al 2004). It is a known fact that water is considered as an important source of mould or fungi growth. These microbes eventually cause several diseases.
Mendell and Smith (1990) carried out an analysis of HVAC systems versus the prevalence of SBS systems. In their investigation, they classified all HVAC systems into five categories: water based humidification with air conditioning, air conditioning devoid of humidification, simple mechanical ventilation and natural ventilation. It was found that SBS symptom prevalence was much higher in buildings with air conditioning than in buildings with natural ventilation (Atthajariyakul & Leephakpreeda 2004). Odds rations of 1.3-5.1 were found for symptoms that are related to the central nervous symptoms; mucous membrane symptom prevalence and upper respiratory symptoms had odds ratios of 1.4-4.8. However, air conditioning systems that had steam humidification were not found to have greater levels of SBS symptom prevalence than those ones without humidification. Those air conditioning systems that had liquid water as the basis for humidification were found to be more associated with SBS prevalence than the ones that had no humidification (Magalhaes et al 2009). Simple mechanical ventilation systems were not found to have higher SBS symptoms than the ones with natural ventilation. The authors noted that HVAC systems types do not directly affect health symptoms; nonetheless, they believed that these systems tended to be surrogates for other exposures that directly affect SBS. In other words, when looking at the effect of HVAC systems with regard to indoor air quality and worker’s health, one should analyse the risk factors of those HVAC types. It was explained that workers were subjected to certain risk factors when using particular HVAC types. For simple mechanical ventilation, HVAC systems could be dirty during the installation process or may acquire dirt along the way (Jinming 2005). This causes them to release bad odours and pollutants into the environment. Such a system also had poor control of temperature because it did not cool it. It also subjected workers to excessive noise and humidity. Air conditioning systems on the other hand were found to have condensed moisture. They also had the ability to harbour microorganisms and thus affect workers’ health. Those systems that had duct fans, coolers and humidifiers posed the danger of harbouring microbial growth. They also contributed to the overflow or leakage of water from the humidifiers. Chemicals could also be prevalent in the steam generators during water treatment. For all HVAC systems with recirculation, there was the risk of draft, noise, the spread of indoor air pollutants and contaminations of the HVAC system through re-circulated pollutants (Lin et al 2004). For decentralised systems or systems that had cooling and heating coils in different parts of the room, equipment failures were likely to occur due to inadequate maintenance.
As stated earlier, HVAC systems are a threat to the workers’ health because they contribute to recirculation of air. It has been shown by Jaakkola and Miettinen (1995) that Sick building syndrome symptoms are more prevalent among workers who have mechanically ventilated office buildings with recirculation of air than those who do not have any recirculation of air in their workplaces (Wargocki et al 2008). The authors found odds ratios of 1.6 for nasal discharge. They also found odds rations of 1.3 for allergic reactions. However, these effects are dependent on the external ventilation rates (Zagreus et al 2008). If external ventilation rates go below 13.6 L s-1 per person, then recirculation can actually have the opposite effect-it can reduce SBS symptom prevalence. Once outdoor ventilation rates are greater than the above mentioned figure then the effect is as expected, i.e., higher ventilation rates. The reason behind these observations is that although air recirculation has the ability to disperse indoor pollutants, it also has the capacity to reduce indoor air concentrations of pollutants near the sources (Graudenz et al 2005). Recirculation of air also has the ability to filter particular concentrations. This is why recirculation of indoor air creates certain benefits and risks too (Morawska et al 2009, Pui et al 2008).
The importance of having natural ventilation system cannot be underestimated in indoor environments. Zweers et al (1992) realised that many workplaces had greater numbers of noise complaints, temperature complaints and skin complaints when they had sealed windows. The opposite was true for places that had windows that could open.
Bjorkroth et al (1998) wanted to find out whether HVAC components and ducts have the ability to emit chemicals and other sensory emissions. They did this study through the use of microbial and chemical measures; they also utilised a trained sensory panel. In the analysis, they found that almost all parts of the HVAC were considered to be sources of pollution. However, used filter fibres were found to be the worst cases. Some surfaces in the HVAC were dusty, oily and dirty. This caused them to produce a lot of contaminants (Mossolly et al 2008). Even increasing the airflow did not in any way contribute to the improvement of these contaminants. This study therefore proves that HVACs can be serious sources of pollution of the indoor air environment.
Sometimes used filters can be sources of pollution. Hitchcock et al (2006) wanted to find out how susceptible HVAC air filters were to fungal colonisation. They got new and used air filers, and treated them with antimicrobials. However, some were left untreated. They were all suspended in an area with high levels of humidity. It was found that fungal colonisation of the untreated filters was significantly higher and faster than in the treated ones.
Shea et al (2005) carried out an analysis of how the HVAC systems can exacerbate the level of VOCs in an office building. They found that if a VOC source was somewhere near the building, the HVAC source could distribute the contaminant into the workplace though the internal air flow patterns. Their study also wanted to show how HVACs led to increased vapour intrusions. It was found that the presence of air exchange gradients and air pressure differences contributed to a greater level of vapour intrusion and this affected the indoor air quality.
In section 1, it was explained that HVAC s affect indoor air quality through a myriad of avenues. They cause recirculation of air which minimises ventilation rates. They have limited ways of controlling contaminants and thus cause the indoor air environment to have pollutants. They may sometimes be associated with bad outdoor air supply and this leads to the spread of contaminants in the indoor air environment. HVAC systems also facilitate pollutant transfer through air streams. Alternatively, they cause excessive humidification if that component of the system has operational challenges. Excessive humidity also leads to growth of microbes. Generally speaking, it was found that poorly functioning or poorly maintained HVACs can lead to thermal discomfort, excessive humidity, poor ventilation rates and prevalence of microbes. These may lead to the development of SBS, lower work productivity, worker discomfort and Multiple Chemical Sensitivity (MCS).
It was also found that three major factors may contribute towards low indoor air quality and these include: A HVAC system that is contaminated (through dust, VOCs and other particles), and this ends up contaminating the air that is flowing through the HVAC. Alternatively, the system may be okay, but it could be the air that is being drawn through it. The air is normally contaminated through a wide range of outdoor sources. Lastly, it may be a HVAC system that keeps re-circulating indoor air; that is, providing a mixture of outdoor air and return air. This may contribute towards the spread of contaminants throughout the building and may eventually compromise the health of workers in the building.
In section 2, it was stated that air filters ought to be selected on the basis of their ability to protect the HVAC system as well as the indoor environment. An analysis of some case studies was carried out. It was found that most of these prevalence rates for SBS symptoms were much higher in air conditioning HVAC systems (without or with humidification) compared to those workplaces that used natural ventilations. For HVAC system with humidification, it was difficult to assess whether they had an actual effect on SBS symptom prevalence. The reasons identified for the existence of greater SBS symptoms in air conditioned HVAC systems and mechanically ventilated ones included: the inadequate maintenance, operation, design and construction of the system. In the case studies, it was also found that HVACs are problematic because they cause recirculation of air. They also increase the quantity of VOCs in the indoor air environment. HVACs increase fungal colonisation, reduce ventilation rates and can emit chemical pollutants.
Maintenance was found to be an important component of proper HVAC performance because it allows one to detect temperature control issues, blockages, water spillages, poor planning capacity and many other components that may not be working well. Lack of proper maintenance leads to poor temperature control, poor ventilation rates and even poor humidification levels.
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