Mexico, DF, ID number: 299643
3 Design Considerations
3.11 Laboratories .1 System Schematics.1 System Schematics
Figure 3.11: Laboratory
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Mr. Gerardo Gutierrez, Sr.
Mexico, DF, ID number: 299643
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Figure 3.12: Typical Laboratory Room HVAC Detail (with Pneumatic Actuators)
3.11.2 System Design Considerations
• There are four exhaust ducts shown for the laboratory, two of which service fume hoods. One services analytical equipment through flexible drops and the other keeps the laboratory at negative pressure in relation to the corridor or other adjacent spaces when fume hood airflow is low or when room cooling requirements require additional supply air. Laboratory facilities may serve these ducts with individual fans or with a single exhaust plenum held at constant pressure and serviced by one or two larger exhaust fans. This is common for facilities with a number of rooms and hoods. In such a design, care should be taken to avoid settling of exhausted solids inside the duct when fume hood flow is low.
This Document is licensed to
Mr. Gerardo Gutierrez, Sr.
Mexico, DF, ID number: 299643
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• Laboratories using volatile solvents or radioisotopes should be negative (commonly via airflow tracking) relative to corridors, offices, and adjacent occupied space. Air from offices or technical spaces adjacent to laboratories should transfer into the laboratory. Classified clean laboratory spaces should be positive (via airflow tracking) relative to corridors, offices, and adjacent occupied space. A high pressure bubble airlock should be provided where activities in positively pressurized spaces pose a threat to corridor air quality.
• Where chemicals or other hazardous materials are handled in the open, air systems should be 100% exhaust.
Risks of recirculation of laboratory air should be evaluated if energy costs become prohibitive. Glove boxes to reduce dilution volumes and total airflow may be justified.
• Recirculation of air in microbial and in-process or materials testing laboratories that do not employ volatile organic solvents may be considered. A ductless laboratory hood may be justifiable. These hoods recirculate air to the room through activated carbon filters that remove vapor contamination. It is important that the carbon is prevented from becoming saturated, and therefore, ceasing to absorb airborne vapors. This type of hood is uncommon, because maintenance is critical to the safety of the user.
• VAV control systems are recommended for increased safety through monitoring capabilities and decreased energy usage (using hood diversity and variable flow). Airflow tracking (fixed difference between supply and exhaust) is common.
• Occupancy sensors and night setback can enhance the energy saving potential of VAV systems. Where the minimum ventilation rate (for building or fire code) is greater than the total exhaust from hoods, VAV supply is not recommended. Minimum ventilation rates of 8 to 12 are recommended for most laboratories. Minimum ventilation rates below 6AC/hr for occupied laboratories are not recommended.
• Non-aspirating type diffusers are recommended to be selected and located to minimize velocity and turbulence near the hood face; design cross drafts should not exceed 30 FPM within 24 inches of the hood opening.
• Galvanized exhaust ducts, boxes, and attenuators may be used except where process or research activity requires special corrosion resistance. Laboratory hood exhaust ducts and accessories that are inaccessible should be stainless steel (304). Laboratory hood exhaust ducts which handle large quantities of acids should be high grade stainless steel, Hastelloy, FRP, or other suitable material (stainless steel will corrode rapidly in the presence of high molarity concentrations of hydrochloric acid).
• Perchloric acid digestion hood exhaust requires special handling and cleaning systems. These systems represent an explosion hazard, should be segregated, and designed by experienced professionals. The use of dilution air fans to maintain stack velocity creates noise and requires extra energy. The exhaust from most chemical laboratories primarily is composed of air. As the objective is to get exhausts to a height where prevailing winds can carry them away, high exhaust stacks are preferred. Stack height above a building roof should be maintained at a 10 ft 0 inch minimum; although a stack height equal to 30% of the building height is preferred.
If necessary, variable geometry stacks can maintain velocity at reduced airflows. Stacks should be located to avoid re-entrainment of air into HVAC systems (considering the prevailing winds although many locations will experience winds from all directions).
• Automatic hood closing systems with obstruction detection should be considered for energy savings. VAV boxes should not be oversized. Oversized boxes yield poor airflow control and have a limited range.
• VAV systems should be sized with a diversity factor to allow for savings in airflow and first cost of central heating and cooling equipment. A factor of 70% of installed load is common; however, the diversity factor should take in to account the anticipated hood use. If 50% sash height is considered as full flow, a further diversity factor should not be used.
• A general room exhaust should be provided only when the hood flow at minimum sash position requires an air supply rate less than that required to satisfy heat loads or the specified minimum air change rate.
This Document is licensed to
Mr. Gerardo Gutierrez, Sr.
Mexico, DF, ID number: 299643
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• Air change rate or exhaust quantity will usually dictate the supply air quantity. Exhaust quantities should be reset upward when additional cooling is required.
• Mounting VAV laboratory controls in accessible panels either flush in alcove outside laboratory or in dedicated rooms should improve ease of maintenance.
• Manifolded exhaust systems are considered acceptable, except for perchloric acid hoods which should be on a dedicated exhaust system.
• Approved exhausted chemical storage cabinets should be considered for solvents and hazardous materials.
• Heat should be recovered from laboratory utility equipment, wherever possible.
• Temperature alarms should be provided on refrigerators or freezers. Where critical, these should be connected to the BAS.
• Where laboratory offices are on the exterior wall, heating at the perimeter wall is recommended.
• Central draw-through air handlers are common. Distributed AHUs may be justified for areas that are frequently shut down.
• Supply Air Filtration – MERV 7 and MERV 13/14 (in series). If required by product, HEPA may be needed for classified rooms.
• Exhaust Air Filtration – As required by application. Where energy recovery is employed MERV 7 filters are required. Scrubbers may be required for some dedicated hoods. HEPA filtration may be required for formulation laboratories, BSL3&4, etc.
• While discouraged in supply duct to product processing areas, in-duct silencers can help decrease noise from exhaust manifold valves. Packless type silencers can be used for chemical exhaust applications located between the volume control box and hood.
• Biosafety laboratories are outside the scope of this Guide. Biosafety levels are described in the ISPE Baseline® Guide on Biopharmaceutical Manufacturing Facilities (Reference 13, Appendix 12).
3.11.3 Vivarium
Vivarium facilities should consist of individual suites, each capable of maintaining its own microenvironment for the duration of the product study. Guidances are published by the Association for the Assessment and Accreditation of Laboratory Animal Care International (AAALAC), ASHRAE, and others.