With his extensive experience in healthcare and laboratory application engineering, Nolan Hosking oversees the development of all associated air distribution, ceiling system, control valves and DDC control solutions. He is also a voting member of the ASHRAE 170 committee which is responsible for the North American standard governing ventilation of healthcare facilities. During our May diner, Nolan presented an overview of Laboratory Airflow Solutions. 

The main topics covered were:

• Blade Damper vs Venturi Air Flow Valve Considerations
• Laboratory Air Pressure Monitors and sensors
• Laboratories Without Fume Hoods
• Laboratories With Fume Hoods

Blade Damper vs Venturi Air Flow Valve Considerations

Air flow in laboratory settings can be more difficult to control with blade dampers due to the low resolution at low turndown and slow feedback loop of the transducer, controller and actuator required to provide pressure independent response.
 

Conversely, venturi valves offer significantly higher turndown ratios necessary to achieve the minimum exhaust flow rates permitted by ANSI Z9.5 for laboratory fume hoods. Furthermore, the mechanical pressure independence inherent to the venturi valve design offers the fastest response to changes in duct static pressures without the need for complicated control solutions. This mechanical pressure independent characteristic allows the flow through the valve to be controlled without the need for any in-stream airflow sensing. Instead, each venturi valve is characterized in the factory with a position vs. flow relationship completely eliminating the need for airflow sensors and the associated inspection, cleaning and maintenance necessary for such components. Venturi valves can have a greater capital cost but can save in operating costs due to their maintenance free operation and higher turn down ratios.
 

Laboratory Air Pressure Monitors and Sensors

Laboratories are typically designed to operate under a negative air pressure with an offset between the air supply and exhaust. The airflow is from a cleaner to a less clean space. Room pressure monitors provide visual indication of laboratory pressure with audible alarm options. The indicators can be ball-in tube type or the more versatile digital type. The digital indicators can be easily configured and networked into the BAS. 

There are several types of laboratory room pressure sensors: diaphram; hot-wire anemometers; or thermal MEMS sensors. Each has its advantages and disadvantages; the Diaphragms are the least susceptible to dust but are typically less accurate; the hot-wire anemometers are more susceptible to dust but offer more accuracy; and the thermal MEMS sensors are digital which offer both accuracy and minimal contamination risk.

Laboratories Without Fume Hoods

The best method to control air flow in Laboratories without fume hoods is to use VAV dampers with standard speed actuators to control the air supply and venturi valves to control the exhaust flow. VAV boxes in the supply stream are quieter, less expensive and operate at lower pressures than venturi valves. The venturi valve controlled exhaust with electronic flow feedback would be unaffected by airborne lint and provide stable system pressure.

Laboratories With Fume Hoods

Fume hoods typically require a face air velocity of 100cfm. The face velocity can be controlled by sash position sensing, sidewall sensing (face velocity measurement) or hybrid sensing. An air flow valve response time of less than 3 seconds after completion of the sash movement is acceptable for most operations. Faster response times may improve hood containment following the sash movement. Presence sensors can be added to the system which detects motion in front of the fume hood. These allow the face velocity to be reduced when unoccupied.