Conduction, convection, or radiation?

[cleller]

My wife has a favorite chair near a window. (double pane) On cold mornings she will pull the shade down to minimize the cool air coming off the surface of the window. Yes, it is well caulked, and I personally installed it with the help of a master carpenter.
Is the coolness you feel cause by conduction of cold air thru the panes of glass, convection by air currents passing over the panes of glass, or purely by radiation?

This makes it look like possibly a combination of all three.
http://www.ppg.com/corporate/ideascapes/resglass/builder/education/Pages/EducationWindow.aspx

I wish I knew why this is tormenting me, but at least it keeps my mind of football for a few minutes.

[olevetonahill]

Is it a double paned Thermal window?

[pphilfran]

I would think radiation would be more heat related...the other two I can see...

[Jacie]

Any heat loss is due to conduction through the glass unless it is double pane and radiation.

The cold air your wife is feeling is the loss of heat you paid dearly for via radiation through the window. Closing the shade greatly reduces it and makes her feel warmer.

[Tulsa_Fireman]

Any heat loss is due to conduction through the glass unless it is double pane and radiation.

The cold air your wife is feeling is the loss of heat you paid dearly for via radiation through the window. Closing the shade greatly reduces it and makes her feel warmer.

This. Strictly radiated heat in the case of the shade.

[cleller]

These are decent double pane windows, I'm happy with them, but they are sure not the super expensive stuff. We like windows, though I know they are considered an energy drain.
I did plan the house for a big south exposure for passive solar heat. Here's a pic of the south side of the house during construction: it chops off a couple more windows on the right hand side.

http://i701.photobucket.com/albums/ww14/cs6000/IMG_0615.jpg

Only the two in the dormer are low-e windows. I wanted all the others clear, for max heat in the winter. I have retractable awnings over those two big ones, to keep sun out during the mid-spring and mid-fall, when it can get too warm. We have geothermal heat/air, plus a big woodstove that we use all winter.

You can argue about whether or not the windows lose to much heat, but we started a fire for the first time yesterday. Have not used the heater yet this season, and the a/c has not been used in probably 6 weeks. I love the setup. If the sun shines we never need any type of heat during the day.

[Lott's Bandana]

Get that tree a brother and it looks like you'll be golden.

[cleller]

Get that tree a brother and it looks like you'll be golden.

That would be the optimal thing to do, but the septic tank is out in that area, so I'm afraid to plant anything close. There are trees all along that west side for shade, though.

[SoonerBread]

All three are types of heat transfer. Heat is a form of energy that has a propensity to travel from a region of high to low energy. The hotter something is, the more heat energy it contains. Energy cannot be produced or consumed without the consumption or production of equal amounts of energy (energy isn't lost and found, only transfered).

Let's simplify - your wife is cold in front of the window for one of two reasons. Either A) the window's seals are leaking, or B) the "thermal barrier" in your thermal windows is insufficient.

If A, you will know this if your house gets colder per the wind direction. If B, you'll know this when your windows condense between panes. Can't be radiation. Impossible. If A, convection. If B, conduction.

[Tulsa_Fireman]

Negative. Because of the properties of heat transfer, heat WILL be radiated through transparent objects to the area of less heat energy. It's the exact same principle as to why the mini-blinds of a neighboring house to a structure fire will literally melt on the side facing the fire with no fire involvment in the home. The only difference is that it's acting in the inverse.

To mitigate the radiated heat, a reflective or opaque surface between the window and the room is needed, hence why the room remains warm when Wife drops the shade. Were the heat being lost via conduction through the glass, convection through the air space between the panes, and thusly conduction through the second pane to the outside, the heat loss would be constant and indifferent to the shade. Just like with the inverse of our original scenario, a bright summer day or a fire shining on that window, the only heat penetrating the glass would be radiated and would penetrate by virtue of its transparency. Hence why thermal windows are so nice. To conduct/convect, the heat energy either inside or outside the home has to conduct through the glass, convect in the air space which in turn heats the second pane, escaping via conduction to the outside. The air space between is in a constant state of heating and cooling instead of the space inside the home.

So if you want to get technical, it's actually all three. But the most prevalent, the most impacting, is radiation.

[SCOUT]

Is the window open?

[cleller]

Is the window open?

Nuts!


So, even if the window is tight- heat will migrate out the panes thru conduction. This would leave the pane of glass cooler than the surrounding indoor air nearby. Right?

The window is fairly tall, so this cooler air would sink, and would would feel it while sitting in the chair near the lower portion of the window. This would be convection, right?

I'm willing to forget about radiation for now, if it seems that both forces are at play.

