Anti sweat resistance heater wire question

[kengineering]

I am building a custom self select air screen. It will have side windows of insulated glass trimed in stainless. Currently I use a resistance wire in the top of the air plenum where the cold air curtain meets the ambient air to prvent sweating on the metal and I plan to use it on the side windows for the same reason. How warm should this actually be? Because the length of the wire changes the temperature for each application, I use differant ohm ratings of wire but so far I'm only shooting from the hip (guessing at the wire size and heat output). There must be a way to know exactly what wire to use to produce the desired result. But then I'm not even sure what result I am looking for except for the prevention of condensation. Can anyone shed some light here. Ken

[taz24]

I I plan to use it on the side windows for the same reason. How warm should this actually be? Because the length of the wire changes the temperature for each application, I use differant ohm ratings of wire but so far I'm only shooting from the hip Ken

Is it a low temp display?
I have worked with trim heaters for a long time and find that there is no standard across manufactuers.
As a rule of thumb they tend to be warm to touch. That would make them about 15degC to 20 degC but any temp above the dew point of the air passing over it would do.
Cheers taz.

[Dan]

Hi Ken. I normally see ratings of anti-sweat heaters running between 8 ohm thru 24 ohms per foot depending on duty. If you are medium temperature and doing a single wrap around the glass frame, let's say about 12 feet long?

Try the 24 ohms per foot, that should provide about 50 watts, or 4 watt's per foot. Walk in refrigerators and freezers commonly use 3 or 4 watt's per foot for a double loop around the walk-in doors, although I have seen as high as 8 watts per foot. I worry if you try to get more scientific than this, you will have a passle of calculations that will drive you crazy.

Your next biggest worry is to keep the glass from sweating:)

[Peter_1]

There's no rule, it all depent on the ambient conditions and the manufacturing process.

[kengineering]

Thanks for the feedback.. I did some online searching and was able to find some parameters. 5 to 8 ohms /ft. for a refrigerator and 8 to 12 for a freezer. That gives us something. "case parts" had a formula which seems simple enough to get some informed starting point. You have to remember the closest thing to an enginer where I work is me, Kengineering. This has been a great help. Now does anyone have a source for the wire? I have 2 but am looking for a more reliable one in the States. Ken

[Dan]

www.springfield-wire.com

Had good service from them.

[Dan]

Ken, wouldn't the higher ohms per foot provide you less heat? Is it possible we are talking about watts per foot?

[kengineering]

Dough!!!! Thanks Dan yes of course..I've heard it said that a little informaton is dangerous. Yea that sounds familiar, but somethimes learning takes different paths. This website rocks! I have only been aboard for a short while and I have learned so much.. even if only to super stimulate my own thoughts. Thanks to all. Ken

[chillin out]

Don't mean to hi-jack the thread but, would I be right in thinking that most of these 'trace' heaters are self regulating?

As in to say when cold the current is high and as it reaches temp the current drops?

Chillin:):)

[taz24]

As in to say when cold the current is high and as it reaches temp the current drops?

Chillin:):)
I'm not sure they are.
The drain heater tapes with live and neutral running in parralel are self regulating but these heater wires/tapes are just watts per foot.
I think:D


taz

[Dan]

Ken, the Springfield website was one I was trying to remember when I first read your post. It says it all on the homepage. I still struggle with watts per foot versus ohms per foot. I can add a little more info... the typical heater wire that Anthony doors provides is around 11 ohms per foot. This is good up to thirty foot lengths.

Here's a handy little tool to save on your desktop:

http://ourworld.compuserve.com/homepages/Bill_Bowden/ohmslaw.htm

I wish I could have remembered the website when you first posed the question. It pretty well addressed all your questions, didn't it?


Don't mean to hi-jack the thread but, would I be right in thinking that most of these 'trace' heaters are self regulating?

Taz answered correctly. There are bulk rolls of heater wire for wrapping pipe and such and they are self-regulating when you cap them properly. I used to understand how they worked, but my memory eludes me. I think they were parallel line and neutral circuits that would complete the circuit no matter where you cut the wire, as opposed to a single resistance wire that would be open if you cut the wire between the line and neutral.

[kengineering]

From the research I've done over the last 2 weeks I don't believe a self regulating heat wire is made in the small dia. needed for this application. Ken