New Standard For Fume Hood Minumum Ventilation Rate

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After years of work, the new ANSI/AIHA Z9.5-2012 Standard for Laboratory Ventilation has been released. This new Standard replaces the one issued in 2003 and has a huge impact when it comes to energy efficiency in labs. After years of testing here in the United States and a review of European practices, a new minimum fume hood ventilation rate has been established.movie Cars 3 2017 streaming

The biggest driver of laboratory energy use is outside air. Due to their nature, labs require 100% outside air with no option for recirculation. The biggest drivers of these outside air rates are the required hood minimum flows, thermal loads and air change rates. With the increased usage of demand based control of air change rates and the reduction of sensible heat loads in labs, the main driver in labs is now the required hood minimum ventilation rate.

The previous standard called for a minimum of 25 cfm per square foot of fume hood bench area (work space). This equates to around 250 cfm for a 6 foot hood. The new standard changes this from a cfm per square foot to an air change rate.

Here is the exact verbiage from the new Standard:

When attempting to save energy in typically higher hood density installations, minimum fume hood flow rates in the range of 150 to 375 hood air changes per hour (ACH) have been used to control vapor concentrations inside hood interiors.

Minimum hood flow rates might be selected within the above range if the user complies with provisions below*. An exception being where a written hazard assessment indicates otherwise.

For purposes of establishing a value for the internal volume of the hood used in determining the flow rates corresponding to the desired value of hood air changes per hour, the internal hood volume is approximated and hereby defined as the total internal hood work surface area times the internal height of the hood.”

The following considerations shall be taken into account (as applicable) when setting the minimum hood flow rate for each hood:

  • Control of ignition sources within the hood
  • Design of the hood, the materials used in the hood and the anticipated maximum generation rates,
  • Potential for increased hood interior corrosion,
  • Effect on exhaust stack discharge velocity,
  • Fume hood density,
  • Need to affect directional airflows, and the
  • Operating range of the hood exhaust equipment and the associated control system.

D   So with proper lab design (accurate airflow devices, exhaust fans) and controls (room offsets), 150 ACH is an appropriate minimum flow setting for VAV hoods. For the average 6 foot hood, this means lowering the minimum exhaust from 250 cfm to 100 cfm. Why is this significant? Even in a small lab, with only two fume hoods, this could mean the reduction in the space air changes per hour from 6 to 3…or an approximate savings of $1500/year for the space.

In existing buildings with Phoenix Controls systems, this change could have huge energy savings potential. We would be more than happy to do an analysis of your building to see what lowing the fume hood ventilation minimum could mean for you!

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