There is a number of ways to successfully achieve sound ductwork arrangement. But it is the simplest arrangements that are usually the most effective. Before you begin, determine if you need a wall mounted, ceiling-hung, or roof-mounted arrangement. Consult with your laboratory design team and inquire about weather hoods that protect the motor and pulleys from the blower, when it is mounted to the outside of the building; you may also seek guidance if this is necessary for your laboratory. There are special coatings that can be furnished or factory applied to the blowers such as Harasite, Eisenheiss, Tygon, and Amercote. There are also special impellers, made of stainless steel, monel (primarily composed of nickel), or aluminum available that again you can consult your laboratory design team about. But the best place to begin, in understanding patterns in ductwork arrangement, is with knowledge of individual blowers and ducts, exhaust blowers, supply blowers and general knowledge of arranging ducts. Here is a guide to ductwork arrangement, courtesy of Laboratory Furniture, Inc.
Individual Blower & Ducts Per Fume Hood
“In general, it is suggested that each hood have its own blower and ducts for maximum flexibility of operation and to avoid black-flow from other hoods. However, hoods will perform efficiently when connected to a common duct-work system provided the duct and blowers have been properly sized for the number of hoods units in the system.
In the case of exhaust blowers, recommended practice is to place the blower at the end of a straight length of duct and as near as possible to the final point of discharge. Under these conditions the air flow is smoothly guided into the blower inlet, allowing the blower to operate efficiently. Also, the major portion of the exhaust duct is under a negative pressure relative to its surroundings. Therefore, air leakage throughout slightly open joints into the duct and there is no possibility of discharging fumes from the duct into the laboratory areas.
For supply blowers connected to a supplementary air supply hood, the blower should be placed at the end of a straight run of duct and as near as possible to the hood. Under these conditions, blowers will operate efficiently and loss of pressurized air through duct work is to a minimum.
It is wise to arrange the system so that the air is guided into and out of the blower as smoothly as possible. In addition, the system designed should be such that chances of fume leakage into the laboratory are at a minimum and the system can be easily maintained. Several ductwork arrangements for various laboratory layouts are shown below.
These figures show suggested methods of arranging ducts and blowers for maximum safety. Blowers may be installed within the laboratory or on roof for external wall surfaces. When using constant speed blowers, a damper will be required at the hood outlet to initially adjust the air volume flowing throughout the hood. Blower Platforms are sturdily consulted to support the blower and motor. Dampeners reduce inherent blower vibration.”
We know that hood location is essential to both laboratory safety, energy conservation, and effective experimentation. Determining the best location will allow for optimal air flow patterns. Without blower system, the mechanical devise responsible for air movement throughout your laboratory, there would not be proper air movement throughout your fume hood. Proper installation and maintenance of blowers as well as ductwork allows by lab planning professionals will allow for these devices to do their job. The same is true for walk-in and bench top fume hoods, optimal performance is achieved when fume hood’s are installed and operated correctly. You have the ability of increase your fume hood’s life expectancy by giving it the proper TLC. Laboratory Furniture, Inc, provides us with a condensed breakdown of hood location, blowers, ductwork, and hood operation.
- “Strong drafts interfere with air flow patters in hoods. Hoods placed directly in front of doors, open windows or air-conditioning registers cannot be expected to give optimum performance. If possible, locate hoods in the area of least disturbance in the room.
- The line of traffic movement of equipment and personnel should be determined before the placement of the hood is decided. It is both dangerous and inconvenient to install a hood so that the operator is forced to work in the line of traffic movement.
- If common exhaust or supply air system are to be used for several hoods, laboratory layouts should be made with the idea of locating the hoods so that a minimum of connecting ductwork is required. However, when making these decisions, air flow and traffic flow patterns should be kept in mind. When using common exhaust or supply systems, individual hood dampers and recommended to given satisfactory control or air volume to each hood.
- When hoods are to be used as part of the air-conditioning system to exhaust air from the laboratory, care should be taken to properly locate the hood in relation to the air inlet registers. In general, the hoods should be placed on the opposite wall from the side wall type inlet register.
The hoods should be positioned so that air from registers or diffusers first sweeps through the laboratory working area and then into the hoods. Placement of a hood directly next to a register may result in both poor hood performance and short circuiting of conditioned air from the air register directly into the hood.
Blowers and Ductwork
- Choose a blower of large enough capacity. It should be remembered that dust and other contaminants soon reduce blower output. Blowers should be chosen to allow from some drop in capacity due to fouling.
