Fan System Design

Design considerations for maximum effectiveness and useful life

Ventilation should always be considered a priority in any infrastructure planning. A pitched roof and open ridge vent should be considered before fans. Good facility design will create the most effective air movement. Fans will then help to increase this. Fans are designed to move warm air away from the cow as well as create air movement over the cow's skin to enhance evaporative cooling through sweating.

Fan sizing, type and placement

Element  Specifications 

Fan Cost

$550 - $2,000 each

Recommendations

  • Costs will depend on size, capacity, design and installation.
  • Energy consumption and efficiency of the entire cooling system should be considered.
  • Fans should be mounted above sprinklers so they remain dry.
  • Only use fans with sealed motors.

Fan flow rate

285 - 840 cubic meters / minute

Recommendations

Spacing is determined based on the fan's operating flow rate. As a guide:

  • 900 mm blade, 285 m3/min with a 0.45 kW motor spaced every 6 m
  • 1,300 mm blade, 840 m3/min with a 1 kW motor spaced every 12 m
  • The base of the fan blade should be at least 2.3m from the ground.

Design considerations

  • Ensure that fans used have the capacity to move the volume of air required at >2.0 m/second. If cows are tightly packed, airflow will need to be greater. When used in open spaces, larger-capacity fans are required because they are operating against static pressure, so their efficiency is lower.

  • Doubling the operating capacity of the fan does not double the distance covered by the fan, but it will increase costs. Be prepared to modify the placement of fans and add additional or larger-capacity fans if required.

Seek professional advice from a registered engineer and/or manufacturer.

 

Fan orientation and pitch

Element Specification
Fan Location Work with prevailing wind (Eg. Westerlies)

Recommendations

  • To minimise operating costs, locate fans to take advantage of prevailing winds at the site.

Fan Pitch 20-30 degrees

Recommendation

  • The fans should be tilted 20-30° down from the vertical so they blow down to the floor, to ensure air is forced down around and beneath the cows.
  • This will enhance evaporative and convective cooling. Tilting the fans towards the ground also reduces interaction between groups of fans that are located in series with each other, improving operating efficiency.

Operational considerations:

  • When operated in conjunction with sprinklers, fans will usually be initiated first (i.e. start to operate at a lower temperature than sprinklers).

  • Sprinkler on/off cycles can then be stepped up at different temperature trigger levels

  • If fans are in the dairy they should run continuously when the Temperature Humidity Index (THI) is more than 72.

  • Keep the safety grill around each fan free of cobwebs and dust to maintain their maximum efficiency and effectiveness.

 

Fan design considerations for compost bedded pack structures 

An in-depth literature review of the existing industry best practice has been performed by Dr Phil Chamberlain.  

High-Volume, Low Speed (HVLS) fans are used to circulate the incoming fresh air thorough all areas of the barn and ensure sufficient barn air exchange is achieved. These fans are named due to their large size (2.5 - 7.3 meter diameter) and slow-moving speeds (45 revolutions per minute for a 7.3 meter fan). For a 7.3 meter HVLS (helicopter) fan, there should be a minimum of 20 meters between each fan.

Fan positioning

If they span down the centre of the barn just over the feed alley. If used correctly, moisture, heat and odour can all be greatly reduced. However, these fans often need the assistance of smaller fans, closer to the pack, to establish sufficient airspeed to dry the pack and cool the cows.

Box Fans  are smaller than HVLS fans and provide improved air movement at cow and pack level, to dry the pack and cool the cow.

Commonly, these fans can range from 0.9 meter to 1.3 meter and, therefore, should be spaced 10 meters for 0.9 meter fans and 15 meters apart for 1.3 meter fans.This should also be positioned at an angle that is below the downstream of the preceding fan. These fans may also oscillate. The larger the fan, the more space can be placed between each of them. Fan placement should be concentrated over the cow beds and feed lanes.

Perfect fan positioning