Relative Humidity at School
IAQ In Schools
Nearly 56 million people in the United States spend their days in elementary and secondary schools. According to the Department of Education’s National Center for Education Statistics, in 1999, 43 percent of America’s public schools — about 33,800 — reported at least one unsatisfactory environmental condition (i.e., lighting, heating, ventilation, indoor air quality, acoustics or noise control, or physical security of the building). Approximately 25 percent of public schools reported that ventilation was unsatisfactory, while indoor air quality (IAQ) was reported to be unsatisfactory in about twenty percent of schools. Poor indoor air quality can impact the comfort and health of students and staff, which in turn can affect concentration, attendance, and student performance. Schools that fail to respond promptly and effectively to poor IAQ run the risk of increased short-term health problems, such as fatigue and nausea, as well as long-term health problems like asthma. In serious cases, schools have been shut down and have had to move staff and students to temporary facilities. Delaying remediation of IAQ problems can also be costly and may even lead to liability claims and lawsuits that can damage a school’s reputation. Clearly, IAQ issues are best addressed early and better still proactively.
Indoor mold problems have resulted in school closings and multi-million dollar renovations. School districts and administrators have to deal with the mold panic fueled by these closings and the media coverage. Mold contamination in schools is a serious problem that will affect sensitive teachers and children. Preventing mold problems does not require completely redesigned HVAC systems costing tremendous amounts to install and operate. There are affordable, practical solutions that will eliminate mold growth in schools and avoid the costly mold remediation and mitigation measures necessary after widespread contamination has occurred. For more information, see Mold In Schools.
Mold Spores Only Need Food and Water to Grow
Molds feed on organic materials. The drywall paper, books, wallpaper and paste, wood, paper, some paints and dirt are all a food source for mold. You cannot eliminate the food source for mold. Molds do not require liquid water to grow. They only require humidity levels from 65 to 99 percent at the surface on which they grow. If you control the humidity, you can eliminate mold growth. Building defects like roof leaks or ruptured pipes are commonly assumed to be the moisture source if mold problems are encountered in a school. The truth is that fresh air ventilation is the largest moisture source in a school. The volume of water brought into a building through ventilation is sufficient to sustain mold growth. This humidity also prevents the occasional wetting from roof leaks or other defects to properly dry. This leads to the mistaken belief that simply fixing the defects will fix the mold problem.
Ventilation: You Can’t Live With It, You Can’t Live Without It
Ventilation is the largest moisture source in schools. At the ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers) recommended ventilation rate of 15 cfm per person, nearly 2 gallons of water per hour will be brought into a classroom maintained at 75°F and 50% relative humidity. Multiply that by the number of classrooms and you can easily reach 100 gallons per day. The cost of an HVAC system designed to handle this volume of moisture is tremendous and the operating expense is astronomical. The chart below illustrates the impact of ventilation on typical classrooms. Two classrooms are represented. Both classrooms are air conditioned and ventilated during school hours. The relative humidity in both classrooms rises dramatically throughout this period. After school hours and during the weekend, the relative humidity in the classroom without mold control remains in the range where mold growth can be expected. A week of vacation, or a few days of rain will amplify the mold growth.
Any events that add humidity to this precarious condition will intensify and expand the mold problem. The classroom with mold control contains a single Santa Fe Rx dehumidifier. Overnight and on weekends, this unit dries the classroom and keeps the relative humidity in the range that prevents the growth of mold. During school holidays and vacations the threat of mold growth is eliminated and occasional dampening from building defects, pipe leaks, or cleaning can be dried. It is easy to see that instead of investing in an elaborate, energy hungry HVAC system designed to try to control the humidity during the school day, it is far more sensible to control the humidity after school hours with an energy efficient unit that costs only about a dollar a day to operate.