- As in any well designed ventilation system, blowers and ductwork should be connected to the hood so that pressure loss in the duct system is a minimum. There should be as few bends, loops and other restrictions in the line as possible.
- In supplementary air hoods, supply and exhaust blowers should be operated by one switch to prevent the possibility of an operator turning on supply blower only. An alternate method of wiring is to have one switch operate exhaust blower only. With this alternative method of switching, the supplementary air hood may also be operated as a straight exhaust hood either for convenience or in case of a spill at any location within the laboratory—which requires additional air to be exhausted through the hoods. Because the supplementary air hood is designed on aerodynamic principles, it will also give excellent performance as a straight exhaust hood.
- In some modern plants, fume hoods are used as part of the laboratory ventilating system. Under these conditions the hood blowers should be in operation at all times.
- Include hood blower and ductwork system in the plant maintenance schedule. Dust and other contaminants collected on the blades of the impeller of a centrifugal blower can greatly reduce its capacity. Blowers should be used so that they are accessible for periodic cleaning. Ductwork is susceptible to mechanic and chemical failure. Periodic examinations and ductwork should be made to detect loose joints, leaking packings and porosity due to corrosion.
- A hood should not be used as a laboratory storage depot. Piles of extraneous material in the hood— particularly at exhaust openings at the back of the counter— interfere with hood performance. Poor performance can often be traced to blocking of exhaust openings by unused bottles, flasks, etc.
- Poor operation can sometimes be traced to blockage in the blower systems. Old rages, paper or tools accidentally dropped into the ducts will reduce blower capacity.
- Blowers should be examined to make certain that the direction of the rotation is correct. Centrifugal blowers may still deliver some air while rotating in the wrong direction, but their output is well below rated capacity.”
In a previous blog post we wrote about the ASHRAE test that supports lab performance by using an automatic monitoring for lab air control. The handbook states that, “As the operation, materials and level of hazard of a room change, an increase or decrease in the minimum ventilation rate should be evaluated.” It also states that “Active sensing of the air quality in individual labs is an alternative approach for dealing with the variability of appropriate ventilation rates, particularly when energy efficiency is important or when less may be known about the hazard level.” While this is recommended practice, there is no ‘correct’ ACH (air changes per hour) value for every lab and for this reason ASHRAE is essential to laboratories, as it establishes a balance between conservation of energy without compromising the safety of lab technicians and staff, through its monitoring system. The handbook also recommends that airflow is increased before lab attendees infiltrate the space each day, at least one hour before is recommended, since contaminants may build up overnight. But how does ANSI/AIHA’s updated standard of 2012 play into this?
ANSI is the National Standards Body for the U.S. They adopt industry standards but do not write them. Once these standards are adopted, they often become mandatory after a voluntary consensus by board members such as Harvard, MIT, the US Navy, ASHRAE, and General Mortars have reviewed them. Determining air flow for laboratory venalities systems has stumped research labs for decades. It is for this reason that the ASHRAE test, was the only standing requirement for air change rates until a few years ago when a shift in prescribed ventilation was based more on performances than a prescriptive approach. It was just a decade ago that minimum air change rates, in a laboratory, were recommended to be 8-12 air changes per hour. With growing concern of energy cost, this prescribed rate per hour dropped to 6 but it didn’t stay there for long, and 8-12 air changes per hour became the new normal once again. So why is it that during a lecture at Harvard, an MIT professor declared that “Air changes per hour is not an appropriate concept for designing contaminant control systems”?
Refer to this diagram, courtesy of Yale’s Journal of Chemical Health and Safety that nods to the same evidence for room ventilation rates. Their findings also prove that no ACH (air changes per hour) is appropriate to be applied to all rooms of operation. Research shows that anything above 12 ACH is unwarranted, but below 8 ACH tampers on a hazardous operation and should be reserved for periods of no-occupancy.
ANSI/AIHA Z9.5-2012 Laboratory Ventilation Standard states that “An air exchange rate (air changes per hour) cannot be specified that will meet all conditions. ANSI Range standards provide standards for air changes per hour, by stating all contaminants should be controlled at the source and that specific ventilation rates should be established and agreed upon by the owner or their laboratory designer. Energy can be used more efficient in your laboratory by reducing exhaust air requirements but the best, and safest way, to achieve this is by using variable volume control. The ANSI/AIHA Standard allows for you to reduced fume hood, minimum, flow rate for variable-volume hoods. While this all depends on aspects of laboratory operation. A typical hood in the U.S. uses 3.5 times the amount of energy as a home. So when it comes down to hospital laboratories, research and development, compounding pharmacies, or educational laboratories ventilation rates need to continuously asses standards and codes for a balance of safety and energy efficiency.
