How do you keep barn ventilation running in a power cut?

Keep the fans, the climate computer and the alarm on a power source that takes over by itself, and make sure the alarm reaches you. That source can be a standby generator with an automatic switch, a battery system that runs as an island, or both. Which one fits depends on how many kW your fans draw and how long a cut can last. Our guide to the right emergency power supply for your business compares UPS, generator and battery in general. This article applies it to a barn full of animals. For the battery side, see our business battery systems.

You know the moment. The phone goes off at night, or worse, it does not. The fans have stopped, the air in the barn is getting thick, and the old generator needs three pulls and a lot of luck. On a rural line you are often the last to get power back. And a cut does not always mean all three phases: sometimes one phase drops and half the fans stop.

What most farmers do not see is where the real risk sits. It is rarely the generator itself. It is the alarm that shares the same power, the switch that nobody tested under load, and the restart of every fan at once. Buying a bigger generator does not fix any of those. A system that takes over by itself, and that you test, does.

A farm in Tielt shows another set-up. It runs on solar panels and a battery of 123.2 kWh, and the grid connection only charges the battery. In Wingene the full 3 x 400 V, 63 A supply comes from the battery alone. There, the grid has become the emergency power.

How long can pigs or poultry cope when the barn ventilation stops?

Minutes to a few hours, depending on the animals, the weather and the barn. Varkensloket names the factors. How long does the cut last, how old are the animals and how many share a section? Is the ventilation natural or mechanical, and how is the barn built and insulated?

Varkensloket cites a US trial in which the ventilation was stopped in a barn with 2,000 piglets. For piglets of about 23 kg, the temperature was the first problem: it rose too high after 60 minutes. CO2 (carbon dioxide, the gas the animals breathe out) became too high after 95 minutes. For piglets of about 7 kg, CO2 became too high after 150 minutes.

Poultry leave even less time. The University of Kentucky writes that poultry can survive only 20 to 30 minutes at temperatures above 97 °F (about 36 °C) in still air. The Flemish broiler guide from Proefbedrijf Pluimveehouderij adds a warning for heavy broilers. Above 28 °C in the barn they eat less and grow less, with a risk of higher mortality.

What does the law require for barn ventilation and alarms in Belgium?

Do your animals depend on mechanical ventilation? Then you need an emergency system for fresh air, and an alarm that warns you when the ventilation fails. The alarm must be tested regularly. This comes from EU Directive 98/58/EC and applies to every farm animal, pigs and poultry included.

In Belgium the rule sits in the Royal Decree of 1 March 2000 on the protection of animals kept for farming purposes. The Flemish Department of Agriculture lists it in its conditionality checklist for animal welfare (RBE 11). In Wallonia, SPW Agriculture lists it under ERMG 10 for pigs and ERMG 11 for all farm animals.

• Emergency system: an "appropriate" back-up that supplies enough fresh air when the main system fails. The text does not say what it must be.
• Alarm: it must go off when the ventilation fails. Varkensloket adds that the signal must be noticed in all cases, which is why most farms link it to a mobile phone.
• Testing: "regularly". Varkensloket gives every three months as an example.
• Daily check: all automatic or mechanical equipment needed for the animals must be inspected at least once a day. Defects must be fixed at once, or the animals must be protected in another way.

So in Belgium the law asks for a result, not for a machine. It does not name a generator. The electrical safety code AREI (the Belgian rules for electrical installations) adds its own layer. It names a building for industrial livestock farming as an example of a critical installation. For those, the operator decides the measures in a risk analysis and keeps a list and plans that are checked at the inspection. Its rules on overload protection even use the ventilation motors of such a building as an example.

Which alarm warns you when the power fails in the barn?

A good barn alarm watches three things: the power supply, a minimum temperature and a maximum temperature. Varkensloket names exactly these control parameters. The Flemish broiler guide says the alarm must report temperatures that are too high or too low, and power failures.

Then check the weak points that farmers run into:

• The alarm needs its own power. An alarm that runs on the same circuit as the fans falls silent at the worst moment. Give it a battery, and check that the phone dialler or GSM module still sends when the grid is gone.
• One phase can fail on its own. On a three-phase site a cut sometimes takes one phase and leaves the other two. Make sure the alarm, and your back-up, also react to a missing phase.
• Someone must answer. Agree who gets the call first, who is second, and what each person does in the first 15 minutes.
• Test it for real. Switch off the main supply on purpose, and check that the alarm reaches the phone and the back-up takes over. Write down the date.

Standby generator or battery backup: what keeps the barn fans running?

The best back-up is one that starts without you. The options differ in how fast they take over, how long they last and who has to act.

Auburn University put it bluntly for poultry houses. A generator on a tractor PTO, or one connected with a manual switch, "simply will not meet the need". The generator must start by itself and switch over by itself. Varkensloket also mentions a generator that you start by hand after the alarm, but that only works if someone can be there in time.

A battery system with an island function (it runs on its own, without the grid) keeps the fans turning without a gap. According to Victron, its MultiPlus-II takes over in less than 20 milliseconds. A Victron GX controller can also start a generator automatically when the battery gets low.

A farm in St-Georges-sur-Meuse used to run fully on a generator, because the street had no connection. With solar panels and a battery, the generator now only serves as back-up. The same logic works on a farm with a grid connection: the battery covers the first hours, the generator the rest. Our article on a generator with a battery explains how the two work together.

How big should the backup power for a barn be?

Size the back-up on the moment all fans restart, not on the fans that are already running. Electric motors draw two to twelve times their running current for a few seconds when they start, according to Auburn University. When the power returns or the back-up takes over, all fans want to start at once.

Work through these questions before you choose a generator or a battery:

Can a farm battery do more than wait for a power cut?

Yes, and that is what makes it pay. A battery that only waits for a cut earns nothing on the other days. A battery that also runs the farm every day covers its cost faster, and is ready when the grid fails.

In Tielt the connection was too small for the farm to grow, and the next step would have been medium voltage. The battery system (45 kVA, 123.2 kWh) now gives the site more power, so a heavier connection was not needed. The farm expects to take only about 5% of its yearly use from the grid. A smart control sends surplus solar power to the boilers.

In Wingene the supply of 3 x 400 V, 63 A comes from the battery alone (45 kVA, 150.4 kWh). The grid only charges the battery, for example during heavy use or when there is too little solar power. A generator can be connected too. In Maasmechelen a customer who already had a generator for emergencies can now choose between the grid and the generator to charge the battery.

Our semi off-grid system works on the same principle. When the public grid is interrupted, the site keeps working on the off-grid installation. That works for powers up to 75.6 kVA (3 x 400 V + N, 63 A). A battery that already carries the farm every day leaves no gap for the fans when the grid fails.

Is your connection already too weak for new fans or a bigger climate system? Then our article on more power without a heavier grid connection shows the options.

What happens when you ask us to secure your barn?

We start with what must keep running, not with a device.

1. Step 1: Analysis and sizing. We list the fans, the climate computer, the alarm and the other circuits that must keep going, and we look at what they draw. If data is missing, we can monitor your consumption for a short period first.
2. Step 2: Technical design. We choose the battery, the inverter power and, where needed, an automatic generator start.
3. Step 3: Installation and commissioning.
4. Step 4: Monitoring and support. You follow the system in the app and the VRM portal, and you get an alert when the battery runs low.