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  • Page 2 of 2 FirstFirst 12
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    Thread: Warm Air Aeration?

    1. #21
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      Quote Originally Posted by KoiRun View Post
      Just a real life scenario from my observations. I run a hot air duct from the basement to my 1500G covered pond. The pond is covered with insulation measuring 12x14x(1feet above ground). R20 insulation for the most part. It is keeping my water temperature at approx 13.2C no mater how cold it is outside. This is because the colder it is outside the more out furnace kicks-in. The temperature inside our house is 18C, the air temp inside the enclosure is 15C, water temp is 13C. Now this is the part that would relate to the OP. I also run 2 air pumps. One pump runs 1300 ccx 4 outlets and another 1300 cc x2 outlets. Using six airstones. The units are situated indoors in the basement with lines bunched up together and insulated that traverses the lawn into my covered pond. I can only assume that the warm air being pumped by the airpumps is also helping warm the pond at one time. Until the lines got blocked with ice! (post #4). The water temp since the blockage I've notices went below 13C. It would go to 12.7-12.8. Since then I have re-routed my airlines from the the basement THROUGH the heated duct and into the pond. This is what I should have done in the first place. Since doing this my pond temp has been above 13C (once again). My next experiment would be to situate the airpump unit itself INSIDE the the main vent in the basement so that it would draw much warmer air. For me what make sense actually works - that pumping hot air, whether in the water or the air above the water would actually heat the pond.

      KR.
      That works for two reasons. First, the pond is covered and you are trying to prevent heat loss from the pond as opposed to trying to raise the temperature of an already cold pond, and second and more importantly, a typical furnace, even down here in the south, can deliver 60,000-120,000 BTU/Hour. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree F. One US gallon of water is 8.345 pounds, so, assuming all of the output is being directed to the pond, a 100,000 BTU/hour furnace can raise the temperature of 11,983 US gallons by 1 degree F per hour. A 100,000 BTU furnace could raise the temperature of a 3000 gallon pound by nearly 4 deg F per hour.

      For reference, 100,000 BTU is equal to 29,307 watts. Using your furnace to maintain the temperature of the pond is a far different situation than pumping air that is being heated by a halogen light bulb into a pond using a typical pond aerator pump.

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    2. #22
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      GREAT posts here... I've learned quite a bit~

      I guess I'm still curious about changing the temperature of the water by using a typical aerator and cold or very cold air, especially if there is no discernible difference in using warm or hot air. As I see it, there should not be any difference and therefore I could place the aerators anywhere in the water, right?

      Thank you everyone for all the fantastic discussion~

    3. #23
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      Quote Originally Posted by DViolante View Post
      GREAT posts here... I've learned quite a bit~

      I guess I'm still curious about changing the temperature of the water by using a typical aerator and cold or very cold air, especially if there is no discernible difference in using warm or hot air. As I see it, there should not be any difference and therefore I could place the aerators anywhere in the water, right?

      Thank you everyone for all the fantastic discussion~
      I believe your thinking is correct. From this quote taken from RickF's post above...

      If you were trying to increase the temperature of a 3000 gallon pond, and you assumed that there was no temperature loss or gain other than from the air that is being pumped into the water, you would have to pump 100 liters of 104 deg F air per minute into the pond for 107.63 days (more than 15 weeks) to raise the water temperature by 1 deg F. On the other hand, if you were pumping air at 32 deg F, you would have to pump 100 liters per minute for 1545 days (more than 4 years) to drop the water temperature by 1 deg F.
      ...cold air would have less effect on water temp change than warm air.

    4. #24
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      Quote Originally Posted by Sweetwater View Post
      I believe your thinking is correct. From this quote taken from RickF's post above...



      ...cold air would have less effect on water temp change than warm air.
      The difference is not cold or hot air. It is how different the air and water temperatures are. In the example I gave, the difference between the cold air and the water was only 5 deg, but the difference between the warm air and water was 67 deg. That is why it takes so much longer for the cold air to have an effect. If the cold air is -30 (30 degrees below zero), then it would drop the temperature of a 37 deg pond just as quickly as 104 deg air would raise it.

