Tag Archives for " ceiling fans "

How to choose the right ceiling fan (other than the color)

Everyone has a “style” in their home, and glancing at the number of pages of ceiling fan choices in any online hardware or home decor store, there is a ceiling fan for every style!   You’ve got modern, traditional, glam, rustic, minimalist, and everything in-between.  Knowing the characteristics of the best-performing ceiling fans will make your choices easier within the style and color you like, so take a minute to check out these tips.

The object of a ceiling fan is to circulate air, so air flow should be near the top of your list.  Airflow is measured in cubic feet per minute, and although some manufacturers like to give measurements of velocity (feet per second or meters per second), they are not the same.  Airflow is what “mixes up” the air in a room and breaks up stratified air (thermal layers) so that your air conditioning system becomes more efficient.    The most efficient ceiling fans are High Velocity Low Speed (HVLS) types; these are the ginormous fans that you may see in a warehouse store or sports arena.  They typically measure 6 feet in diameter and larger, many topping 20 feet or more.  Surprisingly, they move the most air with the least amount of energy, but you do need a high ceiling so that each fan is between 20-25 feet above the floor.  If you aren’t looking for such an industrial size fan, Aeratron makes the most efficient ceiling fan in normal sizes.  Their fans incorporate several designs that help them to achieve this efficiency:

• Blade shape: Blades can get super-fancy, but the most efficient are oar-shaped, or in Aeratron’s case, with a “winglet” to reduce drag.

• Motors: the more powerful the motor, the more efficient the fan.  The most recent developments are “DC” or direct current motors, which can be adjusted to an infinite number of speeds.  These are electronically controlled and are typically quieter, smaller and lighter than AC (alternating current) motors.  

• Number of blades (Less is More): Did you know that the lower the number of blades, the better the efficiency?  More than two blades just cause more turbulence and do not move more air.  

• Slower is better:  Operating a ceiling fan at a slow speed continuously is better than higher speeds.

• Having a downrod (an extension that lowers the body and blades of a fan away from the ceiling) is critical to a fan’s ability to move air.  Even a 3” to 4” downrod increases efficiency by approximately 40% over a flush-mount fan (one that hugs the ceiling).  Check out downrod specifications below. 

So, after giving all this information, there is one number that could guide you to the most efficient fan in your style preference.  It’s called cubic feet per minute per watt (CFM/W).  Basically, it’s analogous to gas mileage for fans–how much air it can move per watt of energy expended.  Although 75 is the minimum to make a fan efficient, the higher the better, and the most efficient fans have a CFM/W over 400.   Here’s a list of the most efficient as compiled by EnergyStar.gov.

So, now that you think you have found the most efficient, stylish fan in your budget, we just wanted to make sure you know the following interesting information:

Ceiling fans don’t actually cool a room.  Say whaaat?  That’s right, ceiling fans don’t cool a room because they can’t remove heat, the way an air conditioner can.  In fact, because ceiling fans expend energy and a portion of that energy produces heat, they actually add heat to a room.  The cooling effect you feel is the wind chill effect, which is the temperature which a person feels with respect to the wind.  (cielowigle.com)  According to Consumer Reports, using a ceiling fan, can make you feel up to 4° F cooler, and you can save 3 to 5 percent on air-conditioning costs for each degree you raise the thermostat, so using ceiling fans and raising the thermostat setpoint can theoretically save you 12-20% in air conditioning costs.  Pretty cool!

Remember the rule above about the less blades, the better?  Well, an improvement on a two-bladed ceiling fan might just be a ceiling fan without blades.  There are actually quite a few products that advertise to be “bladeless”, but in reality, the blades are enclosed in a casing (enclosed fans, by the way, are great choices for kids’ rooms and near bunkbeds, to avoid the chance of getting fingers or toys caught in them).  One of the true “bladeless” fans is the Exhale Fan, which features a stack of spinning discs modeled after Nikola Tesla’s bladeless turbine.  Instead of shooting the air straight downwards like traditional fans, Exhale fans move air at a 45 degree angle, which accomplishes a lot: it creates a vortex and de-stratifies the temperature layers of the room, more effectively mixing the air.  The fans themselves move over 5,000 cfm of air, which is pretty amazing since they have no “blades”!  No blades also means very little noise.  In addition, they are preferably mounted directly to the ceiling, eliminating the use of downrods.

