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Air inlet systems For optimal control of both bird performance and energy usage a modern poultry house should ideally have three inlet systems With each inlet system specifically designed to obtain very specific objectives: Minimum Ventilation Inlet Systems Michael Czarick The University of Georgia Hot weather inlet system Designed to produce maximum bird cooling Rapid air exchange Produce high air velocities over the birds Tunnel fans with side wall inlets Tunnel ventilation It is important to realize what makes tunnel ventilation so effective in producing bird cooling is not really the fan power…but rather the inlet system. Moderate weather/temperature control inlet system If you were to operate all your tunnel fans through your side wall inlets, birds would not receive nearly the same amount of cooling. 500 ft/min 250 ft/min 1,000 ft/min Designed to control house temperature during moderate weather with older birds. 150 ft/min to 50 ft/min Broilers/turkeys Breeders Pullets = 4 to 5 cfm per ft2 of floor space = 3 to 4 cfm per ft2 of floor space = 2 to 3 cfm per ft2 of floor space 1 Moderate weather/temperature control inlet system For our moderate weather ventilation system we need approximately 1 ft2 of inlet area for every 750 cfm of exhaust fan capacity used for temperature control Example (40’ X 500’ broiler house): Fan capacity = 40’ X 500’ X 4 cfm/ft2 = 80,000 ft3/min Roughly four 48” fans Inlet area = 80,000 / 750 = 106 ft2 Last but not least… We need a minimum ventilation inlet system specifically designed to bring in just enough fresh air to maintain air quality during cold weather: If we were to install a typical 44 ¾” X 5 ¾” air inlet…. Inlet area = (44.75” X 5.75”)/144” = 1.8 ft2 Number of inlets = 106 ft2 / 1.8 ft2 = 60 Minimum ventilation inlet system Traditionally we have used our moderate weather inlet system for both temperature control and minimum ventilation but… Maximize heating of incoming cold air before moving down to floor level Distribute small amounts of cold fresh air evenly throughout a house without causing drafts they may not be ideal for use during minimum ventilation Our traditional inlet systems are typically designed for maximum air flow 4 to 6 cfm per square foot of floor space Which is significantly more than we would like to use during cold weather. 2 The problem is that with traditional side wall inlets The fact is.. That with young birds will generally use 1 cfm per square foot of timer fan capacity or less. 40’ X 500’ house would generally require 20,000 cfm of timer fan capacity on younger birds or less. 900 800 700 600 500 400 300 200 100 0 = 0.6 X 20,000 = 12 square feet Moderately tight house (0.8 square feet per 1,000 ft2) Leakage area But this is for a perfectly tight house… Even a very tight house has a significant amount of leakage How much do 60 inlets need to open for minimum ventilation? Very tight house (0.6 square feet per 1,000 ft2) Leakage area = cfm / 750 = 20,000/750 = 27 square feet 0.12 0.11 0.1 0.09 Static pressure 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 750 cfm/ft2 Inlet area required Leakage area When we want to bring in a little air from an inlet system designed to bring in a lot of air we end up with very small inlet openings. Inlet opening 0 Cfm per square foot How much would our 60 inlets need to open to bring in 20,000 cfm = 0.8 X 20,000 = 16 square feet Inlet area required For a very tight house we need to provide = cfm / 750 = 20,000/750 = 27 square feet 27 – 12 ft2 (leakage) = 15 ft2 of sidewall inlet opening For a moderately tight house we need to provide 27 – 16 ft2 (leakage) = 11 ft2 of side wall inlet opening 3 How much do 60 inlets need to open for minimum ventilation? Most inlets tend to direct incoming air up…not out along the ceiling when opened a small amount Very tight house Inlet opening 85.0°F = 15 ft2 / (60 X 44”/12) = 15 ft2 / 220 = 0.068’ = 0.8” 80 70 Very moderately tight house Inlet opening = 11 ft2 / (60 X 44”/12) = 11 ft2 / 220 = 0.05’ = 0.6” 60 50.0°F Plus very small openings don’t tend to throw the