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

*Low-temperature Technologies*

**Figure 6.**

*weak electrostatic force.*

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

duce carbon dioxide, our bodies require approximately 5 m3

needed, and this will generally be set at between 15 and 20 m3

requirement for air is relatively small: 0.15 m3

or drawing off polluted air.

well-being of the human inhabitants.

opportunistic pathogens [18, 19].

microns from passing through [21].

Humans consume approximately 30 liters of oxygen per hour. Hence, our

*Model of electrostatic attraction mechanism, depends on charging the fiber to retain the small particles by a* 

to maintain carbon dioxide concentrations below life-threatening levels. When installing an air-conditioning system, it is advisable to determine the amount of air

hour. However, larger volumes of air might be necessary for managing temperature

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

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

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

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).

/h. However, because we also pro-

/h of fresh air in order

per individual per

**184**

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

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


**Table 1.** *Particle size ranges of Standard 52.2.*


#### **Table 2.**

*Particle size ranges of common pollutants specified by Standard 52.2.*

**Figure 7.**

*How to read an ASHRAE 52.2-2007 test report.*

Unfortunately, filters that use the principle of electrostatic attraction can "fool" the test by providing a high MERV during tests. However, due to the loss of electrostatic attraction during operation, a much lower value is obtained during application. Hence, the user may not be getting the particle removal efficiency that they originally specified.

Multiple studies have shown that coarse-fiber media (charged synthetic media), unlike fine-fiber media (fiberglass media), perform differently in real-life applications. Coarse-fiber media depends on an electrostatic charge to achieve the published filter efficiency. When atmospheric air, in which 99% of the particulate matter less than 1.0 micron in size, passes through a filter, the very fine particulate matter will dissipate the charge, and the filter rapidly loses efficiency.

Qian [23] isolated Streptophyta from dust samples collected from the filters of air-conditioning systems at a rate of 45%, whereas the rate in the indoor air was found to be only 2.4%, which provides an indication of the efficiency of HVAC filter systems (preventing particles sizes that are larger than 3 μm).

**187**

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

The main advantage of fiberglass filters is they are very cheap, easy to install, and readily available in stores. Accordingly, although they have a lifespan of only 1 month, replacing them on a monthly basis would not pose an inordinate financial burden. Unfortunately, they are not particularly effective in terms of trapping particles.

These filters are more effective with regard to trapping dust than fiberglass filters. They can trap approximately 45% of airborne debris. Their MERV rating typically lies somewhere between 10 and 13. They also have a 1-month lifespan but

These filters use electricity to attract charged particles, which are trapped internally. They are very efficient at trapping dust particles and debris and have a

They are the most economical type of filter, which can be removed and cleaned as directed, dried, and then reinstalled. Furthermore, they do not need replacing at monthly intervals. These filters can prevent the passage of debris and tend to func-

These filters comprise a cardboard frame and filter material. As their name

HEPA filters are considered the best type of filter because they trap even the smallest particles and keep premises smelling fresh. They can capture up to 97% of

The type of air filter is the first factor people take into consideration before

Air filters and electrostatic filter cleaners are typically rated according to the minimum efficiency reporting value, commonly known as the MERV rating. The MERV scale is a measurement scale developed in 1987 by ASHRAE to rate the effectiveness of air filters, which determines efficiency in terms of the size of particle that the filter will capture. Values vary from 1 to 16, with a higher number indicat-

Recently, UV lights have been widely employed in the ducts of HVAC filtration

systems. These lights facilitate effective and inexpensive control and solve the

tion better when dirty. However, they have a MERV rating of only 1–4.

implies, it is necessary to replace them when they become dirty.

all particulate matter and remove all allergens from indoor air.

ing the greater efficiency of the filter in trapping airborne particles.

**5.1 UV lights and filtration systems for cleaner indoor air**

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

tend to be more expensive than fiberglass filters.

*4.2.1 Flat fiberglass filters*

*4.2.2 Pleated filters*

6-month lifespan.

*4.2.4 Washable filters*

*4.2.5 Disposable filters*

*4.2.6 HEPA filters*

**5. Modern HVAC filters**

deciding on which air purifier to purchase.

*4.2.3 Electrostatic air filters*
