Well, better than answering those 2005 postings where the people are
waiting for info where to buy a repair part, eh?
AHA! Thanks for finding that bit of info. THAT explains why the office
fan runs for about 10-15 minutes before it seemed like the temp started to
rise! In otherwords, fan at first good, over time bad. I haven't gotten up
on ladder [10 ft ceilings] to check the motor housing to see just how hot
it does get. But then heat means power, so why not just run Heat Pump for
a bit? EVERYTHING eats power. These houses were built like energy is free.
Simple example is the 7 ceiling spot lights in the kitchen at 60W each,
that's a whopping 420W just to see! A microwave runs on that! well almost.
However, back to fan, with the UP direction not so noticeable. But that
direction was contrary to intuition AND to that TV show. so had to check.
Thanks for confirming there is little advantage to running fan without
anyone in room, unless the Air Handler is anemic, but that's another topic.
It's quite real. It's one of those short info articles that magazines
like to use for filler. I suspect that it might have been shortened
through over editing.
I have to confess that I didn't read it thoroughly and criticially.
You're right. The article has problems.
Nope, they're about the same. A running ceiling fan will burn about
75 watts going full blast. A light bulb might burn about 75 watts.
Both convert most of the 75 watts into heat. It's the power
consumption in watts that's important, not the surface temperature. If
I place a sealing fan motor, and a light bulb, in two seperate
marginally insulated cardboard boxes, and let them run for a while,
the final temperature will be the same.
Yeah, probably true.
Yeah, also true. However, please remember the audience. It's mostly
home owners that are interested in alternative energy for their homes,
not engineers and energy professionals. For such an audience,
generalizations are useful.
True, if you assume uncoated glass. With a Low-E coating, much of the
IR is reflected. I can grind the numbers for how much later if you
Jeff Liebermann email@example.com
150 Felker St #D http://www.LearnByDestroying.com
On Thursday, July 24, 2014 1:42:35 PM UTC-4, Jeff Liebermann wrote:
I don't think that's true in the case of the fan. A lot, hoefully most
of the energy is going into moving the air, not generating heat. It's like
saying 1 hp = 745 watts, so a 1 hp water pump is generating 745 watts in
heat. In fact, most of that energy is going to moving the water.
If it wasn't you'd have a resistance heater, not a pump.
It's the power
Per the above, I don't think so.
Not really, because again most of the energy from the motor is
not resulting in heat. I made that mistake myself, suggesting that
you could measure the wattage using a Kill-a-Watt. You can measure it,
but you can't then say because it's pulling 50W that it's generating
50W of heat in the room.
That makes no sense. The window doesn't heat the room because the glass
is at 100°F, it heats the room because it allows radiant heat in.
Comparing the temperature is totally invalid and not useful in any way.
I understand your thinking, but all the power a fan is using in a closed up
room is going to generating heat.
Part of the power to turn the motor is being used in the wiring, part is
lost in the bearings of the motor, and whatever is left over is moving the
air. When the air is moving, that movement is being converted back to heat.
If it was being used to blow air out of the room, then much of the enegry
used to move the air would be dissapated as heat outside the room.
Just plucking out numbers from the air, say the fan draws 100 watts from the
AC line. All 100 watts will be heating the room unless you blow air out of
the room. The fan may only use 25 watts to heat up the motor due to
electrical and mechanical losses. The other 75 watts will be converted to
heat when the air molicules rub against each other and slow down. Just like
rubbing your hands together.
Same as a light bulb. So much goes to generating the light, and whatever
the light hits heats up. So unless there is a window that lets a few photons
out, all the power of a light bulb of any kind will go to heating up the
room. Some types of bulbs are just more efficiant in making light than
others so you can get an equivilent ammount of light with less wattage and
On Thursday, July 24, 2014 2:13:39 PM UTC-4, Ralph Mowery wrote:
OK, I agree with your analysis. As long as the air stays within
the room, then the increased energy of the air that the motor transfers to
it has to go somewhere and I agree it would result as heat in the room.
From what I can see, these fans are typically ~75W. From a heat standpoint,
just pushing the hot air from the ceiling down is going to have a bigger
effect than the 75W ever will. For example, when I turn one of my fans
on I can feel the hotter air moving down suddenly. Once it evens out,
the breeze makes the room feel more comfortable. But from an energy
standpoint, I would bet that the fan constantly moving hot air from higher
levels instead of just leaving it be, raises the temp of the lower levels
of the room a couple orders of magnitude more than the 75W of the fan
generated heat. You also have to wonder on it's effect of using more
AC. Two scenarios. One is leave the air stratified, so the hottest air
is up high where no one is. Or use the fan to bring the hot air down,
where the AC has to deal with it. I guess if you leave the AC slightly
higher because you now have a breeze, it could make up for it. Otherwise,
with the hot air being pushed down, I'd expect the AC is going to have to
It depends on the season.
In the northern hemisphere, you prolly want to run your ceiling fan clockwise in January. In July, you'll prolly want to run it counterclockwise.
In the southern hemisphere, it's the opposite. In January, you'll likely run it counterclockwise and in July run it clockwise.
