Canopy Hood Designs

Canopy Hood Designs: An Important Consideration for Your Lab

CSS_Scott Mechler_Headshot
Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

You have a lot of choices when it comes to ventilation solutions for your autoclave and some are better than others. Canopy hoods are an optimal solution for handling odors, steam moisture and low-levels of chemical vapors.  The following are guidelines from the National Institute for Health for the design of autoclave door canopy hoods.

  • The canopy should extend 1 foot wider (6 inches on each side) than the open autoclave door and the front end of the hood should extend so that it is at least 6 inches further out from the fully open autoclave door.
  • The height of the hood above the autoclave door should be from 3 inches to a maximum of 3 foot above, with the shortest distance possible to prevent employees from hitting their heads on the hood and allow access to controls.
  • The total flow rate for the canopy hood is calculated using the following equation (Industrial Ventilation Manual 25th Edition; please see the note below):

Qt = 6.2 x L x b1.33Δt0.42

where: Qt = total hood air flow, cfm
L = length of the canopy hood, ft
b = width of the canopy hood, ft
Δt = difference between temperature of the hot source and the ambient, F.

Note: This equation is applicable if the distance between the hood and the hot waste does not exceed the length/width of the waste or 3 ft, whichever is smaller. Please note that this equation applies to hot processes but does not account for the effects of high pressure. Since a canopy hood is a receiving hood not a capture hood, the airflow rate to the canopy should be at least 10% higher than the rate of steam and gas generated from the autoclave.

Sample calculation: if an autoclave operated at 250F has an opening of 3 ft length and 2 ft width (room air temperature is 70F), the required total hood air flow is

Qt = 6.2 x (3+1) x (2+1)1.33 x (250 – 70)0.42 =  950(cfm) *

*Note: 1 foot added to the length and width of the canopy hood per the design guidelines listed above

Consolidated does not provide specifications for exhaust hoods or canopies. We leave the particulars of the lab ventilation system to the HVAC engineers. We do however strongly urge all of our clients to invest in such equipment.

While there is the concern that a lab ventilation system can create exorbitant costs related to energy use and loss of conditioned air, engineers at Consolidated recommend the following simple energy saving feature: Use Dry contacts to tie the canopy hood into the autoclave control system such that the ventilation only occurs when needed (i.e. when the autoclave door is opened after a cycle). In addition to dry contacts, some hood designs are more energy conscious by being demand-based, which only ramp up when particles (steam, smoke) or heat is detected.

Contact us today to learn more about our ventilation recommendations for autoclaves or to talk to one of our service technicians about other solutions.

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