Reduce High Humidity/IAQ Problems in Below Grade Classrooms

Unless your school is in an arid climate, it’s likely that any below grade classrooms have high humidity/IAQ issues. The EPA says that “the key to mold control is moisture control.” The recommended humidity levels are “ideally 30–50%.” This is difficult for conventional classrooms, and even more of a challenge for below grade.

What exactly is relative humidity?

Relative humidity is a measurement of the amount of moisture the air holds at a given temperature. If the temperature is 77°F and the RH is 60%, this simply means that the 77°F air is 60% full of water. If the air warms, it can hold more water and vice-versa. A 1°F change in temperature change RH by about 2%. With the same actual water content, 78°F air has 58% RH, and 76°F air has 62% RH.

The cool earth surrounding a below-grade classroom means lower temperatures, which makes for higher relative humidity. This higher relative humidity creates and environment ripe for mold growth. It’s why caves are “musty” and it’s why basements “smell like basements.”

To control humidity, moisture must be removed from the air. There are only two strategies to choose from — use an air conditioner with “reheat”, or use a dehumidifier. Reheat is a method of adding heat to an area to make A/C run more.

Air-Conditioner With Reheat: An A/C removes water as a byproduct of cooling the air. Since a below grade room is cooler than above grade room, the A/C runs little, so humidity levels are elevated. “Reheat” adds heat to trigger the A/C unit. This is quite energy-intensive. Electric reheat removes only about 6/10 of a lb. of water per kWh vs. about 5 lbs. of water per kWh for the most efficient dehumidifier.

Dehumidifier: The simplest, most energy-efficient way to control humidity is to shut off the A/C unit and operate a high efficiency, high capacity dehumidifier. Get humidity control even during humid, cooler conditions. During unoccupied times, shut off the A/C and let the temperature rise. The dehumidifiers will handle humidity and you’ll see tremendous energy savings.

Therma-Stor offers schools a free, no obligation demonstration of our dehumidifiers. As part of the demonstration we include data loggers to monitor temperature, RH, and dew point to verify performance. Therma-Stor’s most commonly used units in schools are the self-contained Santa Fe Rx and the ducted Ultra Aire 150H.

Santa Fe Rx: This unit is a powerful, self-contained, portable unit designed specifically to be quiet. Wheel it in, run the hose to a drain (from the built-in condensate pump), and set the dehumidistat. The Santa Fe Rx is Energy Star® rated as the most efficient unit in the industry — using only 5.4 amps and removing up to 74 pints of water per day! It is sized for 2,200 sq. ft. typical and has the option of HEPA and/or charcoal/permanganate air filtration.

Ultra Aire 155H: This is a powerful, energy-efficient ducted dehumidifier. It can typically handle about 3,500 square feet. The unit removes up to 155 pints of water per day but still simply plugs into a standard 115-volt outlet. The 155H also has an optional 95% high-efficiency (MERV 14) filter.