Understanding The Difference Between Temperature And Heat

If you have a ten watt heat source, it generates ten watts of heat.

If you put insulation around that heat source, the temperature between the heat source and the insulator rises – but the amount of heat generated remains the same. What the insulator does is move some of the thermal gradient away from the heat source, and into the insulator.

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41 Responses to Understanding The Difference Between Temperature And Heat

  1. Bloke down the pub says:

    The point that some of the ghg fact challenged may be missing is that more energy is radiated out when there is a larger differential between the object and it’s surroundings. In the example you give above, the insulation will raise the temp which will then stabilise at an higher level when the energy flow re-achieves balance.

    • It is exactly the same in either case.

    • daveburton says:

      Bloke, I think you and Tony are actually in agreement. Tony, I don’t think Bloke means that the amount of energy from the 10W heat source changes, nor that there’s a difference in the radiated energy outside the system after things stabilize.

      If you wrap your 10W heat source in a thicker insulator, there’s an initial drop in the radiated energy from your system, which causes the temperature inside the insulation to rise. The rate at which heat traverses the insulator increases as the temperature differential across the insulator rises (which is what Bloke said), so the higher the temperature inside rises, the faster it loses energy (cools).

      [That’s a very fundamental negative (stabilizing) feedback mechanism for temperature, BTW.]

      At some point, the temperature inside the insulator will have risen so much that 10W of power is once again traversing the (now thicker) insulator. The temperature inside the insulator will have ceased rising, and the system will be radiating exactly the same 10W that it was radiating before you added the extra insulation (which is what Tony said).

      For an electrical analogy, consider a constant 10W power source driving current through a resistor, which dissipates the 10W of power as heat. (The resistor is like your thermal insulator, and the voltage from the constant power source it is like the temperature of your heat source.)

      If you increase the resistance of the resistor (analogous to increasing the R-value of your thermal insulation), but continue to produce 10W of power, then the voltage across the resistor (analogous to the temperature of your heat source) must increase: V = sqrt(P×R)

      E.g., if the resistor is initially only 10Ω, then the voltage will be 10v (for generated & dissipated 10W of power). But if you increase the resistor to 40Ω, then the voltage across the resistor will have to increase to 20v, to keep the power dissipated at 10W.

    • kuhnkat says:

      There is a piece that is being ignored. Take a 10 watt electrical bulb for example. It is stable at 10 watts without the insulation. If your added insulation slowing the radiation actually raised the temp of the filament it increases the electrical resistance. Similar issues happen with other heat sources. In other words there is a limit on how much the temp can rise based on the type and power of the power source behind the 10 watt heater.

      In the real world there are numerous feedbacks interfering with the process. For instance, heating the atmosphere expands it increasing the distance between particles and the radiation escaping.

  2. QV says:

    I don’t believe the BBC thinks they are doing anything wrong.
    “All’s fair in love and war (and climate change)” seems to be their motto.
    They are so used to producing propaganda in general that it goes unnoticed.
    Their response to complaints on the news on programmes such as “Newswatch” is indicative of their attitude, i,e, they are never wrong.
    There needs to be a truly independent complaints procedure.

  3. Mack says:

    Hell, I always thought that temperature was just a measurement of heat. …you know.. the numbers that are read out on a thermometer. ..an extrinsic property.
    Btw. Steve, …. “it generates ten watts of heat” Shouldn’t that read ..”ten watts worth of heat”?
    Watts are a measurement of power., not heat. Boy,o boy you’re going to have to be more careful with this nomenclature stuff…it is after all the essence of what science and physics is all about..

  4. Edmonton Al says:

    How about this:
    The insulator is a solid and impedes the heat flow, like the insulation in my attic.
    CO2 is a GAS. it expands when heated and rise, carrying the heat away more quickly.
    If I put dry ice in my attic instead of insulation what happens?

    • Many double paned windows have CO2 in the gap as an insulator.

      • Edmonton Al says:

        It cannot expand. It is a closed system.

      • squid2112 says:

        Hmm, interesting. I was always led to believe most double glazed windows used Argon.

        • nickreality65 says:

          Me too.

        • Robert Austin says:

          Maybe because argon is much more common atmospheric gas than CO2? To be serious, monotomic inert gas filling in sealed double glazed windows has a lower heat capacity than poltyatomic gases such as CO2 and air.

      • squid2112 says:

        I wonder why CO2 is the most widely used industrial coolant …. wow, that CO2 sure is some magical stuff! Gotta get me some of that!

        • Edmonton Al says:

          I think that the scammers are pushing double glazed windows with CO2 to say that the CO2 traps heat and back radiates it to cut down your energy bill. Or not.

        • nickreality65 says:

          Since when?

        • nickreality65 says:

          “Since when” was supposed to go w/ Squid2112. Any examples of those applications? None come to mind for me.

        • squid2112 says:

          nickreality65,

          Do they have Google where you live?

        • There is no substitute for victory. says:

          I don’t know but I think that CO2 is much cheaper to manufacture in industrial amounts. All that is required is an acid and a base, mix the two and presto-changeo, instant Carbon Dioxide.