cold air very far To get the air to throw properly it often takes a fairly large inlet opening (i.e., 2”) 90.0°F 90 100.0°F 100 90 90 90 90 90 80 80 80 80 80 70 80 70 80 70 60 70 60 70 60 70 60 50 60 40.0°F 45.0°F 50.0°F 55.0°F 60.0°F 65.0°F So…. In order to maximize environmental control during cold weather producers typically convert their temperature control inlet system to a minimum ventilation inlet system by latching closed ½ or more of the side wall inlets 50.0°F Minimum ventilation inlet system It works, but requires a fair amount of management time: Latching inlets closed during the night possibly unlatching inlets during the day Which typically means it will not get done like it should 4 Furthermore, if we are not careful environmental conditions can become highly variable What we ideally need is a stand alone minimum ventilation inlet system With a few inlets, widely spaced, opened a lot. 90.0°F 90 80 70 60 55.0°F Specifically designed for use for very cold weather for use with just a few exhaust fans. For a 40’ X 500’ house Air cannons? 1 – 2 cfm per square foot (broiler, breeder, pullet). Maximum of 40,000 cfm Minimum of 20,000 cfm or less Maximize heating of incoming cold air before moving to floor level Distribute cold fresh air evenly throughout a house without causing drafts While at the same time keeping fuel usage to a minimum Recessed minimum ventilation inlets Solair wall 5 A better example of a minimum ventilation inlet is an attic inlet Attic inlet systems Attic inlets are typically located near the center of the house That is where your hottest air tends to accumulate Maximizes the distance between the cold incoming air and the birds Everything about an attic inlet system makes it well suited for use as a minimum ventilation inlet Attic inlets are typically located above a house’s heating system Insures a quick interaction between the coldest and hottest air in a house 99.0°F 99.4 97.4 95 94.2 90 92.1 89.6 86.1 85 83.6°F Attic inlets above directing air above a houses heating system Attic inlets with a hot water heating system 6 Attic inlets tend to maximize the throw of cold incoming air Attic inlet above heating system Maximizes the throw/conditioning of the incoming air Top of the inlet is the ceiling… Air comes in straight along the ceiling... Attic inlets pull their air from the attic 100.0°F 100 Which is less affected by strong winds and… 90 80 70 60 55.0°F Daytime attic temperatures 1-Feb 30-Jan 28-Jan 26-Jan 24-Jan 22-Jan 20-Jan 18-Jan 16-Jan 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 14-Jan Temperature (F) (typically 5–30oF higher than outside) 12-Jan is often warmer than outside air. Date attic outside 7 Drawing in warmer air can lead to reduced fuel usage 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 5 to 15% lower fuel usage House tightness Management Time of year 85.0°F 85 78.2°F 75 80 70 75 65 30-Jan 29-Jan 28-Jan 27-Jan 26-Jan 70 25-Jan Temperature (F) Nighttime temperatures are the same as outside 60 65 55 60.0°F Date attic outside But more importantly slightly higher daytime house temperatures… 53.1°F resulting in higher daytime ventilation rates… 300 250 82 Cubic feet per hour 50 Conventional Inlets Attic inlets Side wall inlets Attic inlets Attic inlets 2-Feb 1-Feb 2-Feb 1-Feb 80 75 70 65 60 55 50 45 40 35 31-Jan 4-Jan 6-Jan 8-Jan 10-Jan 12-Jan 14-Jan 16-Jan 18-Jan 20-Jan 22-Jan 24-Jan 26-Jan 28-Jan 30-Jan 1-Feb 3-Feb 5-Feb 7-Feb 9-Feb 11-Feb 13-Feb 15-Feb 17-Feb 19-Feb Relative humidity Total cubic feet of air moved / 10,000 13,000 12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Attic inlets Higher ventilation rates lead to lower Rh both day and night… 27-Jan which leads to higher overall daily ventilation rates of around 20%... Date 31-Jan 28-Jan 2-Feb 1-Feb 1-Feb 31-Jan 31-Jan Date Conventional Inlets 0 26-Jan Set temperature 30-Jan 30-Jan 29-Jan 29-Jan 28-Jan 28-Jan 70 30-Jan 72 100 30-Jan 74 150 29-Jan 76 200 28-Jan 78 29-Jan 80 25-Jan Temperature (F) 84 Conventional inlets 8 and a lower daily Rh over the course of the flock… and drier litter – lower ammonia 80 75 Relative humidity 