Simple way to cut your factory heating bill by 20-30%?

We are just fitting what is called a High Volume Low Speed (HVLS) fan to our factory to break up stratification between the roof of our factory and the factory floor. They are large diameter fans that use very little power, in our case ~1kW for a 6.6m fan. I am expecting this will cut our factory heating bill by 20-30% and pay for itself (￡7k) before the end of the winter. I will report back on our experience but I thought it might be useful to explain why I believe HVLS fans are so effective.

The physics is quite simple - high ceilings mean that you get stratification and the air next to the roof is much hotter than floor level. Our factory roof is not very well insulated and the eaves are about 7.5m high and the difference between the temperature at the ground level and the peak of the roof space is 10C. I have measure 31C at the apex when at ground level it is 21C which is what we are aiming for. The taller the building the worse this effect. Heat loss is proportional to the temperature difference, so if it is 0 degrees outside and my roof is at 31C then I will lose 1.5x as much heat through the roof as I need to compared to having the whole building at 21C and the air fully mixed. If it is 10C outside then I lose 2x as much heat through the roof without the fan.

This is where HVLS fans come in. They are very large diameter (4-6m) fans that move lots of air very slowly. Moving lots of air slow uses very little energy, especially when you compare it to the amount that you can save on your heating bill. I am expecting the fan that we are installing to reduce the temperature difference between the roof and the ground to less than 1C. This should cut our heating bill be about 30%. If you have a taller building it might save you more. The factory volume is about 7,000 m3 and the unit supposedly moves 360,000 m3/hr for just 1kW, so we will recirculate the air about 40-50 times every hour with just one big fan.

I am not being paid in anyway for this post, but anything to reduce energy demand for companies this winter has to be a good thing. The UK company that we have used is called Megafans and our contact Mark Oldham has been very helpful. The US company where I first came across the concept of HVLS fans is called 'Big Ass Fans' - not very PC but very memorable...