Sizing your fan is very important.  The larger your room, the greater the diameter of the ceiling fan you need to circulate air effectively.  This sizing guide is very simple to use, and when in doubt, it’s best to go one size larger!   The reason for this is that it’s more efficient to operate a large fan on lower speed, than to operate a smaller fan on its highest setting.    

Choosing the correct downrod length is very important.  It’s not common knowledge, but if you have a standard 8’ ceiling, you should have a short downrod on your fan (3”).  When I purchased my home, even though all of the ceilings are 8’ or more, 6 out of 7 ceiling fans were flush-mounted (mounted directly to the ceiling).  Flush-mounting is only recommended for ceilings lower than 8’, and a flush-mounted fan moves approximately 40% less air!   So, before purchasing a ceiling fan, measure your ceiling height and check this handy guide.  If a fan accommodates a downrod, you can always adjust the length by purchasing the right downrod separately.  Basically, you’ll want the fan to be at least 7’ from the floor and 8-9’ for optimal airflow.

LED lights continue the savings.  If you are going for efficiency, it makes sense not to squander savings from the fan by using incandescent light bulbs.  Many high-end fans now have permanent LED bulbs and LEDs that can be adjusted for color in cooler or warmer tones. 

You can’t have too much air circulation!

When clients ask advice on choosing air purifiers, some of the first questions we ask are about the layout of their home and how air circulation is accomplished.  This topic is covered in our article “Which air purifier should I choose for my home?  Part 1: Airflow”.  Airflow is super-important, and if outdoor conditions like heat, cold, humidity or pollution restrict your ability to open windows for good cross-ventilation, fans are necessary to get air moving.  Moving air helps any kind of air purifier and also your home’s heating and cooling systems to work more efficiently.  We’ve put together a few visuals on how common (and not so common) fans work. 

What about Radiator Fans?  

Radiators with fans are common installations in older buildings and to be sure, they are better than not having a fan at all.  However as shown in the below diagrams, there tends to be an area in the middle of the room that doesn’t get much mixing action.

Source: Study “Influence of Sensor Position in Building Thermal Control: Development and Validation of and Adapted Zone Model”

“Basket Fans”

Although you may not have heard of this description before, when seeing a basket fan you can easily understand why it’s called that:

Whether sitting on a desk, standing on a floor or hung from the ceiling, these types are generally economical and when placed near where you are sitting, seem to be efficient in moving air.  However, scientific study about their circulation effects show otherwise.  There can be large “void spaces” where virtually no air is moving.

Source: Read this before investing in basket fans for air circulation

Regular Ceiling Fans

Ceiling fans are great tools for getting more air circulation.  Traditional ceiling fans tend to create better air circulation in a room than regular floor-or tabletop- fans (excluding “air circulators”, which we will visit separately in this article).  The image below shows that the fan shoots air with greatest velocity down near its center, and airflow moves along floors until it reaches walls and moves upwards again.  There are entrainment zones around the fan that do not get optimal mixing, however, if the fan is sized correctly for the room (check our article on choosing a ceiling fan), it’s definitely an improvement over not having a fan at all.

Image: Study: Measurement of airflow pattern induced by ceiling fan with quad-view colour sequence particle streak velocimetry

HVLS Fans

Some big rooms can be serviced by one or more High Volume Low Speed (HVLS) fans, which turn more slowly but generate much bigger cubic foot per minute (cfm) airflows in a space (read more about HVLS fans here).  Because the airflow along the floor is much deeper with HVLS fans than with normal ceiling fans, these currents on the floor are called floor jets.  The image below also shows how such a fan can cool even more effectively when fresh air vents at the bottom of the room, and exhaust vents at the top, are opened.

