The School District of Hillsborough County (Tampa, FL) is the ninth-largest district of all 13,500 school dis-tricts in the U.S.

In May 2006, this district commissioned a nationally recognized environment testing laboratory to give us what may be the only certified IAQ test report of this type in the U.S. for public school classrooms. The objective was to determine if reduced fresh air ventilation in public schools can be done while still achieving good IAQ for students, staff, and the public. The report included the classroom air quality in several schools in the district. A free copy of this $100,000 engineering and scientific report is available for the asking.

TABLE 1. Intermittent student occupancy usage factor for the Hillsborough County School District.

Testing Parameters

The eight schools evaluated consisted of offices, conference rooms, classrooms, media centers, gymnasiums, locker rooms, cafeterias, and restrooms. Testing by the laboratory included a visit to the site, a walk-through of the spaces monitored, and continuous monitoring of the carbon dioxide parameters indoors and out-doors.

Technicians placed Telaire Model 7001 monitors at various locations throughout the schools to measure CO2 levels. The monitors were placed in two locations per AHU zone, one at the beginning of the ductwork system and one at the end of the ductwork system. The sampling instruments utilized continuous datalogging capabili-ties and were placed in areas appearing to be typical of building conditions.

ASHRAE has recognized CO2 levels within an occupied space as an indicator of air quality and air exchange rates within a space. When using the air quality approach, ASHRAE 62.1 stipulates that in an effort to ensure adequate ventilation, indoor CO2 levels should not exceed a site-specific value. That value is generally obtained by adding 600 ppm to the average outdoor value. Indoor CO2 concentrations may periodically fluctuate, and attention should focus on responsible factors such as inadequately functionally control equipment, periods of in-creased occupancy, and environmental conditions.

General discomfort, malaise, and increased perception of body odors have been observed when concentrations are greater than 600 ppm above outside concentrations.

Codes throughout the U.S. require 15 cfm of fresh air per student to conform to ASHRAE Standard 62.1. How-ever, a code change (Chapter 423 of the Florida Building Code) was published recently in Florida that states the amount of fresh air can be reduced to 7.5 cfm/student. It was scientifically proved that based on code’s “inter-mittent student occupancy usage factor,” obtaining 7.5 cfm of fresh air will achieve good IAQ, even though 5 cfm/student tested satisfactory.

The “intermittent student occupancy usage factor” for our district is calculated in Table 1.

To ensure that this was a viable code change, three groups of schools were randomly selected and tested. The district chose 15 schools (five1 with 5 cfm/student, five2 with 7.5 cfm/student, and five3 with 15 cfm/student).

TABLE 2. The district’s cooling equipment/systems designed for the two ventilation rates of 15 and 7.5 cfm/student in these schools.

The Results

The results indicated no difference in CO2 levels, occupant acceptability, or absenteeism in any group regardless of whether it was an elementary, middle, or high school and regardless of the socioeconomic student mix. There was no academic difference in the results of standardized Florida Comprehensive Academic Testing (FACT).

Table 2 shows the district’s cooling equipment/systems that were designed, signed, and sealed by four inde-pendent HVAC engineers, required for the two ventilation rates of 15 and 7.5 cfm/student in these schools.

The collective collateral economic and environmental impacts of using 15 cfm/student of fresh air is huge. For example, reducing the amount of fresh air to 7.5 cfm/student reduced the size of the cooling equipment and saved approximately $100,000/school in lower equipment costs. The cost of the energy saved is approximately $10,000/yr/school. Nationally, the approximate construction cost savings would be $1.645 billion/yr, and the approximate energy and maintenance savings would be $329 million/yr.

Unfortunately, the USGBC LEED® program will recognize a new school if it provides 15 cfm/student. Extra credit is allowed if 20 cfm/student is used. This is wrong and needs to be changed. Credits should be allowed when less fresh air is used in a way so the classroom still maintains good IAQ.

Alternate Causes

Our school district has never had an IAQ problem attributable to 5 cfm/student (or 7.5 cfm/student). The IAQ problems that occur are due to either negative building air pressure, leaky roofs, missing vapor barrier, broken chilled water valve, oversized DX equipment, control calibration, leaky windows, dirty filters, or the like. Maintaining a continuous positive pressure in the school is critical for good IAQ, for the life of the school. It is not optional.

There is no need to overventilate any school unless more outdoor air will remedy a building pressurization problem.

Lastly, we chose to not use ventilation/demand limiting because it offers no chiller reduction savings, requires additional automatic control, and involves hundreds of CO2 detector sensors, and as mentioned, we have never had an IAQ problem due to 5 or 7.5 cfm/student.

Additionally, the exhaust systems have to automatically modulate as the fresh air modulates to avoid the dreaded building negative pressure.

This Florida District was recognized by the Association of Energy Engineers in 2009 with the regional (Eastern U.S.) energy award for this accomplishment.

For the sake of the students, staff, and the public, fresh air ventilation requirements in schools should be re-evaluated. ES


1. Burns Middle School opened in 1986; Armwood High School opened in 1984; and Alafia Elementary School opened in 1987.
2. Randall Middle School opened in 2000 and Bevis Elementary School opened in 2000.
3. Mulrennan Middle School opened in 2003; Wharton High School, opened in 1997; and Burnett Middle School opened in 1996.