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Part1:Determining Supply Air Needed

Introduction 

The use of chemicals and other potentially hazardous compounds separates laboratories from other types of building spaces. Protecting the health and safety of laboratory and building occupants must be the primary concern. Energy-efficiency and comfort are also of considerable importance. The space temperature must remain comfortable for occupants while maintaining an appropriate temperature for chemical processes. At the same time, facilities are under pressure to minimize operating costs. 

Even including the general criterion of safety, not all laboratories are alike. Different laboratories contain different hazard levels and uses. A host of criteria, including safety, energy efficiency and comfort, must be considered when a laboratory is planned or renovated in order to determine the optimal design. 


General Goals of Lab.

Safety

Laboratories are designed to maintain the health and well-being of occupants. Potentially hazardous substances used in different laboratories include chemicals, radioactive materials and infectious biological agents. These materials can be manipulated daily as part of experiments, research or production. Safety must remain the primary goal of a laboratory.

Regulations, guidelines and standards to ensure laboratory safety have been published by many industry groups. Complying with those requirements is a primary step in achieving laboratory safety objectives.


Energy Efficiency

Laboratories are normally designed as once-through systems, without recirculation. Conditioning, supplying and exhausting the large volumes of air used in laboratories consumes sizeable quantities of energy. Reducing these energy costs has a direct impact on a company’s bottom line. Laboratories must be designed so that energy efficiency gains do not reduce safety and comfort.


Comfort

Laboratory safety has to be balanced with worker comfort. Comfort primarily is concerned with maintaining appropriate temperatures and air velocities. Worker productivity will suffer if the space is too warm or too cool. Air currents also impact safety by limiting containment in fume hoods and other protective equipment. 


Intelligence

Local control of your laboratory spaces is only the first step to optimal safety and building efficiency. Linking the laboratory controls to your Building Automation System (BAS) enables the implementation of building-wide strategies.

+ Night setback of flow rates and temperatures to reduce operating expenses

+ Automated data collection, trend analysis and report generation

+ Reports validate safe operation of labs and trend energy consumption

+ Remote diagnostics


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LABORATORY VENTILATION

The key concept of laboratory ventilation is that air entering the laboratory must exit the laboratory. The inflowing air volume, normally composed of supply air and infiltration, will exactly equal the outgoing air volume, or air exhausted through room exhaust, fume hoods, canopy hoods, biological safety cabinets and exfiltration. All airflows must be accounted for when designing a building with laboratories. 

In practice, the volume of air supplied into a laboratory is less than the amount of air exhausted, creating negative pressure. The additional air exhausted creates a negative pressure environment, pulling air in from adjacent spaces through cracks in the wall, the door undercut, unsealed duct and piping openings or other wall penetrations. 


Determining Supply Air Needed

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 Three drivers determine the required volume of supply air in a laboratory: temperature, exhaust, and ventilation.

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Temperature-driven laboratories hold a lot of equipment to perform chemical analysis or ovens and heating elements to speed up chemical processes. Without an adequate supply of cool air, the laboratory housing these equipment will become uncomfortably warm. Lights, laboratory personnel, and even heat transmitted through the building also contribute to the cooling load of a laboratory. Determining the necessary supply air volume for cooling involves summing up all of these loads. However, loads other than the building envelope should be determined according to expected usage. For example, engineers revise supply air volume downward if all of a laboratory’s equipment will not be used simultaneously. 

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Exhaust-driven laboratories, such as teaching laboratories, are virtually filled with fume hoods and canopy hoods. Fume hoods exhaust large quantities of air in order to contain gasses, vapors, particles and other contaminants. All air exhausted from the laboratory, including fume hood exhaust, must be replaced to prevent excessively negative room pressures within the laboratory. 


Finally, some laboratories have low cooling loads and few, if any, fume hoods and other exhaust equipment. These ventilation-driven laboratories still require high supply air volumes to dilute contaminants. The ventilation rate is normally expressed in units of Air Changes per Hour (ACH), calculated as the total air volume supplied in one hour divided by the room volume. Occupied laboratories often have ventilation rates on the order of 8 to 10 ACH, although it could be as low as 4 ACH when unoccupied. In comparison, offices usually see a much lower ventilation rate, often on the order of 4 ACH. 



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