Desiccant dehumidification compared to other humidity control technologies
There are three primary ways to remove moisture from air: Cooling it to condense the water vapor; Increasing its total pressure, causing condensation; Passing the air over a desiccant, which pulls moisture from the air through differences in vapor pressures.
Understanding how humidity works
When comparing the different humidity control technologies available in the market, it’s important to have a basic understanding of how humidity works. Key concepts to understand are relative vs. absolute humidity, and how they relate to dew point and condensation.
Absolute humidity (AH)
Absolute humidity, by contrast, measures the actual amount of water in the air—typically in grams per cubic meter (g/m³). It doesn’t vary with temperature, making it a fixed and direct indicator of moisture content. For example, air with 10 grams of water per cubic meter has that absolute humidity whether it’s hot or cold. While absolute humidity tells you how much water is present, RH is more practical for understanding comfort levels and the likelihood of condensation.
Relative humidity (RH)
RH is the percentage of water vapor in the air relative to what it can hold at that temperature. At 50% RH, air is half-saturated. Warmer air holds more moisture than cooler air. So, the same amount of water vapor can result in different RH values depending on air temperature.
Dew point
The dew point is the temperature at which air reaches 100% RH and begins to condense. As air cools, its ability to hold moisture decreases. When it hits dew point, water vapor turns into liquid. This is what causes water droplets to form on a cold drink—or on pipes and walls in industrial settings.
Condensation
If any surface cools below the air’s dew point, condensation forms. This leads to rust, corrosion, mold, and material damage. Keeping moisture levels low, or surface temperatures above dew point is one way to prevent condensation. But directly lowering the dew point with dehumidification means drier air, fewer surprises, and greater process stability.
Moisture control strategies: dehumidification vs. heating
For a number of industrial processes and preservation applications, temperature control systems do double duty as humidity control solutions. While heating can provide some level of moisture control, it’s imprecise, inefficient, and costly. When humidity is the primary issue, dehumidification—not heating—is the most effective solution.
Using heating for moisture control
Some facilities try to heat the air to solve humidity problems. Heating does reduce the relative humidity, since warmer air holds more moisture. But since it doesn’t remove water from the air, absolute humidity stays the same. Once the area cools down, the relative humidity rises again.
Using heat alone is also inefficient. Energy is waster over-heating the space, while the humidity remains a long-term problem. In warmer climates, heating makes A/C systems work harder to cool the air – wasting even more energy.
Heating may also create an uncomfortable working environment by making rooms uncomfortably hot.
Solving moisture issues with dehumidification
Dehumidification fixes the root cause of excessive moisture in the air by directly removing it from the building or process. There are two types of dehumidifiers available, desiccant and refrigerant based systems.
Both technologies remove humidity from the air, but they use different methods and have different applications. The most common system used in commercial and industrial applications is a desiccant dehumidifier. These systems are much more effective at humidity control than heating.
They can provide precise dew point control reliably, and use far less energy than heating.
How desiccant dehumidification works
Desiccant dehumidifiers operate very differently from refrigerant-based dehumidifiers. Instead of cooling the air to condense its moisture, desiccants attract moisture from the air by creating an area of low vapor pressure at the surface of the desiccant. The pressure exerted by the water in the air is higher, so the water molecules move from the air to the desiccant, and the air is dehumidified.
The essential characteristic of desiccants is their low surface vapor pressure. If the desiccant is cool and dry, its surface vapor pressure is low, and it can attract moisture from the air, which has high vapor pressure when it is moist. After the desiccant becomes wet and hot, its surface vapor pressure is high, and it will give off water vapor to the surrounding air. Vapor moves from the air to the desiccant and back again depending on vapor pressure differences.
There are five typical configurations for desiccant dehumidifiers:
- Liquid spray-tower
- Solid packed tower
- Rotating horizontal bed
- Multiple vertical bed
- Rotating Honeycombe®
Each configuration has advantages and disadvantages, but the most effective choice for most applications is usually a system built around a Honeycombe® rotor.
Desiccants wheels and rotor technology
A desiccant wheel (also known as a rotor) consists of a semi-ceramic structure impregnated with a desiccant, set inside a metal wheel. The exact formula of the desiccant used is customized based on the application and the required level of moisture control.
Read more about the Munters patented rotor technology.
Choosing the right dehumidification solution
When controlling humidity with dehumidification, there are two widely available technologies – desiccant and refrigerant based dehumidifiers. While both technologies dehumidify the air, they have very different properties and use cases.
Desiccant based dehumidifiers
Desiccant dehumidifiers are ideal for critical environments like pharmaceutical production, cold storage, or cleanrooms as they deliver consistent, reliable performance in the toughest conditions. They provide consistent and extremely precise humidity control at any temperature or relative humidity level. They are the only systems capable of maintaining the precise, extremely low dew points required in critical environments like pharmaceutical production or cleanrooms, battery manufacturing, cold storage, and food processing. Desiccant dehumidifiers are also the most energy efficient solution, and offer lower operating costs.
Refrigerant based dehumidifiers
These units use cold coils to condense moisture from the air. They perform best in warm, humid conditions with high moisture loads. They’re low in cost for moderate conditions (e.g., 50% RH, above 10°C/50°F). However, they struggle at low temperatures—coils can freeze—and can’t reliably achieve very low RH levels. While they’re a good solution in nondemanding conditions where only a small system is required, they’re not appropriate for most industrial and commercial applications.