Industrial and commercial desiccant dehumidifiers play a crucial role in controlling humidity in manufacturing, storage, and processing environments. However, in many applications, simply removing moisture from the air via desiccant, is not enough. Additional air treatment – such as pre-cooling, pre-heating, post-cooling, or post-heating – can significantly enhance system efficiency, improve process outcomes, and ensure a turnkey solution for the customer.
Understanding the Need for Pre- and Post-Treatment in Desiccant Dehumidification
Desiccant dehumidifiers work by using a hygroscopic material (Innovative Air Technologies utilizes silica gel) to adsorb moisture from the air. This process inherently involves temperature changes: air leaving the dehumidifier is always warmer and drier than it entered. In some applications, this temperature shift must be corrected to maintain optimal leaving air conditions.
Pre-cooling, post-cooling, and allow for precise climate control by adjusting the temperature before or after the dehumidification process. The choice of which to implement depends on the specific environmental requirements of the space being conditioned.
Pre-Cooling: Reducing Load on the Desiccant Wheel
When to Use It:
Pre-cooling is essential when the incoming air is hot and humid, as it reduces the thermal load on the desiccant wheel, improving its efficiency.
Example:
Consider a food processing facility in Florida dealing with an incoming air temperature of 95°F (35°C) and a relative humidity of 60%. The absolute humidity at these conditions is approximately 150 grains per pound of dry air (gr/lb). By incorporating a pre-cooling coil to bring the temperature down to 55°F (12.8°C) before the air enters the desiccant wheel, the absolute humidity is reduced to 64 gr/lb, easing the moisture removal burden on the dehumidifier and improving leaving air moisture content. The desiccant wheel alone cannot take the ambient condition of 148 gr/lb down to say 10 gr/lb which is what can be achieved if the pre-cooling and desiccant are combined to supplement one another.
Benefits:
Reduces the moisture load on the desiccant material
Improves energy efficiency by decreasing regeneration energy demand
Post-Cooling: Controlling Temperature After Dehumidification
When to Use It:
Desiccant dehumidification naturally releases heat as a byproduct of the drying process, meaning the air exiting the system is often significantly warmer than it entered. In temperature-sensitive environments, post-cooling is necessary to maintain a stable climate.
Example:
A cleanroom used for semiconductor manufacturing requires a stable environment of 70°F (21°C) and 20% RH. Without post-cooling, the air exiting the desiccant system might be 110°F (43.3°C) at <1% RH. A post-cooling coil brings this down to the desired 70°F (or lower if internal heat load is covered by the dehumidifier), allowing for occupant comfort and the space conditions to be more favorable to the product.
Benefits:
Maintains occupant and equipment comfort
Prevents overheating in temperature-sensitive spaces
Supports regulatory compliance in controlled environments
Adding pre-cooling or post-cooling, (or a combination of these features) to an industrial desiccant dehumidification system enhances control over temperature and humidity, ensuring optimal conditions for various applications. The specific strategy chosen depends on environmental conditions, process requirements, and system efficiency goals.
By tailoring air treatment to the needs of a given space, industries such as pharmaceuticals, food processing, electronics manufacturing, and aerospace can maintain precise climate control, reduce energy costs, and improve overall operational effectiveness.
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