Application of adsorption rotary dehumidifier in air conditioning

Abstract: Air conditioning is mainly aimed at providing a comfortable living environment. Especially in our country, it is basically just temperature control, with occasional humidity control. However, with the development of science and technology, especially the development of biology, electronics and chemical technology, human beings are increasingly concerned about their own environment and strive to create a comfortable and qualified living and production environment. This is beyond the reach of air conditioning that only provides comfort for human life, especially in environments with high demands for industrial production, scientific experiments, and more. The emergence of special air conditioners precisely addresses the special environmental requirements of industries such as biology, chemical, electronics, and glass in modern industry.  

Keywords: adsorption rotary dehumidifier, direct current fresh air system, primary return air

  Air conditioning is mainly aimed at providing a comfortable living environment. Especially in our country, it is basically just temperature control, with occasional humidity control. However, with the development of science and technology, especially the development of biology, electronics and chemical technology, human beings are increasingly concerned about their own environment and strive to create a comfortable and qualified living and production environment. This is beyond the reach of air conditioning that only provides comfort for human life, especially in environments with high demands for industrial production, scientific experiments, and more. The emergence of special air conditioners precisely addresses the special environmental requirements of industries such as biology, chemical, electronics, and glass in modern industry.

The so-called special air conditioning refers to industrial air conditioning that is different from the general purpose of creating a comfortable living environment for humans, specifically providing qualified environments (spaces) for industrial production, scientific experiments, etc. In addition to temperature requirements, it also has requirements for cleanliness, humidity, noise, and static electricity. Here, we will only discuss the control of humidity in special air conditioning.
The adsorption rotary dehumidifier uses the method of adsorption to remove moisture from the air. As shown in Figure 1, a dehumidification wheel made of hygroscopic substances (molecular sieves, silica gel, lithium chloride, etc.) loaded with special materials is divided into a 90 ° regeneration zone and a 270 ° treatment zone by a stationary sealing strip. As the wheel slowly rotates (8-10 revolutions per hour), it adsorbs water in the treatment zone and then turns to the regeneration zone for regeneration (desorption), and then enters the treatment zone to adsorb water, continuously processing air, Make it reach the required humidity. For different production environments or laboratories, there are different humidity requirements, and different materials of wheels can be used. The rotary dehydrator can provide dry air with a dew point temperature ranging from -20 to -60 ℃.
There are several common combinations of rotary dehumidifiers in air conditioning systems. The following is a list of air conditioning systems in various production workshops with different humidity requirements, explaining the application of rotating wheels in air conditioning.
Solution: Continuous flow fresh air system

In this system, outdoor air with a temperature of Tw and a humidity of RHw is refrigerated and dehumidified, reaching a certain state point Ti and Rhi (usually T=7 ℃, RH=95%) before entering the rotary dehumidifier. The outlet state points are To and Rho (Rho can be less than 2%, and the dew point can reach -25 ℃), and then sent indoors after temperature treatment to ensure the indoor state parameters Tn and RHn. This type of system can provide environmental parameters with RHn=2%~10%, and is commonly used in small spaces with high humidity requirements, such as laboratories or production sequences with humidity requirements.
For example, a laboratory in a certain research institute covers an area of 25 square meters, with two people working indoors. The required temperature is 25 ℃ and the relative humidity is less than 2%. This system uses Monte's M1100 rotary dehumidifier and adopts a brand new air system. The fresh air is cooled and dehumidified to 8 ℃ through several sets of direct evaporative refrigeration units, and 95% RH enters the rotary dehumidifier. Its outlet temperature is 29-33 ℃, and the relative humidity is 1-1.3% RH. Then, it is cooled to 20-22 ℃ and sent to the room. After testing, the room temperature is around 25 ℃, and the humidity is about 1.5%, which fully meets the user's requirements.

Scheme 2: Circulating system with primary (secondary) return air
In this system, outdoor air with a temperature of Tw and a humidity of RHw is frozen and dehumidified, reaching a certain state point of Tw ', Rh' (usually T=7 ℃, RH=95%), and then mixed with indoor return air. It is cooled again to state Ti, and RHi enters the rotary dehumidifier. Due to the relatively dry indoor return air and low moisture content Dn, the dew point temperature of the outlet air can reach -60~-40 ℃, and then it is sent indoors after temperature treatment to ensure the indoor state parameters Tn and RHn. This type of system can provide environmental parameters with RHn<1%, and the indoor dew point temperature Td can reach -40 ℃. It is commonly used in large spaces with high humidity requirements, such as lithium battery production workshops or chip production workshops.
For example, a production workshop in a certain factory in Shanghai covers an area of 400 square meters, with 18 people in the workshop. The required temperature is 22 ℃, and the dew point temperature Td is lower than -40 ℃. Due to the high humidity requirements and large space of this system, a return air circulation system is adopted. The rotary dehumidifier uses two imported dehumidifiers with an air volume of 9000, each forming an independent supply and return air system. The fresh air of the system (accounting for 10-20% of the total air volume) is cooled and dehumidified to 7 degrees, and after 95% RH, it is mixed with the room return air (24 ℃, dew point -42 ℃). After the mixed air cools down again, it enters the rotary dehumidifier, and its outlet dew point is -60~-48 ℃. After actual measurement, the dew point of the drying room is -38~-43 ℃.
Scheme 3 Auxiliary System of Central Air Conditioning System

In this system, outdoor air with a temperature of Tw and a humidity of RHw is refrigerated and dehumidified, reaching a certain state point Ti and Rhi (usually T=7 ℃, RH=95%) before entering the rotary dehumidifier. The outlet air (state points To and Rho, Rho can be less than 2%, and dew point can reach -25 ℃) is mixed with the existing central air conditioning system supply air and then sent indoors, or mixed in the air conditioner before being treated and sent indoors. This type of system is commonly used in large spaces with humidity requirements of RH=10%~30%, such as glass industries or biopharmaceutical factories.
For example, a biological preparation factory in Guangzhou has an area of about 500 square meters and 20 people working inside. The indoor air parameters require 22 ℃ and a relative humidity of<10%. The design adopts a Montessori rotary dehumidifier M7000 and retrofits its existing central air conditioning. After the renovation, the indoor parameters were measured to be 24 ℃ and 8-10% RH. Basically meeting user requirements.
The above briefly explains three system schemes for rotary dehumidifiers. In fact, in addition to this, there are also dual wheel systems, cascade systems, and so on. And the above system is only for dehumidification, and there is no requirement for the lower humidity limit. Sometimes, we require humidity to be within a certain range, even constant temperature and humidity. Therefore, in system design, we can flexibly use rotary dehumidifiers, refrigeration dehumidifiers, heaters, humidifiers, and control them with temperature controllers, humidity controllers, or microcomputer programmable controllers according to different temperature and humidity requirements to meet the requirements.