Moisture in Motion
Moisture is always moving, from areas of high pressure to areas with low pressure. As water vapor accumulates indoors, it becomes essential to remove it. In the past, people have relied on air conditioners, not only to cool the air but to remove moisture indoors. As air conditioners become more energy-efficient the amount of water vapor that enters buildings or is produced by occupants, exceeds the rate that an air conditioner can remove moisture, causing indoor humidity levels to rise (Do HVAC Systems Dehumidify?). A dehumidifier is a helpful solution to condense and withdraw moisture trapped inside.
How much water can a dehumidifier remove?
The answer will vary depending on three variables, (1) the power of the dehumidifier (capacity), (2) the room temperature, and (3) the relative humidity (R.H.) of a room. A dehumidifier rated for 25 pints at AHAM, can only pull 25 pints when the conditions of the room are 80° F and 60% R.H. The amount of moisture a dehumidifier can withdraw from the air will ALWAYS vary as temperature and relative humidity change; the total amount of water vapor that air can hold will change as temperature changes. Warmer air can hold more moisture than cooler air, therefore a colder room with relative humidity below 60% will not hold as much water vapor.
The amount of moisture a dehumidifier can pull from the air is directly impacted by the dehumidifier’s capacity, room temperature, and indoor relative humidity.
The Amount of Water Vapor in the Air Changes
The chart above (Figure 1) represents the amount of moisture/ water vapor in the air at a range of temperatures and varying percentages of relative humidity1&2. The chart shows that warmer air always has more moisture than cooler air. The moisture content of air is much higher at AHAM (80°F/60% R.H.) when the air can hold 22.72 pints of water vapor. If temperature and R.H. are reduced to 70°F and 50% R.H. there is only 13.60 pints of water vapor in the air. Reducing the temperature by only 10° F and the RH by 10% causes the water vapor in the air to decrease by over 9 pints.
Before 2019 most dehumidifiers rated their unit’s capacity at AHAM (80°F/60% R.H) and many portable dehumidifiers measured the capacity at SATURATION (90°F/ 90%R.H.).3 In June of 2019, the Department of Energy (DOE) finalized new energy conservation standards for dehumidifiers. Energy efficiency metrics are now based on Integrated Energy Factor (IEF), which includes the energy the dehumidifier uses when it cycles off to represent more closely “the expected annual energy consumption of dehumidifiers”. The new ENERGY STAR 5.0 testing standard reduces the temperature by 15°, resulting in a smaller capacity than when tested to the old standard (ES 2012). 4
| ES 5.0|
65°F/ 60% R.H.
80°F/ 60% R.H.
90°F/ 90% R.H.
|Portable Dehumidifier A||20||30||58.8|
|Portable Dehumidifier B||25||40||78.4|
|Whole House Dehumidifer A||70||80||156.4|
Once the indoor humidity reaches the dehumidifier’s setpoint the unit will stop collecting water, which is not a bad thing. This means that there is not enough water vapor in the air for the dehumidifier to condense, once humidity increases or moisture is generated indoors the dehumidifier will begin running and removing moisture again. The goal of a dehumidifier is to remove moisture and maintain indoor relative humidity below 60%. Referencing Ahmad A. Pesaran’s article, “removing excessive moisture from materials is usually the most practical and effective means of stopping mold and mildew. Air humidity must be controlled below 60% relative humidity (RH) to avoid the growth of mold and mildew.”
Tankless Dehumidification System Designed for Multifamily Housing
The IW25-4 Wall Mounted Dehumidifier with combined Bi-polar Ion Generator condenses water vapor in the air to lower indoor humidity. The ENERGY STAR® Version 5.0 certified IW25-4 dehumidifier was designed to accommodate apartments and smaller spaces. Created for versatile installation the IW25-4 easily installs directly through interior wall or mounts on wall. The built-in dehumidification system runs independent of HVAC system, with digital controls hidden behind the tamper-proof cover, the simple solution to hands-free dehumidification. The Innovative Dehumidifier Systems team is eager to help find the best fit for the IW25-4 in your multifamily property.
What’s your Plan to Lower High Humidity?
1. Engineering ToolBox, 2005, Moist Air – Weight of Water Vapor. [online], accessed October 2022, available at: <https://www.engineeringtoolbox.com/water-vapor-air-d_854.html>
2. Refrigeration Service Engineers Society, The HVACR Training Authority 2009, accessed October 2021, <https://www.rses.org/assets/serviceapplicationmanual/630-16.pdf>
3. AER Industries, AHAM vs Saturation Explained, October 2016, accessed October 2021 <https://aerindustries.com/blog/2016/10/03/aham-vs-saturation-explained/>
4. ENERGY STAR: Additional Information about Dehumidifier Testing and Capacity, Dehumidifier Performance and Testing, accessed October 2021, <https://www.energystar.gov/products/dehumidifier_testing_and_capacity>
5. National Renewable Energy Laboratory, Ahmad A. Pesaran, June 1993, Office of Scientific and Technical Information, accessed October 2021, <https://www.nrel.gov/docs/legosti/old/7010.pdf>