Also in the milking parlour, additional air movement ensures cooling on hot days. Not only the milker, but also the milking cows take advantage of the additional air movement. The cows stay calm, due to the presence of fewer flies.
Please visit our website for more information on this topic.
The compact and efficient V50 series fans are stepless controllable. They have an air capacity of - m³/h. These fans blow horizontally over the cows and are suitable for an area of ca.30-50 m. Optionally they are equipped with guards.
The PV600 is a ceiling fan for use in the milking parlour. The fan &#;presses&#; the air down and ensures optimal air distribution during hot and cold periods.
Download product leafletThere is no one perfect ventilation design that can be used universally given the wide variety of dairy barns that lend themselves to a variety of ventilation solutions.
Dairy producers must decide whether to use natural, cross, tunnel, hybrid, or positive pressure delivery systems to ventilate the barn. We recommend that whatever system is chosen, the plan should adhere to the following design criteria:
1. Provide target air speed in the cow&#;s resting area microenvironment.
We need to provide fast moving air in the resting area in the summer and a gentle breeze in the winter. This may be achieved passively through inlet location and baffle placement or actively through the use of fans and positive pressure tube delivery systems.
2. Exhaust the heat, moisture, dust, and noxious gases from the barn at an adequate rate year-round.
Ventilation is the provision of fresh air to the building space, which displaces contaminated, warm, humid air. If we do not effectively exhaust this air, then the cattle will be at risk for heat stress (summer/hot climate) and poor respiratory health (winter/cold climate).
3. Ensure that the system works well across all seasons.
Too often, the design of the ventilation system is effective for one season (most commonly the summer), but fails in the winter when the air exchange rate is reduced. It is important to design a system from the start that can function equally well at low and high ventilation rates.
If engineers adhere to these design criteria, the system will be a success for the cow and the dairy producer.
Ventilation Design Checklist:
Dairy cows generate a lot of heat. A cow milking 120 lbs (54 kg) of milk per day generates about 6,300 BTU (British Thermal Units) per hour &#; twice as much heat as a cow producing only 40 lbs (18 kg) of milk per day (3,300 BTU/h), and 19 times the 330 BTU/h a human produces at rest.
While cows are quite cold tolerant, they are heat stressed at a temperature that most humans find comfortable; their thermoneutral zone is in the range of 40 to 70 oF (4 to 21 oC). Therefore, when designing a comfortable thermal environment for dairy cattle, it needs to function independent of human intervention. Cows cannot wait for us to turn the fans on!
We often keep cattle too warm in the winter, compromising air quality so that workers are not chilled, and in the summer, we do not activate cooling systems at a low enough temperature.
The challenge for barn design in the winter is to achieve sufficient turnover of air within the barn to obtain good air quality. This will limit the risk for respiratory disease, and typically means that we need to ventilate the barn at around 4 to 8 air changes per hour. Meanwhile, during the summer, the requirement for clean fresh air to ventilate the barn continues at a greater rate of around 40 to 60 air changes per hour.
We know that cows are susceptible to the combination of both heat and humidity. To account for both, we use the Temperature Humidity Index (THI), which adjusts temperature to account for the impact of high humidity to describe climatic conditions.
THI is calculated as:
THI = (dry bulb) Outdoor Temp oF &#; (0.55- (0.55 x (Relative Humidity %/100)) x (Outdoor Temp oF &#; 58)
THI takes into account the impact of relative humidity (RH) on the cow. Cow behavior and performance are impacted at about a THI of 68. At 20% RH, this would be at 75 oF (24 oC), but at 90% RH, cows would be stressed at 69 oF (21 oC). Thus, the more humid it is, the lower the ambient temperature at which the cow will experience heat stress.
Cows accumulate heat rapidly while lying down (about one degree F (0.5 oC) per hour of rest) and dissipate heat when they stand (about a half a degree F (0.25 oC) per hour). As temperature increases, the number of lying bouts per day stays the same, but lying bout duration decreases. Daily lying times may rapidly fall to as low as 6 hours per day during times of heat stress as cows stand more and thermal pant to cool. Cows may exhale more than 4 gallons (15 liters) of water from her lungs per day! This significant behavioral change, coupled with the physiological changes occurring due to heat stress, are responsible for the clinical signs we associate with hot weather.
A cow fitted with a vaginal temperature logger and an activity logger determining when the cow is standing (upper horizontal orange line) and lying (lower horizontal orange line). Notice how the cow&#;s core body temperature increases when she is lying down and decreases when she is standing up. (From Atkins et al. (). Transactions of the American Society of Agricultural and Biological Engineers (ASABE).61(5):-, )
Bunching is a common complaint during the summer, particularly in freestall barns where cows gravitate toward the center of the barn and away from sidewalls. There is a simple explanation for this behavior &#; cows are grazing animals and are hard-wired to seek shade when hot. Bunching cows are trying to tell us that they are hot and that the current heat abatement strategies are failing to cool the cows sufficiently. Bunching is also a reaction to fly worry and can be caused by stable flies entering the barn.