      Sent from my SM-G900V using Tapatalk
      Last edited by RickF; 02-04-2016 at 09:06 PM.

    5. #25
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      Quote Originally Posted by RickF View Post
      The difference is not cold or hot air. It is how different the air and water temperatures are. In the example I gave, the difference between the child 2 air and the water was only 5 deg, but the difference between the warm air and water was 67 deg. That is why it takes so much longer for the cold air to have an effect. If the cold air is -30 (30 degrees below zero), then it would drop the temperature of a 37 deg pond just as quickly as 104 deg air would raise it.

      Sent from my SM-G900V using Tapatalk
      Thanks for clearing that up Rick.

    6. #26
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      Rick, great point for me... So if the air going in is either VERY warm or VERY cold (relative to the water temperature), there's a chance it could change the water temperature, somewhere down the road based on a number of factors.

      You mentioned that it's not really the transfer of (heat) energy from the bubbles of the aerator that makes as big a difference, but the agitation at the surface and transfer of (heat) energy there. Covering a pond makes a ton of sense when there are going to be dramatic extremes. Like our NY winters. Doing so would protect the surface from a number of elements, including debris, wind, snow, ice, heat loss, etc...

      So, in a covered pond, what are the drawbacks of using a heatlamp (UV/IR) at the point of aerator agitation on the surface (where the bubbles break the surface of the water and where energy transfer occurs the most). Would the energy transfer from such a source be better than the transfer capacity of air?

      I'm truly intrigued by the physics of the conversation, which led to my experiment with the halogen bulb contraption in the first place. To me, it would now seem that keeping the heat in, by a reflective and insulated cover, and then increasing the potential for energy transfer at the best point of transfer (water agitation point) would be an efficient method of maintaining some temperature so the pond wouldn't freeze like a block. Or even enough to compromise the health of my fish. The most it has frozen is ~ 4-5 inches, with two aerator stones about a foot below the surface with whatever the outside air temperature is, and a warmer on the surface to keep a hole open to let gasses escape.

      Is there a better (more efficient) method? Other than moving to a warmer climate... LOL

    7. #27
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      I think you are confusing two points, and that might be my fault for not being clear. Exchange of gas (adding oxygen and removing carbon dioxide) occurs primarily at the surface. Aerators increase agitation at the surface and increase the amount of "new" (i.e., different) water that is in contact with the surface, which improves gas exchange. The amount of gas that is exchanged along the column of bubbles, rather than at the surface, is insignificant.

      Heat exchange occurs wherever the warm (or cold) air is in contact with the water. If the purpose of using hot air is to keep a larger hole in the ice, then the closer the air stone is placed to the surface and the more focused the stream of bubbles is, the less heat from the warm air will be lost to the cold water, and therefore, the more heat will actually reach the area where the ice is. This will help keep a larger hole in the ice, but will not significantly affect the temperature of the water. The deeper the air stone is and the wider the stream of bubbles is, the more heat that will be lost to the water before the air gets to the surface, and therefore, the smaller effect the previously warm air would have on the size of the hole in the ice. Although the heat is lost to the water, because of the vast difference in mass of the water compared to the air, there is a negligible effect on the temperature of the water. In this instance, water is a heat sink - water takes the heat out of the air, but because the heat is distributed so vastly, there is not a measurable change in the temperature of the water. For every degree that is lost from the air, the temperature of an equal volume of water is only increased by about 0.00113 degrees. When you add in the fact that the volume of water (usually) is much larger than the volume of air, the effect on temperature is even smaller.

      Anything that prevents heat loss from the pond will affect the water temperature. Covering the pond reduces evaporation, and evaporation adds to the heat loss. Air movement at the surface of the pond both increases evaporation and increases radiant heat loss (i.e., heat is lost from the water as it warms the new supply of cold air). Covering the pond traps air that ultimately becomes the same temperature as the water, thus preventing further radiant heat loss.

