SIZING INLETS FOR MECHANICAL VENTILATION PART 3 of 3 EILEEN FABIAN WHEELER Assistant Professor Environmental Control Agricultural And Biological Engineering Inlets require thoughtful sizing, placement, and control. The air inlets are the most im portant part of a ventilation sys tem since they are responsible for providing good air distribution and movement. To the credit of agricultural fan manufacturers, there are many good fans that will provide the desired air exchange. But, to many people, ventilation is still “a fan" and solutions to venti lation problems are often solved by the addition of more fans. Ad ditional fan capacity is justified in some situations but more often the cause of poor air quality in poultry structures is improper inlet func tion. Mechanical ventilation com ponents include fans, inlets, and controls, each of which is neces sary. They need to function to gether as a system. In mechanical ventilation, fans are responsible for the amount of air exchange while inlets control the air distri bution within the ventilated space. Air exchange is simply fresh air delivery to all birds and mixing of fresh air with stale air prior to re moval from the building. Inlets come in many shapes and sizes with varying levels of use fulness. The three functions of an air inlet are to provide fresh air throughout the building, control direction of air flow, and maintain fast inlet air velocity. If these three functions are not achieved, then poor air distribution, uneven temperatures, and drafts are the re sult. Fast inlet velocity is essential for providing air mixing and desir able circulation patterns. Inlet design and operation demand that some technical aspects of air flow be understood. In addition, there is an “art" to in let operation that comes with ex perience. The art and experience aspects are what make inlet func- No Re Be Inle Baff Upstream restriction ai 2 times max inlet area and often provides hurdles in diagnosing and solving ventilation problems. How Big Should Inlets Be? Air moves into a poultry build ing in response to a static pressure difference created by the fan(s). Air moves from a region of higher pressure to lower pressure and will enter an exhaust-ventilated house through any inlets (or holes) in the structure. The static pres sure difference required to venti late a building is very small, on the order of 0.05-inch water. When maintaining a relatively constant static pressure of this magnitude, one can calculate how much inlet area will provide the requited inlet air speed requited for proper air jet mixing and con trol. Provide 1.7 square feet of in let area per 1,000 cubic feet per minute, (cfm) of fan capacity. An other way to measure this is as 1 square-inch of inlet area per 4 cfm fan capacity. For continuous slot inlets, providing 2 square feet per 1,000 efin is even better. (Note that tunnel ventilation inlet sizing is based on a different criteria than outlined above.) Stay within this range of inlet size. A smaller inlet will create faster inlet jet velocity but increases resistance to air flow that can overload fans. Larger in lets cause more problems by creat ing drafts, not distributing air properly, and allowing dead air zones in the building. The inlet opening size is adjusted each time the fan exhaust rate changes. We want to maintain a reasonably constant static pressure around 0.05 inches in the building to pro vide fast inlet jet velocities. Con trollers arc used to adjust inlet opening size while maintaining correct static pressure. Restrictions or obstructions to air flow before or after the inlet must be avoided. Obstructions af ter the inlet deflect air into unde sirable drafts and can destroy good air circulation. Obstructions include waterlines and 2x4s in the air jet path. Restrictions before an inlet baffle will increase resistance to air flow. This lowers air speed. The minimum upstream restric tion should be no less than twice . Example: Need at least a 12-inch upstream clearance the maximum baffle inlet width (see figure). For example, consider the typi cal four-foot long by 10-inch wide box inlets spaced evety eight feet in a broiler house. If the maximum baffle inlet opening is 8 inches, then at least a 16-inch clearance is recommended for air coming .in the eave soffit and over the side wall construction at the cave. Not many house constructions can provide this space. In fact, field observations suggest that some houses do not even provide eight inches of clearance. One solution would be to provide more box in lets so that with a narrower baffle opening the upstream clearance criteria is met. Another solution is to switch to tunnel ventilation for high volume air circulation during hot weather. Inlet Design Checklist • Building Width. Mid West Plan Service agricultural engi neers recommend that for build ings up to 38 feet wide, place con tinuous slots at the ceiling along both sidewalls. For wider build ings, add one or more interior ceil ing slot or box inlets. This is based on how far a ceiling air jet can tra vel across a building with an ob jective to provide