Signs of Heat Stress
Producers may be skeptical of the impact of heat stress on their cows. Dairy records can be used to determine if there is a significant effect on cow performance to decide whether or not to invest in cow cooling measures.
The tell-tail signs of heat stress to look for in the dairy&#;s records are:
Any or all of these signs indicate a heat stress problem worthy of attention.
Heat Stress Check List
Cooling Cows
Cows lose heat through sensible and latent heat mechanisms. Sensible heat loss occurs without a phase change &#; such as the movement of air over the skin, breathing in cool air, and cooling by contact with a cold surface. Latent heat loss occurs with a phase change &#; such as the evaporation of sweat and thermal panting. As ambient temperature approaches body temperature, latent heat loss becomes more important than sensible loss, such that it may constitute 80% of the total heat loss at 81 oF (27 oC).
An effective ventilation system must accommodate both sensible and latent heat transfer, and the system must impact the microclimate of the cow&#;s resting area &#; removing the accumulated heat to maintain a favorable heat transfer gradient, with the aim of keeping the cow resting for longer periods.
Unfortunately, most ventilation specifications ignore the simple fact that air is not distributed evenly within the barn. The cow lives within a pen inside of the barn, and within that pen, she lies in a stall. Effective ventilation design must account for different microenvironments within the barn, which usually means that whatever ventilation system we choose, we need to employ fans or baffles to impact air movement in the resting space.
The concept of the barn, pen, and stall microenvironment (Veterinary Clinics of North America, )
It is also apparent that the cows remain affected by heat stress after the ambient temperature begins to decline for the day. Systems that are controlled solely by ambient temperature turn off ventilation and cooling too early, when cows still need help. We therefore recommend systems that are controlled by THI if possible, with overrides to ensure that they continue to run past nightfall.
The goal of any ventilation design is to provide air speeds of 200 to 400 ft/min (1 to 2 m/s) to as many cows as possible in the resting area using baffles or fans.
Air speed may be directed into the cow&#;s resting area microenvironment using fans or baffles, depending on the design of the ventilation system. Baffles are most commonly used in cross-ventilation designs, while fans are used in both mechanical and naturally ventilated barns.
How fast is fast?
While cows demonstrate a behavioral preference for fast moving air in hot climates, very few studies have asked how fast the air needs to travel. The available research since suggests that the Minimum Cooling Air Speed (MCAS) that should be provided to every cow in the resting area is 200 ft/min (1 m/s). There is evidence that there are some incremental benefits to providing increased air speeds of up to 400 ft/min (2 m/s), but there is little evidence to support providing air speeds in excess of this. Air speed within this range has been shown to reduce the cow&#;s respiratory rate at increased temperatures, decrease the negative effects of humidity on respiration rate, decrease wet skin temperature, and decrease hair resistance thereby improving thermal conductance of the hair layer. High air speeds have not been shown to increase lying times in controlled studies, but anecdotally this has been seen on farms with improved ventilation systems.
Use of Baffles
With the goal of redirecting air into the cow&#;s resting area, the use of baffles is only recommended in mechanical cross-ventilated barns. In these barns, a curtain or metal baffle is located above the stalls.
Different baffle heights, angles, and locations have been tried and modeled, which have led to the following basic recommendations:
Use of Fans
Previous recommendations for fan placement in barns stated that fans should be spaced at 10 fan diameters apart and angled toward the cows. This recommendation does not meet the goal of providing sufficient air speed to as many cows as possible in the resting area and should no longer be used.
When air is discharged from a fan, it immediately contacts the &#;still&#; air within the barn. Some of the barn&#;s air becomes &#;entrained&#; into the air jet, causing the jet to slow down and widen, creating an &#;angle of entrainment&#; within the air jet. The angle of entrainment is 22 to 24 degrees, and is well-defined near the fan, but becomes billowy with greater distance from the fan. This phenomenon creates a cone of fast-moving air leaving the fan that widens at an increasing distance from the fan. The use of louvers in front of the fan does not significantly impact this air cone.
Obviously, there is a wide range of fan types and diameters used for this purpose, with fan diameters ranging from 36 to 72 inches (91 to 183 cm). Larger capacity fans may move greater amounts of air further at higher speed, allowing the use of fewer fans with greater spacing distances, and less associated wiring and installation costs. However, the cows standing and lying in the stalls will act as baffles themselves, redirecting the air around them, so the desire for optimal air speed distribution would drive us to more frequent fan placement with less distance between them.
