An artificial environmental chamber was used to simulate the environment of the underground workface, and its dimensions were 3 m × 2.5 m × 2.2 m (length × width × height). The artificial environment chamber consisted of a refrigeration unit, electrical heating equipment, vapor humidification unit, fan, data collection unit, and computer. The environmental parameter control system provided control over the temperature of the air in the compartment, humidity, wind speed, and wall temperature. The dry bulb temperature of the cabin could be controlled in the range of −15 °C to 50 °C (±0.5 °C), and the relative humidity could be controlled in the range of 30–95% (±2%). The temperature of the cabin was calibrated before the test using a primary standard thermometer (minimum 0.05 °C, Hongxing Instrument Factory, Hengshui, China) and the humidity was calibrated using a JT-IAQ indoor thermal environment comfort tester (precision ±1.5%, Beijing Century Jiantong Technology Co., Ltd., Beijing, China). In some deep mines, the air temperature in the workface may exceed 26 °C. In high temperature mines the air temperature reaches 35 ℃, and the relative humidity often exceeds 85% [2,4]. To protect the workers and ensure production safety, as specified in the Safety Code for Coal Mines of China, the working times must be shortened when the air temperature of the workface exceeds 26 °C, and the operation must be stopped when the air temperature of the workface exceeds 30 ℃. Therefore, the environmental parameters in this test were controlled at 22 °C/90%, 26 °C/90% and 30 °C/90%, which represent three thermal conditions: cold, neutral and hot, respectively. The airspeed was controlled at 1.5 m/s, and the wall radiation temperature was equal to the air temperature, as shown in Table 2. The temperature conditions in the test process were random, and they were not carried out in the order of temperature increasing step by step.

Climate Chamber Thermal Environment Settings.

* Calculated as a human wearing a neat cotton coverall sitting still in that environment.