Did you unpack and install the inlet openings that came with your tunnel ventilation fans? They were probably in the box, but are hard to see, and easily overlooked. Tunnel ventilation air inlets must be installed properly – at the end of the barn opposite the fans – in order for the system perform effectively. Inlet size determines air exchange rate, operating static pressure, and air speed. Placement determines distribution of fresh air in the animal space. Improper size and placement can result in short circuiting of air, dead spots, increased energy consumption, and inadequate air exchange. Don’t worry if you mistakenly threw them away, they can be easily replaced and installed to improve air quality and cow comfort.
The primary objectives of a tunnel ventilation system are: 1) provide a rapid air exchange – to control moisture, gas, temperature, and pollutant levels in the animal space – and 2) provide a breeze to improve the cow’s ability to get rid of heat. Designed, installed, and operated properly tunnel ventilation systems can play a significant role in keeping cows comfortable and productive during hot weather.
Ideally tunnel ventilation fresh air inlets are located uniformly across the width of the barn end wall opposite the fans. For end wall inlets, two square feet of inlet area per 1,000 cubic feet per minute (cfm) of fan capacity is recommended. For example, a fan delivering 25,000 cfm needs approximately 50 square feet of inlet area. A stall barn tunnel ventilation system using four 25,000 cfm fans (100,000 cfm total) requires 200 square feet of inlet opening, or a clear opening approximately 5.25’ x 38’ uniformly across the width of the barn. Six 25,000 cfm fans (150,000 cfm total), need 300 square feet of inlet, or an opening of approximately 8’ x 38’. Wall studs, floor joists, beams, and grates block inlet opening, so more end wall or mow floor covering may need to be removed to provide the recommended inlet.
Some stall barn layouts do not allow end wall inlets to be used, so air needs to be drawn in through sidewall openings. Sidewall inlets tend to send incoming air toward the middle of the animal space, away from the cows, creating dead spots at the front end of the stall rows. Recommended opening for sidewall inlets is 3.5 square feet per 1,000 cfm – divided between both sides – to encourage incoming air to ‘turn’ sooner and provide better air distribution in the feeding alleys.