An education in humidity control
February 1, 2007
In the summer, school is the last thing on many pupils’ minds. But for school officials and teachers, there is still work to be done. It’s the time when teachers prepare for fall and maintenance crews can tackle construction projects such as replacing HVAC equipment.
But in southeastern Texas, those major engineering projects can be a challenge due to the state’s high heat and humidity. HVAC upgrades, such as chiller change-outs, are best done when temperatures are mild and the air is dry. Unfortunately, that’s not always possible in southeastern Texas.
Ronnie Martin, energy manager and HVAC supervisor for the Texas City Independent School District, needed to figure out how to replace aging chillers at three elementary schools in Texas City, Texas.
Northside, Roosevelt-Wilson and Heights Elementary 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 equipment and upgrade the air handlers in the schools.
Removing the chillers, though, would eliminate the ability to control air movement inside the schools for weeks, making conditions ripe for mold and the climate unappealing to custodians working the summer shifts. Of special concern were the school’s libraries, located in the center of each school. These areas would be most susceptible to high humidity that can cause mold and damage the book collections.
Heat and humidity“Fighting humidity is an ongoing battle in Texas City,” said Martin. “It’s not uncommon to have 90-degree temperatures and 90 percent relative humidity. Even during the summer, with very few personnel in the schools, it’s necessary to run the chillers periodically so we can control conditions.”
Martin sought a solution that would keep areas inside the schools at or below 60 percent humidity. He recalled a presentation by Munters Moisture Control Services about the company’s water damage restoration services and contacted the company to determine if they had a solution for his current dilemma.
After analyzing the project, Jeff Bogran, a Munters industrial account manager, suggested Martin use the company’s humidity control unit to handle conditions inside the schools.
Munters officials say the unit combines cooling and desiccant dehumidification in one energy-efficient system to control dew-point temperatures in hot, humid climates. It is ideal for use in structural drying, temporary humidity control in building construction, and condensation and corrosion control in surface preparation and coating applications.
The unit removes humidity with a packaged refrigeration system in conjunction with an active desiccant wheel using titanium and silica gel. The system’s desiccant wheel is regenerated using recycled heat from cooling components.
“Because the HCU utilizes the DX (direct-expansion) coil and the desiccant wheel where they are most efficient, the unit functions with a low specific-heat ratio and very high energy-efficiency rating,” said Bogran. “The waste heat from the condenser coil drives moisture off of the desiccant wheel, so no extra energy needs to be expended for this purpose. This saves energy dollars associated with ventilation and overcooling.”
The control unit is capable of delivering dew points below 45 degrees in even the highest humidity-load conditions and its use can result in as much as 40 percent overall energy savings, while providing comfortable outlet temperature, Bogran added.
A testBogran devised a plan to control the indoor environment by placing an HCU 3000 unit, featuring 2,400- to 3,400 nominal cfm ratings, on each end of the school.
In this design, the units would push dry air from both ends of the school toward the middle of the building, supplying 45-degree dew-point air into the space and providing for a minimum of 0.5 air changes per hour.
Martin approved the plan and Munters Moisture Control Services placed the equipment outside the schools at the pre-determined locations. Munters personnel ducted the equipment through temporary access panels provided by the school. Air distribution within the school was delivered by disposable, lay-flat ductwork.
Bogran strategically placed smaller, portable refrigerant dehumidification units in each of the school’s libraries as an additional precautionary measure to protect the sensitive items in them.
Munters personnel were on site to start and calibrate all of the equipment, and provided equipment operation training.
The units remained 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.
Martin and members of the Texas City Independent School District were pleased.
“I was extremely satisfied with the project results and have even bragged to other personnel in the district about the results,” said Martin. “I recall one particular day when it was 92 degrees outside and 90 percent relative humidity, but inside the schools it was 80 degrees at 40 percent relative humidity.”
Besides controlling humidity inside each school, the units provided a light-cooling load that made the environment more comfortable for the custodians performing remodeling projects and other summer maintenance work.
Martin also learned firsthand about the innovative, energy-efficient design of the Munters unit.
“We only used a 100-amp service for two units to keep the buildings around 80 degrees and around 30 percent humidity,” said Martin. “We may outline this project at a future energy managers meeting to introduce the HCU to our colleagues from around the state of Texas.”
Martin is even pondering permanent installations for use during summers to control humidity and save on energy costs.
“The new chillers require more energy to run - 400 (to) 500 amps with air handlers - whereas two HCU units use 70 amps total,” he said. “If we can keep from running a 250-ton chiller during the summer and run an HCU to keep the school reasonably cool and dry, we definitely will save energy costs.”
This article and its images were supplied by Munters Moisture Control Services.