A complete analysis of humidity control in air-cooled chillers and heaters

In modern industrial production and living environments, many fields have strict requirements for precise control of temperature and humidity. As a common air-conditioning equipment, air-cooled cooling and heating units must not only achieve precise temperature regulation, but humidity control is also crucial. This article will deeply explore the humidity control principles, methods and related key points of air-cooled cooling and heating units.

Brief description of the working principle of air-cooled cooling and heating units

Air-cooled cooling and heating units use air as the cooling (heating) source and water as the cooling (heating) medium. They are integrated equipment that can be used as both cooling (heating) sources for air conditioning systems. They are divided into cooling-only type and heat pump type according to their uses. The heat pump type integrates cooling and heating functions, which can achieve cooling in summer and heating in winter.

In the refrigeration cycle, the compressor sucks the low-pressure superheated refrigerant vapor in the dry evaporator, which is compressed into high-temperature and high-pressure superheated steam, releases heat to the environment in the condenser, condenses into saturated or supercooled refrigerant liquid, flows into the dry evaporator through the expansion valve throttling and pressure reduction, absorbs the heat of the refrigerant water in the dry evaporator and vaporizes, and then is sucked in and compressed by the compressor to start a new cycle, thereby cooling the refrigerant water and introducing it into the air-conditioned area. In the heat pump cycle, the refrigerant is reversed by reversing the four-way reversing valve to achieve the heating function.

Importance of humidity control in air-cooled chillers

Production process requirements: In some industrial production processes, such as electronic chip manufacturing, pharmaceutical production, printing, etc., slight changes in humidity may have a serious impact on product quality. For example, excessive humidity in an electronic chip manufacturing workshop may cause a chip short circuit; improper humidity in a pharmaceutical production environment may affect the stability and shelf life of the drug.

Human comfort: In living and office environments, appropriate humidity can significantly improve human comfort. Generally speaking, the human body feels more comfortable when the relative humidity is between 40% and 60%. Too high humidity can make people feel stuffy and sticky, while too low humidity can cause dry skin, respiratory discomfort and other problems.

Humidity Control Method for Air-Cooled Chillers

Condensation dehumidification

Principle: By utilizing the low temperature of the evaporator surface of the refrigeration system, the water vapor in the air condenses into water droplets on the evaporator surface and is discharged through the drainage system, thereby achieving the purpose of dehumidification. When the air flows through the low-temperature evaporator surface, the temperature decreases, and the saturated vapor pressure of the water vapor in the air decreases accordingly. When the actual water vapor partial pressure is higher than the saturated vapor pressure, the water vapor will condense into liquid water.

Control method: The dehumidification capacity can be adjusted by controlling the running time and cooling capacity of the refrigeration system. When the humidity is high, increase the running time of the refrigeration system or increase the cooling capacity to enhance the dehumidification effect; when the humidity is close to the set value, reduce the cooling capacity or shorten the running time. For example, in some constant temperature and humidity air conditioning units, the start and stop or frequency conversion operation of the compressor will be controlled according to the difference between the indoor humidity detected by the humidity sensor and the set humidity, thereby adjusting the cooling capacity and dehumidification capacity.

Rotary dehumidification

Principle: For air-cooled chillers equipped with a rotary dehumidification system, the rotary wheel absorbs moisture from the air in the moisture absorption zone, and then discharges the moisture in the regeneration zone by heating, etc. The rotary wheel is usually made of special hygroscopic materials, such as silica gel, molecular sieve, etc., which have strong hygroscopic capacity.

Control method: The dehumidification effect is adjusted by controlling the rotor speed and regeneration temperature. Increasing the rotor speed can increase the dehumidification capacity, but it will also increase energy consumption; increasing the regeneration temperature can enhance the regeneration effect of the rotor and improve the dehumidification capacity. In actual applications, the rotor speed and regeneration temperature will be reasonably adjusted according to the humidity requirements and system energy consumption. For example, when the humidity requirement is high and the energy consumption is allowed, the rotor speed and regeneration temperature are appropriately increased to quickly reduce the air humidity; when the humidity is close to the set value, the rotor speed and regeneration temperature are reduced to save energy.