Here are the ANSI/AIHA standards:
- “Adequate laboratory chemical hoods, special purpose hoods, or other engineering controls should be used when there is a possibility of employee overexposure to air contaminants generated by a laboratory activity.”
- American National Standards change for sash-closers, “The adverse effects on energy consumption when the operators feel it is their responsibility to close the sash; and the adverse effects on energy consumption when the operators do not feel it is their responsibility to close the sash.”
- The average face velocity must produce adequate containment of hazards chemicals generated. The flow measuring device should test for small-volume generation and large-volume generation for areas of reverse flow, stagnant zones, escape, vortex regions and clearance. Any visible escape beyond the plane of the sash constitutes a failed performance.
Steel, an alloy of iron and carbon, is constructed to withstand the maximum stress that a material can undergo without stretching or breaking. It is for this reason that the laboratory industry entrusts in the strength and dexterity of this element. It holds the infrastructure of buildings, automobiles, ships, appliances. But surely that’s not the only reason we like gravitate towards steel in commercial and industrial workspaces, it also falls back to what aesthetically pleases the eye. Steel is clean, contemporary, and devoid of trends. It has been around long before our grandparents age and will outlive the human race.
You’ve just bared witness to our ode to steel but now for the realists inquiry, how on earth are you suppose to clean it? It’s challenging to scratch or damage, yes, but steel does expose fingerprint smudges and water marks with great ease. If you have a steel refrigerator you know it’s nearly impossible to keep your loved one’s handprints off the handles and the same goes for fume hoods. Their sole purpose is to be a vessel for experimentation. With experimentation comes test tubes that runneth over and eventually layers of unknown gunk, aka genius, that even the most OCD of folks have given up on tending to. We are here to offer you the cleaning guide to both stainless and powder coated steel:
Direction of the Grain
Before we break into what to use to clean you must master the art of how to clean. Cleaning in the direction of the grain is especially important for stainless. If you look closely at your fume hood, or lab cabinetry, you can visually see a horizontal or vertical direction in which the grain moves. Do not rub in a circulation direction, although you gravitate towards this wax-on-wax-off motion, you must flow in the direction of the grain for optimal results.
Many will recommend vinegar as an all-natural cleaning solvent for pretty much anything in your home but when it comes to degreasing your kitchen range hood, or removing bacteria or mold from your fume hood, there are many other household cleaners better equipped for the job. A recent study in the Journal of Environmental Health confirms that, “Vinegar was more effective in reducing microbial containment than alternative cleaners but least effective in removing soil”. If you strive to remove biological microorganisms from your lab then vinegar can be used but if your goal is to remove liquids or other matter then reach for an alternative solution. Since dirt is often the most common containment you will be cleansing your laboratory or home of see our alternative below.
Cleaning Alternative / Types of Containment
What should you use as an alternative? Regular dish soap and water! Grab a bucket and mix soap with a few drops of liquid detergent in warm water. You can use a lint-free rag to wash the surface (of powder coated steel) making sure that you clean beneath the grooves and alongside the not so visible surfaces. Disclaimer: be mindful of sharp corners, often they are squared, sharp, and with adequate pressure applied they can wound. Follow up by rinsing with cold water. Powder coated finishes resists rust caused by oxidation so you can actually allow the water to dry on the surface without harming the paint (similar to baked on powder coated finishes of a car). If that doesn’t do the trick then try using a pH-neutral household cleaner. Avoid solvents, these are liquids or gasses that can dissolve or extract substance like grease, oil, or paint and they can obstruct the finish of your powder coated furniture.
We recommend using a bristle brush, sponge, or clean cloth. Avoid paper towels and cotton rags as they will stick to the coating. Also avoid using a carbon steel brush or steel wood because they may leave particles along the surface which can lead to unfavorable rusting. Once you have cleaned the surface with soap or a household cleaner, be sure to conclude your cleansing by applying an additional layer of water to rinse away any leftover soap or cleaning product. As for stainless, you can spot treat greasy fingertip smudges by using a glass cleaner or rubbing sodium carbonate with water (with a soft rag). Again, rinse with water afterwards. Avoid using chloride-contained detergents.
Since all steel furniture have varying finishes, we are happy to speak with you further and lend advice about the best cleaning regimen. We hope you reach out to us via Twitter @geniescientific or you may feel free to call us at (714) 545-1838.
What is the advantage of having a custom built fume hood over a standard?
