Assess ventilation carefully before investing in cooling tech to ensure the most effective system is installed and there’s a good return on investment. Two building specialists tell us more.
TEXT RACHAEL PORTER
Thinking about adding fans to housing to help keep cows cool? Then check ventilation is spot on before investing in additional equipment, says AHDB’s building specialist David Ball, and ‘know your fans’.
He says both are important considerations to ensure that fans don’t work against the natural ventilation process, but complement each other in buildings. Ideally the building should allow the ‘stack effect’ to operate. “Warm air should rise up and out through roof outlets, which then draws fresh air in through the sides of the building if the system is designed correctly,” explains Mr Ball.
volume, low speed (HVLS), or what he calls helicopter-type fans, can, if set up correctly, support this stack effect. But, in his experience, Mr Ball says many fans push air downwards into the shed – contrary to the stack effect. “We actually want warmer, stale air to be pushed up and out of the building – not back down into the shed.
“Although vertically-mounted high-speed (HS) fans work in a different way, increasing air flow across cows’ backs and through buildings, these fans should be installed to work with the prevailing wind – not against it,” says Mr Ball.
“So the start point for producers looking to install fans in cow buildings to improve ventilation and keep cows cooler – particularly for all-year-round housed herds – is to look at the building’s existing ventilation, and to improve that first, perhaps by opening up sides or additional roof outlets.
"A smoke-bomb test is a great idea and helps identify areas where fans may be able to assist air movement.” He also stresses that taking impartial advice is vital, not least because every shed and set-up is different. “I know producers who have installed HVLS fans and contrary to my thoughts, they’re extremely happy with them. So they may suit some cow houses but without the correct inlets and outlets they will only be recirculating the warm air in the shed.
Stack effect
“But, on the whole, producers should be looking at the best way of encouraging and enhancing the stack effect to create an environment where there’s airflow to cool the cows and reduce humidity in the cow house,” says Mr Ball.
“Ask questions about how the fans work and what return on investment can be expected through increased cow performance. And remember that companies rarely sell the complete range of fans. Many specialise in either HVLS or high-speed tech. So talk to non-commercial sources about what you want to achieve. This goal is to create an airflow speed of two metres per second at cow level to optimise ventilation, and create a comfortable and healthy environment for your herd.”
VES Artex’s Huw Jones agrees that it essential to assess existing housing and ventilation before considering fan installation, and he’s also keen to understand the impact of heat stress seen on farm by analysing milk and reproduction data.
If heat stress, particularly for all-year-round housed herds, is an issue then there will be summer milkyield drop or a fall in pregnancy rate. “It is important to assess herd performance during the other parts of the year to understand the impact of heat stress. For example, if I see a herd with a pregnancy rate of 15% in the summer and between 35% and 37% in the winter then heat stress is clearly playing a significant role here – it’s not a breeding management issue,” he says. “An accurate return on investment (ROI) calculation can only be given by analysing data.”
, check there’s sufficient natural ventilation – fresh air can enter through the sides and stale air can move up and out through the roof. “Smoke-bomb tests are useful, but also use your own senses,” says Mr Jones. “If you come away from housing smelling of cows and ammonia, there is an air-exchange problem. We look for ammonia levels that are less than 25ppm, because that also demonstrates good air exchange through a building, whether that be mechanically or via natural ventilation. Pushing stale air around a building isn’t the aim. The fans are pulling fresh air into the building, and distributing it at cow level at a speed relevant to temperature.”
High speed fan: key to effective cooling velocity
Air velocity
After assessing the cow-house environment, Mr Jones will then work on a plan, using high-speed fans to help accelerate that rate of air exchange and target air velocity relative to temperature at cow level. This is known as effective cooling velocity (ECV).
“We calculate an accurate ROI that takes into account installation, 365-day running costs, maintenance, and on-farm data,” says Mr Jones
“Calculations look particularly at improving pregnancy rates, which can be as much as 10% or 15% higher following fan installation, based on customer feedback, as well as maintaining milk yields. Cooler cows maintain feed intakes and milk yields, and avoid a dip in fertility.” The VES-Artex ECV fans are designed to direct air velocity and air exchange at cow level. “Regardless of fan design, they must move air at sufficient velocity for cooling at cow level. If fans are not directed at cow level, electricity, time and money is wasted,” says Mr Jones Fans are variable speed to ensure electrical efficiency and to enable 365-day use, and to improve air quality, reduce respiratory disease and keep bedding drier during the cooler months of the year. “We aim for an air speed of two metres per second across the cow that’s furthest from the fan. That’s the best way to reduce temperatures and humidity, keep bedding dry and keep cows cool and comfortable all year round.”
Cow-house fan facts
HVLS (high volume low speed)
● Large open fans – typically 4.8 to 7.5m diameter. Also known as ‘propeller’ or ‘helicopter’ fans.
● Move high volume of air at low speed (about 2km/hour) across wide area.
● A six-metre fan will typically move around 3,500m3 /minute of air.
● Can be set to draw air up or push air down.
● Suspended from ceiling.
● Effective in multi-span buildings.
● Can create even air movement throughout shed.
● Where used to pull air up, the right inlet and outlet is vital to prevent air recirculating.
HS (high speed)
● About 2.2m2 with directional louvres
● Operate at high speed and move air in a focused area.
● Each fan typically moves about 1,360m3 /minute of air.
● Work by pushing air out of the sides of the building.
● Usually positioned in line above cubicle beds.
● Produce high velocities of air in a localised area.