1) The structure of the test box affects the temperature uniformity of the operation center to a great extent, because the structure is difficult to be completely symmetrical, and then has adverse effects on the temperature uniformity. The structure of a commonly used cryogenic or humid heat box is shown in the figure. In front of the gate, the air conditioning room is at the back of the box, with upper air supply and lower air return. Obviously, the left and right symmetry of the structure is good, and it is easy to reach the left and right temperature uniformity, but the structure is not symmetrical, and the front and back are completely different, which has an uneven impact on the temperature of the working space. Nevertheless, if the single duct structure is properly planned and handled, it has been proved that the operating room can be used from 0.l to 300 m3, and its temperature error can meet the standard requirements.

2) Because of the heat conduction on the wall of the box, heat leakage (high temperature box) or cold leakage (low temperature box) occurs. In order to compensate for the heat loss, there must be a temperature difference between the supply air of the high temperature box and that of the low temperature box. The temperature of the supply air of the high temperature box is higher than that of the work in the box, while the temperature of the supply air of the low temperature box is lower than that of the work in the box. Because there must be a temperature difference in the air supply, the temperature in the operating room is not uniform.

3) Because of the unequal heat transfer coefficients on the six sides of the box wall, some have local heat transfer such as piercing holes, which makes the temperature of the box wall uneven, and then makes the radiation convection heat transfer uneven on the box wall, which affects the uniformity of the temperature field.

4) The sealing of the box is not good, such as the leakage of the door, and then affects the uniformity of the temperature field in the working space.

5) If the test temperature error requires that the test sample be placed in the operating room, when the volume of the test sample is too large, or the way or orientation of the test sample is inappropriate, the air convection will be blocked, and a large temperature error will occur.