70 65 60 55 50 45 3-Jan 5-Jan 7-Jan 9-Jan 11-Jan 13-Jan 15-Jan 17-Jan 19-Jan 21-Jan 23-Jan 25-Jan 27-Jan 29-Jan 31-Jan 2-Feb 4-Feb 6-Feb 8-Feb 10-Feb 12-Feb 14-Feb 16-Feb 40 Attic inlet house Side wall inlet house There are a variety of attic inlets on the market Single direction Single direction attic inlets above tube heaters Two way / Bidirectional 95.0°F 90 71.5 57.9 43.4 80 70 60 55.0°F 9 Bi-directional attic inlets above tube heaters 44.5 Bi–directional inlets 95.0°F 58.2 73.7 90 80 70 60.0°F Four way door inlets and four way drop bottom inlets There are a couple of different methods of opening/closing attic inlets as well Counterweighted or spring Machine actuated 10 Counterweighted or spring Door opening static pressure is typically between 0.05” and 0.07” The opening static pressure can be modified by adding weight to the counterweight 5/8” nut will increase the opening static pressure to 0.07” Or adjusting and external counterweight Adjustable external counterweight Adjustable external counterweight Adjustable internal spring 11 Attic inlets Attic inlets All these attic inlet systems have proven to work well as minimum ventilation inlets and have been used broiler, layer, turkey, and swine houses for decades. . Installation tips How well they will work depends, like many other things, on proper installation and of course management House tightness is very important The effectiveness of an attic inlet system is heavily influenced by house tightness Minimum house tightness standard = 0.13” using 1 cfm/ft2 of floor space of exhaust fan capacity Minimum ventilation fan capacity 1 – 2 cfm per square foot (broiler, breeder, pullet) Attic inlet systems are typically designed for 1.5 cfm per square foot of floor space 40’ X 500’ house Attic inlet capacity 0.8 ft2 of leakage per 1,000 square feet Many manufacturers of attic inlet publish a rated capacity of their inlets Number required? The tighter the house the more air that will enter through the attic inlets = house size X 1.5 cfm/ft2 = 40’ X 500’ X 1.5 cfm/ft2 = 30,000 cfm 12 Double L – TJ4200 Aerotech ceiling inlets How many four way attic inlets should be installed Be careful about how the capacity of the attic inlet was determined The rated capacity of the Double L TJ4200 and Eagan four way inlets is approximately 1,800 cfm per inlet A minimum attic inlet capacity should be determined when opened at 2” to 3” …not 6” to 12” Number required: 40’ X 400’ =12 40’ X 500’ =15 50’ X 500’ =18 60’ X 500’ =22 Minimum ventilation inlet open too much will lead to drafty conditions The greater the capacity per inlet…the fewer installed…the greater the distance between attic inlets Highly variable environmental conditions When an inlet capacity is over estimated they will tend to open more than they should. 13 Attic inlets opening too much during minimum ventilation Attic inlets opening too much during minimum ventilation 95.0°F 90 80 70 60.0°F What is the capacity of a 24” two directional attic inlet Though they can open 5 or 6 inches their capacity should be determined around 3 to 4 inches. Inlet capacity = (length X opening size)/144 X 750 cfm/ft2 = (48” X 4)/144 X 750 = 1,000 cfm Do not put in more than specified! Attic inlets are for MINIMUM ventilation, not temperature control When an excessive number of attic inlets are installed: House with 56 attic inlets When minimum ventilation fans come on they don’t even open They will not operate as effectively when used with minimum ventilation fans May have to latch half of them closed during very cold weather. House may become drafty Do not put in more than specified! They are for MINIMUM ventilation, not temperature control When an excessive number of attic inlets are installed: They will not operate as effectively when used with minimum ventilation fans May have to latch half of them closed during very cold weather. House may become drafty House will tend to have problems with overheating during mild/hot weather. 