Or better yet, actually measure it using a Kill-A-Watt or similar. I agree, I don't believe a small motor like that is going to generate much heat. From what I see, typical is 50 to 75W or so. I just felt the motor on mine, running on medium speed, and it doesn't feel warm at all.
The comparison to the windows is totally absurd.
+1The advice that the fan only helps if you're there to benefit from the breeze I agree with.
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 want.
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.
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 het.
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 run more.
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 thermostat.
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.
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.
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 would love to see some numbers.
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
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, lol. .
Agreed. I suspect you may have misread what I scribbled. See my quote above.
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.
It does both. Touch the glass: if it's hot, it's heating the air inside the room.
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)
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.
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 in.
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 bad idea.
Just the best skylight made, bar none.
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 window.
As Clare pointed out, you risk losing the window if you insulate it from below.
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