2.4. Operativización del modelo desde la Ecológica interna y
2.4.5. Los Marcadores de salud
There are three key strategies that occupants can adopt to improve the indoor air quality of their homes. They are: Eliminating the source, Ventilation and Filtration. There is possibly a fourth strategy, which is Moisture control. It is important to note that all four strategies must be employed to achieve the best indoor air quality possible (Waterfurnace, 2016). Using only
one or two methods is generally insufficient. Bluepoint Environment (BE) (2016) also outline similar solutions to reduce indoor air pollution. However, there are no clear established standards and regulation stating to what proportion should these strategies be used on different types of buildings. That is, to know the appropriate balance in the use of each one of the strategies. “Therefore, there is the need for the establishment of criteria to select on which strategy shall the priority be put on” (EC, 2003).
Eliminate the Sources – The general consensus is that the most effective strategy for reducing indoor air pollution is to eliminate or reduce the sources of contaminants such as radon, smoke, CO2 and other volatile organic compounds and particulate matter (EC, 2003). Reducing, and/or removing the source of the indoor air pollution in households cannot be overemphasized. With the exception of off-gassing of new building materials, sources of indoor air contaminants can usually be controlled or managed by the homeowner. These include proper use of bathroom and kitchen exhaust fans, discontinuing indoor tobacco smoking, proper ventilation of gas stoves and furnaces, proper storage of cleaning supplies, fuels and chemicals, adequate cleaning procedures including the indoor air conditioning coil and duct system, and removal of contaminated carpet, wall, or even ventilation (HVAC) system (Waterfurnace, 2016). The need to smoke outside cannot be overemphasized. There are an endless list of contaminants and resulting adverse health effects caused by smoking. IAQ can also be improved by not spraying combustible products indoors or near ventilation units. This can cause rapid spread of contaminants and fire through the ventilation systems. Another strategy is to maintain clean roof, gutters, and storm drainage (BE, 2016).To prevent water leaks, and moisture build-ups in the home, basement, etc. thereby eliminating the sources where pollutants and allergens can develop.
However, the European Commission states that source control at all levels means much more than what was outlined above. It implies essentially, a basic attitude in tune with the concept of sustainability, which shall influence the whole urban design process. Therefore, they have proposed three criteria in which designers and mechanical engineers can refer to in order to achieve sustainability when designing for indoor air quality. It states:
“Source control shall be an objective:
in the urban design of the city itself, be it a new quarter or a retrofitting project, in order to reduce the needs for energy and, for instance, to facilitate the aeration of the building and surroundings;
in the design of the building itself at every single decision regarding the space distribution and orientation, the use of materials and its needs for energy; and
in the selection of all building products in tune with the specific requirements of the Construction Products Directive 89/106.”
Ventilate the Space — Ensuring proper ventilation is one of the most effective ways of keeping the indoor air clean. Effective ventilation increases the amount of clean outdoor air, removes pollutants through filtration and helps reduce the build-up of excessive moisture. Once the sources to pollution have been removed, the air must be cleaned and circulated with natural outdoor air. The concentrations of indoor air pollutants are dramatically reduced when they are mixed with fresh outdoor air. Increase the amount of outdoor, natural air coming indoors. Open windows, doors, turn on fans in windows, attics, crawl spaces, turn on kitchen and bathroom exhaust fans, and air conditioning units with vent open (BE, 2016). Make sure that fuel burning furnaces, fireplaces, heaters, range tops, exhaust fans and other appliances are vented to the outside well away from windows and heating ventilation and air conditioning (HVAC) intakes. Although ventilation can be achieved by simply opening a window, the air coming inside is unfiltered, and enters the home at a generally higher or lower temperature than the indoor air, causing additional heating or cooling requirements (Waterfurnace, 2016).