      A heat lamp directed at the ice will melt a hole in the ice, but it would take a lot of heat lamps to actually raise the temperature of the water. As I mentioned, one BTU is the amount of energy required to raise the temperature of one pound of water by 1 deg F. One BTU per hour is equivalent to 0.29307 watts, and one pound of water is slightly less than one US pint of water. Heat lamp bulbs are typically 250 watts, so one heat lamp bulb delivers 853 BTU per hour. Therefore, a heat lamp bulb could raise the temperature of approximately 53 gallons of water 1 degree F per hour. Looking at it another way, it would take approximately 56 hours for a 250 watt heat lamp to raise the temperature of a 3000 gallon pond by 1 deg F (assuming all of the energy of the bulb is going into the pond and there is no other heat loss or gain taking place). A heat lamp directed at the ice will have its energy concentrated on a small volume of water, so that water will increase in temperature quickly, and a hole in the ice will form.

    8. #28
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      Quote Originally Posted by RickF View Post
      The difference is not cold or hot air. It is how different the air and water temperatures are. In the example I gave, the difference between the cold air and the water was only 5 deg, but the difference between the warm air and water was 67 deg. That is why it takes so much longer for the cold air to have an effect. If the cold air is -30 (30 degrees below zero), then it would drop the temperature of a 37 deg pond just as quickly as 104 deg air would raise it.

      Sent from my SM-G900V using Tapatalk
      One minor disagreement with that thinking- very cold air generally has very low humidity while warm air usually has high/higher humidity. So, when it comes to aerating your pond, pushing cold air with low humidity, because it has very very low mass will not impact your water temp much at all. While (at least theoretically) pushing warm moist air will have a greater impact. So in the experiment that OP did he warmed very dry air up, but because of the very low mass of warm dry air it would have little impact.

      Rick, I liked your analogy of sticking your hand in a hot oven compared to into hot water.

      Regarding keeping any pond warmer during the winter I think that energy conservation is money more well spent than any form of heating. As of Feb 8 my pond, here in Minnesota, is still at 43 degrees F. With no heat added whatsoever. We have had a somewhat mild winter by historic norms, but we have had I think 7 nights with subzero temps.
      I am dreaming up a pond rebuild for next year that will be insulated to a point where I can keep the water close to 55 with very little heat added. This will require that my filter pit be as well insulated as the entire pond with no water lines exposed to outside of the insulated zone.

    9. #29
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      Quote Originally Posted by mplskoi View Post
      One minor disagreement with that thinking- very cold air generally has very low humidity while warm air usually has high/higher humidity. So, when it comes to aerating your pond, pushing cold air with low humidity, because it has very very low mass will not impact your water temp much at all. While (at least theoretically) pushing warm moist air will have a greater impact. So in the experiment that OP did he warmed very dry air up, but because of the very low mass of warm dry air it would have little impact.

      Rick, I liked your analogy of sticking your hand in a hot oven compared to into hot water.

      Regarding keeping any pond warmer during the winter I think that energy conservation is money more well spent than any form of heating. As of Feb 8 my pond, here in Minnesota, is still at 43 degrees F. With no heat added whatsoever. We have had a somewhat mild winter by historic norms, but we have had I think 7 nights with subzero temps.
      I am dreaming up a pond rebuild for next year that will be insulated to a point where I can keep the water close to 55 with very little heat added. This will require that my filter pit be as well insulated as the entire pond with no water lines exposed to outside of the insulated zone.
      The difference in the warm moist air versus the cold dry air, again, goes to the difference in mass. The density figure of 1.127 kg/m^3 for air at 40 deg F assumes zero humidity. I will have to look for the density at 90 % RH, but it will still be insignificant compared to the 999 kg/m^3 of water. You are correct, though, that humid air weighs more than dry air.