[SoonerBread]

I'm not going to argue with you because there's no money in it, but there's no way radiant heat transfer is involved in this. To try to explain otherwise is ignorant of the principal of that type of heat transfer. If you understand sensible heat and heat transfer, you cannot conclude radiant is one of the possible modes of energy transfer in this scenario. If you're going the route of radiant cooling, don't bother. There's no heat energy removal vehicle.

[NormanPride]

Tell your wife to suck it up and use a blanket.

[cleller]

Tell your wife to suck it up and use a blanket.

Closing the window has solved most of the problem, but the science is still interesting.

[I Am Right]

None of the three, relationships

[jkjsooner]

Negative. Because of the properties of heat transfer, heat WILL be radiated through transparent objects to the area of less heat energy.

What is the source of this radiant energy? What is radiating at a level that wouldn't be considered minimal?

I have to a agree with others. It would have to be conduction or convection.

[hawaii 5-0]

If I get cold in the Winter I just close the windows.

A coupla times a year I feel like putting on long pants.

5-0

[Tulsa_Fireman]

What is the source of this radiant energy? What is radiating at a level that wouldn't be considered minimal?

I have to a agree with others. It would have to be conduction or convection.

The heat in the room itself. Just because the heat in the room is not of a level that would imply radiated heat as we commonly understand it does NOT mean that heat is not transmitted via radiation from the space.

Both conduction and convection require a medium. The design of the window itself(assuming the window is the means of heat transferring from the space, not crappy insulation around the window or other means) establishes that conducted heat must travel through the multiple panes, heating the air space between the panes which is then conducted through the outside pane to the outside world. The problem with this is the very premise of a thermal window. As heat is conducted to the air gap between the panes, you have the balance of the heat entering the gap along with the heat being lost from the gap to the outside. This area becomes the heat transfer interface as opposed to the room itself.

Secondly, the fact of the shade being lowered eliminating the cold spot in the room is being entirely ignored. Conduction wouldn't be affected by the shade as the solid medium for conduction is easily understood as the panes of the window itself. Convection wouldn't be affected by the shade as the fluid medium (the air in the room) isn't affected by the insertion of an opaque object. The air behind and inside of the shade remains fluid and transfers heat amongst itself via convected currents regardless of whether the shade is up or down. Which leaves us radiation.

We have heat energy that regardless of amount, is radiated from the space electromagnetically because of its sheer presence. This method of heat transfer is blocked easily by an opaque object. The heat in the space is hitting the walls, the ceiling, the floor, the chair, the wife, yet when it hits the window, because of its transparency, is passed through the transparent object to the outside resulting in a net loss of heat within the space centralized at the window. Where other opaque objects in the room (walls, chairs, wives) are absorbing this heat and are being raised to equilibrium with the room, the area at and surrounding the window is unable to obtain equilibrium because the loss of radiated heat due to the transparency of the window. Blam, you have a cold spot as this radiated heat doesn't stop radiating, but continues out the window instead of heating the wall/chair/wife. Insert a shade (making the transparent object opaque) and NOW the radiated heat (which again is present due to the presence of heat itself) is being absorbed by this new opaque object instead of being lost through the transparent one. Eventually the shade reaches equilibrium with the rest of the room and the cold spot goes away.

Again, it's radiation. While conduction and convection are coming into play, with thermal windows and the fact of the shade being pulled warming the room, the most heat is being lost via radiation because of the reasons posited.

[jkjsooner]

Interesting, I don't think I realized the radiant proponent of heat loss for normal objects. I guess thermal sensors work from this radiant energy so I suppose it makes sense.

I sorta just assumed that most things that aren't lights/fires/etc. radiate very little energy but lose most heat due to conduction (i.e. kinetic energy transfer to the surroiunding air) and then convection.

Learned something new.

[Penguin]

Oh, no! Radiation! Put this sign by your window:



http://www.myradiationsign.com/img/lg/S/High-Radiation-Area-Danger-Sign-S-2925.gif

[cleller]

This is kinda relevant. New "smart windows" with nano-crystals that block solar radiation in summer, then let it in during winter. The change is caused by a weak electrical current applied across the window.

http://www.npr.org/2011/11/28/142848063/tenergy-saving-possibilities-of-smart-windows

[Jacie]

Again, it's radiation. While conduction and convection are coming into play, with thermal windows and the fact of the shade being pulled warming the room, the most heat is being lost via radiation because of the reasons posited.

Thank you for explaining it in detail.

Now to see if your post puts this thread to rest . . .

[C&CDean]

All this time I thought this thread was about ovens, convection ovens, and microwaves. Bunch a geeks.

[Howzit]

*snicker*

He said, "well caulked."