It’s no great secret by now that Big Ass Fans has a test lab – the biggest facility of its kind, and the only one specifically designed for the testing of HVLS fans. So, I’m sure it’s no great surprise to hear that we test fans (hey, we had to do SOMETHING in there).

Big Ass Fans facility certified LEED Gold

But we don’t just use it to test Big Ass Fans. We test EVERYBODY’s fans. So we know, in great detail, not only how our fans perform, but how other makes perform as well. And we know which performance claims can be trusted and which ones can’t.

There are other companies selling HVLS fans these days, but none of them have the kind of testing capabilities that we have here at Big Ass Fans; which means that we probably know more about the performance of other makes of fans than their own manufacturers do. It’s an interesting thought, and maybe one that’s a little scary if you happen to be one of those other manufacturers… but knowledge is a good thing.

So, if you hear a claim that makes you curious, and you’re wondering if it’s too good to be true or if the product really performs the way they say … go ahead and ask.

We know.

As a resident (electronic) card carrying geek, the work I do at Big Ass Fans is focused on the technology we use to create better fans. Computer simulations of components, fan performance and usability are all done in house, using some of the best equipment and software available. Yes, at the end of the day, we make fans, but making the best fans is our ultimate goal.

Measuring the effectiveness and quality of our fans (like any product), is a straight forward idea. However, with very large fans, this can be difficult. Finding a suitable location for testing, be it an indoor soccer field or a shopping mall, is easy enough. Letting us set up all of our testing equipment around the place, muttering numbers and equations would be stretching our welcome a bit.

In many instances, technology comes to the rescue with CFD, or Computational Fluid Dynamics. Using our 3 dimensional models of our fans and the spaces where they are installed, simulations calculate the fan’s interaction with the air in the space. What was in reality vast amounts of air particles becomes nodes of digital points in space, points that push and pull on themselves as they are moved by the fan’s rotating airfoils. These simulations show us visually how the fan is moving the air, as well as what direction it is moving. Using this data, we can better refine the shapes and angles of our foils, as well as the locations at which the fans are more effective. This makes the process of testing new, better designs faster and more frequent.

Heat circulation, heat recirculation, heat distribution, destratification…regardless of your preferred description, they all work the same way. With winter upon us, there is no reason for your Big Ass Fan to sit idle. The benefits of ceiling fans during the summer are well known and appreciated by many. Not so common, however, are the benefits of Big Ass Fans in the winter to improve comfort and reduce energy costs.

Stratified Space

Less dense than cold air, hot air will rise and remain at the ceiling, (Fig. 1), keeping your ceiling comfortable and warm. This benefits…no one, aside from a few nesting bugs. Heat recirculation is the process of mixing the air to evenly distribute heat trapped near your ceiling down to the occupants, rather than escaping through the roof for good.

Big Ass Fans® are designed to operate efficiently at low speeds, so turning the fan very slowly in the forward direction (counterclockwise) will provide enough air movement to circulate the hot air at the ceiling down to the floor without causing drafts. Regardless of the square footage or ceiling height within your space, the goal is to mix the air in the space and keep the air speed at the floor below perceptible levels, approximately 40 feet per minute or ½ mph.

Hot air emerging from your furnace is approximately 5-7% lighter than the air present in the room. As this hot air rises, it contributes to a significant temperature difference between the floor and the ceiling, further increasing the workload on your furnace, not to mention increasing your energy bill.

Destratified Space

Running your Big Ass Fan in the winter months will result in an equalized air temperature throughout (Fig. 2). Considering all the heat supplied by the furnace now reaches the occupants and the thermostat, the furnace will run less frequently with less heat escaping through the roof.

“We have been using the Big Ass Fans for heat stratification in the winter time,” said Mike Donnelly, Vice President / General Manager for Lock, Joint, Tube in Chattanooga, Tenn. “We do have equipment inside the building that generates heat but no heating register so we are able to bring that heat back down from the ceiling. It is because of the fans that I took out the heating system,” he added.

Goodway makes products to keep HVAC systems clean and operating efficiently. What a coincidence! We don’t clean them but Big Ass Fans do improve HVAC efficiency by circulating the conditioned air, making HVAC systems work less. And when it comes to HVAC, less work is less money. We’re sure this is why Goodway recently sang the praises of HLVS fans. Read their blog post about HVAC and HVLS. Thanks Goodway!

Move that hot air trapped at the ceiling on down to the floor.

Big Ass Fans saves you money in the winter by circulating the hot air trapped at the ceiling back down to the floor. We do this by slowing the fan’s rotation, not reversing it, below the level of a perceived breeze. We asked our resident air  movement guru, Dr. Richard Aynsley, to give us a few words on why it’s actually a bad idea to reverse ceiling fans in the winter. Below is what he gave us:

As an architect and engineer, I can understand why the architects for some projects seek truly reversible air movement from ceiling fans. This simplistic notion of ceiling fan use has been around for decades. Let me explain as an architect with a Masters degree in Engineering, why this is not a sound idea.

The use of ceiling fans for air movement to provide energy-efficient summer comfort is straight forward. In summer, providing air movement of 160 fpm in the occupied zone will allow the thermostat to be raised 4.7°F while maintaining the same thermal comfort. Raising the thermostat 1°F typically saves between 3% and 4% of cooling energy cost*. Raising the thermostat 5°F will typically save between 15% and 20% of cooling energy costs. In summer, providing air movement of 230 fpm (2.6 mph) in the occupied zone of an air conditioned space will allow the thermostat to be raised 10°F while maintaining the same thermal comfort. This thermostat increase would save 30% to 40% of air conditioning cooling costs.

Use of ceiling fans at low speed with air flow downward for energy efficiency by destratification in winter is well established.

Move that hot air trapped at the ceiling on down to the floor.

Circulation of indoor air at 3 to 4 times per hour, particularly in spaces with high ceilings, can allow the thermostat to be set 10°F to 15°F lower while maintaining the same thermal comfort. For each 1°F the thermostat is lowered in winter the typical heating energy cost saving is 1% per 8 hour period, or 3% per day. Lowering the thermostat in winter by 5°F from 85°F to 80°F will typically save approximately 15% of heating energy cost per day.** Field data from clients using Big Ass ceiling fans indicates monthly winter gas consumption can be cut by up to 30%.

Here is the catch. If the airflow from the ceiling fan is reversed with airflow upward, even at low speed, the velocity of air across the ceiling above the fan is high, typically around 400 fpm. At this speed, the heat transfer coefficient at the ceiling is around 1.87 Btu/h.ft2.°F. However if the ceiling fan is running at low speed with airflow downward the airflow across the ceiling is low, typically 80 fpm. At this speed, the heat transfer coefficient at the ceiling is around 0.051 Btu/h.ft2.°F.

In short, reversing the air flow direction from ceiling fans in winter the heat loss through the ceiling is increased by a factor of around 3.7 times due the increase in surface conductance.

*Exeloncorp, formerly Consolidated Edison, www.exeloncorp.com
** US Dept of Energy, www.eere.energy.gov

Richard Aynsley, Ph.D., M.ASHRAE,
B.Arch (Hons I), MS(Arch.Eng), Registered Architect, QLD.
Director Research & Development
Big Ass Fan Company
Lexington, KY, USA