Findings

A key component of the study was to identify the age and number of portable classrooms in use throughout the state’s K-12 school system. The findings revealed that at the end of school year 2001 nearly 30 percent (79,191) of the 268,030 classrooms in California were portables. Of those units, 22, 094 (27.9%) were more than 15 years old; 25,974 (32.8%) were between 6 and 16 years old; and 31,122 (39.3%) were less than 5 years old. In addition, 4,100 new units were expected to be added in the 2002 school year. The study does not reveal how many permanent classrooms were added in 2002.

As part of the study on portable classrooms, Field Technicians inspected the HVAC systems of typically two portable classrooms and one traditional classroom per selected school. Some of the most notable findings were:

? The difference in ventilation air, total supply air and age of the HVAC systems were not significantly different between portable and traditional classrooms.

? HVAC systems in portable classrooms typically had thermostats controlled by teachers.

? A high percentage of teachers (68%) in portables reported turning off their HVAC due to noise.

? The air filters in portable classroom HVAC systems were less likely to be changed than those in traditional classroom HVAC systems.

? Outside air intakes were shut off or otherwise blocked on the HVAC systems more often on portable classrooms than traditional classrooms (10.8% vs 2.7%).

? Both portable and traditional classrooms experienced school-day average concentrations of carbon dioxide (CO2) greater than 1000ppm and one-hour averages over 2000ppm. These results indicate insufficient ventilation in a substantial portion of California classrooms, both traditional and portable.

All classrooms exceeded the new ANSI acoustical standard for classroom noise levels (35dbA) and a substantial percentage of both traditional and portable classrooms exceeded outdoor noise limits, typically 55dbA.

Analysis

The findings of this report suggest that education facility managers and suppliers responsible for providing clean and comfortable classrooms need to rethink HVAC design and operation. Instead of focusing on heating and air conditioning  systems that can also provide ventilation and filtration, perhaps schools and suppliers should be thinking in terms of ventilation and filtration systems that can also heat and cool.

Justification for the need to think in these terms is found in the fact that users of portable and conventional classroom heating and cooling systems do not understand the importance of their systems’ ventilation and filtration capabilities. Most of the HVAC systems examined in this study appeared to be capable of doing the job required of them according to Title 24 requirements, but many were being turned off by teachers who objected to the noise generated by them.

Title 24 code requirements for ventilation stipulate that a classroom be ventilated during all occupied times. It also provides several methods by which you can comply. Continuous ventilation during occupied times is the preferred method for classrooms.

Continuous Ventilation of a classroom requires that 15cfm of outside air per occupant be brought into the classroom. The typical expected occupancy of a classroom is 30 students and 1 teacher; 31 occupants times the 15cfm of outside air per occupant equals 465cfm of outside “ventilation” air. The classroom ventilation system must be set up to provide this level of ventilation during occupancy.

The code requires that the classroom be ventilated prior to expected occupancy in an amount equal to three complete air changes. That amount of ventilation air and time required is calculated by using the following formula:

Step 1: Classroom square footage x Classroom ceiling height     
960 sqft x 8.5 ft = 8,160 cubic ft

Step 2: Multiply Classroom cubic feet x 3 (air changes)
8,160 x 3 = 24,480 cf

Step 3: Divide the sum of Step 2 x 465 cfm 
24,480 cf  / 465 cfm = 52

The answer calculated in Step 3 is how many minutes before expected occupancy we need to begin ventilating the classroom, 52 minutes.

Solutions

At least two companies have partnered with California schools to better understand the acoustic, ventilation and indoor air quality issues that prompted the Portable Classroom Study. These companies used feedback provided by facilities and teaching staff at the various school sites to enhance their product offering for classroom specific use. The following concepts are the direct result of this research:

Since 1992, most of the HVAC systems used on portable classrooms utilized a  set-back type thermostat with a programmable fan setting, in order to meet the California Title 24 energy code requirement. The problem with this type of thermostat is that teachers frequently override the fan program, which turns off the ventilation system. Today there are new thermostats that have a programmable ventilation program and a key-pad lockout feature that prevents system from being shut-off by the occupant. While this product is a great improvement over previous models, teachers continue to complain about noise from the HVAC systems. Some of this noise is from the equipment itself, but primarily it is due to the excessive amount of air or CFM being blown into the  classrooms.

As a result, the obvious question is: “How can ventilation system noise be reduced?” Results from the test classrooms reveal that teachers are happier when they do not hear the HVAC system operating. This suggests that upgrading to new, quieter and more energy-efficient equipment should be seriously considered by each school district. With budget concerns being what they are today, a school district might consider retrofitting existing HVAC systems to two-speed, continuous blower models, if new equipment purchasing is not a possibility. This type of modification can be administered to select brands of portable classroom HVAC systems, and in most cases will reduce air noise significantly. In addition, many of these HVAC systems can be retrofitted in the field with devices to provide the necessary ventilation for the classroom. These products have adjustable settings that are easily accessible and critical to assuring that the correct amount of fresh air passes into the classroom.
 

Conclusion

There is definitely a correlation between learning environments and how well students and teachers function within them. Therefore, it makes good sense that everyone involved in specifying, operating and maintaining HVAC systems understand the importance of proper ventilation and noise reduction. The California Portable Classroom Study findings suggest that correct implementation and operation of these systems would dramatically improve the indoor environment for classroom occupants. In order to accomplish this, suppliers and end users will need to continue to partner, share information, innovate, improve and most importantly, educate those people responsible for controlling classroom environments.

For more information about this paper, Layne Miller can be reached at layne@gearypacific.com or (800) 444-3279 ext. 104.
   

* Report to the California Legislature: Environmental Health Conditions In California’s Portable Classrooms