Posts Tagged ‘Air Conditioning System Installation’

Indoor air quality (IAQ)

Friday, December 2nd, 2011

Indoor air quality (IAQ) is an hvac industry term to define the characteristics of a comfortable home. For maximum comfort, three factors must be taken into account. They are temperature, humidity level, and the cleanliness of the air.

The temperature is maintained at a comfortable level by the home’s hvac system. It is easily adjusted at your thermostat.


Humidity level is a measure of the amount of water vapor in the air and is usually stated as a percentage. This is normally expressed as relative humidity which is a comparison of the actual water vapor in the air to the total amount the air can hold. As a general rule, warmer air has a higher capacity to hold water vapor than colder air.

There are several sources of water vapor in a home. These include baths/showers, clothes dryers, cooking, and people breathing. The average family of four puts about three gallons of water into the air of the home each day.

In the colder months, the home’s humidity level can go down due to the fact that the colder air outside cannot hold as much moisture. Air normally moves in and out of the home. The amount of this movement varies a lot depending on how the home is constructed. As the warm moist air exits the home, the cold dry air from outside replaces it. This results in a drop in the relative humidity of the home.

The recommended indoor relative humidity level is based on the outdoor air temperature. It is designed to provide the most comfort as well as to avoid condensation on the home’s windows and other surfaces. That condensation can cause damage to the wood materials in the home. The following chart shows the recommended relative humidity in the home for a given outdoor air temperature.

OUTSIDE AIR TEMP———-RECOMMENDED RELATIVE HUMIDITY

+40 F————————-45%

+30 F————————-40%

+20 F————————-35%

+10 F————————-30%

0 F—————————25%

-10 F————————-20%

-20 F————————-15%

At levels above 50%, microbial growth such as mold is possible. This can have an adverse impact on the health of family members due to the release of spores. The best way to avoid mold is to remove the moisture.

A dehumidifier is required to do this in certain conditions, such as a basement. A properly designed air conditioning system should maintain proper humidity levels during warmer months.

Our mold removal guide will help you to eliminate the problem after you find and fix the source of moisture.

If the home’s humidity level becomes less than 30%, eye, nose, and throat irritation can occur. Another indication of low humidity level is usually the presence of static electricity. The remedy for low humidity levels is a device called a humidifier.


The final part of indoor air quality is concerned with the amount of pollutants in the air. When we think of pollutants, the image of factories spewing things into the air come to mind. In many cases, the air in the home can be more polluted than the outside air.

These pollutants are particles, chemicals, and even tiny organisms. The effects of these things can be classified as SICK BUILDING SYNDROME (SBS). SBS is a condition where adverse health effects can be attributed to time spent in a certain building. These effects usually subside after leaving the building. Normally, no specific illness or cause can be found.

The effects can include eye, nose, and throat irritation. Some of the pollutants can lead to allergic reactions, headaches, and various cancers. Other unexplained symptoms can include difficulty in concentrating, fatigue, and sensitivity to odors.


Radon is one of the pollutants that affects the indoor air quality of most homes. It is a radioactive gas that is produced by the decay of uranium. Uranium is present in all soils and rocks but the amount varies from area to area.

Normal outside air contains about .4 piCi/l of this gas. The average indoor level is 1.3 piCi/l. If your homes’ level is above 4 piCi/l, it is recommended that you take action to lower the level.

It is a simple do-it-yourself matter to test your home. A kit called an alpha track detector is used. These are very inexpensive and contain instructions to use them.

This gas can enter your home through cracks and other openings in your foundation. A basements’ sump is another common entry point. The gas can make its’ way up through your crawlspace as well.

Methods of lowering the level include sealing those cracks and other openings. A vent system, called a soil suction radon reduction system, can be installed by a licensed contractor. Proper hvac system design can also help by bringing in fresh air which will dilute the concentration of the radon as well as promote overall indoor air quality.


Indoor air quality is affected by another common class of pollutants called volatile organic compounds. These are chemicals that are released from products in a process called out-gassing. Some sources of these chemicals include paints, cleaning supplies, building materials, and even the furniture.

Have you ever noticed that “new home smell”? A lot of that smell comes from these pollutants. One of the leading compounds is formaldehyde which is present in certain glues and especially in pressed wood products.

The concentration of these chemicals tends to decrease with product age.


There are three approaches to improving indoor air quality. They are source control, improved ventilation, and air cleaning or ultraviolet air purification.


Source control is usually the easiest, most effective, and least expensive method of promoting good indoor air quality.

This includes minimizing the use of household chemicals. Also, limiting smoking or the use of unvented appliances can make a big impact. The choice of materials in building products can be a big factor.


The next method, of improving indoor air quality, is improved ventilation. This is a process of replacing a portion of the home’s inside air with fresh air from outside. This dilutes the concentration of pollutants in the home’s air.

The uncontrolled exchange of air between the inside and the outside of the home is called infiltration. In older homes, this infiltration was sufficient to maintain healthy air inside but heating and cooling bills were higher because of it.

Modern home building practices minimize this infiltration and therefore concentrations of pollutants can build up over time. The earliest solution to this problem was to leave a window open slightly to allow fresh air in. Today, that is not a practical solution from a security standpoint.

The easiest and least expensive way to accomplish this is by installing and using bath fans and range hoods. The most advanced bath fans include timed controls which automatically start the unit. This ensures that units run for a sufficient length of time each day. These things can usually be purchased and installed by the average homeowner. These fans will remove the pollutants and excess moisture as they are introduced. At the same time a fresh air duct is connected to the existing hvac duct system. The main drawback to this method is that the air brought in must be conditioned.

The other way of introducing this air is through a device called an energy recovery ventilator. These units use the air that is being removed from the home, to condition the incoming air. This saves energy and lowers the impact on the utility bill while still improving the indoor air quality.


The last approach, to improving indoor air quality, is air cleaning. This is accomplished by mechanical filters, electronic air cleaners, or ion generators.

Mechanical filters can be installed in the central hvac system. These are usually made of activated charcoal. This is effective at removing chemicals but they are expensive and must be periodically replaced.

Electronic air cleaners remove very small particles. Some are portable while others are added to the central ac system. These units work by drawing air through an electric field. This field charges the particles then collects them on a screen with an opposite electrical charge.

Ion generators are devices that produce ozone. These devices are usually portable and expensive. This is simply an oxygen molecule with an extra oxygen attached. We won’t go in depth, but basically this extra oxygen separates and attaches itself to things in the home. Then it attracts the chemicals, dust, etc. removing them from the air. There may be some health effects from this ozone (research is being done).

Air purifiers is a common term for these units.

Source: http://www.hvac-for-beginners.com/indoor-air-quality.html