Ventilation rate is one of the key performance issues that have to be factored in when designing a HVAC system. The performance is based on the ability of the system to be able to handle or the pollution load of the spaces and also the capability of the ventilation air to dilute the pollution in the rooms. Mechanical ventilation in not the only way to ventilate spaces or rooms in a building. Natural ventilation is another to effectively ventilate buildings provided that the outdoor air is certified to be clean enough to be used fro the purpose of indoor ventilation. Better, yet, a combination of the two that is a hybrid form of ventilation is rather the best way to ventilate buildings now. Good ventilating of building spaces using natural means lies on well-defined and controlled dimension of the building openings, location and conditions of operation, which are incorporated in the building design.
Ventilation in and of itself does not affect residents’ health. What does though is the amount of pollutants that is subject to the rate of ventilation. A ventilation rate below 10L/s per person means the rate of ventilation is insufficient to dilute the amount of pollutants in the room, which in turn causes increase in health issues of residents. On the other hand, a
ventilation rate of up to 20L/s per person removes or greatly reduces the health effects associated with poor indoor air quality (EC, 2003). The European commission has a given formula in which to calculate indoor concentration, in which ventilation/flow rate, air concentration, pollutant generation rate, and pollutant removal rate are all considered. The formula is given as:
C
in=C
s+[(S/V
)/
(λ
v+Σλ
other)]Where:
C
in = the indoor concentration,C
s = the concentration in the air entering the space,S/V
= the indoor pollutant generation rate per unit air volume,λ
v = the ventilation rate equal to outside air flow rate divided by indoor volume,Σλ
other = the sum of all other indoor pollutant removal rates.In practice, all four variables are not constant and may be had to measure. Therefore, a further explanation on the formula is given below.
“In practice, the situation is not as simple as suggested by the equation. The indoor pollutant emission rate (source strength) is usually not well known and not even constant. Indoor pollutant source strengths are highly variable among buildings, and considered the biggest cause of the variation in pollutant concentrations among buildings. Pollutants may be adsorbed by room surfaces during high concentration periods and desorbed again into the air during low concentration periods.
In many buildings, ventilation rates are not constant. For example, ventilation systems may not operate at night, and during operation rates of ventilation may change with internal heat loads or with outdoor air temperature. Pollutant concentrations may not reach equilibrium until several hours after ventilation rates stabilize. Thus, the indoor air quality is also dependent on operation schedule of the ventilation system. Additionally, the concentration of pollutants in the air entering the space is affected by five major factors: (1) the level of pollutants outdoors; (2) possible recirculation of return air; (3) the location of outdoor intake relative to outdoor air pollution sources; (4) pollution sources in the air handling
system; and (5) pollutant removal from supply air by filters, sorbents, or deposition on duct surfaces.
The quality of the outdoor air has a significant effect on the cleaning capacity of ventilation air and should be taken in consideration while designing the ventilation. The air quality may vary depending on the time of the day in urban areas, for example the pollution from traffic is usually higher in the daytime as pollution from industrial sources and energy production is more constant over the time. The ventilation rates should reflect this variation.”
Filter the Air — Another way of improving indoor air quality is through cleaning the air. That is, removing particles and/or gasses in the air. The most common method of cleaning is through filtration or through using filters. Proper filtration/cleaning using high efficiency filters (unlike the common, inexpensive filters found in hardware stores) is a key strategy to improve air quality. Forced air heating and cooling systems move air within the home constantly during operation. Homeowners who neglect to change or clean the system’s filter subject themselves to higher levels of indoor airborne particles, along with higher heating and cooling costs (Waterfurnace, 2016). There is the controversy on the effective and efficiency of air filters to actually remove particles and gasses from the indoor air because filters vary in quality so much. some filters are even feared to be made of pollutant emitting materials. There is also some controversy about the efficiency of filters in particular in what regards the potential for incubating microorganisms and emitting smelling odours.
