Low Profile Cross Ventilation Barns
New design could yield ideas about summer cooling, environmental control, and economics of alternatives
Offering a more consistent year round environment for dairy herds, the low-profile, cross ventilated (LPCV) barn has become popular in the U.S. Midwest. Also known as a wide-body barn, this eight-row-wide freestall design takes up less space and can be better ventilated than two four-row naturally ventilated barns built side-by-side.
The other advantage of an LPCV barn, according to researchers, is its ability to provide a better environment than other freestall housing in all seasons, including summer, because of evaporative cooling systems.
The first LPCV dairy barn began operation in South Dakota during fall 2005. New barns are now under construction in seven states and being considered in 10 or more. The concept has been extended from eight to 24 rows, but structures with 12 and 16 rows of freestalls are the most common.
The LPCV design has yet to make an appearance north of the border. Direct application here may be limited due to the minimum practical size-400 freestalls. However, there is a lot to learn from these barns about summer cooling, year-round environmental control and the economics of design alternatives.
As the LPCV name suggests, the low-profile barn looks like an industrial building with a roof slope of 0.5 to 12 and a 12 to 13 foot outside wall height, as shown in Figure 1. Barn width is proportional to stall numbers, about 215 feet wide for an eight-row tail-to-tail configuration, and 230 feet wide for an eight-row head-to-head design.
An open curtain wall on one side and a bank of fans on the opposite side creates a tunnel ventilation effect across the barn's width. Air exchange rate is an important consideration. During warm weather, the targeted air exchange is 60 to 120 seconds. Fans have to move enough air to change the air completely every one to two minutes.
Baffles increase air speed over the stall areas and keep air flow at cow level. Installed from the ceiling, these drop panels run continuously across the barn parallel to the free stall rows and perpendicular to the air flow as shown in Figures 2 & 3. They effectively decrease the cross section of the barn.
Depending on the number installed, baffles can increase air speed to 525-700 feet per minute (fpm) from 175-250 fpm. An air speed of 450 to 525 fpm is recommended in the freestall area to promote stall usage and improve cow comfort during hot weather. LPCV barns need at least one baffle for everytwo rows of free stalls to achieve these speeds.
The bottom of baffles should be at least seven feet above the floor to avoid cow and equipment contact. Skid-steer equipment sometimes damages rigid baffles. As a result, some barns have baffles made of flexible natural ventilation curtain material.
Evaporative cooling lowers the temperature in most LPCV barns. Outside air temperature, relative humidity, and the evaporative cooling system all affect the indoor temperature.
Because air temperature decreases and humidity increases as moisture is added to the air, the lowest temperature occurs when air is saturated at 100 per cent humidity. If two air streams at the same temperature have different relative humidity levels, the less humid stream can be cooled to a lower temperature than the stream with high humidity.
These barns primarily use evaporative cooling pads, or high-pressure mist systems as an alternative.
The evaporative pad system consists of a saturated cellulous material with channels allowing air to pick up moisture as it passes through the openings. Manufacturers recommend a maximum air speed of 400 fpm through these panels to achieve effective cooling.
Water is distributed along the top of the pad and flows down through the cellulous material, causing it to become saturated. Excess water at the bottom of the pipe is collected and recycled back to the top. Six inch-thick pads, usually 10 feet high, are commonly used as the most economical choice. The ideal temperature is reached when the air absorbs 75 per cent of the available moisture.
High-pressure mist systems spray fine water droplets into the air stream. The potential exists for nonuniform air temperature drops from top to bottom along the sidewalls, so multiple rows of nozzles provide uniform moisture distribution to the incoming air stream. An automated controller determines the number of nozzles operating and the volume of water sprayed into the air stream based on ambient relative humidity. The system needs about 2.5 high pressure nozzles per running foot of building length to be effective.
In the Upper Midwest, where the relative humidity tends to be above 50 per cent, air temperatures inside LPCV barns using evaporative cooling are consistently four to eight degrees Celsius cooler than the ambient temperature. The temperature difference is a function of relative humidity.
Guidelines are relatively unknown for operating fans during the winter, and currently each barn appears to have an individual operational mode. However, two modes have emerged as most popular.
The first decreases the air exchange rate by turning off the fans to maintain a minimum inside temperature. This strategy prevents frozen manure, but leads to increased ammonia levels and condensation within the building.
The second mode uses several smaller fans along the exhaust side of the building. They are set to maintain a minimum air exchange regardless of outside or inside temperatures. This results in colder inside temperatures and frozen manure.
Despite differences in operating systems, there's some agreement on recommending an eight-minute air exchange for cold weather. The winter inlet should be near the top of the sidewall to allow cold air to warm before it contacts the cows or alleys. Another option uses a split curtain, with the top curtain rolling upward and the lower curtain rolling downward, creating an inlet in the middle. This results in the inlet air entering the barn at cow level, increasing the potential for drafts directly on the animals.
I had the opportunity last November to observe several LPCV barns operating in Wisconsin. In late November the outside temperature was only minus four degrees C, so I did not get to see them under extreme conditions.
Operators were quite happy with this housing style compared to the temperature extremes they experienced with multiple four-row, naturally ventilated barns operating side-by-side. They were quick to point out they would much rather work in their wide-body barns in the winter than in their other facilities.
From a cow viewpoint the story may be different. These new-style barns incorporate all the comfort features the dairy industry has adopted, such as sand bedding and larger more comfortable freestalls. When I was in the middle of a 400-foot-wide LPCV barn, however, I missed the natural light and air flow, and the ceiling just felt too low.
Late June, a tour organized by the Progressive Dairy Operators (PDO) visited several of these barns in Wisconsin. Producers on the tour can decide for themselves if the design has an application in Ontario.
Harner, J.P., J.F. Smith, J. Zulovich and S. Pohl. Cooling Air in Low Profile Cross Ventilated Freestall Facilities. Proceedings of the Dairy Housing of the Future - Opportunities with Low Profile Cross Ventilated Housing Conference. September 10 and 11, 2008. Sioux Falls, SD;
Harner, J.P. and J.F. Smith. Design Considerations for Low Profile Cross Ventilated Freestall Facilities. Proceedings of the Dairy Housing of the Future Opportunities with Low Profile Cross Ventilated Housing Conference. September 10 and 11, 2008. Sioux Falls, SD;
Harner, J.P., J.F. Smith, J. Zulovich and S. Pohl. Moving Air into the Free Stall Space. Proceedings of the Dairy Housing of the Future-Opportunities with Low Profile Cross Ventilated Housing Conference. September 10 and 11, 2008. Sioux Falls, SD;
Smith, J.F., f.P. Harner, B.J. Bradford and M. Overton. Opportunities with Low Profile Cross ventilated Freestall Facilities. Proceedings of the Dairy Housing of the Future-Opportunities with Low Profile Cross Ventilated Housing Conference. September 10 and 11, 2008. Sioux Falls, SD.
This article first appeared in the Ruminations column of The Milk Producer Magazine, July, 2009.
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