14 Install attic inlets throughout the house Not just on the brooding end Attic inlet placement Will result in poor temperature/air quality uniformity What would happen if you just put conventional inlets on the brooding end of a house 40’ wide Alternating just either side of the peak of the house Hottest air from the peak of the attic Most of the benefits associated with attic inlets occur after the birds are turned out. 40’ The primary benefit of attic inlets is not fuel savings, but rather increased ventilation rates Attic inlets in a 40’ wide house Attic inlet placement 40’ wide Alternating just either side of the peak of the house Hottest air from the peak of the attic Maximizes distance from the side wall 40’ Attic inlets tend to do a very good job of throwing air along the ceiling Sometimes too good of a job… Air from attic inlet rolling down side wall 95.0°F 95.0°F 90 90 80 80 70 70 60.0°F 60.0°F 15 Four way attic inlet too close to the side wall Two way attic inlets can be problematic in narrower houses 40’ wide house 10 four way inlets 10 two way inlets Four way inlets break up fresh air into four smaller jets 40’ wide house Four smaller air jets 95.0°F 95 250 250 250 250 90 85 80 500 500 75 70.0°F Two larger air jets can lead to significant side wall cooling Two larger air jets 95.0°F 95 95.0°F 95 90 90 85 85 80 80 75 75 70.0°F 70.0°F 16 Two larger air jets can lead to significant side wall cooling Two larger air jets can lead to significant side wall cooling 95.0°F 95.0°F 90 90 80 80 70 70 65.0°F Four air jets are less likely to cause side wall cooling 65.0°F Generally speaking you typically need more two-way attic inlets that four way 95.0°F 90 80 70 65.0°F The four way attic inlets can also be rotated 45 degrees to increase distance to side wall Attic inlet placement 50’ wide Alternating approximately 2’ – 3’ from the peak of the house Allows room for center feed/water lines. Facilitates the installation of a center row of circulation fans. 17 Attic inlet placement Four way attic inlet placement (40’ vs. 60’ wide housing) +60’ wide Alternating approximately 6’ to 8’ from the peak of the house Improved distribution of fresh air Prevents center of the house from becoming too drafty with four way inlets 40’ wide 15 inlets Inlets spacing = 32’ 60’ wide 22 inlets Single row of four way inlets in 60’ wide house Inlets spacing = 22’ Four way attic inlet placement in 60’ wide house 2’ – 4’ between rows 10’ – 12’ between rows Two way inlet can be advantageous in wider houses with large number of attic inlets +20 – four way inlets Two way attic inlets in 66’ wide house 98.0°F 90 +20 – two way inlets 80 70 65.0°F 18 Bidirectional attic inlets with two rows of tube heaters Single direction attic inlets with two rows of tube heaters Two rows of single direction attic inlets can also be effective in wider house Counterweighted or Machine actuated? Both have similar advantages when it comes to reduced fuel usage, improved air quality, drier litter, etc when properly installed and operated But each system has unique advantages and disadvantages. Machine actuated Machine actuated - disadvantages - - advantages - Higher initial cost. Inlets, machine, cabling, wiring Ideally should have a controller specifically designed to handle to both inlet systems. Easy to close the attic inlets when not in use. Directly controlled by the houses environmental controller. A inlet machine will insure that the attic inlets close when not in use. 19 Attic moisture damage? When you put a hole in your dropped ceiling for ANY type of attic inlet there is the potential for warm, moist air traveling from the house into the cold attic space and condensing. Deterioration of ceiling insulation Possible weakening of trusses Insufficient weight holding doors closed To minimize leakage into the attic space… To minimize leakage into the attic space… Pre-opening attic inlets A significant amount of warm, moist air can enter the before the exhaust fans start to turn on When installing attic inlets make sure there is a tight seal between the attic inlet and the ceiling (common problem) Attic inlets should close snuggly when not use. Counterweighted attic inlets sufficient counter weight/spring tension that when installed at an angle still