(continued from previous page) —simple, discharging directly through the wall or window to the outside—model FSJG-3.5F (motor power N = 0.18 kW) diagonal-flow fan may be selected; if the system is more complex, a centrifugal fan should be selected. If the duct run is not too complex, model F4-72-3.5A (3.6A) with a 0.75 kW or 1.1 kW motor may be selected. If the client requires a relatively large air volume and the system is more complex, model F4-72-4A with a 1.1 kW motor may be selected. The resistance of a single fume hood system is about 80–100 Pa, and the resistance of each elbow is about 40–50 Pa. When selecting fans, since the parameters of domestic manufacturers contain a certain degree of overstatement, an appropriate margin should be allowed. ③ For multiple fume hoods and complex systems—for ventilation systems with two or more fume hoods—rooftop high-level discharge or outdoor discharge is generally adopted, and centrifugal fans are generally selected. The fan model can be selected according to the system's total exhaust volume and system resistance. For fans that can satisfy both the system exhaust volume and system pressure, we should select a fan with a larger model and smaller motor power as far as possible. ④ For a system in which one fan drives two or more fume hoods, in order to control the opening and closing of each fume hood independently, an electronic air-volume control valve should be installed on each fume hood. The electronic air-volume control valve is generally Φ315 mm.

X. Ventilation Site Conditions

• 1. Building site conditions
     • 1.1 Total number of floors of the building;
     • 1.2 Floor height of the building;
     • 1.3 Specific locations and dimensions of beams or other objects in the building that affect the installation of the ventilation system;
     • 1.4 Site conditions on the roof—whether there is space to install fans;
     • 1.5 Whether there is an air shaft in the building; if so, provide its specific location and dimensions;
     • 1.6 If there is no air shaft in the building, which parts of the building exterior the client agrees can be used for duct runs without affecting the effectiveness of the ventilation system, other facilities, or the overall aesthetics of the building.
• 2. Client requirements
     • 2.1 The fan installation location required by the client (indoors, side wall, or rooftop);
     • 2.2 The ventilation system material required by the client (PVC, fiberglass, galvanized sheet iron, stainless steel, PP, etc.);
     • 2.3 Whether the client needs the company to provide services such as wall openings, equipment foundations, and waterproofing;
     • 2.4 Whether the client needs exhaust gas treatment for the ventilation system;
     • 2.5 Specific parameters required by the client, such as the face velocity to be achieved by ventilation terminal equipment;
     • 2.6 The noise control range required by the client for ventilation terminal equipment, etc.

Section 3 Medical Laboratory Air-Conditioning System

I. Classification and Characteristics of Air-Conditioning Systems link

Laboratory buildings differ from ordinary buildings; different laboratories have different requirements for parameters such as temperature, humidity, pressure, and cleanliness (truncated at bottom of page)

(continued from previous page), and airflow between different laboratories must not cross-contaminate; airflow from laboratory areas must not flow into office areas. Therefore, the air-conditioning requirements of laboratory buildings are far more complex than those of ordinary buildings: functional zones should be divided independently, independent systems should be adopted, and the principle that air-conditioning zones can be mutually sealed to avoid cross-infection via air pathways must be observed; rooms with cleanliness requirements and heavily contaminated rooms should each form a separate system. By arrangement, air-conditioning systems can be divided into decentralized air-conditioning systems, centralized air-conditioning systems, and partially centralized air-conditioning systems.

1. Decentralized Air-Conditioning System link

A decentralized air-conditioning system means that each laboratory uses its own independent air-conditioning unit; common units include ceiling cassette air conditioners, wall-mounted air conditioners, floor-standing (cabinet) air conditioners, and window air conditioners. Ceiling cassette air conditioners are often used in laboratories because they occupy no usable space, have low noise, and offer superior overall performance. Window air conditioners are not recommended because of their relatively high noise; wall-mounted and floor-standing air conditioners can be used in ordinary laboratories depending on the laboratory area.

The advantages of decentralized air-conditioning systems are easy installation, flexible use, convenient management, little mutual interference between laboratories, simple maintenance, individual control, and energy savings. The disadvantages are the absence of a fresh air system, the large number of outdoor units, the limited distance between outdoor and indoor units, and the need to consider the placement and aesthetics of the outdoor units. They are suitable for ordinary laboratories with no particular pressure differential or cleanliness requirements between them, and are commonly found in construction projects with low investment and small scale.

