AIRHANDLING SYSTEMS

The location of the smoke detectors should be based on an engineering survey of the area to be protected. Factors such as air flow, proximity to airhandling system diffusers and other physical features of the installation need to be taken into account. Smoke tests can be run to verify that the air flow within the protected area favors the smoke detectors. 

Figure 2.6 illustrates the main components of an airhandler system, including fans, heat exchanger coils, dampers, ducts, and instruments. The system operates as follows Outside air is admitted by the outside air damper (OAD-05) and is then mixed with the return air from the return air damper (RAD-04). The resulting mixed air is filtered, heated, or cooled, and humidified or dehumidified as required. The resulting supply air is then transported to the conditioned zones (groups of offices) by the variable-volume supply fan station. 

When general construction of the clean room is completed, steps 2A-2J of Appendix B describing coarse cleaning can be implemented. Following coarse cleaning the protective him can be removed from the HEPA filters and the airhandling system started. 

Each hood intended for toxic work must have a face velocity of 100 linear feet per minute. When many hoods are employed, the volume of tempered air that must be supplied (summer and winter) is quite large. The required airhandling equipment is so massive that minor misadjustments may make it difficult to get out of a room because of air pressure on a door. One way to deal with this is to vent the doors and keep the hallways at a slightly higher pressure than the labs. When an airhandling (supply) unit falls short, the hallway provides needed makeup air. Computers can operate air handling systems more precisely than can traditional systems and an alarm system that pinpoints defective elements for early repair can help avoid gross imbalances. 

Of all the requirements that have to be fulfilled by a manufacturer, starting with responsibilities and reporting relationships, warehousing practices, service contract policies, airhandling equipment, etc., only a few of those will be touched upon here that directly relate to the analytical laboratory. Key phrases are underlined or are in italics Acceptance Criteria, Accuracy, Baseline, Calibration, Concentration range. Control samples. Data Clean-Up, Deviation, Error propagation. Error recovery. Interference, Linearity, Noise, Numerical artifact. Precision, Recovery, Reliability, Repeatability, Reproducibility, Ruggedness, Selectivity, Specifications, System Suitability, Validation. 

The airflow schematics of the two systems (Figs 24 and 25) indicate airhandling units with return air or recirculated air, having a percentage of fresh air added. Fig. 25 is a schematic diagram of an air-handling system serving rooms with horizontal unidirectional flow, vertical unidirectional flow and turbulent flow, for rooms A, B and C, respectively. 

There are numerous potential locations for filters in an HVAC system. The most common filter placement location is in the mixed airstream within an airhandling unit. Using that location results in filtration of both outside air and return air, and it protects coils and other downstream components from fouling. Filters could also be located directly in the outside airstream, at supply to individual spaces, on the return from individual spaces, in the common return, and on exhaust air (if there is concern about the consequences of contaminated exhaust). Stand-alone filtration devices that recirculate and clean air within a single zone might also be desirable. 

General exhaust A system for exhausting air from a general work area, accomplished mechanically airhandling units that drain air from the space. 

Filter selection is controlled by airhandling capacity and filtration efficiency. Although the one dictates filter size and the other the grade of element, they are interrelated and cannot be considered independently. For standard systems, operating at about 7.5 bar, filter selection should begin by determining the maximum air... 

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