Practically, with roof supports typically spaced at 10 to 12 feet (3 to 3.7 m) on center, we recommend spacing a single 48-inch to 55-inch (122 to 140 cm) fan above the stalls at 24 to 30 feet (7.3 to 9.1 m) intervals, turned from one side of the stall platform to the opposite side, angling the fan to target the stall below the next adjacent fan in line. Each row of stalls should have fans above them. In head-to-head pen layouts, a single fan can be angled across the platform or they may be staggered on each side of alternating support posts. Greater distances may be used when fan throw distance is known to exceed the above general guidelines or when fans are doubled up, side-by-side. For example, 72-inch (183 cm) cyclone fans may be spaced every 40 to 60 feet (12.2 to 18.3 m).
Air jets from the black fan provides fast moving air directly under the red fan when spaced at 24-foot (7.3 m) intervals. Without the red fan, the jets from the black fan would not reach the 20-foot (6 m) zone under the blue fan before the blue fan&#;s jets reach the floor (Veterinary Clinics of North America, ).
The direction of the fans should be in line with the prevailing winds or in the direction of the fan exhaust in mechanical systems. The fans should be activated above 68 oF (20 oC).
High volume, low speed (HVLS) fans are not designed to optimize the provision of target air speeds in the cow&#;s resting space. If they must be used, fan spacing of 40 feet (12.2 m) is preferred, with the fan located directly over the resting area.
Positive pressure tube delivery systems can successfully be installed over stalls to assist in cooling cows by providing fast moving fresh air over the resting area. They are of particular use in poorly ventilated barns where they provide a secondary advantage of delivering fresh air into the barn. These systems will supplement natural ventilation, but they will not be able to achieve the desired ventilation rate of 40 air changes per hour or more in the summer alone.
Challenges of installing positive pressure tube systems over stalls:
Pen lengths may exceed several hundred feet, making the task of supplying sufficient air along the length of the tubes challenging. Current fan availability restricts this type of system to smaller pens that are less than about 128 feet (39 m) in length.
A tube system installed above a single row of stalls in a freestall facility.
Once fast-moving air has been provided in the resting space, the barn may be ventilated to provide the target air changes per hour with a variety of natural, mechanical, and hybrid options to suite climate conditions and economic circumstance.
Provided that the site constraints for natural ventilation are minimal, we have a strong desire to retain some option for natural ventilation in adult cow barns in temperate climates. However, if the location reduces the ability for the barn to ventilate naturally and in climates that create heat stress year-round, we believe mechanical ventilation systems are necessary for the maintenance of cow health and well-being.
Natural ventilation is an effective, least cost option for many situations. Fresh air enters the barn and stale air leaves largely as a result of a difference in wind pressure across the building, and to a lesser extent, a difference between the inside and outside temperature. Wind blowing across the open ridge creates a suction effect, drawing warm moist air out of the barn and pulling fresh air in through the eaves and open sidewalls. In the summer, the ridge opening plays a relatively minor role. The ability to capture winds from the south and southwest (in North America) through open sidewalls is of much greater importance. On still days, thermal buoyancy drives air out through the ridge opening, a process called the &#;chimney effect&#;.
As air enters into the barn via the open eaves and sidewalls, it interacts with the air already inside of the barn differently depending on the time of year and wind conditions, and eventually exits through an open ridge.
The chimney effect is facilitated by the temperature difference between the inside and the outside of the barn. During the night at low wind speeds (<10 mph or <16 kph), the inside temperature of the barn will be 1.5 to 4 degrees higher than outside, while at higher speeds, the difference may only be about 2 degrees. The use of roof insulation to increase this temperature difference has been explored. However, insulation with an R value up to 14.3 yielded a relatively modest temperature difference of less than 2 degrees &#; equivalent to increasing the stocking density of the barn from 1 to 1.2 cows per stall in a 4-row barn. Roof insulation has therefore not been viewed as a significant benefit in all but the most severe of climates.
Key Criteria for Natural Ventilation
In order to achieve adequate air movement for optimal natural ventilation, four key criteria must be met:
1. Locate the building free of wind shadows
In most of North America, barns should be oriented east-west in order to capture the common prevailing southwesterly winds. See the Iowa State University &#; Iowa Environmental Mesonet website for regional wind rose maps at http://mesonet.agron.iastate.edu/sites/locate.php. Because most of the prevailing winds in North America come from the southwest, close proximity of nearby structures to the south and west of a naturally ventilated barn are therefore a potential problem for the optimization of natural ventilation because of the wind shadow effect &#; a phenomenon where airflow is disturbed downwind of an obstruction, such as a building, tree, silo, or hill.