remains closed. When installing attic inlets make sure there is a tight seal between the attic inlet and the ceiling (common problem) Attic inlets should close snuggly when not use. Counterweighted attic inlets sufficient counter weight/spring tension that when installed at an angle still remains closed. Attic inlet machine should NOT pre-open the attic inlets before the exhaust fans come on. To minimize leakage into the attic space… When installing attic inlets make sure there is a tight seal between the attic inlet and the ceiling (common problem) Attic inlets should close snuggly when not use. Counterweighted attic inlets sufficient counter weight/spring tension that when installed at an angle still remains closed. Attic inlet machine should NOT pre-open the attic inlets before the exhaust fans come on. Attic inlet cabling should be checked from time to time to make sure the inlets are closed when they are supposed to. 20 To minimize leakage into the attic space… Machine actuated attic inlets open during tunnel ventilation Counterweighted inlets - advantages Counter-weighted inlets should be cleaned on a regular basis Counterweighted inlets - advantages - No, wear an tear on an inlet machine On a five minute timer an inlet machine can move up to 576 times day. Can utilize very short timer cycles 81 80 79 Temperature 78 77 76 75 2:10 AM 2:05 AM 2:00 AM 1:55 AM 1:50 AM 1:45 AM 1:40 AM 1:35 AM 1:30 AM 1:25 AM 1:20 AM 1:15 AM 74 Time Counterweighted inlets - advantages Basic attic inlet operation What about a 3 or 2 ½ minute cycle? 81 80 79 77 76 75 2:10 AM 2:05 AM 2:00 AM 1:55 AM 1:50 AM 1:45 AM 1:40 AM 1:35 AM 1:30 AM 1:25 AM 1:20 AM 74 1:15 AM Temperature 78 Time 21 Between flocks use attic inlets to help remove moisture from the litter Attic inlets between flocks Keep end wall doors closed, curtains up, Use two to three 36” fans for minimum ventilation Operate off a timer with attic temperature override of approximately 70oF Attic inlets can typically increase daytime house temperature approximately 10oF above outside air temperature. Side wall inlets 85oF outside = 95oF inside The tighter the house the greater the heating produced. With attic inlets (spring) (spring) 63.1 85.0°F 85 85.0°F 85 92.7 80 80 75 62.0 75 62.7 69.1 76.4 70 65 65 60.0°F Side wall inlets 70 60.0°F With attic inlets (summer) (summer) 100.0°F 100 100.0°F 100 95 95 90 90 85 85 80.0°F 80.0°F 22 With attic inlets Attic inlets between flocks (summer) Attic inlets can typically increase daytime house temperature approximately 10oF above outside air temperature. 100.0°F 100 85oF outside = 95oF inside The tighter the house the greater the heating produced 95 Improved litter drying 90 Lower ammonia levels 85 80.0°F Once chicks are placed… Attic inlets used prior to chick placement 110 105 100 95 90 Temperature/Rh Close some or all the attic inlets on nonbrooding end during cold weather. 85 80 75 70 65 60 55 50 Set side wall inlet machine to maintain a static pressure of 0.11” to 0.13” 45 6:00 AM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 12:00 AM 40 T im e tre a tm e n t co ntro l tre a tm e n t rh Do not try to operate attic inlets at a high negative pressure. Attic inlets work very well at relatively low static pressures Higher static pressure settings tends to reduce the effectiveness of attic inlets This will keep the side wall inlets closed during timer fan operation! The side wall inlets will begin to open as the second stage “temperature control fans” come on con tro l rh With any attic inlet system… At night there is no warm air in the attic. Do not open until birds are spread evenly throughout the house. Leakage area Moderately tight house (0.8 square feet per 1,000 ft2) Leakage area = 0.8 X 20,000 = 16 square feet 0.05” – 0.07” 23 900 800 700 600 500 400 300 200 100 0 = 0.6 X 20,000 = 16 ft2 Leakage amount = 16 X 550 cfm/ft2 = 8,800 cfm Attic inlets = 0.6 X 20,000 = 16 ft2 Leakage amount = 16 X 820 cfm/ft2 = 13,120 cfm Leakage area Less warm air enters the center of the house, more “cold” air enters the ends of the house This results in greater temperature differentials