2. Centralized Air-Conditioning System link

A centralized air-conditioning system means that the laboratory building adopts an overall central air-conditioning system, so that when the system is on, the entire laboratory building's air conditioning is "all on at once." Since office areas and laboratory areas generally coexist in a laboratory building, and laboratory areas contain different laboratories, some problems arise—for example: for laboratories that are not used synchronously, a centralized air-conditioning system wastes considerable energy and makes it difficult to meet the different temperature and humidity requirements of various laboratory types; for laboratories with different cleanliness requirements, the large air volume handled by a centralized system results in excessive investment and cannot adapt to the differing requirements of precision instrument rooms and other laboratories in the building; nor can it meet the different air-conditioning needs of laboratory areas and office areas. A centralized air-conditioning system uses a unified refrigeration plant and uniformly arranged piping, and its temperature, humidity, and air-exchange design easily satisfies human comfort requirements; it is suitable for large office areas in a building, but is not recommended for mixed-use zones where laboratory areas and office areas are used simultaneously.

3. Partially Centralized Air-Conditioning System link

A partially centralized air-conditioning system uses multiple air-conditioning units to separately control zones of the laboratory building that have different air environment requirements, while a variable-frequency control system adjusts energy consumption according to changes in the used zones, thereby achieving energy savings. Partially centralized air-conditioning systems combine the advantages of decentralized and centralized systems and are widely used in laboratory buildings.

[Figure: Air-conditioning floor plan layout — arrangement of indoor air-conditioning units/outlets in each laboratory room, with dimensions and piping annotations]

II. Factors Considered in Air-Conditioning System Design

A laboratory air-conditioning system must meet the laboratory's research requirements. In addition to strict control of temperature and humidity, sufficient ventilation volume is needed to handle smoke, odors, and airborne contaminants, and to meet the ventilation needs of exhaust equipment and the laboratory's heat load. The air-conditioning system must fully consider system reliability and allow for surplus capacity. Zones of different natures require different relative pressures, and energy savings must be considered in accordance with relevant standards. In addition to the factors considered in conventional air conditioning, laboratory air-conditioning system design must also take into account the laboratory's characteristics, comprehensively analyzing various factors before selecting a suitable air-conditioning system.

III. Airflow Organization

A laboratory must maintain a certain temperature gradient and airflow conditions. Under normal circumstances, the laboratory is kept at negative pressure relative to corridors and non-laboratory areas, with airflow moving from low-risk zones to high-risk zones; the entire building must be kept at positive pressure relative to the outside to prevent the infiltration of harmful, unfiltered air.

The supply air to corridors must take into account the make-up air for laboratories and the positive-pressure requirement of the entire building. On the premise of a rational building floor plan, the locations of supply, return, and exhaust air outlets and the matching of supply, return, and exhaust air volumes must be fully considered to establish rational pressure gradients between rooms, ensure orderly air movement, and prevent cross-contamination. Laboratory design must consider not only the direction of airflow but also the flow rate and the pressure differentials between rooms of different cleanliness classes or different functions—typically 5–10 Pa; for biosafety laboratories, the pressure differential between adjacent rooms with different functions is typically 10–15 Pa. The routes of personnel and material flows must be fully considered to minimize indoor backflow and turbulence, and to prevent contaminants from spreading indoors and endangering personnel and environmental safety. Special attention must be paid to the influence of fume hoods on indoor airflow organization; turbulence should be avoided as far as possible in areas near laboratory fume hoods and biosafety cabinets, as the influence of turbulence at the side of the hood is far greater than at the front.

1. Air Pressure Control of Airflow

Laboratory pressure control mainly uses the direct pressure-differential control method and the excess air volume (airflow offset) control method.

1.1 Direct Pressure-Differential Control Method link

The direct pressure-differential control method measures the pressure differential relative to a reference zone with a pressure differential sensor; after comparison with the set differential, the controller adjusts the supply (or exhaust) air volume according to the deviation to achieve the required differential. This is feedback control; the system response time is long and the control accuracy is low.

1.2 Excess Air Volume (Airflow Offset) Control Method link

Maintaining a certain air volume difference (called the excess air volume) between the laboratory's supply and exhaust air volumes inevitably creates a certain pressure differential between the inside and outside of the laboratory. When the total supply air volume is greater than the total return and exhaust air volume, air is discharged through excess-pressure valves and room gaps, establishing positive pressure relative to adjacent zones and preventing environmental contaminants from entering the room—suitable for places requiring high cleanliness.

