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Author Topic: infared heat??  (Read 4549 times)
Brassman
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« Reply #30 on: November 17, 2011, 07:16:18 PM »

I've used Presto parabolic dish infared heaters for years. They work great heating the guy in the chair, though the overtemp sensor always goes bad after a couple of years.

OBTW: Sean's right.
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TedsBUSted
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« Reply #31 on: November 18, 2011, 05:23:12 AM »

There's a lot of abstract theory that just doesn't come into play in the real world. I tried to underscore that from my entrance into this discussion. For example, when that box is being pushed around the shop floor, if 100% of the work is being converted to heat at the friction point with the floor, then what's happening with the energy being used to displace air? Never mind, I don't want to know, but I think it underscores my point.

Back to the coach heater. IF hypothetically 100% of  fan energy that is dispersed in air handling and parasitic heat loss could be immediately collected and added as heat input to a coach, it would amount to something close to  a whopping additional 3/100ths of the heater's output. Basically that'd be about the same amount of resistive heating that goes on within a turn signal flasher.

I realize that some probably don't  want to believe that a fan's mechanical energy doesn't quickly revert to added heat within a coach. Just as it's tough to believe without seeing that a "choked" fan draws less current. Therefore I  propose that we conduct a real experiment, very relevant to bus heating. So some cold night, in my coach, give me a blanket and a measly 1500 Watts and a heating element. No fan at all, I'll  just rely on convection in still air. In your coach, use whatever size fan you desire. Let the fan hurl and ricochet air molecules throughout the coach until they're in a heated frenzy. Shoot, go ahead and add another fan or two. In fact, go ahead and use as many fans and Watts as practical, and I'll even throw in the heat from the fan motors, which we haven't factored yet.

We can then continue this discussion in earnest the morning after the experiment. Meanwhile we can consider this to be just a friendly splitting of hypothetical hairs.

Ted
« Last Edit: November 18, 2011, 05:27:43 AM by TedsBUSted » Logged

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Sean
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« Reply #32 on: November 18, 2011, 08:36:38 AM »

There's a lot of abstract theory that just doesn't come into play in the real world.

Ted, the First Law of Thermodynamics is neither abstract, nor a theory.  And it comes into play in the real world every single day -- this is precisely how engineers such as myself calculate things like how much air conditioning is required to cool a room.

Quote
I tried to underscore that from my entrance into this discussion. For example, when that box is being pushed around the shop floor, if 100% of the work is being converted to heat at the friction point with the floor, then what's happening with the energy being used to displace air?

It's negligible, and I omitted it from the example, but if you insist, it also becomes HEAT because moving air against itself or the walls is no different from moving cardboard against the floor -- friction is what damps the air and that causes it to heat up.

Quote
Back to the coach heater. IF hypothetically 100% of  fan energy that is dispersed in air handling and parasitic heat loss could be immediately collected and added as heat input to a coach, it would amount to something close to  a whopping additional 3/100ths of the heater's output. Basically that'd be about the same amount of resistive heating that goes on within a turn signal flasher.

Well, true, but you were the one who brought it up in the first place, insisting that the work done by the fan became something other than heat, which is incorrect.  The discussion then grew to incorporate the concept that lots of things in a coach that consume electricity turn it into heat, not just heaters.

Quote
I realize that some probably don't  want to believe that a fan's mechanical energy doesn't quickly revert to added heat within a coach.

Some don't want to believe?  You mean, just because you say it, we should believe it, even though it's wrong?  Ted, this is basic, freshman-year physics.  The First Law often runs counter to people's intuition, which is why it is drummed into the brains of scientists and engineers early on.  You are continuing to argue from an intuitive position -- your sense is that a fan consuming 100 watts of power makes less heat than a light bulb consuming 100 watts of power.  But unless the fan is blowing on a windmill, it does exactly that -- 100 watts of electricity becomes 100 watts of heat, whether it's a fan, a lamp, or a toy train running in circles.

Quote
... Therefore I  propose that we conduct a real experiment, very relevant to bus heating. So some cold night, in my coach, give me a blanket and a measly 1500 Watts and a heating element. No fan at all, I'll  just rely on convection in still air. In your coach, use whatever size fan you desire. Let the fan hurl and ricochet air molecules throughout the coach until they're in a heated frenzy. Shoot, go ahead and add another fan or two. In fact, go ahead and use as many fans and Watts as practical, and I'll even throw in the heat from the fan motors, which we haven't factored yet.

OK, but I want the bus insulated by a perfect vacuum.  Look, we all know these will produce two different results -- but NOT because the fan generates less heat.  As I said way up at the beginning, it is because the fan will move whatever heat is already in the coach past leaky or poorly insulated windows and other heat sinks.  IOTW, the same heat will be generated, but one of these methods will end up moving more of it from inside the bus to outside -- again, I said this in my very first post.  That has nothing to do with your assertion that "work" does not become heat.

Quote
... Meanwhile we can consider this to be just a friendly splitting of hypothetical hairs.

Well, again, it's not hypothetical, and I want to make sure that the folks reading this discussion have the right answer.  I'd like for you, too, to come away from this with a better understanding of thermodynamics, but that requires an open mind.

The "thought experiments" that I have described, such as the "black box" concept, or the example of the box on the floor, are standard pedagogical constructs used to teach these concepts.  The idea is to look at the very limited, non-real-world circumstance and develop an understanding of where the energy is going, since the First Law says it can not disappear, only change form.  Then take that understanding and apply it to larger, more complex scenarios in the real world.  Students who look at the thought experiments and disbelieve them because they are somehow "unrealistic" or can not apply the concepts to the broader world are generally not cut out for science.

