[Greenbuilding] Speed of ceiling fan

[John Straube]

A ceiling fan is a completely different animal than a fan in an enclosed telco box of fan. So that analogy is not useful. 
200 fpm is high but I know that it makes 80F 20 per cent RH air feel like 72 for normal summer office attire which is why I used that value. 
T shirt and 50F dewpoint 80F air results in about the same
All of this is in ASHRAE Standard 55 if you want to calculate it. 

I have a Kestrel anemometer ($120) and a Kill-A-Watt meter which tells me that a 36" ceiling fan in my 8' ceiling bedroom can indeed deliver 200 fpm lying below it and draw 20W. Of course there are lots of variations.  


Sent wirelessly from my BlackBerry device on the Bell network.

-----Original Message-----
From: RT <Archilogic at yahoo.ca>
Sender: greenbuilding-bounces at lists.bioenergylists.org
Date: Wed, 31 Aug 2011 16:17:00 
To: Green Building<greenbuilding at lists.bioenergylists.org>
Reply-To: ArchiLogic at chaffyahoo.ca,
	Green Building <greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] Speed of ceiling fan

On Wed, 31 Aug 2011 09:55:00 -0400, Sacie Lambertson  
<sacie.lambertson at gmail.com> wrote:

> John, honing in on that last bit regarding the fan moving at 200 mph  
> over a body, what is the  speed of a ceiling fan--at the low, middle and  
> high
> speed?

Assuming that the question actually is:

"What air velocity does a ceiling fan yield at the LOW, MEDIUM and HIGH  
speed settings ?"


Obviously the air velocity (and hence the cooling effect one feels) would  
vary with fan blade size, fan motor size, ceiling height, downrod length,  
distance of the person away from the face of the fan etc.

ie A person standing 8 inches away from the fan blades of an 8 ft diameter  
fan driven by a 1/2 HP direct drive motor with the fan speed set on HIGH  
may very well feel like the fan is moving air past her face at 200 mph(!).

However, a person standing 12 feet down and 20 feet away from the face of  
a 42 inch Home Despot ceiling fan or even 2 feet away from a little  
computer fan might feel negligible air movement and negligible cooling  
effect.

To determine air velocity one typically uses an anemometer (various types  
exist), and typically, it's an item that most people don't have hanging  
around in their "miscellaneous tools" drawer.

For Sacie's purposes, I suspect that a rudimentary anemometer could  
probably be rigged up using a bicycle with a front wheel (preferably  
reasonably well trued) whose bearings have been well greased (so that it  
spins with a minimum of friction) and which has a bicycle computer  
attached. The latter are available for less than $10, delivered to your  
mailbox and are capable of a $#!+-load of functions (ie odometer, trip  
odometer, maximum speed,average speed, elapsed time, time of day clock,  
temperature ... and instantaneous speed, usually in your choice of miles  
per hour or kilometres per hour.

200 ft per minute = ~ 3.7 kph

For the arithmetically-challenged:
(kilometres per hour)  x   ((1000 x 3.281) / 60) = feet per minute

So it would be a matter of laying the bike on its side so that the front  
wheel (with the speed sensor) spins freely and then maybe you tape some  
paper cups or some old DD bra cups or such-like at say, a minimum of 8  
spots around the edge of the wheel to "catch" the wind. Turn on the fan  
and hopefully the bike wheel starts spinning and VOILA! The LED display of  
the bike computer should eventually tell you the air velocity once the  
wheel gets up to a constant speed. (Note: I've *not* tried this at home. I  
am a professional.)

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  C A >
(manually winnow the chaff from my edress if you hit REPLY)

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