Best way to use my hot air to heat water.

gtxkidgtxkid Solar Expert Posts: 34 ✭✭
What is the best way to heat water in a 55 gallon steel drum.
Not looking to boil water or anything.
Just looking for the best way to use my hot air to help preheat water.
Want a simple general way to do this.
Probably pull the hot air down from top of collector to bottom of collector into some sort of duct around 55 gallon drum.
Only 6 foot of duck work needed to go from Collectors to drum.
It is the wraping of drum i am having trouble with.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,783 admin
    Re: Best way to use my hot air to heat water.

    www.builditsolar.com/ has a pretty good selection of solar related DIY type projects.

    Is there some reason for Hot Air instead of Hot Water? Also, if you mount the tank "below" the collector--you are going to need Fans/Pumps (and a controller/solar panel/etc.) to circulate the heat "down".

    Just building an insulated box with a glass lid pointing at the sun is usually a pretty simple and reliable project.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Best way to use my hot air to heat water.

    as bb indicated put it into the sun, but paint it a flat black so the drum absorbs more of the heat. be aware that a black painted object will also lose heat equally well when the sun's rays are removed and can also be influenced by the ambient air temp for that rate of dissipation.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Best way to use my hot air to heat water.
    niel wrote: »
    flat black absorbs more of the heat. be aware that a black painted object will also lose heat equally well when the sun's rays are removed .

    Exactly what I've found to be true. Yet I was shot down in flames a while back for daring to bring up this obvious fact. Hahaha
    Thanks Niel, for restating this truth.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Best way to use my hot air to heat water.

    Paiint it flt black, place it under glass, insulate the sides and bottom of the box, makes a pretty easy batch or preheat tank. I might consider a cast off water heater tank (stipped of its jacket) or galvanized tank instead of a 55 gal tank.

    With a rql Ater tank, you can plumb pressurized water into it and then feed your conventional water heater. Don't forget freeze protection, and a T&P valve.

    Tony
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Best way to use my hot air to heat water.

    i'll try to copy this small segment of an old physics book i have. i apologize to the authors and the publisher if this violates anything and if so i shall delete this from the post upon notification. it came from "basic physics" by marsh w white, kenneth v. manning, and robert l. weber.
    001.jpg 128.6K
  • BB.BB. Super Moderators, Administrators Posts: 31,783 admin
    Re: Best way to use my hot air to heat water.

    From a 2 year old post (PDF link is still good):
    BB. wrote: »
    Niel is correct... Generally what radiates heat well also absorbs heat well.

    I remember years ago that NASA spent a bunch of time and money trying to find the right "paint" that would reflect heat from the sun well and radiate heat to space well... If I recall correctly, the best material was not much better than any of the other options.

    In the case of solar panels, I am not sure that it would make any difference at all... You have a slight insulation effect (paint is not a good conductor of heat, plus the back of the panels are plastic--also not a good heat conductor). And, you may end up with warranty problems--paints have solvents and additives which could attack the membrane materials on the back of the panels.

    If you want to keep your panels cool--ensure there is at least 5-6 inches of airspace behind/under the panels and a way for air to circulate.

    Ah--found one NASA report from 1983 (PDF file)... Has a whole bunch of information about colors/materials and their absorption and emission of heat. Hmm, looking at the results--I would probably be more tempted to paint the back of the panels white than black... Very similar emission results, and much less absorption with white.

    But of so much variability (materials, coating thicknesses, the way it is applied, mounting differences, etc.)--You would really have to do A/B testing of your specific panels and coatings.

    Don't think it is worth doing it...

    -Bill

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Best way to use my hot air to heat water.

    Black = good radiator makes sense. The locations with the highest heat loads on the shuttle have black ceramic panels instead of white. The ceramic panels are designed to radiate heat and not absorb it like the heat shields on Mercury/Gemini/Apollo (which then radiated the heat away by burning)
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Best way to use my hot air to heat water.

    BTW, you'll get far better heat transfer using a liquid-based solar thermal collector. Air-to-liquid just won't do well.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Best way to use my hot air to heat water.
    techntrek wrote: »
    BTW, you'll get far better heat transfer using a liquid-based solar thermal collector. Air-to-liquid just won't do well.

    Totally agree! Heating air, then using that air to heat water will be grossly inefficient compared to directly heating the water through a proper hot water panel.
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Best way to use my hot air to heat water.
    BB. wrote: »
    From a 2 year old post (PDF link is still good):



    -Bill

    Bill-

    I am not sure that I am following the logic here. In the case of a heat collection panel that is covered with a layer of glass, it makes a big difference in what color the collector surface is. Sunlight that has a peak energy at about 0.5 micrometers passes through the glass with high efficiency over the range from about 0.35 to 3.0 micrometers. The panel reaches a temperature of 150 F or so, but it radiates with a semi-blackbody radiation that peaks at 8 or 10 micrometers, and glass is opaque for radiation beyond about 3 micrometers, so that radiation is mostly trapped.