      The big influence of humidity is on the amount of heat lost to evaporation. When the humidity approaches 100%, the evaporation rate approaches zero. The phase shift from liquid to gas requires energy and causes the temperature to drop, so humid air causes less temperature drop due to evaporation than dry air does.

    10. #30
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      So I had a chance to look up the affect of humidity on the density of air. At sea level, 0 deg C (32 deg F) and 0% humidity, the density of air is 1.292 kg/m^3 . Under the same conditions, but 90% humidity, the density is 1.290 kg/m^3, so the difference is very small and, counter intuitively, lower at higher humidity than it is at lower humidity. At sea level, 90 deg C (104 deg F) and 0% humidity the density is 1.127 kg/m^3 and under the same conditions but at 90% humidity, the density is 1.099 kg/m^3, a slightly larger difference than at 0 deg C, but again, in the opposite direction of what I had expected - humid air is less dense than dry air.

      Humid air at the pond surface will cause less cooling because there is less evaporation, but the effect of humid air on warming water is not much different than the effect of dry air.

      The reason high humidity increases the heat index has to do with the inability of the body to lose heat through sweating and evaporative cooling. Similarly, wind chill is greater at low humidity than at high humidity because evaporative cooling becomes more efficient the faster the air is moving and the lower the humidity. These are important considerations for the human body, but the humidity of air that is pumped into the water has almost no effect on the temperature of the pond. Humidity and wind at the surface of the pond will have a big effect on the amount of heat that is lost by the pond at the surface, but whether air that is being used to aerate the pond is hot or cold or dry or humid, has negligible contribution to the temperature of the pond.

      Here is a link to the calculator I used.

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    11. #31
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      I think I figured out why air density decreases as humidity increases. At 40 deg C (104 deg F) and 90% humidity, the density of the water that is in the air is only 45.88 grams/m^3. At 0% humidity, the density of air is 1.127 kg/m^3. As humidity increases, the water that is now a gas displaces air, and apparently the amount of air that is displaced weighs more than the weight of the water that is displacing it. At 90% humidity, the 45.88 g/m^3 of water must be displacing 74 g/m^3 of air to get a final density of 1.099 kg/m^3

    12. #32
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      Rick,

      Thank you for the clarification and truly comprehensive information. I am very appreciative. I thoroughly enjoyed doing the experiment and reading the pros and cons and scientific data here. I'm sure I could have simply read the answer to my initial question somewhere, but sometimes discovery by doing is actually more educational. Certainly the discussion here with you and the other members is evidence that learning by discovery and interaction with mentors is far far better.

      Thank you all again for your time, passion, and willingness to share and help! I'm planning several changes to my pond for winterization, mostly because of these discussions. None of them with a heat lamp or halogen bulb and copper tubing contraption, however. That was simply fun.

      DV

    13. #33
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      Rick, that is so counter intuitive isn't it? Wow. Well, I would argue the point, but I have learned never to argue with science. That is almost always a dead end.
      Thanks for sharing.

    14. #34
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      Rick,
      In regards to you post #31, that's why it's harder for aircraft to fly in more humid and therefore less dense air (specifically rotor craft) than dry cold more dense air. I was a flight medic for many years and this concept seemed confounding especially since humid days seemed so more oppressive. The air just "seemed" heavier. It was most definitely more difficult to fly in hot humid weather. There was less air density and so it was harder to create as much lift. Ther just wasn't air for the rotor blades to push on. I'm amazed at the actual numbers and just how less sense humid air is.

    15. #35
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      I knew temperature, altitude, and atmospheric pressure all had a big effect on air density, and therefore on the ability of aircraft to fly, but until I went through this exercise, I did not realize that humidity also had a significant effect.

    16. #36
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      Good post rick!

      Keeping a hole open on the surfsce takes much more heat than it takes to heat a similar area of water one degree! Water requires one degree of heat to raise it's temperature one degree but it takes 144 btus of heat to change the same pound of water of water from 32 degree ice to 32 degree water!