air distribution to the center of the building. • Maximum Distance. The maximum distance between fan and inlet is 75 feet Air moving (his far in confinement animal housing has picked up enough moisture, odor, dust, and/or heat to be considered stale air and should be discharged from the building. • Near Fans. Close inlets within 6 to 8 feet of each side of a fan during cold weather to prevent air short-circuiting out the fan before distributing throughout the build- ing. • Sectional Inlets. Inlets should be installed in sections so that op timal slot opening and air distribu tion can be effectively controlled. Some buildings have sections that arc not used for part of a produc tion cycle, such as during partial house brooding of broilers, so only the populated half of the house has functional inlets. Box inlets, which are spaced rather than continuous, can provide con trol over air distribution as build ing bird population and weather Restriction Before Inlet Baffle is Undesirable This rt control flow wl undesi change. • Cold Weather Inlets. Controll ed inlets are essential to direct in coming cold air and to provide mixing. Inlets are placed high on the sidewalls so that air can be tempered with room air before it reaches (he birds. The attic can be a wind-protected air inlet. This prevents wind and driven precipi tation from entering through side wall inlets. Often only a portion of the building inlets are used in the winter. For example, every other section of a continuous baffle inlet may be closed for the winter while the remaining sections are con trolled to provide ventilation inlet area. This allows half the inlets to be open one-half inch rather than trying to keep all the inlets open one-quarter inch. Generally, con struction irregularities will pre vent uniform openings less than one-half inch wide on long build ings. • Hot Weather Inlets. It is best to bring fresh air directly from outdoors. Roof insulation reduces sun warming of the building and is required if using attic ventilation ■ BUY. SELL. TRADE OR RENT THUI HIl ill INI ——>l^ (CLfISSIFIiP APS) PHONE 717-626-1164 or 717-394-3047 FAX 717-733 6058 Men , Tues , Wed . Fn 8 AM to 5 PM Thurs 7 AM to 5 PM IM CONSTRUCTION EQUIPMENT Ingersol Rand hydro boom track dnll. ECM-250 diesel, 750 CFM Worthington compressor. 717/786-1720. JD 450 B Track Loader w I Hoe, $12,500. Balt. Co (410)823-2640. JO 555 1980 bad trans, otherwise good condition. Ripper. Extra parts in cluded complete parts trans, ROPS, bucket, etc, $9,700. Offers considered. Washington Co, MD, leave message, (301)842-3844. Myers Snowplow C-8 Power Angle w/Mounting Frame, Lights, Controls $1,200.; 10' Oallion Dump Body w/Coal Chute, Sand Blasted Epoxy Primered w I Light Package, Very Good Condition $1,200.; 20’ Storage Trailer, Tandem Axel, Double Rear Door, $1,150.; MBW Plate Tam per, w/Water Tank, Excel lent Condition $1,050.; Fiber Glass Truck Cap, 88 Chevy or Newer $150.; Knack Construction Site Gang Box, 60’Lx30"Wx48"H w/Lock $400.; Trail King, 10/Ton Equipment Trailer w/Air Brakes, Excellent Condi tion, $6,650. (717)2745619. Lancaster Fanning, Saturday, January 30, 1999-D7 in hot weather. Outdoor air can be blown directly onto older or adult birds (not recommended for the very young) to create a wind-chill effect for enhanced cooling. Hot weather inlets need to be sized to provide a large amount of air. • Inlet Screens. Screen tire in take with three-quaiter-inch hard ware cloth or bird netting. More restrictive screening or residen tia'-typc sofGt vents with pinholes will drastically reduce air flow and will clog with dust for further resistance to air flow. • Inlet Size. Provide 1.7 to 2.0 square feet of inlet area per 1,000 cfin fan capacity. Provide at least double this area upstream of con trol point of inlet More information is available in “Inlets for Mechanical Ventila tion Systems in Animal Housing,” G-91, an eight-page fact sheet This and other agricultural engi neering publications on ventila tion of agricultural buildings are available free from Agricultural and Biological Engineering Ex tension, 246 Agricultural Engi neering Building, University Park, PA 16802, (814) 865-7685. 1967 Ford Boiler Truck, Excellent Condition $5,500.; 72 R-600 Mack Dump Truck, $8,500.; 68 R-700 Mack Dump Truck, $8,500.; 65 Mack Dump Truck. $8,500.; 64 CAT D6-C Bull Dozer, Excellent Condition $12,500. (914)895-3995. Forklift Wholesalers 2000 to 02000 Lb. Lifts Avail able. 70 In Stock. Sale- Rental-Finance w/ Warranty. Chalk Equip ment (410)686-6800. IH Rough Terrain Forklift 20’ High, Excellent Condi tion Asking $lO,OOO. 609-607-2004. Bridgewood molder, Whit ney planer, Newman jointer, Hermange power feed saw, DeWalt saw, Marbel pinch roller- well maintained. Call (301)791-7880. Case WlO, 4WD, wheel loader, cab, 6-cyl diesel, 4-1 bucket, lights, flashers, beacons, mirrors, new glass, $7300. 717-240-0881 717-766-9275 Cat D3B dozer, 6-way blade, new UC, owner/ operator machine, $26,000. 717/754-3000. Caterpillar D-2 & D-4 bull dozers, 50% U IC, $B5OO for both. 008-735-5813
Significant historical Pennsylvania newspapers