    Even for collectors not covered with glass, the amount of radiation absorbed is greater than the amount of radiant energy lost. We know that like black cars get a lot hotter than white cars. Therefore, better to optimize the absorbed energy. It is hard to visualize what things look like at 10 micrometer wavelengths anyway; white and black paints might be similar radiators at that wavelegth, just like glass is completely opaque at that wavelength.
  • BB.BB. Super Moderators, Administrators Posts: 31,783 admin
    Re: Best way to use my hot air to heat water.

    Just was posting some interesting information... In general, flat black is going to absorb heat better than anything else (and better than glossy surfaces). And, of course, adding insulation and a glass panel will help a lot too (ideally, low iron glass? But not sure if that makes much of a difference--avoid tinted/low-E glass etc. for a collector box).

    Regarding preventing re-radiation heat loss--From what I know, the "green house" effect is not from the glass blocking long wave IR re-radiation. The glass is stopping convective air currents/winds from mixing the local hot air with the surrounding environment.

    You might check with these guys and see if you can order their top cover from them to build your own panels (if you wish): www.solarroofs.com They use a double wall Polycarbonate for the top cover (I have seen similar material used on "plastic" green houses--and it seems to hold up well there). Not too expensive and is light. And supposedly, the 8% loss of sun shining in is made up by the double insulation reducing heat flow back out (PDF from company). Should get around 10-15 year life, and fairly cheap to replace.

    Using the similar (same?) material on the green house--There was a side with UV protective coating and you just installed that side pointing out to the sunlight.

    Solar Guppy has used these guys before and was very happy with their product and service.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Best way to use my hot air to heat water.
    BB. wrote: »
    ...

    Regarding preventing re-radiation heat loss--From what I know, the "green house" effect is not from the glass blocking long wave IR re-radiation. The glass is stopping convective air currents/winds from mixing the local hot air with the surrounding environment.
    ...
    -Bill

    Yes, the greenhouse effect is exactly that, the transparency of glass to sunlight (say 0.35 micrometers to 3 micrometers) and the fact that the glass is opaque to radiation longer than 3 micrometers. To wit:

    from http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/grnhse.html
    "Greenhouse Effect
    The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature. Besides the heating of an automobile by sunlight through the windshield and the namesake example of heating the greenhouse by sunlight passing through sealed, transparent windows, the greenhouse effect has been widely used to describe the trapping of excess heat by the rising concentration of carbon dioxide in the atmosphere. The carbon dioxide strongly absorbs infrared and does not allow as much of it to escape into space."

    from http://www.thefreedictionary.com/greenhouse+effect,
    "greenhouse effect
    1. (Physics / General Physics) an effect occurring in greenhouses, etc., in which radiant heat from the sun passes through the glass warming the contents, the radiant heat from inside being trapped by the glass"

    Admittedly, a greenhouse provides a warmer atmosphere by both the greenhouse effect and the reduction of convective heat transfer (air currents carrying off the heated gases), but the "greenhouse effect" refers specifically to the radiant heat trapping by the glass. That is why it is used in analogy with CO2 being transparent to visible radiation but absorptive to infrared radiation, with the result that the earth is heated to a higher temperature than it would be without an atmosphere.

    But the good news is that we both agree that flat black paint makes a fine solar absorber on earth. I thought that your quoted material was trying to challenge that conclusion.
  • BB.BB. Super Moderators, Administrators Posts: 31,783 admin
    Re: Best way to use my hot air to heat water.

    From a 3 year old post of mine:
    A Green House does not work this way. The Green House Effect is caused by the prevention of Convective Currents in the air which cools the ground by caused by the heating of the sun. Glass walls simply prevent the atmosphere from circulating next to the warmed ground. This effect was first tested, that I could find, (scientifically) by Professor R.W Wood around 1909 (or a bit earlier):
    THERE appears to be a widespread belief that the comparatively high temperature produced within a closed space covered with glass, and exposed to solar radiation, results from a transformation of wave-length, that is, that the heat waves from the sun, which are able to penetrate the glass, fall upon the walls of the enclosure and raise its temperature: the heat energy is re-emitted by the walls in the form of much longer waves, which are unable to penetrate the glass, the greenhouse acting as a radiation trap. I have always felt some doubt as to whether this action played any very large part in the elevation of temperature. It appeared much more probable that the part played by the glass was the prevention of the escape of the warm air heated by the ground within the enclosure. If we open the doors of a greenhouse on a cold and windy day, the trapping of radiation appears to lose much of its efficacy. As a matter of fact I am of the opinion that a greenhouse made of a glass transparent to waves of every possible length would show a temperature nearly, if not quite, as high as that observed in a glass house. The transparent screen allows the solar radiation to warm the ground, and the ground in turn warms the air, but only the limited amount within the enclosure. In the "open," the ground is continually brought into contact with cold air by convection currents.

