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Design Specifications and Application Principles for Air Supply Temperature Difference in Clean Rooms
2026/4/9
Part 01 Design Specifications
01 Relevant regulations require:
"Design Code for Cleanrooms" (GB50073-2013): Although it does not specify the exact numerical value of the supply air temperature difference, it does have requirements for the temperature and humidity control accuracy of the cleanroom. For example, the temperature control accuracy is generally ±2℃, and the relative humidity control accuracy is ±5% to ±10%. This indirectly affects the design of the supply air temperature difference.
At the same time, the regulations specify the air change rate for clean rooms, and the air change rate is interrelated with the supply air temperature difference, jointly influencing the airflow organization and temperature/humidity stability of the clean room.
"Technical Specifications for Hospital Clean Operating Rooms" (GB50333-2013): For Class I clean operating rooms, it is stipulated that during the operation, the purification air conditioning system should be able to operate with the supply air temperature being lower than the room temperature.
Professor Essend of the Technical University of Berlin in Germany conducted research and concluded that the optimal range for the supply air temperature is below the room temperature by no less than 0.5℃ and no more than 2 to 3℃.
02 Air supply temperature difference between different cleanliness levels of clean rooms:
B+A grade area: In summer, the air supply enthalpy difference is approximately 1.15 kJ/kg, and the air supply temperature difference △t = 0.97△h ≈ 1.12℃; in winter, the air supply enthalpy difference is approximately -0.67 kJ/kg, and the air supply temperature difference △t = 0.98△h ≈ -0.66℃.
C grade area: In summer, the air supply enthalpy difference is approximately 2.77 kJ/kg, and the air supply temperature difference △t = 0.97△h ≈ 2.69℃; in winter, the air supply enthalpy difference is approximately -1.62 kJ/kg, and the air supply temperature difference △t = 0.98△h ≈ -1.58℃.
D grade area: In summer, the air supply enthalpy difference is approximately 3.46 kJ/kg, and the air supply temperature difference △t = 0.97△h ≈ 3.36℃; in winter, the air supply enthalpy difference is approximately -2.02 kJ/kg, and the air supply temperature difference △t = 0.98△h ≈ -1.98℃.
Part 02 Application Principles
01 Based on the indoor load:
Impact of personnel and equipment heat and moisture dissipation: When there are equipment for heat and moisture dissipation in the room, the situation is rather complex. The heat and moisture dissipation of the room not only directly affects the supply air temperature difference, but also influences the cooling and heating methods, fresh air ratio, and ventilation frequency.
When there are no personnel or equipment for heat dissipation and moisture removal indoors, the air supply temperature difference can be relatively easily determined. For example, in the D-class area, the air supply temperature difference in summer is approximately 3.36℃, and in winter it is approximately -1.98℃.
Impact of heat and moisture ratio: The heat and moisture ratio is an important factor in determining the supply air temperature difference. Generally, the relationship between the heat and moisture ratio, enthalpy difference, and temperature difference can be determined using the enthalpy-humidity chart.
For instance, during the summer, the purification air conditioning system is usually in the cooling mode. The values of the heat and moisture ratio, Δt, and Δh can be obtained according to the relevant tables.
02 Consider air flow organization and cleanliness requirements:
The influence of air supply temperature difference on air distribution: When the air supply temperature is 0.5℃ to 2℃ lower than the room temperature, a stable laminar airflow can be formed, such as in a Class I clean operating room. This can effectively suppress thermal plume disturbances and ensure a uniform airflow speed of 0.20m/s to 0.25m/s in the surgical area, maintaining the cleanliness of the core sterile zone.
For every 1℃ decrease in temperature difference, the sterile area in the center can expand by 15% to 20%.
Avoid problems caused by excessive or insufficient temperature differences: If the temperature difference of the air supply is too large, the air flow will sink too quickly, affecting the temperature and humidity in the surgical area; if the temperature difference of the air supply is too small, the air flow will be unable to cover the working area, increasing the risk of contamination.
03 Considering the characteristics of the system and operating conditions:
Matching of air supply volume and temperature difference: The air supply volume is between 3000 and 4000 m³/h, with the maximum allowable temperature difference being 2-3℃; when the air supply volume is between 4000 and 5000 m³/h, the maximum allowable temperature difference is 1.5-2℃; when the air supply volume is above 5000 m³/h, the maximum allowable temperature difference is ≤ 1℃.
Seasonal factors: During winter operation, the air conditioning system can be started in advance to eliminate the building's heat load. According to the German DIN1946-4 standard, it is required to start 4 hours in advance. In summer, it is necessary to prevent condensation. The surface temperature of the radiant cooling should be ≥ the indoor dew point temperature + 1℃.