      • Ben Vorlich says:

        I think that Argon is more common as an insulating gas in double glazed units

        Argon is the most commonly used gas, due to its excellent thermal performance and cost-efficiency in comparison to other gases. Argon gas reduces heat loss in double glazing by slowing down convection inside the air space. It is extremely cost-efficient, and works well with Low-e coated glazing. Argon and Krypton are colourless, odourless, non-flammable and non-reactive inert gases.

        It is generally accepted that the double glazed unit should achieve a 90% fill gas concentration. Over time this concentration will gradually evaporate, at an estimated rate of 0.5 to 1% per year. Double glazed units filled with argon do not degrade significantly until they reach 75% concentration, giving up to 20 years of high performance.

        Argon gas is quite inexpensive and quickly produces cost-savings to justify the cost.

        Krypton is more effective at reducing heat loss, but is roughly 200 times more expensive than argon per unit volume. Because Krypton works best at smaller pane spacings (8 mm), it is often used in triple and quadruple-glazed windows to minimize the overall thickness of the unit.

        Other types of gases can be used (for example, sulphur hexafluoride, carbon dioxide) to reduce sound transmission, but these gases do not offer the improved thermal performance of the inert gases mentioned above.

        http://gugsconservatories.co.uk/energyefficientwins4.htm

        Also

        http://www.alldoubleglazing.co.uk/articles/Argon-filled%20double%20glazing.aspx

        http://www.thermosealgroup.com/machinery/howtomakeasealedunit

        • Ron C. says:

          On the other hand , Krypton protects against Superman intruding.

        • The bigger the molecule, the slower it moves for a given temperature. Therefore, the fewer times it bounces between the two panes. Krypton and sulfur hexafluoride are big gas molecules but the biggest are the fluorohydrocarbons. They should fill the window with freon. Or better yet, a vacuum. The worst thing to fill your window with would be H2 or He.

        • That second link says argon is 6 times denser than air. Horse manure. Air is 28 for N2 and 32 for O2, argon is 35. Marketing people are like AGW people.

      • KevinK says:

        Few (very few, in fact almost none) doubled paned windows have CO2 in the gap. Argon is more abundant and cheaper to produce. Dang those ever practical engineers.

        Also a double paned window work by reducing conduction (not totally eliminating it), not via any magical “radiation physics” process.

        You could use a vacuum inside and get the same effect, but then you would have to worry about the differential pressure (outside air vs inside gas) pressing on the glass, and as everybody knows glass is “fragile”.

        Gas filled double pane windows have been around since the 1950’s, you can be sure that if filling them with CO2 had any advantages (due to “radiation physics”) engineers would have switched over by now. Any claimed advantages of filling double pane windows with CO2 are marketing BS.

        Cheers, Kevin.

  5. nickreality65 says:

    A watt is a power unit, a rate of heat or energy, i.e. Btu/h or kJ/h. Use English hours w/ Btu/h and metric hours w/ kJ/h. Plus you can deliver 10 watts at 60 F, 32 F, -60 F. What’s the operating temperature of the heater and what’s the temperature of the surroundings?
    A 10 watt heater is producing 34,120 Btu/h. Heat capacity of air is 0.24 Btu/lb-F. Density of air is 0.763 lb/cu ft. How large is the space? How high will the temperature rise? How fast? Insulation will slow the heat transfer, but not stop it.
    How well your house is insulated determines how fast, the rate, (time, i.e. hours) at which it loses Btu’s and how big the furnace has to be to replace that lost heat in a reasonable time.
    This is kind of off the cuff. I’d like to do an example, but I’ll have to go dig out my college heat transfer text book or reference an engineering web site.

    • David A says:

      ? Would a large rock (say 150 sq’ of surface space) at say 100 F be emitting a certain amount of energy, Watts per square meter? Now how hot would a tiny 1 /2 sq inch rock have to be to emit the same Watts per square meter. Would it need to be a blow torch tip?

      Is this a difference between heat and energy? The rock could never heat a colder object above its emitting T. The torch tip, though of equal watts per sq meter energy, can heat any object of most ANY size to a T far higher then the rock, depending on the insolating capacity of the material being heated. (depending on the residence time of the energy within the material being heated)

      Is it possible that likewise SW energy of equal watts per sq meter to LWIR energy, can, over time, add far more energy to the oceans, which have a very long residence time to the energy entering them?

      • This argument is a straw man, and indicates a complete failure to understand the most basic concepts of science.

        Insulators keep things warmer than they would be without insulation. Do you have any idea how dumb your argument is?

        • David A says:

          My comment, or more accurately questions, with very few assertions, or Nickreality?

          I am certainly not arguing, but trying to understand some concepts, so asking questions. Insulation, like heat capacity, appears to be a function of residence time. A GHG molecule which , upon receiving a boost of energy, either through radiation or conduction, but especially through receiving conducted energy, and then sends (radiates) said packet of energy to space, cools the earth, relative to same packet of energy conducting to a non GHG where it would stay within the atmosphere, while mean input continues, thus more energy = more warmth.