When the room's total supply air volume is less than the total return and exhaust air volume, air enters the room from adjacent rooms and from outdoors, and the room is at negative pressure; such negative-pressure systems ensure environmental safety, guaranteeing that untreated contaminants do not flow outdoors—for example, biosafety laboratories and negative-pressure animal rooms. Advantages of the excess air volume method: accurate pressure differential control, small system fluctuation, and rapid balancing. In the absence of external disturbance the system is feed-forward control, with short response time and high control accuracy; most cleanrooms use this pressure control method.

For places requiring pressure control with stable pressure (such as biosafety laboratories), the excess air volume method is mostly used as the basic control method, with pressure sensors and controllers added to set the excess air volume. The supply and exhaust air volumes are determined from the excess air volume that produces the pressure differential, and the excess air volume is monitored; when the excess air volume deviates from the set value to a certain degree, the system automatically alarms, at which point the measuring device or potentially leaking equipment (such as the duct system or the building envelope) must be dealt with. Combining excess air volume control with pressure control enables dynamic control of the system, ensuring the accuracy of the pressure system's differential.

2. Exhaust Equipment

The quantity and exhaust volume of laboratory exhaust equipment are important factors considered in laboratory air-conditioning system design. Common laboratory exhaust equipment includes fume hoods, articulated extraction arms, atomic absorption hoods, bench-top ventilation hoods, biosafety cabinets, ventilated reagent cabinets, and glove boxes.

3. Cooling and Heating Load Factors

Laboratory air-conditioning system design must fully consider the laboratory's potential heat and cold sources, so that a scientifically accurate cooling capacity can be calculated and variable-frequency air conditioning adopted to achieve energy savings. Common cooling and heating loads in laboratories include sensible heat from personnel, sensible heat from animals, laboratory instruments and equipment, computers, lighting, cold rooms, and warm rooms.

IV. Air-Conditioning Systems for Ordinary Laboratories

The air-conditioning system of an ordinary laboratory is one with no special cleanliness requirements; it can generally be designed as comfort air conditioning. The suitable temperature should be 18–28°C in summer and 16–20°C in winter, and the humidity preferably between 40% (winter) and 70% (summer). To ensure that laboratory airflow does not contaminate surrounding public areas, a slight negative pressure is generally maintained relative to public areas.

Some precision instrument rooms require constant temperature and humidity to ensure normal instrument operation. Precision instruments such as prism spectrometers have even higher temperature and humidity requirements: because the refractive index of a prism varies with temperature, large temperature fluctuations can significantly affect wavelength measurement accuracy; therefore prism spectrometers have strict environmental requirements, generally requiring a spectrometer room temperature of 20 ± 5°C and a relative humidity of 65% ± 5%.

For physical and chemical laboratories with many fume hoods, in addition to using a VAV control system for the ventilation system, the make-up fresh air system of the air-conditioning system must be rationally configured to achieve energy savings and to avoid excessive negative pressure caused by too much air being drawn out of the laboratory; when the indoor–outdoor temperature difference is large, the make-up air must also be preheated or precooled.

V. Air-Conditioning Systems for Clean Laboratories

The main difference between a cleanroom air-conditioning system and an ordinary air-conditioning system is that it adopts multi-stage filtration technology, special measures to prevent dust particles from entering the system and the cleanroom, and airflow organization that meets cleanroom requirements.

A clean laboratory is a fully enclosed environment; through the primary, medium, and high-efficiency filters of the air-conditioning supply and return systems, the indoor air is continuously circulated and filtered so that the concentration of airborne particles is controlled to a specified level. The main parameters that must be controlled in a clean laboratory are pressure differential, temperature, humidity, dust particle count, colony count, air change rate, illuminance, and noise.

[Figure: Floor plan of air outlet arrangement in a clean laboratory. Legible rooms/areas include: laundry, washing and disinfection room, clean air cabinet, reserved, preparation room, culture room 3, culture room 2, culture room 1, quality control room, cell separation room 2, cell separation room 1, second changing room, shoe change, preparation room, testing 1, testing 2, storage room, power distribution room, as well as waste corridor, clean corridor, general zone corridor, etc.; HEPA supply outlets and return air louver outlets are arranged in the figure.]

No.	Legend	Material Name
1	[legend symbol]	HEPA supply outlet GKF-5
2	[legend symbol]	HEPA supply outlet GKF-10
3	[legend symbol]	HEPA supply outlet GKF-15
4	[legend symbol]	Return air louver outlet 400×400
5	[legend symbol]	Return air louver outlet 400×300
6	[legend symbol]	Return air louver outlet 320×250

Fig. 6-33 Air Outlet Arrangement