Source: “Need for Ventilation”

Air Circulators/Destratification Fans

“Destratification” is the gold standard of air circulation in a room, because temperatures in the top, bottom and sides of the room can show that the air is being thoroughly mixed!  Without destratification, thermal “layers” can develop, and air conditioning (including heating) as well as purifiers cannot effectively service the entire volume of air.  There are several different types of fans that can break up these thermal layers.  Airius, an Australian company, makes a different type of high volume fan that is termed “bladeless” because the blades are hidden in the body of the fan but still generate significant airflow.  Their systems are termed “airflow circulation cooling fan and destratification system” and are designed to be mounted close to the ceiling; many applications are found in convention centers, dealerships and indoor stadiums. 

Source: Airius Fans Vs. HVLS Fans

Real “bladeless” fans

For residential or commercial use, true “bladeless” ceiling fans (modeled after Nicola Tesla’s bladeless turbine) offer similar destratification to circulator fans, with less noise.  According to Exhale Fans’ fact page, “The airflow is a vortex: The airflow profile makes the real difference in how you feel while in your space. Air exits the Exhale Fan in all directions 360° horizontally and at a 45° angle. This unique airflow starts a gentle rotation of the air much like a vortex. The vortex airflow profile generated by the Exhale Fan is unmatched in the ceiling fan industry. Air is not simply directed straight down but moves around the room in a pleasant cyclonic flow. What we have created is a destratified environment where floor to ceiling, wall to wall, you have a temperature balanced and comfortable space.”  The video of an Exhale Fan working in water to lift and circulate particles off the floor of the water tank is impressive!

Source: Air Destratification

Source: How does it work?

An “air circulator” like the Vornado ($92) is purported to have a similar pattern to ceiling and HVLS fans, however it shoots air across a room.  Here is a video comparing Vornado, Dyson and generic tabletop fan.  The reviewer (Filipino) and commenters mostly prefer the Vornado for power and value.  Another great air circulator option is the Dreo ($99); this video comparing Vornado and Dreo declares Dreo the winner, although it's virtually the same price as the Vornado.  The Dreo uses a brushless DC motor so it has more range of speeds, and uses less power than the Vornado, which uses an AC induction motor.  Dreo is also quieter across the range, even at the highest setting.  There are more economical versions of each brand that incorporate less technology but move the same amount of air.

Source: Vornado 293HD literature

Although the Dyson bladeless fans claim to be “air multipliers” because more air is entrained than is taken in through the pedestal of the fan, they lack the power to destratify and circulate air in a whole room.

Source: How does the Dyson Air Multiplier Work?

Now that you know which types of fans help to truly get all of the air in the room moving, you can decide how and where to use/place them.  Perhaps you’ve never turned on your ceiling fans…now is the time to clean them and get them running!  Considering that the purpose of an air purifier with HEPA is to filter all the air within a room, the fan used in the purifier or a separate fan paired with it is very important to the purification function. It should either have a high Clean Air Delivery Rate (CADR), or be used with a separate fan that is able to destratify the room.  

In this test, a 705 cubic foot space (approximately 9x10 foot room with 8 foot ceiling) was filled with incense smoke and different purifiers were operated to clear all traces of PM1.0ug/m3, PM2.5ug/m3 and PM10.0 ug/m3 particulate matter.  Although the location of the particulate measurement devices were not disclosed (how close to the purifier they were), the purifier with the highest CADR proved to be the fastest to clear the air (BlueAir Pure Fan Auto, in only 27 minutes); the other two purifiers tested took 1 hour 24 minutes and 2 hours 11 minutes!   However, it’s possible to pair a purifier with lower CADR with a ceiling fan or circulator or destratifier fan to improve performance..

In conclusion, the best way to purify air with a HEPA filter is to use a purifier with a high CADR, or to use the purifier in conjunction with a fan that improves whole-room circulation (and thus destratification).  In addition, we’ve always stated that the Germ Defender/Mold Guard and Air Angel units work differently from HEPA, because they send out ions into the room instead of pulling all the air through the device to filter it.  However, their function also improves when coupled with an air circulator, in order to deliver the ions more widely and evenly throughout the space.