In the black box experiment we saw that, inside a perfectly insulated box, a fan drawing a certain amount of energy can not be distinguished from a lamp drawing the same energy -- each will heat the box exactly the same amount.  Now, if you don't believe this part, you can do the actual experiment and see that it is true.

The box itself is merely a learning construct -- when you take the box away, the energy involved still does the same thing it did when the box was there -- it's just a lot harder to measure.

-Sean
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« Last Edit: November 18, 2011, 09:12:53 AM by Sean » Logged

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« Reply #33 on: November 18, 2011, 08:45:30 AM »

Something that occurred to me while reading this thread (that I'm sure was obvious to many of you - I apologize for being slow)... is that the movement to LED-based interior lighting will result in a lower A/C load, and a higher heating load. Maybe the delta is nominal, but for me, it's an interesting thing to think about.

While lots of people think about the heating/cooling load impact of stoves (as well as microwaves and ovens), the impacts aren't limited to these items. In fact, all of the decisions we make about energy consumers of any kind (including lighting, toilet fans, etc.) have an impact on the heating and cooling loads.

-jbn
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Sean
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« Reply #34 on: November 18, 2011, 09:19:34 AM »

Something that occurred to me while reading this thread (that I'm sure was obvious to many of you - I apologize for being slow)... is that the movement to LED-based interior lighting will result in a lower A/C load, and a higher heating load. Maybe the delta is nominal, but for me, it's an interesting thing to think about.

While lots of people think about the heating/cooling load impact of stoves (as well as microwaves and ovens), the impacts aren't limited to these items. In fact, all of the decisions we make about energy consumers of any kind (including lighting, toilet fans, etc.) have an impact on the heating and cooling loads.

Yes, which is why I thought it was important to clarify the concepts.  Good to see that someone is getting something out of it -- otherwise it's just so much arguing for no reason.

FWIW, heating a bus is much easier and less expensive, generally, than cooling it, which is one reason why LED lighting is such a boon, even if you are not running strictly from batteries.  Even fluorescent lighting adds less heat to the coach for a given amount of light than incandescents.

-Sean
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Rick 74 MC-8
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« Reply #35 on: November 18, 2011, 09:55:47 AM »

Question If a fan draws less Power when air is blocked off. Would the dampers and shutters on the MCI cooling system draw less hp when blocked off thus increasing my MPG.



            Rick 74Mci
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« Reply #36 on: November 18, 2011, 10:34:26 AM »

To add just a tidbit to the discussion.....
If you agree that an impeller type pump moving water is very similar to a fan moving air then I had an experience that might be of interest.

I had a self priming irrigation pump that lost it's intake.  It ran for hours just churning the water in the pump housing until it boiled and melted the PVC pipes connected to it.  It wasn't the motor that overheated but the pump just from the friction of the impeller in the water.

So, I think that a fan in an enclosed box would continue to get hotter and hotter, just from the friction of the blades against the air, not even counting the heat from the motor.
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bigjohnkub
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« Reply #37 on: November 18, 2011, 10:57:09 AM »

I have a better understanding of the dynamics of heat in a coach due to this thread. Please continue post like this.

Big John
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« Reply #38 on: November 18, 2011, 11:47:52 AM »

arguing for no reason

I like to think of it as informational banter... Smiley
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Scott Bennett
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« Reply #39 on: November 18, 2011, 12:10:38 PM »

Um. So in baby terms what's being discussed is:

Any electric device that uses 100 watts, will produce 100 watts of heat regardless of device?

Thanks in advance.
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« Reply #40 on: November 18, 2011, 12:58:35 PM »

...
Any electric device that uses 100 watts, will produce 100 watts of heat regardless of device?

Not quite.  As I described in earlier posts, if the energy has someplace else to go, it does not become heat, or at least not right away.

An example would be a battery charger.  While chargers do produce plenty of heat, which, BTW, is a waste byproduct of the charging process, and why no charger is 100% efficient, at least some of the energy going into them ends up being stored in a battery.

If you measure the amount of energy that ends up in the battery, and the amount of energy consumed by the charger, the difference between these two numbers is the amount of energy that must be dissipated as heat (either in the charger itself, or the heat given off by the battery as it charges).

Likewise, if you have a pump which pumps a fluid from a low place (lower potential energy) to a higher place (higher potential energy), the difference in energy potential of the fluid does not become heat; you can think of this as "gravitationally stored energy."  BTW, such systems exist, on a very large scale; where large electric pumps take river water and pump it uphill to a reservoir, then, later, the water is let out through those same pumps, now operating in reverse as electric generators.  One such example is the San Luis Reservoir near Los Banos, CA, which stores water from the Central Valley Project.

An electric fan in a closed box (such as a bus) will dissipate all its energy as heat, because the air that it is moving will heat up from friction, with no place else for the energy to go.  But if you put a windmill in front of that fan, and connected the blades to a generator, and then ran the output someplace else, then all the energy produced by the windmill will not end up as heat -- at least not until it gets to its point of use.  But again, that process would be very inefficient, and frankly, most of the fan's work would still end up as heat.

On a bus, for all intents and purposes, you can assume that every watt that goes in becomes heat, with only a few exceptions, which I listed in my very first post.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #41 on: November 21, 2011, 03:08:13 AM »

So update on the infared heat.........

Here in iowa where it has been droppiiing into the teens at night and about 35the during the day...... and my fish has all the original windows and really no added insulation to speak of........
the heaters keep it about 55......not "warm" but better then 3
13h degrees!
I think with some insulation added and sealing her up a bit that it really should be quite good....I will repost after we make those upgrades.....

Thank you again for everyone's knowledge and help!

Noah and family
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