Laboratory design is a specialized field commonly used in industries, including chemical, biological, animal, and physical laboratories. The design of air conditioning and ventilation systems involves several components, including air treatment, refrigeration, heating, dehumidification, airflow organization, control, and safety, all of which are integrated rather than independent systems. Understanding the laboratory’s function is a key factor in selecting and designing the ventilation system. The primary goal is to provide a safe environment for laboratory staff. The designer must thoroughly study all factors to determine the most suitable design. The construction of a chemical laboratory typically includes wet chemical rooms, heating rooms, constant temperature and humidity rooms, general testing rooms, injection molding rooms, and office areas. Except for the constant temperature and humidity rooms, other areas only require temperature control and do not have cleanroom requirements.

Laboratory Air Conditioning and Ventilation Design Parameters

• Indoor and outdoor temperature and humidity requirements
• Air quality
• Equipment and process heat load, including sensible and latent heat
• Anticipated increase in internal load
• Minimum air exchange rate
• Fresh air intake and makeup air
• Type of exhaust equipment
• Control and alarm systems
• Adjustment of fume hood dimensions and numbers
• Room pressure differential
• Backup equipment and power supply

1. Selection of Air Exchange Rate

The Chemical Heating, Ventilation, and Air Conditioning Design Specifications stipulate that the minimum air exchange rate for laboratory rooms is generally between 6 and 8 times per hour. According to ASHRAE, the overall ventilation rate in a laboratory should be determined by the following factors:

• The total airflow is exhausted by local exhaust devices or from other rooms.
• The cooling airflow is needed to carry away the room’s heat load.
• The minimum air exchange rate requirement.

In practice, a minimum air exchange rate of 6 to 10 times per hour is required. Typically, an air exchange rate greater than 10 times per hour is considered suitable. However, in laboratories with high heat load equipment, or in rooms with substantial local exhaust, the air exchange rate may need to be increased. For instance, a wet chemical room with fume hoods or a heating room with large furnaces would require an increased ventilation rate. The calculation for fume hoods follows the Chemical Heating, Ventilation, and Air Conditioning Design Specifications, which specify a minimum face velocity of 0.5 m/s for the operation opening of the fume hood in rooms with makeup air at the ceiling. The utilization rate for fume hoods, when the number exceeds two, should be 60%-70%. Heating furnaces are calculated based on maintaining thermal balance within the furnace. The total safety ventilation volume is calculated by comparing the air exchange rate with the ventilation load, and the maximum value of the three factors is chosen.

2. Supply and Exhaust Air Systems

According to the Chemical Heating, Ventilation, and Air Conditioning Design Specifications, when the exhaust volume in a laboratory is high, an outdoor fresh air makeup system should be installed and the fresh air load should be accounted for.

The Laboratory Building Design Specifications state that each exhaust system should have an independent exhaust system. All exhaust devices in the same laboratory should share the same exhaust system. Laboratories that continuously use exhaust systems during working hours should also have a supply air system, and the supply air volume should be 70% of the exhaust volume. The supply air should be purified according to the process requirements. In heating regions, the supply air should be heated in winter. The supply airflow should not interfere with the normal operation of the laboratory exhaust devices.

All gases exhausted from chemical laboratories must be directly released outdoors and cannot be recirculated. Therefore, unless the chemical laboratory also has cleanroom requirements, it must be maintained at a negative pressure relative to adjacent areas. Whether to choose a 100% fresh air supply system should be considered a crucial part of the laboratory’s risk assessment. Laboratories are typically designed with independent exhaust systems, with exhaust outlets installed on the roof. Wet chemical rooms and heating rooms, which generate toxic, corrosive, and high-temperature gases, must use 100% fresh air treatment. For general laboratory rooms, such as those for computer analysis or material testing in constant temperature and humidity rooms, 100% fresh air systems are not always necessary. For such rooms, air recirculation treatment can meet the requirements, thus reducing energy consumption.

3. Room Pressure Differential

The Chemical Heating, Ventilation, and Air Conditioning Design Specifications stipulate that laboratory rooms should maintain a relatively negative pressure.

All gases exhausted from chemical laboratories must be directly released outdoors and cannot be recirculated. Therefore, unless the chemical laboratory also has cleanroom requirements, it must be maintained at a negative pressure relative to adjacent areas. This rule depends on the specific object in question. For example, constant temperature and humidity rooms, which require strict control of temperature and humidity ranges, should be designed as positive pressure environments. If designed as negative pressure, air from adjacent areas may enter, potentially disrupting temperature and humidity control and posing safety risks. Wet chemical rooms and heating rooms must be designed as negative pressure areas to prevent the release of toxic, corrosive, or high-temperature gases. Office areas in laboratories should maintain positive pressure relative to corridors and laboratories. Airflow in the laboratory should move from lower-risk areas to higher-risk areas, and finally, through various exhaust devices or heating equipment, the air is expelled outdoors.

4. Control Systems

The control system should integrate the factors mentioned above to meet the laboratory’s room pressure, differential pressures between rooms, ventilation volumes, temperature and humidity control, and safety requirements, while reducing energy consumption. Laboratories often contain numerous chemical pollutants that harm human health, especially harmful gases, so their removal is essential. However, energy consumption is frequently high, so the ventilation control system has evolved from early constant air volume (CAV) and dual-state systems to variable air volume (VAV) systems, and now to the latest adaptive control systems. The aim is to provide the safest, most comfortable environment while minimizing energy consumption. The system should respond quickly to ensure human safety, balance the supply and exhaust air precisely, and maintain stability. It is important to minimize the initial investment and reduce costs in terms of operation, energy consumption, and maintenance.

For chemical laboratories, whether to use constant air volume (CAV) or variable air volume (VAV) systems depends on the comprehensive consideration of the required functionality, initial investment, and operating costs. A constant air volume (CAV) system is designed to provide a fixed exhaust airflow for all fume hoods and heating furnaces, regardless of whether they are in use, maintaining a constant airflow. This method uses mechanical limiters to restrict the damper openings, which may reduce airflow by up to 40%. A variable air volume (VAV) system, on the other hand, adjusts the system’s capacity, reducing airflow by more than 10% or 20% depending on the specific design.

The primary issue in laboratory ventilation design is safety, but other factors such as creating a comfortable working environment, managing temperature, airflow, and noise, while ensuring minimal energy consumption and system stability, are also crucial. The design should focus on safety, comfort, energy efficiency, and reliable operation.

Laboratory air conditioning and ventilation systems are critical for ensuring safety, comfort, and efficiency. Proper design involves maintaining temperature control, air quality, and safe airflow while minimizing energy consumption. To meet industry standards, it’s essential to select the right air exchange rate, exhaust systems, and pressure differentials. Modern control systems, like VAV, optimize energy use and enhance system reliability. Ensure your laboratory meets regulatory requirements and provides a safe, efficient environment. Contact us today to learn how our lab design solutions can help you optimize safety, comfort, and energy efficiency in your laboratory operations.