To find the minimum distance between the windward obstruction and the building to be naturally ventilated (Dmin), the following equation has been suggested:
Dmin = 0.4*(height of the obstruction in feet or meters)*[(length of the obstruction in feet or meters)0.5]
For example, a building placed downwind from a structure 13 feet (4 m) high and 96 feet (29.3 m) long would need to be 0.4 x 13 x 960.5 = 5.2 x 9.8 = 51 feet away (0.4 x 4 x 29.30.5 = 15.5 m). For a 30-foot (9.1 m) high, 500-foot (152.4 m) long barn, the separation distance should be at least 268 feet (81.7 m).
These distances for larger buildings are not viable with current construction standards, the footprint available for barns on most sites, and the cost of linking the barns together. Stowell has a rule of thumb for the minimum building separation distance &#; take the square root of the height x length of the building. For example, a 30-foot (9.1 m) high and 500-foot (152.4 m) long building would yield a minimum separation distance of 123 feet (37.5 m) &#; still more than the typical 100 feet (30.5 m) we commonly see in the industry.
Barn orientation also impacts heat stress. When barns are oriented north-south rather than the preferred east-west, there will be greater solar exposure along the west side of the barn during the afternoon hours, creating bunching issues and reducing the usage of the outside row of stalls.
Sun angles of an east-west oriented freestall barn for August 21, 40 degrees north latitude (Omaha-Springfield).
Sun angles of a north-south oriented freestall barn for August 21, 40 degrees north latitude (Omaha-Springfield).
2. Adjust the sidewall opening so that at least half of the sidewall surface area can be opened in the summer, and 1 inch per 10 feet (2.5 cm per 3 m) of building width in the winter.
In the winter, the eave inlets should be opened 1 inch for every 10 feet (2.5 cm per 3 m) of building width on each side of the barn. Under conditions of minimal wind speed and mild temperatures, natural ventilation is driven by thermal buoyancy and the chimney effect. Eave openings less than 0.5 inches per 10 feet (1.3 cm per 3 m) of width will fail to provide for the minimum ventilation requirements of four air changes per hour. This should be viewed as the minimum opening year round, no matter what the weather conditions are. Any sign of condensation will indicate a need for an increased opening of the eave inlet. Ideally, the eave should never be closed completely.
In the summer, at least half of the total area of the sidewall should be opened. Curtain sidewalls are preferred so that the whole wall can be opened in the heat of the summer and the inlet area controlled in the winter. Curtains that are located two thirds of the way up the sidewall keep the material out of the way of the bedding in the winter and allow the opening of the upper third to be easily adjusted to create an inlet size that is half of the ridge opening on each side of the barn so that the total eave opening equals the total ridge opening.
For naturally ventilated barns, sidewall height typically ranges between 14 and 16 feet (4.3 and 4.9 m), allowing 12 feet (3.7 m) of opening to facilitate air flow. With large sidewall openings, 3 to 4 feet (0.9 to 1.2 m) of roof overhang is recommended to shield the opening from snow and driving rain.
3. Ensure that the ridge is sufficiently open to draw air out of the barn
The ridge opening width should be at least 6 inches (15 cm) wide for barns up to 30 feet (9.1 m) in width, and 2 inches wide per 10 feet of building width (5 cm per 3 m of building width) for barns wider than 30 feet (9.1 m).
An appropriately sized ridge, coupled with the correct animal density, typically does not result in a lot of precipitation entering the barn. However, the opening can be modified to reduce precipitation entering the barn if it is a problem.
Some barns are fitted with adjustable ridge ventilators that can be minimized during severe weather. The most common ridge ventilator is one using a PVC pipe and nylon cord to raise and lower the pipe.
The simplest ridge modification without compromising the opening is to add a vertical baffle on either side of the ridge opening. This will significantly reduce snow blow-in, but will not completely eliminate it. The vertical upstand is typically sized at 1.5 to 2 times the ridge opening width.
Other solutions to reduce precipitation coming into the barn include the installation of a ridge cap or the use of an overshot roof.
Ridge caps run the risk of limiting air flow through the ridge, so they must be designed correctly. With these designs, vertical baffles deflect the air over the ridge cap. These are often used when bedded areas are located below the ridge rather than a concrete alley. The total ridge opening width must be held constant as the air moves under and around the cap.
An alternative ridge cap used in Ohio dairy herds appears to preserve airflow while preventing the entry of precipitation into the barn. For a typical 20-inch (51 cm) opening, a cap is located 20 inches (51 cm) above the roofline with a 4-inch (10 cm) baffle. The cap overlaps the ridge opening by 6 inches (15 cm) on either side.
Use of an overshot roof has become popular in recent years. However, in our experience, these openings have not solved the concerns over precipitation, and depending on the direction of the wind, may reduce the draw of air through the ridge and direct snow into the barn.
If you want to learn more, please visit our website Windmax Power.
Ridge modifications can significantly add to the cost of the building. For example, an overshot roof compared to a simple ridge may cost about $60 USD per foot (30 cm) more.
