**3. Traditional types of household air filters**

Humans consume approximately 30 liters of oxygen per hour. Hence, our requirement for air is relatively small: 0.15 m3 /h. However, because we also produce carbon dioxide, our bodies require approximately 5 m3 /h of fresh air in order to maintain carbon dioxide concentrations below life-threatening levels. When installing an air-conditioning system, it is advisable to determine the amount of air needed, and this will generally be set at between 15 and 20 m3 per individual per hour. However, larger volumes of air might be necessary for managing temperature or drawing off polluted air.

Ensuring that air is free of dust and aerosols is not only important for maintaining buildings and their interior but also essential for maintaining the health and well-being of the human inhabitants.

This may be due to the higher foot traffic during business hours. The air output of these places is relatively high, and the cleaning of air-conditioning units may prove difficult, which could favor microbial growth and increased accumulation of dust on filters and in ducts. With respect to building contamination, it has been found that hospitals tend to have higher levels of contamination than other types of building examined. Given that hospitals are permanently inhabited by patients, this accordingly increases the potential for contamination and possibly infection by opportunistic pathogens [18, 19].

Al-Abdalall and Al-Abkari [20] examined the most commonly used filters incorporated in air-conditioning systems, namely, sponge, polyester, and HEPA, in order to assess the efficiency with which these filters can prevent the passage of fungi and bacteria. They accordingly found that complex filters were the most efficient in terms of purifying air, with efficiency rates up to 91.8% for bacteria and 100% for fungi. Sponge filters were deemed to be the least efficient filters, with estimated filtration rates of 2 and 50% for bacteria and fungi, respectively. This difference can probably be explained in terms of the passage of air through filters, with filters containing smaller pores being able to trap the larger cells of bacteria or fungi more efficiently. In other words, sponge filters are less efficient for air purification due to the large filter pores, whereas the filters of HVAC systems are able to capture particles smaller than 0.5 microns and prevent all particles with sizes greater than 3 microns from passing through [21].

In this regard, there are a number misconceptions concerning the relationship between filter efficiency and particle size, and in order to resolve this issue, a number of companies have developed certain filter-related standards based on particle counts at the most penetrating particle size (MPPS). The European Standard applies to HEPA ULPA filters used in the field of ventilation and for technical processes (e.g., for clean room technology or applications in the nuclear and pharmaceutical industries).

**185**

**Table 1.**

*Particle size ranges of Standard 52.2.*

*Impact of Air-Conditioning Filters on Microbial Growth and Indoor Air Pollution*

Many indoor air quality problems can be solved or avoided by cleaning or replacing air filters on a regular basis. Since using air filters is one of the most common methods of purifying air, it is recommended that filters be checked at 3-month intervals or that arrangements are made for a certified technician to change the

Filters tend to become clogged, and once their holding capacity has been reached, particulate matter tends to be released downstream in the system and into the heat exchanger and can thereby cover the interior of the ductwork and the blower motor. This matter can subsequently cause problems and malfunctions in the mechanical and electrical parts of the system, resulting in high repair costs and even the need for replacement. The dispersed matter will circulate back into the house, potentially resulting in the proliferation of molds and other fungi. Dirty filters can also have a detrimental effect on energy consumptions due to impeded

According to the American Society of Heating, Refrigerating, and Air-

**Range Size (microns)** 1 0.3–0.4 2 0.4–0.55 3 0.55–0.7 4 0.7–1.00 1.00–1.30 1.30–1.60 1.60–2.20 2.20–3.00 3.00–4.00 4.00–5.00 5.00–7.00 7.00–10.00

Conditioning Engineers (ASHRAE) Standard 52.2-2007 [22], the performance of an air filter is determined by measuring the particle counts on both the upstream and the downstream sides of the air filter device being tested. Through provided capture efficiency values for a range of particle sizes, it facilitates the selection of a filter that has the best efficiency with regard to removal of the target contaminant. To simplify filter selection, the Standard defines a minimum efficiency reporting value. The MERV is a single number that simplifies the filter selection process by providing the specifier, or the user, with a single value of specification for filter selection. For most filters with mechanical-based filter operation, this number will most probably be a minimum value at installation and throughout the life of the filter. The particle size ranges specified by Standard 52.2 and an illustration of how to read an ASHRAE 52.2- 2007 [22] test report are shown in **Tables 1** and **2** and **Figure 5**, respectively (**Figure 7**).

*DOI: http://dx.doi.org/10.5772/intechopen.88548*

filter at the beginning of each season.

airflow, resulting in an increased in fan runtime.

**4. Types of most common HVAC filters**

**4.1 Minimum efficiency reporting value (MERV)**

*Impact of Air-Conditioning Filters on Microbial Growth and Indoor Air Pollution DOI: http://dx.doi.org/10.5772/intechopen.88548*

Many indoor air quality problems can be solved or avoided by cleaning or replacing air filters on a regular basis. Since using air filters is one of the most common methods of purifying air, it is recommended that filters be checked at 3-month intervals or that arrangements are made for a certified technician to change the filter at the beginning of each season.

Filters tend to become clogged, and once their holding capacity has been reached, particulate matter tends to be released downstream in the system and into the heat exchanger and can thereby cover the interior of the ductwork and the blower motor. This matter can subsequently cause problems and malfunctions in the mechanical and electrical parts of the system, resulting in high repair costs and even the need for replacement. The dispersed matter will circulate back into the house, potentially resulting in the proliferation of molds and other fungi. Dirty filters can also have a detrimental effect on energy consumptions due to impeded airflow, resulting in an increased in fan runtime.
