FAQ

Question:
How does a desiccant surface attract and retain moisture in the air?

Answer:
Nearly all “solid” material can attract moisture from the air.  Desiccant materials just happen to be very effective at this.  The basic process is that the vapor pressure near the surface of the desiccant is much lower than the “higher vapor pressure” of the water contained in the air that is passing over or thru the desiccant material.   This causes the water in the air to move from the air to the desiccant material.

Question:
Some desiccants are called ADsorbents and others are called ABsorbents.  What is the difference?

Answer:
An ADsorbent desiccant is similar to a sponge as the water is held on to the surface and in the narrow passages of the material.  Silica Gel Rotors, the desiccant of choice for all Bry-Air equipment is an example of an ADsorbent desiccant. 

An ABsorbent is a material that undergoes a chemical or physical change to collect moisture.  These are usually liquids or solids that become liquid as they absorb moisture. 

Question:
Psychometrically, how is the dehumidified air “different” leaving a desiccant compared to air leaving a mechanical cooling device (ie. “cooling coils”)?

Answer:
Air leaving “cooling coils” is typically at or near 100% relative humidity, at or near the surface dry bulb temperature of the coil.  The dry bulb temperature of the leaving air is typically much lower than the “space” that is being serviced.

In the case of desiccant systems, the relative humidity of the air that can be achieved is in the single digits %.  The dry bulb temperature, in the case of ‘rotating wheel’ desiccant dehumidification, will likely be much higher than the “space” that is being serviced. 

Question:
What are realistic achievable “dew points” for rotating desiccant dehumidification wheel systems?  In other words, just how dry can a desiccant dehumidifier make my air?

Answer:
“Dew points” in the range of – 50 deg. F or slightly lower are achievable for these types of systems. 

Question:
What is the relationship between the reactivation air conditions and the amount of moisture removed from the process airstream?

Answer:
In simplest terms, the hotter and drier the reactivation air stream, the more water that can be removed from the process airstream.  This, of course, needs to be balance by other needs of the user.  Some of these needs include energy costs, desired RH and dry bulb temperature of the process leaving air, unit controls, and other factors.

Question:
As a system designer, how do I know if a desiccant system is “right for me” for air dehumidification?

Answer:
This is a challenging question.  It has many factors. 

There are some industrial processes that require dehumidified air with such a low moisture content that desiccant dehumidification is the only answer. 

Also, with increased IAQ concerns around the country in comfort cooling applications, the extra moisture removal that a desiccant dehumidifier can add to an integrated HVAC system is becoming more and more necessary to meet some state and local indoor air quality requirements.

If you have questions or concerns about your specific application, don’t hesitate to contact Bry-Air for your consulting needs.