RE: Ventilation and Fresh Air Induction

Dear Website Customer:

"The high temperature today will be 97 degrees, with a heat index right at 104!"

We all talk about the weather. It leads the evening news, makes the cover of the newspaper, chatters over the radio at drive time. The goal of the environmental systems in our home and office building is to tame back the forces of nature and provide a refuge of dry, temperate, clean air in which we can survive more comfortably. Many of our air conditioning systems address the heat or cold, but ignore the dry, fresh, and clean parameters required for true comfort.

"Dry, fresh, and clean" are simple terms to describe the more ambiguous term, "Indoor Air Quality." IAQ is difficult to judge accurately without special instruments. In severe cases, people in poor air quality areas will become more sick more frequently, get headaches, have less energy, and so forth.

One of the many studies done on IAQ issues shows that the majority of the indoor air quality complaints have been classified as ventilation problems. Included in these ventilation complaints were: a shortage of fresh (outdoor) air, drafts, stagnate indoor air, poor temperature control, and inadequate humidity control. In short, more than half of the IAQ problems surveyed were caused by an HVAC system that did not satisfy the basic requirements for comfort air conditioning.

Assuming that the outdoor air is of suitable quality, a continuous supply of fresh air should be flowing throughout a building. This flow is required to dilute the moisture and pollutants that are generated by the occupants and their activities. Outdoor air is also required for fuel burning equipment that draws combustion air from the indoor space. Most important of all, outdoor air is required for the comfort and health of a building’s occupants!

Accepted standards and guidelines furnish a method for estimating how much outdoor air is required and at what rate of exchange. The Dallas City Code requirement for outside air in office buildings is 10% of the air provided by an air conditioning system. For example, a 10-Ton air conditioning and heating unit is designed to flow 4,000 cfm (cubic feet per minute). The proper balance for this unit would be 3,600 cfm return air and 400 cfm outside air.

Now, to bring outside air into a building, inside air must be taken out. In most cases, this ventilation is done naturally through restroom exhaust fans, opening of outside doors, and normal building leakage. Natural ventilation is unpredictable and unreliable, however, Therefore, some type of mechanical ventilation system (supply and exhaust fans) must be utilized if the fresh air requirements aren’t being met. When this is the case, keep in mind that outside air in the summer is hot and the air conditioning system must be designed to handle the additional load of cooling this air for comfort!

If you are interested in more information or have a ventilation problem in your facility, please call me at 631-1010. I’d like to hear from you.

Sincerely,

KAHN MECHANICAL CONTRACTORS

Ann R. Kahn

TACL A370C