          A GHG molecule which takes a packet of energy, especially LWIR that non GHG molecules do not interact with, and redirects it towards the lower atmosphere or the earth, is warming, as it is increasing the residence time of said energy, while mean input continues, thus more energy = more warmth.

          The atmospheric balance and ratio between LWIR, conducted energy, convection, and of course evaporation and capacity of disparate w/l to warm the oceans, is certainly complex physics beyond my capacity. My questions and illustration regarding a large rock of low T, and a small flame of undetermined T but = watts per sq meter, are sincere and anyone willing to attempt an answer, I appreciate.

          I accept, because it is beyond me, the direct affect warming of GHG, assuming that on balance it warms more then it cools, but do not know the physics well enough to quantify the numbers.

  6. nickreality65 says:

    Yep, off the cuff. It’s 3,412 Btu/kWh, not watt hour. So 10 watts is 34.12 Btu/h.

  7. davidswuk says:

    Wot a loada PESTICKALS!

  8. Billy Liar says:

    Have I blundered onto the ‘Thermodynamics Today’ blog? Better start looking for my Steam Tables.

  9. Robert B says:

    There might be a problem if you think of the GHE as a black ball being illuminated evenly in a vacuum and then encasing it in a glass coat. The rate of heat loss through radiating LWIR should be the same with or without the glass at equilibrium temperatures, some directly from the ball’s surface and for those wavelenths that the glass is opaque to, from the glass’s surface. Both would be the same temperature if the glass behaves like a black-body emitter for the relevant wavelengths. There is no insulating effect from half being re-radiated back to the surface. If the glass needs to be at a higher temperature for the same heat loss as without the glass coating, then there is an insulating effect like a space blanket made from a poor emitter (adding more GH gasses does the opposite).

    The Earth’s atmosphere has a temperature gradient so if some wavelenghts of radiation from the surface are absorbed by the atmosphere and need to be emitted at very high altitudes, then the temperature at high altitudes needs to increase so that the energy emitted from the atmosphere and ground/sea is the same as it would be if there were no atmosphere. And if the gradient remains the same then the ground will also be warmer.

    Adding more GH gasses means more energy has to be emitted at high altitudes but its pretty much opaque to the relevant wavelengths already.

    Then there is everything else to take into consideration.

  10. nickreality65 says:

    If a pound of air at 70 F & 50% RH has to absorb 9 Btu of energy without any change in its water vapor content, the dry bulb temperature would have to increase about 37.5 F, (9 Btu/lb) / (0.24 Btu/lb-F), or 107.5 F & 16% RH.

    However, by evaporating water into the air until saturated (clouds) that same energy could be absorbed by that pound of air – with absolutely no change in the dry bulb temperature! 0.0078 lb water/lb air to .016 lb water/lb of air.

    Water vapor is considered the most powerful GHG for a reason. It is water vapor, clouds, precipitation that regulate the atmospheric temperatures, CO2’s influence is less than trivial.

    If a 100 watt light bulb is covered by an upside down Styrofoam cooler, it’s going to get really hot inside. So? It’s not that we are missing your point, it’s that you are doing a poor job of making it. Instead of esoteric, sugar coated, analogies, just spell it out.

    • daveburton says:

      Nick, clouds are not made of water vapor, they are made of liquid water droplets (which are formed from water vapor).

      You are correct that the water cycle is a powerful regulator of atmospheric temperature, However, the fact that water absorbs heat of vaporization when it evaporates, and releases it when the water vapor condenses in clouds, has nothing at all to do with its efficacy as a greenhouse gas.

      • nickreality65 says:

        If a pound of air at 55 F and 20% RH increases its RH to 90% through evaporation, its heat content increases by about 1,100 Btu. No sensible heat, no temperature change.

        If a pound of air at 90 F and 20% RH increases its RH to 90% through evaporation, its heat content still increases by about 1,100 Btu. No sensible heat, no temperature change.

        Evaporation is driven by the relative concentration of water vapor, not by the temperature, although that 90 F air will absorb/hold 340% of (not more) the water vapor of the 55 F air. Hot air will evaporate more water out of the ocean because it really, really wants to and cooling the ocean the process.

        Sensible heat of dry air is 0.24 Btu/lb-F.

        My point is that the latent energy of the water vapor/clouds/condensation cycle moves energy into, around, and out of the atmosphere several orders of magnitude greater than the sensible heat transferred by the CO2/H2O/GHGs. BTW IPCC AR5 TS.6 admits they don’t have a good handle/low certainty/high uncertainty about this water cycle.

        Those huge cooling towers at power plants emit water vapor you can’t see in the summer and condensing water droplets (clouds) that you can see in the winter.

  11. Curt says:

    Cover a 100 watt light bulb by a glass shell that lets virtually all of the radiant energy through. It gets a little hotter.

    Replace the glass shell with a black-coated metal shell that absorbs all of the bulb’s radiant energy, and re-radiates it both inward and outward. The bulb gets a lot hotter, even though the metal shell is far more thermally conductive than the glass shell, and both suppress convection equivalently well.

    That is what radiative absorption between a powered warm body and colder ambient environment can do. (I’ve done this experiment. It’s not hard.)

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