I guess that it could also be the humidity of the air and how the fan blows
the sweat off of your skin that makes you feel cool. With no air movement
and high humidity the room has to be cooler to feel comfortable. Most of
the time it is not the actual temperature, but a combination of many things
that makes you feel cool or hot.
Often if the air conditioner is sized correctly, it will run and keep the
humidity low and then with a small ammount of air blowing across you, you
will feel cool at a higher temperature.
At one time I worked at a hopspital and some people in a room were
complaining about it being hot. Two older ladies were visiting a man that
was out of it. They were hot and I dropped down the lid of the air handler
in the room , took out a wrench and screwdriver and made some noise. They
said it felt cooler already. Told them if they got too cool to turn up the
When it's warm in the summer, I keep all ceiling fans on, with doors
open. They are very low wattage.
Keeps air moving throughout the house and eliminates "hot spots."
Without the fans, AC would have to be set 3-5 degrees lower.
Always blowing down. You don't want a "boundary layer" on your skin.
I never, ever run the fans in the winter. YMMV.
The 2 70 inch 5 blade fans I installed at the office are 35 watts wide
open, and they are only running half speed. They are high efficiency
DC motors - likely drawing about 20 watts each the way they are
running right now.
I don't have the numbers, but a10 sq ft Low E2 window in direct sun
will sure add more than35 watts of heat to a room!!!
I just did some quick checking
With 900-1050 watts per square meter peak solar intensity and an SHGC
ranging from 0.42 to 0.67, a aquare meter window in direct sun can
provide 450 -703 watts of heat to a room. That's assuming Low E argon
filled double glazed window
On 7/24/2014 11:10 PM, firstname.lastname@example.org wrote:
I've got a couple of southern facing skylights that I want to add some
sort of protection to. I'm not sure what it will be or how I will do
it, especially since they are 11 feet off the floor. I guess blinds
would be the minimal effort approach, especially if I let someone else
do it, lol. I'm thinking a piece of styrofoam covered with fabric to
make it look nice and seal around the edges. Once side would have a
reflective layer, possibly the reflective bubble wrap stuff. That would
reflect the heat back out and likely work as well when it is cold out,
not emitting as much heat.
With the reflective layer on one side it needs to fold away from you,
into the window well which is not deep enough for it. Folding into the
room means you see the reflector. Also, folding into the well means it
won't seal snug around the edges. Not sure what to do about that.
Trying to make it slide away from the window sounds hard to do. I am
thinking of a hinge with a draw cord. To slide sideways I could use
arms at each corner and swing it away to another spot on the ceiling or
even just let it hang to the side, it won't be in anyone's way up there,
Agreed. I suspect you may have misread what I scribbled. See my
Sure, but give me a few daze. I'm giving a Linux on Chromebook talk
tomorrow and am totally unprepared (as unusual). I'm also trying to
take next week off so that I can claim that I've actually had a
vacation this year.
I found this old meter in my mess:
It has a solar cell on the back, with a 1/2" diameter aperture mask.
It's a "Solar Heat" guess meter, measuring BTU/hr-sqft (F), which can
be converted to something more sane like (5.68) watts/meter^2 (C).
There's no far-IR bandpass filter, so I don't think this is going to
be very useful. It's probably made for solar water heaters. Rather
than play with the calcs, I'll take some measurements today. Bug me
if I forget.
Also, this paper might be of some interest:
"Study of titanium nitride for low-e coating application."
I use it as a cheat sheet for how low-E glass works.
Jeff Liebermann email@example.com
150 Felker St #D http://www.LearnByDestroying.com
Blocking off the skylight could damage the skylight by overheating
it. Just replace whatever you have with a velux and the insulation
situation is solved. Put an external shutter on to control heat if you
are getting too much heat gain. A shade that blocks direct sun in the
heat of a summer day, but allows lowere evening or winter sun to
provide heat (and light)
On 7/25/2014 12:57 PM, firstname.lastname@example.org wrote:
What is a velux?
An external shutter sounds like a bad idea, subject to all sorts of
weather and debris. This is not a vertical surface, it is close to a
45° pitch. A shutter wouldn't even work well as it would end up laying
on the skylight.
On Friday, July 25, 2014 12:57:34 PM UTC-4, email@example.com wrote:
It's no different than putting a shade or blinds on any other window.
Just replace whatever you have with a velux and the insulation
Except of course for the huge cost of the new skylights and installation
and the fact that heat will still come in. I have Velux and heat comes
Put an external shutter on to control heat if you
Yes, that should be real practical on the roof. I've seen a lot of
skylights, never one with a shade on the roof.
Or he can just put up a shade inside. Velux even makes the controls
to electrically operate them, so I guess they don't think it's such a
On 7/25/2014 9:11 PM, firstname.lastname@example.org wrote:
I just had new skylights put in when the roof was redone. They are
supposed to be good units but I'm not sure since the builder was the guy
up the road and when I asked for the paperwork couldn't come up with it.
lol I'm not likely to put in new ones. Even a Velux is not nearly as
good as what can be done with real insulation. After all, it *is* a
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