The advantages of a custom, floor mount, walk-in fume hood along with the disadvantages of a standard size, fume hood, are as follows:
First and foremost the disadvantage of a standard floor mounted fume hood is basically one size fits all. Standard depth is not deep enough, standard height is not high enough, and standard width is not wide enough. It is up to the end-user to make the appropriate interior size to meet their needs and often it is safer for the laboratory and better suited for experiments to have a custom design.
The most common mistake made purchasing standard hoods are undesired, without the consideration of support apparatus such as vacuum pumps, water chillers, lattice grids pass-through ports, which are needed to operate with essential equipment such as reactors and large columns.
The advantage of a Genie Scientific custom fume hood is that this fume hood will fit your equipment needs, not only in the interior dimensions but also a host of other custom features that will make your hood extremely functional. By doing so this will add product productivity but most of all safety.
Genie Scientific’s custom designed fume hoods are not only about the right size but are engineered for the correct exhaust air flow to meet OSHA, NFPA, ASHRAE 110 tested, and manufactured to SEFA 8 standards.
At Genie Scientific we stand behind our product and have done so for over 30 years in the industry. It is our mission to not only communicate with you, the end-user, but we make sure that we achieve your desired goals. We are able to do this while keeping in mind regulations of fire department, city, and state regulations as we communicate with your general contractor, HVAC engineer, plumber, electrician, and property management.
The last thing you want is nowhere to turn when an agency or contractor has questions, or concerns, that need to be answered. At Genie we can assure you that a line of communication is always open.
We build for you!
Ductless hoods are often referred to as re-circulating range hoods. They filter the air, generally through a carbon filter, and then return the clean air back into the space. Ducted hoods on the other hand remove the air to the outside of the building through a 6” to 10”, approximate, ductwork. They also, quite intelligently, have chemical filtration and detection that provides workers with an increases level of safety. Trying to decide which is best for you? Here’s our breakdown of the two.
Ducted hoods have ventilated enclosures that pull contaminants out of the building. This system is considered the safest for workers in laboratories and its often the easiest for employers to maintain. Ducted hoods have a base, work surface, hood, blower and ducting that carries the air outside of the building. The engineer of the heating, ventilation and air-conditioning (HVAC) system needs to determine if your room has enough air to provide the necessary volume of ventilation to the hood. HVAC can work with your company to provide optimal air supply, and balance, so that everything functions properly within the fume hood. There are a few different subcategories within ducted fume hood such as canopy hoods, by-pass hoods, and conventional hoods.
A canopy hood is hung from the ceiling or mounted to a wall. It’s purpose? To remove steam, heat and odors from equipment that is inconvenient to workers but not hazardous. Due to their unenclosed nature, they pull in massive amounts of air and if you are working with hazardous substance, shifts in room currents could be problematic for workers. Genie turns to canopy hoods for heat plates, water baths or portable equipment. Standard canopy fume hoods are made from a cold rolled steel finish with acid wash and powder coated epoxy paint. Epoxy coated steel has a high heat resistance. We also design stainless steel canopy hoods, fabricated for 18 gauge steel that has a smooth grain finish.
With a by-pass hood design the lowered sash allows a steady velocity at the hood opening. This also offers a more consistent working environment and depending upon the chemicals you are using, this can be a safer choice for your laboratory.
In a conventional hood air enters through the sash opening. When the sash is lowered, the hood needs to maintain a continuous volume of air supply. The only way it’s able to do this is by increasing air velocity. Sometimes this creates currents and high-speed winds within the hood.
Ductless fume hoods are self-contained filtered laboratory enclosures. They are mobile, save energy, are easy to install and cheaper because no ductwork is required. The disadvantage is that workers are at a greater risk of chemical exposure, filter maintenance is required, they can be noising due to the internal blower and there are limited applications for filter options.
Consider the following: In a ductless hood there should be no extreme heating, no more than 10 chemicals should be used per application, small volumes of chemicals should be used (approximately 500 mls or less) and exposure time should be within 2-3 hours per day. Another important question to ask yourself, if you are considering the ductless route, is will the chemicals you are using adequately filter through carbon? There are a range of filters that have different chemical trapping capacities but if your application doesn’t match available filters you’ll be required to move forward with a ducted fume hood. Talk to a fume hood specialist today about various filters for chemical groups. Last determine how often you will be replacing your carbon filter, this will also give you a more accurate financial cost. Keep in mind that the filter life depends on the chemicals used, evaporation rate, chemical volume, duration of usage and the temperature of the chemicals.
There is an art to the installation and design of a ducted fume hood. To ensure your in the right hands, call the fume hood specialist, Genie Scientific, today.