Humidification control

Steam humidification: Steam is generated through a steam generator and injected into the indoor air to increase the air humidity. According to the difference between the indoor humidity detected by the humidity sensor and the set humidity, the power of the steam generator or the opening of the steam nozzle is controlled to adjust the amount of steam generated and injected to achieve precise humidification control. For example, in some environments with high humidity accuracy requirements, high-precision humidity sensors and intelligent control systems are used to adjust the working state of the steam generator in real time according to the humidity deviation to ensure that the humidity is stable within the set range.

Ultrasonic humidification: Use ultrasonic transducers to convert electrical energy into mechanical energy, generate high-frequency vibrations, atomize water into tiny particles, and release them into the air for humidification. The humidification amount can be adjusted by controlling the working time and power of the ultrasonic transducer. Ultrasonic humidification is more common in some small air-cooled cooling and heating units or in environments with small humidification requirements, because it has the advantages of high humidification efficiency, low energy consumption, and uniform humidification.

The process and key links of humidity control

Humidity detection: The humidity of the air is detected in real time through the humidity sensor installed in the air-conditioned area. The accuracy and reliability of the humidity sensor directly affect the effect of humidity control, so it is necessary to select a reliable and high-precision sensor and calibrate and maintain it regularly.

Signal transmission and processing: The humidity sensor transmits the detected humidity signal to the control system, which analyzes and processes the signal, compares it with the set humidity value, and calculates the humidity deviation.

Control execution: The control system issues corresponding control instructions according to the humidity deviation, adjusts the operating status of the condensing dehumidification, rotary dehumidification or humidification equipment, and adjusts the humidity towards the set value. For example, when the humidity is higher than the set value, the control system starts the condensing dehumidification or rotary dehumidification function and adjusts its operating intensity according to the humidity deviation; when the humidity is lower than the set value, the humidification equipment is started and the amount of humidification is controlled.

Factors affecting humidity control and countermeasures

Changes in the outdoor environment: The humidity and temperature of the outdoor air will affect the humidity control of the air-cooled chillers. In a high-humidity outdoor environment, the dehumidification load of the unit will increase; in a low-temperature environment, the humidification effect may be affected. The countermeasure is to reasonably adjust the operating parameters of the unit according to changes in the outdoor environment. For example, in high-humidity seasons, appropriately increase the cooling capacity of the condensing dehumidification or increase the operating time of the rotary dehumidification; in a low-temperature environment, increase the power of steam humidification or ultrasonic humidification to ensure the humidification effect.

Indoor load changes: Factors such as the number of people indoors and the heating of equipment can cause changes in indoor wet load and heat load. When the number of people indoors increases or the operating power of the equipment increases, the wet load will increase and dehumidification will need to be strengthened; when the indoor heat load increases, it may affect the stability of humidity control. The countermeasure is to monitor indoor load changes in real time and automatically adjust the operating mode and parameters of the unit through the control system. For example, an intelligent control system is used to automatically switch between cooling, heating, dehumidification, humidification and other functions according to changes in indoor temperature, humidity and load, and adjust the operating intensity of the corresponding equipment.

Unit performance: The cooling, heating, dehumidification, humidification and other performance parameters of air-cooled cooling and heating units will affect the humidity control effect. If the cooling capacity of the unit is insufficient, condensation and dehumidification may not be effective; if the humidification capacity of the humidification equipment is insufficient, the humidity requirements cannot be met. The countermeasure is to fully consider the actual needs when selecting and installing the unit, select a unit with matching performance, and regularly maintain and service the unit to ensure its stable performance. For example, according to factors such as the area of the air-conditioned area, the number of personnel, and the equipment conditions, accurately calculate the required cooling capacity, heating capacity, dehumidification capacity, and humidification capacity, and select air-cooled cooling and heating units of appropriate specifications; regularly clean the evaporator, condenser and other components, check the working status of the dehumidification and humidification equipment, and replace damaged parts in time.

Humidity control of air-cooled chillers is a complex and critical process involving a variety of control methods, processes and influencing factors. By rationally selecting and applying humidity control technology, taking into account various influencing factors and taking corresponding countermeasures, it is possible to achieve precise control of air humidity, meet the strict requirements of different production processes and living environments for temperature and humidity, and create a comfortable and stable environment for people.