between the centers of ends of the house Use attic inlets with the side wall inlets Do not switch directly from attic inlets to side wall inlets. It is best if you use the attic inlets with the side wall inlets. Going directly from attic inlets to side wall inlets can result in a sudden change in house temperature Fans turn on the center to cool off the house Heating systems turn on the ends to warm up the house = 6,880 cfm Attic is 5 to 30oF above outside air temperature Most importantly fewer fans will operate over the course of the day Total air moved every 15 minutes Total air moved Attic inlets = 11,200 cfm Operating attic inlets at high static pressure Leakage area 0.12 0.11 0.1 0.09 Static pressure 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 Moderately tight house (0.6 square feet per 1,000 ft2) Moderately tight house (0.6 square feet per 1,000 ft2) Close up the attic inlets to get a higher pressure (0.12”) Leakage 0 Cfm per square foot How much would our 60 inlets need to open to bring in 20,000 cfm 1,400,000 1,300,000 1,200,000 1,100,000 1,000,000 900,000 800,000 700,000 600,000 500,000 400,000 300,000 200,000 100,000 0 29-Jan Date Machine attic inlets 28-Jan 27-Jan 26-Jan 25-Jan 24-Jan 23-Jan Counter weighted Side wall inlets 24 Total air moved every 15 minutes Avoiding bird “overheating” 900,000 Total air moved 800,000 700,000 Attic inlets will not lead to “overheating” if an attic inlet system is sized, installed and operated... 600,000 500,000 400,000 300,000 200,000 100,000 0 28-Jan 27-Jan Side wall inlets Time inside outside attic outside Side wall inlets open and overwhelm the attic inlets What about leaving attic inlets open when tunnel-ventilating? 110 108 106 104 102 100 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70 9:50 AM 10:50 AM 11:50 AM 12:50 PM 1:50 PM 2:50 PM 3:50 PM 4:50 PM 5:50 PM inside outside 12:00 AM 11:00 PM 9:00 PM 10:00 PM 8:00 PM 7:00 PM 6:00 PM 5:00 PM 4:00 PM 3:00 PM 2:00 PM 1:00 PM 12:00 PM 11:00 AM 9:00 AM 10:00 AM 8:00 AM 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 6:00 AM 12:00 AM 9:00 PM Temperature (F) inside rh 11:00 PM Time attic 10:00 PM 8:00 PM 7:00 PM 6:00 PM 5:00 PM 4:00 PM 3:00 PM 2:00 PM 1:00 PM 12:00 PM 11:00 AM 9:00 AM 10:00 AM 8:00 AM 7:00 AM inside Temperature (F) Attic inlets in use the day chicks were place 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 6:00 AM Temperature (F) Attic inlets between flocks 7:00 AM 26-Jan Date Machine attic inlets Counter weighted It is not as much as a problem as many people think if the attic inlets are not oversized! Volume coming through tunnel openings is large in comparison to attic inlets. attic 25 Attic inlets left open in tunnel mode 105 100 95 90 85 80 75 70 65 60 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM During the latter stages air brought in by the attic inlets is small in proportion to the air entering through the tunnel inlet Hot air tends to stay near the ceiling. Temperature (F) What about leaving attic inlets open when tunnel-ventilating? Pad end Center (attic temperature=120oF) 95 93 91 89 87 85 83 81 79 77 75 14:30 1.5 F 14:40 front inside 14:50 rear 15:00 95 93 91 89 87 85 83 81 79 77 75 14:30 But if they are not, it is not the end of the world. Outside 2.5 F 14:40 front outside Yes, attic inlets should be closed Temperature (F) 13 attic inlets open (40’ X 500’ Tunnel fan cap. = 200,000 cfm) Temperature (F) No attic inlets Fan end inside 14:50 rear 15:00 outside When should I close attic inlets? When you are no longer going into minimum ventilation mode at night. Summer Winter Fall-Spring =10 days of age =never =no min. vent. at night 26 When should I close attic inlets? Spring actuated inlet with closing cable When you are no longer going into minimum ventilation mode at night. Summer Winter Fall-Spring =10 days of age =never =no min. vent. at night With counter-weighted inlets that are connected to a machine for closing purposes Stage prior to going into tunnel ventilation, possibly sooner. Eagan four way attic inlet (drop bottom) Or adjusting and external counter weight poultryventilation.com 27