The influence of the ridge on ventilation has been explored during the summer. Barns with a sealed insulated ceiling with no ridge outlet have been compared to those with a traditional ridge opening design. When wind blew perpendicular over a barn with an open ridge, additional ventilation was achieved, which was not influenced by making the ridge opening wider than 2 inches per 10 feet (5 cm per 3 m) of building width. At wind speeds of 10 mph (16 kph), the increase in ventilation was about 20%.
4. The pitch of the roof should allow at least 1 unit of rise for every 4 units across (1 in 4)
The vertical separation between the eave and the ridge impacts the pressure differences generated by thermal buoyancy and the chimney effect. Most commonly, new naturally ventilated cow barns are built with a 4 in 12 roof pitch. Adequate slope is essential if the air is to flow unimpeded toward the ridge opening for winter ventilation. This flow is facilitated by a relatively smooth lining to the ceiling, unencumbered by cross beams and roof trusses. Minimize the depth of purlins used to 4 inches (10 cm) if uncovered or line deeper purlins to avoid air becoming trapped between them.
Roof slopes with less pitch (e.g. a 2 in 12 roof pitch) will not stop natural movement of air toward the ridge, but will reduce it.
Requirements for Natural Ventilation Check List
The following situations would make mechanical ventilation more desirable than natural ventilation:
To determine the ventilation specifications for your farm or troubleshoot an existing design, download the Ventilating Adult Cow Facilities Worksheet.
A barn may be ventilated using positive pressure (where fresh air is forced into the barn) or negative pressure (where air is exhausted from the barn and fresh air is drawn in through designed inlets).
All mechanical systems for adult cow barns are specified according to the guidelines laid out in the ASABE Standards , which are principally to:
Practically, these standards are not particularly useful since the heat generation tables on which they are based have not been updated since the s, and cows produce much more milk and generate more heat than they did 70 years ago. Based on our findings and observations from the industry, The Dairyland Initiative provides the following additional supplemental design recommendations for mechanical ventilation systems for adult dairy cattle:
Dairy cow barns have been specified in excess of these standards and, in general, are not detrimental to the cow. The main disadvantage of operating the barn ventilation system at a higher fan exhaust rate is a higher purchase and installation cost, and a higher operating cost.
Positive Pressure Hybrid Barns
This type of system is relatively new to the industry and builds on the advantages of other positive pressure systems in other livestock industries. Basically, the barn is designed as a naturally ventilated barn for the majority of the year, but switches to a mechanically ventilated positive pressure barn in hot conditions (temperatures greater than 68 oF, 20 oC) during the summer. HVLS fans are installed in some for winter use only to de-stratify the air.
In the summer, fans located along each sidewall force air into the center of the barn, directed at the adjacent stall platform. The curtains are closed and the ridge is open. Sufficient fan capacity provides 40 to 60 ACH, depending on the temperature and conditions. The first installations were installed with 1 HP 36-inch (91 cm) diameter fans mounted every 10 feet (3 m). However, these fans were not designed for this purpose and larger fans have been suggested for more recent designs that are more stable under higher static pressures.
This system meets the 3 critical design provided that the barn design is limited to a 4-row head-to-head stall layout with center drive through feeding, and it is relatively low cost to run year-round.
However, the system does have the following disadvantages:
The system has merit for holding areas and other cow barns that are difficult to ventilate that are relatively narrow where the resting area is near the sidewall.
A positive pressure hybrid barn with 36-inch (91 cm) fans located along each sidewall every 10 feet (3 m) in a 4-row head-to-head barn (Courtesy of Dr. Gordie Jones, Hank Wagner)
Tunnel-Ventilated Barns
Tunnel ventilation refers to barns designed with negative pressure mechanical ventilation drawing air through designed inlets at one end of the barn along the length of the barn parallel to the feed lane(s). Most new tunnel barns are designed to ventilate mechanically year-round, usually with polycarbonate composite side walls, negating the need for expensive curtains.
The designs are usually limited to barns that have 1 to 2 feed lanes and up to 12 rows of stalls. The air quality deteriorates as it moves down the length of the barn, making barn length a limiting factor. Typically, these barns are confined to 500 feet (152 m) in length as a rule of thumb. Some longer barns have been constructed where fresh air enters through sidewall inlets at the far end of the barn, roof inlets, or positive pressure fans. However, it is challenging to distribute the air evenly with these designs at the exhaust end of the barn.
We recommend that the majority of the inlet be located at the end of the barn (usually on the south/southwest end of the barn) rather than the sidewall. Air will enter the cow pens directly and evenly across the inlet, and be drawn to the exhaust fans located on the north/northeast end of the barn. Inlets will need to be designed for summer and winter needs. It is very important to make crossover walls as low as possible in these barns (not much higher than the height of a standard water trough) so that air flow into the resting area is not compromised.