      I have to go but I will try to return later tonight and finish where I left off!!!

      Rich

    17. #37
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      A pond will loose 70% of it's heat to evaporation during the summer months; wind chill will raise that loss for the same reason we loose more heat when there is a breeze! As the wind increases, it moves the air that has just gained moisture from the pond and replaced it with drier air!

      As Rick has pointed out, the pond doesn't have to be heated, only a small area of the surface where we might want the hole/hole's

      That evaporation can be lowered with a simple plastic sheet to raise a pond's temperature over 10 degrees in the winter. My own pond will gain about 8 deg with a complete cover and close to that with an awning over it in the winter. Insulation is still worth while in lowering conduction which can reach 10%, in the summer! I can only take a wag at how much that will increase in January, but I expect the evaporation will drop off some unless the air is especially low and it often is in Jan. This can also help cool an especially warm pond in August by creating a trickle tower and a spray fountain can improve on that! The spray should be heavy enough to reduce the loss of mist waters, as compared to evaporated waters, because the cooled water must return to the pond to cool it.

      Electric heat costs about 7 times as much as gas heat around here so a heat duct picking up some of the waste heat of the furnace might be worth looking into but there must continue to be enough heat to cause a chimney effect unless your heater is a central heater with an exhaust blower. Even then the cooler stack air will load the blower down some if your chimney is long!

      The easiest heater will be a low temperature immersion heater right at the location( high temperature heaters used to harm fish(I'm 77 and have seen so many changes that I wouldn't be surprised to find out that has changed to!) I added a immersion heater in the return water to heat a 1000 gallon hospital tank. I mention that because it could have been returned to a spot on the surface to keep the hole open!

      It wouldn't hurt to dig , or drill down to a point a few feet below the frost line in your area and install a 1/2 inch conduit there too act as a test well. the bottom should be capped to keep out dirt and the top can be capped with a threaded cap for the same reason and to facilitate removal when measuring the temperature gradients! I have one on the north side of my house so as to remove the effects of the sun. A 1/2" 'dowel' can be stored there to facilitate isolating the level to be tested or the temperature will be an average of some part of the length of the conduit. The dowel should have a slight groove to accommodate the thermocouple lead a few inches from the bottom of the dowel to the area being tested. If your lead has a bulb at the end, the dowel should be dug out to accomodate the bulb at the end of the lead!

      Mark the dowel at one foot spaces beginning at the full depth so you can measure the temperature rise(remember, this is winter) as you lower the bulb to each level! There won't be much of a change year by year but there will be a slight jump between dry & wet soils!

      So insulation will be a valuable investment down to a foot or so below the frost line, then the earth will begin to warm up to a point where you will be blocking the heat to be gained by the pond!

    18. #38
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      [QUOTE=RickF;2542102]The difference is not cold or hot air. It is how different the air and water temperatures are. In the example I gave, the difference between the cold air and the water was only 5 deg, but the difference between the warm air and water was 67 deg. That is why it takes so much longer for the cold air to have an effect. If the cold air is -30 (30 degrees below zero), then it would drop the temperature of a 37 deg pond just as quickly as 104 deg air would raise it.

      Don't forget cooling water to 33deg takes 4btu/lb and cooling water from 31deg will take an additional 1btu/deg but it will take 144btu to turn water to ice or ice to water! I get what your saying but I would like folks new to water to understand that the transition isn't free!

      heat rising through the water will cause some evaporation. That transition is also called boiling if the evaporation is rapid enough! It comes to 977btu/lb of water being evaporated. That is why the heat appears to do nothing.

      Water comes to the ice hole (Oh geeze! I just discovered all those people are comparing me to a hole in the ice! And you folks call me slow.) and looses 144btu/lb and then reaches the dry winter air which absorbs the water (which cools the water) just heated and is moved away by a slight breeze and brings in some drier air to begin the cycle over again!

      The secret to raising the temperature of the water in the winter or summer is to reduce evaporation with a cover!

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