School’s Out for Summer
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Crump |
Uncontrolled moisture can trigger mold growth, which damages the facility and indoor materials and can lead to health and productivity problems for students and staff.
The situation is exacerbated when custodial and maintenance departments tackle summertime cleaning and repair projects that they couldn’t conduct with classes in session. Typically, this work includes deep cleaning carpets and stripping and waxing floors, which creates moisture and introduces volatile organic compounds to the indoor air.
With the internal HVAC system off or running intermittently to save on energy costs, custodians must seek alternative ways to cool and ventilate the building. This is often accomplished by opening the facility’s windows and doors to increase airflow. However, in hot and humid conditions, this process introduces additional moisture into the building. Consequently, when the building is closed after work each evening, all of the VOC’s and humidity are trapped in the building.
By adding this moisture, the custodial staff creates an environment that is ripe for mold growth. After several days or weeks of this cycle, a musty odor can appear — a sure sign that mold growth is occurring somewhere.
Another common summer project is bonnet buffing carpets. To accomplish this task, custodial staff floods a floor with water and use a brush to scrub the carpet. The process is then repeated.
The custodial staff will usually ask the school to leave the air conditioning on overnight, thinking that this air will effectively dry the wet carpet and any moisture that was absorbed under the baseboard and into the sheetrock walls. But this method has little effect and can lead to the creation of white or gray spots (mold growth) on the carpet and unpleasant odors.
These are just a couple of examples of problems that occur because of incorrect custodial procedures when the HVAC system is shut down. As a result of inadequate humidity control, physical damage to desks, media centers, ceiling tiles, millwork, hardwood floors in gyms and moldy carpeting have become commonplace at school facilities.
Some school districts have learned that it’s not conducive to turn off the internal HVAC system during the summer because the potential remediation costs and poor indoor air quality outweigh the savings in utility or electricity costs. Many will at least cycle the system on and off to attempt to avoid any issues, but there is a more effective moisture-control solution.
Finding a Substitute
One alternative for school operators to consider is use of an energy-efficient desiccant dehumidification unit packaged with a refrigeration cooling system during the summer months to control humidity. ASHRAE standards suggest maintaining the relative humidity inside the building below 60 percent to prevent mold growth.
Use of a desiccant-based system will accomplish that task and is especially beneficial for schools that don’t have an overhead air conditioning system. Schools that have unit ventilators, for example, may only be receiving sensible cooling and not dropping the dew point inside the facility. If it’s hot and humid outside for a prolonged period, moisture will seep into the building because it seeks equilibrium. In this example, the school is likely to have moisture or mold problems during the summer months.
A humidity control company will deliver the portable units to the site on trailers and work with the school district to set up the equipment near the school’s mechanical room.
Temporary overhead ductwork or lay-flat is utilized to distribute dehumidified and cooled air throughout the structure, precluding any reliance on the HVAC distribution system. The amount of dehumidification and cooling will be determined by a variety of factors but mostly affected by the overall cubic feet of air space that is being controlled.
Studying the Benefits
In addition to comfortable indoor conditions, an energy-efficient cooling and desiccant-dehumidification unit leads to cost savings if the school can provide house power because electricity consumption costs for the units are less than running the school’s in-house equipment.
A typical school air-handling unit is a 60-ton unit that requires 200 to 300 amps of power, which equates to 234 thousand kilowatt-hours of energy. At $.10 a kwh, that would cost $23,400 a year in energy costs for one unit and many schools have more than one unit.
A desiccant dehumidification unit such as the Munters Humidity Control Unit 3000 uses only 32 amps and the HCU 6000 uses just 78 amps. The HCU 6000 replacing the same 60-ton air handler would consume 148,000 kwh and cost $14,800 to operate.
With the rental units in place and operational, school officials can conduct routine school maintenance while also completing maintenance on the internal HVAC system.
Additionally, using rental dehumidifiers with cooling will also increase the longevity of the in-house system due to increased downtime.
A Case Study Lesson
Ronnie Martin, energy manager/ HVAC supervisor for the Texas City Independent School District in Texas, was faced with the challenge of maintaining a temporary climate at three elementary schools to prevent moisture and mold issues while providing a comfortable and productive work environment for staff.
All three schools were equipped with 14-year-old chillers that were running inefficiently. With school out for the summer, maintenance personnel deemed it necessary to replace the 250-ton units with new, more efficient equipment and upgrade the air handlers in the schools for the target cfm.
Removing the chillers, though, would eliminate ambient control and air movement inside the schools for weeks, making conditions ripe for mold formation and the climate unappealing to custodians working the summer shifts. Martin sought a solution that would keep the indoor environment inside the schools at or below 60 percent humidity.
After analyzing the project parameters, Martin partnered with Munters to utilize the company’s HCU to control conditions inside the schools. Two units were placed outside the schools at predetermined locations, and Munters personnel ducted the equipment through temporary access panels provided by the school. Air distribution within the school was delivered via disposable lay-flat ducting to ensure even air distribution.
The units remained in operation for eight weeks, overlapping the installation of the new chillers for a week so school officials could verify that controls on the new chillers were set and the upgrade was successful.
In addition to controlling humidity inside each school, the HCU provided a light cooling load that made the environment more comfortable for the custodians performing remodeling projects and other summer maintenance work. The HCU equipment also saved more than $7,000 in energy in three months of operation.
Stoney Crump is key regional manager for Munters Moisture Control Services, a provider of temporary humidity and temperature control services that specializes in providing rental systems that control humidity in a variety of work environments. He can be reached at (800) 422-6379 or stoney_crump@munters.com.