Since barn volume impacts exhaust capacity, tunnel barns are constructed with lower roof pitches than naturally ventilated barns; usually 1 to 2 in 12 pitch. Alternatively, a flat false ceiling can be installed. However, even with this smaller volume for the cow space, the pen area receives only 13% of the total barn ventilation &#; with much of the air moving over the top of the cows and down the feed lane(s).
Baffles cannot be located low enough to impact air flow in the pens nor influence as many stalls as they would in a cross-ventilated barn, so we do not favor using baffles in tunnel barns.
Computational Fluid Dynamic (CFD) models show that optimal ventilation can be achieved in a tunnel barn specified at 40 ACH for the summer (provided this gives at least 1,500 CFM (2,550 m3/h) per adult cow) with fans over the resting areas as previously described.
A tunnel-ventilated 6-row barn with a flat insulated ceiling and large 72-inch (183 cm) cyclone fans over the resting areas
Tunnel Hybrid Barns
Tunnel hybrid barns are essentially a hybrid of a tunnel and a naturally ventilated barn &#; designed to switch between tunnel ventilation in the summer and a form of natural ventilation in the winter. As such, these barns provide great flexibility and address one of the chief weaknesses of tunnel barn design &#; risk for poor ventilation in the winter. Hybrid tunnel barns allow flexibility to switch between systems and can be used where the cows must have access to the outside. They are suitable for more temperate climates with large temperature differences between seasons. They are more expensive to construct because they require the installation of exhaust and circulation fans, curtain sidewalls, and a managed ridge opening; either with a curtain or a cupola (chimney) system with or without exhaust fans &#; an expense that is difficult to justify in regions with very hot climates year-round.
Design and construction are the same as for a tunnel barn, but the sidewalls are fitted with a full or partial curtain to provide a winter inlet. Barns with a single feed lane typically have an off-set roof with a curtain operated ridge opening that can be closed in the summer. In barns with 2 feed lanes, it is more common to see a cupola (chimney) system with exhaust fans in the roof to facilitate the flow of air toward the ridge, especially in barns with a lower roof pitch than the 3 or 4 in 12 pitch considered ideal for natural ventilation.
A tunnel-ventilated hybrid barn with a 6-row stall configuration, curtain sidewalls and a curtain managed ridge opening
Cross-Ventilated Barns
Cross ventilation refers to barns designed with negative pressure mechanical ventilation drawing air through designed inlets along one side of the barn, across the width of the barn perpendicular to the feed lane(s). Most new cross-ventilated barns are designed to ventilate mechanically year-round, with no option for natural ventilation.
While wide-body barns have been constructed with multiple feed lanes and 26 or more rows of stalls, they suffer the same limitations as tunnel barns with regard to the decrease in air quality, particularly during cold weather at low ventilation rates, as the barns get wider. For that reason, we favor barns no wider than about 10 rows of stalls with a maximum of 3 feed lanes. Efforts to improve air quality in wider barns have been made with the use of roof inlet systems, but air distribution at low ventilation rates is still a challenge.
Cross-ventilated barns typically favor feed lanes located on the outer perimeter of the barn so that air entering the inlet is warmed in the feed lane before it enters the cow pen. Sidewalls are typically 13 to 16 feet (4 to 4.9 m) high with a roof pitch at 0.5 to 1 in 12. The ridge is either closed or it can be fitted with a cupola (chimney) system.
These barns can be designed with baffles or fans over the stalls, or with a flat ceiling (referred to as a &#;Big Box&#; design). We favor barns fitted with retractable curtain baffles for the following reasons:
A 10-row cross-ventilated barn with 3 feed lanes using curtain baffles over the head-to-head stall platforms
In hot, low humidity climates, cross-ventilated barns have the added advantage that they are ideally setup for the use of evaporative cooling pads at the inlet to decrease the temperature within the barn.
Since many barns can be designed with multiple ventilation options, we recommend estimating the installation and operating costs of any given barn with different systems for a given location.
We have created a design spreadsheet tool for use in our workshops which estimates the operating costs for each system and as a routine, we calculate the running costs for the following operating systems, using the aforementioned recommendations:
These seven options may be designed and used to calculate the relative costs. As an example, for an 800-cow barn located in Green Bay, Wisconsin using the layouts below, the ventilation system installation costs varied from $104 to $290 USD per cow, and the operating costs varied from $20 to $61 USD per cow per year. By comparison, the estimated marginal loss due to the cost of heat stress for cows in Green Bay, WI is $74 USD per cow per year, which suggests that all available options are cost effective and can be considered based on their relative merits. These costs will vary based on the location of the barn.