    To test the matter I constructed two enclosures of dead black cardboard, one covered with a glass plate, the other with a plate of rock-salt of equal thickness. The bulb of a themometer was inserted in each enclosure and the whole packed in cotton, with the exception of the transparent plates which were exposed. When exposed to sunlight the temperature rose gradually to 65 oC., the enclosure covered with the salt plate keeping a little ahead of the other, owing to the fact that it transmitted the longer waves from the sun, which were stopped by the glass. In order to eliminate this action the sunlight was first passed through a glass plate.

    There was now scarcely a difference of one degree between the temperatures of the two enclosures. The maximum temperature reached was about 55 oC. From what we know about the distribution of energy in the spectrum of the radiation emitted by a body at 55 oC, it is clear that the rock-salt plate is capable of transmitting practically all of it, while the glass plate stops it entirely. This shows us that the loss of temperature of the ground by radiation is very small in comparison to the loss by convection, in other words that we gain very little from the circumstance that the radiation is trapped.

    And gases do not absorb/radiate heat like a black body would. I cannot measure the temperature of a gas with a standard IR heat gun. On a warm/clear night, I can point my IR gun at a clear sky and it simply reads at or near its low temperature limit (attempting the measure the average temperature of "space/universe" and not that of the atmosphere)... That is why they work in the first place because I can point through the "transparent" gases and measure (estimate) the temperature of a physical object. And why I can have water freeze on a cold night that is above freezing under open sky, but it will not freeze if under my trees.

    I cannot find it right now--But convective losses, at the ambient temperatures of the earth with typical air mixing, are something like 20-40x (don't remember exact number) radiative losses. So any "insulative" effect by a trace gas appears to be very small.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Best way to use my hot air to heat water.
    BB. wrote: »
    From a 3 year old post of mine:



    And gases do not absorb/radiate heat like a black body would. I cannot measure the temperature of a gas with a standard IR heat gun. On a warm/clear night, I can point my IR gun at a clear sky and it simply reads at or near its low temperature limit (attempting the measure the average temperature of "space/universe" and not that of the atmosphere)... That is why they work in the first place because I can point through the "transparent" gases and measure (estimate) the temperature of a physical object.
    -Bill

    Let us be very specific. You could certainly measure a radiative temperature of a gas with some types of infrared detectors. I have done it many times, typically measuring the relative strength of rotational or vibrational molecular bands. Water vapor and carbon dioxide provide well known absorption bands in the infrared that must be avoided when using non-contact temperature sensors. Omega Engineering (a very large player in all types of temperature measurements) states in their explanation of how infrared temperature sensors work (http://www.omega.com/techref/iredtempmeasur.html)
    "Some common examples of selective spectral responses are 8-14 microns, which avoids interference from atmospheric moisture over long path measurements; 7.9 microns which is used for the measurement of some thin film plastics; and 3.86 microns which avoids interference from CO2 and H2O vapor in flames and combustion gases."

    So the reason that your infrared temperature sensor does not meaure a temperature due to water vapor and CO2 in the atmosphere is because detectors and filters are chosen specifically to avoid this interference. Do you understand and agree with this single statement?
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Best way to use my hot air to heat water.
    BB. wrote: »

    ...

    I cannot find it right now--But convective losses, at the ambient temperatures of the earth with typical air mixing, are something like 20-40x (don't remember exact number) radiative losses. So any "insulative" effect by a trace gas appears to be very small.

    -Bill

    Let us put a control volume around planet earth, outside the atmosphere, say 500 miles above the surface of the earth. The ONLY heat transfer that occurs with the rest of the universe, and especially our sun, is by radiative heat transfer. Do you agree with this statement?
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Best way to use my hot air to heat water.
    BB. wrote: »
    ...

    So any "insulative" effect by a trace gas appears to be very small.