The United States Environmental Protection Agency (USEPA) provides a comprehensive list of air cleaners ranging from small table-top versions to sophisticated whole-house models. Occupants can further enhance the IAQ of their homes by replacing old filters. Old filters in heating, air conditioning, and ventilation units (HVAC), can be a major cause of indoor air pollution, and must be monitored, and replaced if necessary (BE, 2016). However, the European Commission states that the availability of different options regarding filters emphasize the need to establish a set of criteria and rules on how to select and size the appropriate filter for each specific service.
Today, many houses are designed to keep fresh air out. Therefore, the law requires many buildings, to have mechanical devices that have a positive impact on the air in the home.
Such devices, technologies or systems used to improve air in homes concentrate on two key strategies – ventilation and filtration. These include heat recovery ventilators, super-efficient HEPA filters and a variety of other high efficiency air cleaners and filters (Waterfurnace, 2016). Examples of such technologies are: Heat Recovery Ventilators (HRV), MERV 11 Disposable Filters, HEPA Filters, Electrostatic Air Filters, and Electronic Air Cleaners.
Heat Recovery Ventilators (HRVs): are designed with an air circulatory function that moves stale contaminated air from inside the home, baths and kitchens, to the outdoors, whilst, drawing fresh, oxygen-rich air form the outside, filters it and delivers it throughout the home. This action constantly replenishes the polluted air with an equal amount of clean and fresh air, thereby, providing a balanced system. In order for the new, fresh, and clean air to have the same temperature as the air inside the home, HRVs are built with an aluminium heat exchange core that transfers the heat from the air exiting the home to the fresh air coming in. This is possible because the two air streams i.e. the stale polluted air and the clean fresh air pass each other through the HRV, and are separated by the aluminium core which enables the heat transfer. It is important to note that the two streams pass each other but they do not mix. The effect happens during cooling, and its efficiency is certified 83% (Waterfurnace, 2016). HRVs can be connected to bathroom and kitchen fans.
HEPA Filters: On the other hand, HEPA filters are designed to provide the best filtration possible. It currently is the best choice with regards to filtration. It uses a technology that targets very small particles that particularly find it easy to pass through other filters. HEPA’s filters are 99.9% efficient for particle sizes 0.30 microns and larger (Waterfurnace, 2016).
Minimum Efficiency Reporting Value (MERV) 11 Disposable Filters: This is another filter that’s sold on its ability to trap particles ranging in size from 0.3 to 10.0 microns from the indoor air. These include pollens, mold spores, dust, fungal spores, and pet dander. MERV 11 is currently the best MERV filter among the range. Other filters such as MERV 4 and so on are less efficient - the higher the MERV rating, the more efficient the filter (Waterfurnace, 2016).
Electrostatic Air and Electronic Air Filters: these filters on the other hand use electrical magnetic charges/field generated from polypropylene filtration media and/or non-ionizing polarized media to arrest dusts, pollens, and molds particles. Electrostatic Air filters are 90%
efficient while Electronic Air Filters has a 97% efficiency rating to capture particles of 0.30 microns and above.
Table 2.8: Common Indoor Pollutant
Common Indoor Pollutant Typical Particle Size (microns)
Pollen, mold, plant spores 7-70
La rge r Dust mites 3-10 Hairspray 3-10 Large bacteria 1-20 Auto emissions 1-3 Lead dust 1-3 Fungal spores 0.50-7 Cooking smoke/odors 0.30-1 Paint pigments 0.30-1 Dust 0.20-8 Pet dander 0.15-8 Small bacteria 0.08-1 Tobacco 0.008-0.6 S maller Viruses 0.005-0.01
Volatile organic compounds Less than 0.001
Source: Waterfurnace (2016)
Control Moisture – The simple fact is that mould needs moisture to live. Control moisture and control mould. Greenguard is an organisation responsible for certifying products and materials, and helps buyers identify and trust--interior products and materials that have low chemical emissions, improving the quality of the air in which the products are used. They state that the following can help occupants keep moisture out of their living spaces: keep homes dry using dehumidifiers, take immediate action during floods to clean and dry walls, have exhaust fans in bathrooms, and install filters.