Example layout of an 800-cow barn for cross or tunnel ventilation used for cost comparison purposes
Example layout of an 800-cow barn for natural or positive pressure hybrid ventilation used for cost comparison purposes
Installation and operating costs for an 800-cow barn in Green Bay, WI using the same fan models for each ventilation system. The values in this chart are for illustration purposes only and will change depending on the fan model used and the location of the barn
System Type # Recirculation Fans # Exhaust Fans # Cupola Fans # HVLS Fans Total # Fans Operating Cost ($/cow/year) Estimated Fan Installation Cost ($/cow) Natural Ventilation 68 68 $20.05 $104.00 Positive Pressure Hybrid 192 11 203 $19.68 $268.55 Tunnel Hybrid with Fans 68 57 16 141 $61.12 $247.94 Tunnel with Fans 68 56 124 $55.43 $229.05 Cross with Fans 68 56 124 $55.43 $229.05 Cross with Baffles 56 56 $35.38 $125.06 &#;Big Box&#; Cross 79 79 $48.22 $176.42Such an estimate of costs can allow the dairy producer to make an informed decision regarding which option to choose based on the number of fans that need to be installed and maintained, the operation and installation costs, and the effectiveness of each system relative to each other, balanced against the potential benefits from improved air quality and decreased heat stress.
Once the fan exhaust capacity for the barn has been calculated, fan choice is based upon features, reliability, cost, and performance. Fan choice can make the cost of operation of any ventilation system vary by $30 per cow per year or more &#; making this a very important decision &#; just as important as the type of ventilation system used.
We recommend fans that have been independently tested. In the US, look for AMCA (Air Movement and Control Association) approved testing or independent testing results reported by institutions such as Bess Labs at the University of Illinois at the required static pressure of 0.10 to 0.15 inches H2O (25 to 37 Pa) for negative pressure systems.
Performance metrics to take note of when making a fan choice are:
Fans must be installed correctly and wired with thought to the ramping function used to transition between seasons so that operational fans at each set-point can be distributed evenly. It is also becoming commonplace to have variable speed fans which can operate more efficiently.
According to OSHA standards, fans within 7 feet (2.1 m) of the floor or working level must be guarded. The guard openings must not be greater than 0.5 inches (1.3 cm) in width.
Every fan installed must be cleaned and maintained regularly. Poorly maintained fans can lose 20 to 50% of their performance capacity so we recommend at least a bi-annual maintenance check.
Water Use for Supplemental Cooling
Water may be used to enhance cooling by soaking the cow directly or using a fine mist or evaporative cooling pad to cool the air before it reaches the cow.
Water Soaking Strategies
Effective cow cooling is achieved with a combination of wetting the cow&#;s skin and exposing it to moving air. Because cows produce very little sweat on their skin, water must be used to wet the skin for optimal cooling. This is best accomplished with large water droplets &#; not mists. Optimal cooling range air speeds are from 200 to 400 ft/minute (1 to 2 m/s) (Berman, ). Using a wet skin model, Berman (JDS 91:, ) showed that still air and air moving at 100 ft/min (0.5 m/s) failed to cool the skin. However, at air speeds of 200 to 400 ft/min (1 to 2 m/s), cooling was achieved for a period of about 10 minutes.
At the higher air speed, rewetting needs to occur more frequently as the skin dries and air speed alone has minimal effects. Relative humidity (RH) of the moving air also has a substantial effect on evaporation rate and cooling of the cow. Increases in RH of 10% will reduce the effectiveness of evaporative cooling substantially (Berman, ).
Wet surface temperature changes when exposed to air moving at different speeds (Berman, )
Soaker Set-Up
Soakers have been installed in holding areas, parlors, parlor exit lanes, and over feedbunks in freestall pens because thoroughly wetting the cow is a great way to improve evaporative heat loss. There are controller units to change soaking times and intervals at different ambient temperatures.
However, soaking in the pens along the feedbunk is problematic. The additional water in the alley causes wet manure to be transferred to the freestall bedding, increasing the risk of mastitis. In sand bedded barns, the extra water leads to sand settling in transfer channels and collecting pits, which leads to pumping problems. Also, water is wasted when cows are not at the bunk (19 hours per day!).
One idea to improve soaking efficiency is to develop soaker stations around the pens where cows can voluntarily enter all day long and be soaked by activating an optic sensor when they desire. New soaker control units are now available to facilitate this approach (e.g. Edstrom Cool SenseTM Motion Cooling System with dual motion sensors and temperature activation). As optic sensors become cheaper and more reliable, we are seeing feedline systems where nozzles are activated by the presence of a cow beneath them.
Low-pressure sprinklers (15 to 20 psi, 103 to 138 kPa, or 1 to 1.4 bar) may be used along the feedbunk in the pens, set to provide 0.03 gallons of water per square foot (1.1 liters of water per square meter) of wetted area per sprinkler per cycle above temperatures of 70 oF (21 oC). The wetted area in freestall pens should be set to cover the area 6 to 8 feet (1.8 to 2.4 m) behind the feed line, and the water supply should be sized to provide the necessary flow rate of water.
