An environmental control and humidity maintenance device is an industrial testing instrument that can precisely control and maintain specific temperature and humidity conditions. It integrates systems such as cooling, heating, humidification, and dehumidification to simulate various complex environments like high-temperature and high-humidity, low-temperature and low-humidity, and temperature-humidity variations. It is mainly used to test the performance, reliability, and environmental adaptability of electronic products, automotive components, aerospace products, materials, and chemical products under specific temperature and humidity conditions. This device is widely applied in product quality control, research and development experiments, scientific research, and cultural relic protection, etc.

The constant temperature and humidity test chamber (device) originated from the environmental simulation test requirements of Western developed countries (such as the United States, Germany, and Japan) after World War II. China began to establish and develop the environmental test equipment industry in the 1960s and listed constant temperature and humidity technology as a key national research project. In 1965, a complete set of research results was obtained, including high-precision constant temperature (±0.5℃, ±0.2℃, ±0.1℃) and general precision constant temperature (±1℃) technical design and calculation methods.

Since the 1970s, Beijing Optical Instrument Factory's grating etching room successfully achieved high-precision constant temperature of ±0.01℃, reaching international advanced levels. The humidity control technology has reached ±2%. Before the 1990s, the technology in this industry was generally backward. After the 1990s, with industrial development, foreign investment, and increased research and development investment, the industry received strong promotion. In the 21st century, the number of domestic manufacturers increased, and the technology gradually approached international levels, but the manufacturing capacity of non-standard high-end equipment still needs to be improved.

In recent years, technology has developed towards intelligence, multi-factor coupling, large-scale and customized, and standardization. Representative technological breakthroughs include the application of recent variable-frequency compressors and other energy-saving technologies. The control accuracy has continuously improved, and the application of Internet of Things technology enables the equipment to achieve remote monitoring and predictive maintenance. The modular design concept allows users to flexibly configure functional modules according to their needs.

The constant temperature and humidity device achieves precise simulation of specific temperature and humidity environments through the coordinated operation of the "hardware system + control system". Its core hardware system includes components such as the box structure, temperature and humidity regulation system, and air circulation system. The box structure usually adopts a double-layer insulation design, combined with sealing strips to prevent heat and moisture from escaping. The temperature and humidity regulation system includes cooling, heating, humidification, and dehumidification subsystems. The air circulation system is generally composed of centrifugal fans and the electric components that drive them, providing forced circulation of air in the box to ensure uniformity.

The core of temperature control lies in the precise regulation and real-time feedback of heat. The heating system usually uses large-power resistance wires or nickel-chromium alloy electric heating wires [5] [14]. The refrigeration system generally uses vapor compression refrigeration, and for complex conditions (below -55℃), compound refrigeration is used. The control system monitors through Pt100 platinum resistance and generally adopts PID (proportional-integral-differential) control algorithm, dynamically adjusting the heating/cooling power based on the deviation between the set value and the actual value to achieve stable temperature control, with an accuracy of ±0.5℃.

Humidity control requires handling both "humidification" and "dehumidification" processes.