    -Bill

    from http://greenliving.nationalgeographic.com/natural-greenhouse-effect-2658.html
    "The Greenhouse Effect
    Earth is much colder than the sun, but it is warmer than the space outside its atmosphere. Earth's atmosphere is made up of gases, and these gases allow some solar radiation to reach the planet but also absorb some of the heat radiating from the planet, trapping it and radiating it back downward to the surface. This cycle is called the greenhouse effect, because it is similar to the warming process inside a glass-walled greenhouse. Earth's atmosphere traps enough heat to keep the entire planet warm; without it, the average temperature of the Earth's surface would be much colder than the freezing point of water, about 0 degrees F. (See References 1, 4)"

    and from http://en.wikipedia.org/wiki/Greenhouse_effect
    "If an ideal thermally conductive blackbody was the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 °C. However, since the Earth reflects about 30%[7] [8] of the incoming sunlight, the planet's effective temperature (the temperature of a blackbody that would emit the same amount of radiation) is about −18 °C,[9][10] about 33°C below the actual surface temperature of about 14 °C.[11] The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect.[12]"

    These comments do not refer to human caused global warming, but rather to the importance of the greenhouse gas effect in raising the temperature of the earth to a condition where humans can live as they have evolved. Do you have some (unpublished) scientific knowledge that is different from this widely held understanding?
  • BB.BB. Super Moderators, Administrators Posts: 31,783 admin
    Re: Best way to use my hot air to heat water.
    Lee Dodge wrote: »
    Let us put a control volume around planet earth, outside the atmosphere, say 500 miles above the surface of the earth. The ONLY heat transfer that occurs with the rest of the universe, and especially our sun, is by radiative heat transfer. Do you agree with this statement?

    Obviously yes.

    I don't want to turn this thread into an AGW thread--I was trying to discuss the effects of stopping convective losses when building a solar hot water heater. Radiative cooling effects are a much smaller portion of the losses.

    If we want to continue this interesting discussion--I can move it to its own thread.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Best way to use my hot air to heat water.
    Lee Dodge wrote: »
    The ONLY heat transfer that occurs with the rest of the universe, and especially our sun, is by radiative heat transfer. Do you agree with this statement?
    I almost agree, but the earth also heats up some from particles that strike it. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Best way to use my hot air to heat water.
    vtmaps wrote: »
    I almost agree, but the earth also heats up some from particles that strike it. --vtMaps

    I can only guess that energy from the extremely dilute stream of solar particles would be orders of magnitude less than the radiative heat transfer from the sun, but I would be interested to see any references that state otherwise.
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Best way to use my hot air to heat water.

    Reviewing the "greenhouse effect" discussion in this thread:

    Bill: "Regarding preventing re-radiation heat loss--From what I know, the 'green house' effect is not from the glass blocking long wave IR re-radiation."

    Lee: "The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature. ..."
    Quoting from http://hyperphysics.phy-astr.gsu.edu...mo/grnhse.html

    Lee continued: "Admittedly, a greenhouse provides a warmer atmosphere by both the greenhouse effect and the reduction of convective heat transfer (air currents carrying off the heated gases), but the "greenhouse effect" refers specifically to the radiant heat trapping by the glass. That is why it is used in analogy with CO2 being transparent to visible radiation but absorptive to infrared radiation, with the result that the earth is heated to a higher temperature than it would be without an atmosphere."

    Bill: "I cannot find it right now--But convective losses, at the ambient temperatures of the earth with typical air mixing, are something like 20-40x (don't remember exact number) radiative losses."

    Lee: "Let us put a control volume around planet earth, outside the atmosphere, say 500 miles above the surface of the earth. The ONLY heat transfer that occurs with the rest of the universe, and especially our sun, is by radiative heat transfer. Do you agree with this statement?"

    Bill: "Obviously yes."

    So the point is that if you have a control volume around the earth, and we agree that radiative heat transfer is the only significant mechanism for heat transfer into and out of the control volume, then your statement above about convective losses being 20x-40x greater than radiative losses makes no sense when talking about the greenhouse effect of the earth's atmosphere in raising the Earth's temperature. You must have been referring to the heat transfer in an actual greenhouse or a solar thermal panel, but the term "greenhouse effect" refers specifically to the radiative heat transfer, and not the other heat transfer mechanisms in a greenhouse or solar thermal panel.
  • gtxkidgtxkid Solar Expert Posts: 34 ✭✭
    Re: Best way to use my hot air to heat water.

    I gathered up some more materials.
    I would like to take the water and keep it warm plus warm it up slightly is the goal. What is the best way of doing this with a tank.
    I know most would go with hot water panel's, I also have three of these but not using for this project.
    Main focus is how to simply warm up the water in an easy way without getting carried away.
    Thanks Greg
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