We recommend wetting cycles have soakers on for 0.4 to 0.5 minutes every 12 to 15 minutes for temperatures between 70 and 75 oF (21 and 24 oC). During periods of severe heat stress, soakers should be on for 0.4 to 0.5 minutes every 6 to 10 minutes when temperatures reach ~82 and 85 oF and above (22 and 29 oC).
The nozzles on the water line are typically suspended 6 to 12 inches (15 to 30 cm) above the top of the headlocks, 5 to 6 feet (1.5 to 1.8 m) above the cow alley, and 12 to 18 inches (30 to 46 cm) behind the feed line. The nozzles used in the barn should spray water in a 180-degree arc, and they should be spaced according to their spray diameter, which is usually 6 to 8 feet (1.8 to 2.4 m). Avoid the use of nozzles that create fine mists. Droplets need to be large to penetrate the hair coat and cool the skin of the cow. Always check the alignment of the nozzles to make sure that the water is actually landing on the cows&#; backs, and use nozzles with check valves to prevent the distribution line from draining after each cycle.
Recommended pipe diameter for different TeeJet nozzle capacities based on feed line length.
The nozzle capacity influences the time required to apply 0.05 inches of water per square foot (1.3 cm of water per square meter) per on-cycle.
Pipe Diameter (inches) TeeJet Turbo Nozzle Capacity (gallons per minute (gpm)) Inlet Water Demand (gpm)** 0.5 gpm 1.75 gpm 1.0 gpm Feedline Length (feet) Number of Nozzles* Feedline Length (feet) Number of Nozzles* Feedline Length (feet) Number of Nozzles* 1.00 200 25 140 18 100 12 12 1.25 320 40 210 25 160 20 20 1.50 480 60 320 40 240 30 30 2.00 800 100 530 70 400 50 50 2.50 200 125 800 100 100 On-cycle time to apply 0.05 inches of water per square foot 2.5 minutes (150 seconds) 1.7 minutes (100 seconds) 1.25 minutes (80 seconds)
Pipe Diameter (cm) TeeJet Turbo Nozzle Capacity (liters per minute (lpm)) Inlet Water Demand (lpm)** 1.9 lpm 2.8 lpm 3.8 lpm Feedline Length (m) Number of Nozzles* Feedline Length (m) Number of Nozzles* Feedline Length (m) Number of Nozzles* 2.5 61 25 43 18 30 12 45 3.2 98 40 64 25 49 20 76 3.8 146 60 98 40 73 30 114 5.1 244 100 162 70 122 50 189 6.4 488 200 305 125 244 100 378 On-cycle time to apply 1.4 cm of water per square meter 2.5 minutes (150 seconds) 1.7 minutes (100 seconds) 1.25 minutes (80 seconds)
*Assume nozzle spacing is 8 feet (2.4 m) on center using agricultural spray nozzles with a minimum of 20 psi (138 kPa or 1.4 bar) pressure at the outlet of the nozzle.
**Water demand based on a maximum of 5 feet per second (1.5 meters per second) flow velocity in the pipe.
From &#;Heat Stress Abatement in Naturally Ventilated 4-Row Freestall Barns (Head-to-Head Stalls) Using TeeJet Turbo Jet Nozzles.&#; JP Harner, JF Smith, G Boomer, and M Brouk
Diagram of sprinkler system components (KSU Extension Bulletin)
Controllers
Filter: 50-micron canister filter that meets required flow capacity
Electric Solenoid Valves
Pressure Reducer
Nozzles and Tips
Suppliers
Nozzles:
Teejet Technologies &#; www.teejet.com
Edstrom Industries &#; www.avidityscience.com
Nelson Irrigation Corporation &#; www.nelsonirrigation.com
Senninger Irrigation Inc &#; www.senninger.com
Controllers:
Edstrom Industries &#; www.avidityscience.com
FarmTek &#; www.farmtek.com
Misters and Evaporative Cooling
When water is used to cool the air moving toward the cow, conditions of relatively low humidity are required. Misters can be added to fans to help cool the air cone leaving them, or evaporative cooling pads can be used to cool the air stream as it is drawn through an evaporative cooling pad. This type of cooling can be modestly effective under conditions of low humidity with temperature drops of more than 10 degrees F (5 oC) possible. However, with relative humidity greater than 55%, the temperature drop may be less than 1-degree F (0.5 oC), making this type of cooling ineffective (see Berman study below).
In climates where humidity frequently exceeds 60%, evaporative cooling is less reliable, making soaking the cow directly the preferred cooling method.
Efficacy of evaporative cooling at different relative humidity % (Berman, JDS 89:, ) with the cooled air at 65% RH
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Ambient Temperature Relative Humidity % At 93 oF 15 25 35 45 55 Temperature Drop (degrees) 24 18 12 7 1