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Thermal Problem

Wow.... That seems like a lot of heat from just fluorescents! But yeah, if you are growing coral then a lot of light is probably a necessity. I don't know what is going on there, but whatever is causing the heat rise in the tank, the source is bound to be hot. If the heat "is" coming from the lights (radiation "can" be a significant source of heat transfer, sunlight is about

1 kW / m**2), then there must be something in the tank to absorb the heat (coral?). I wouldn't think that water would absorb much heat, but my heat transfer book says its emissivity is 0.96 where 1.00 is a perfect black body.

Eb = Watts / m**2 = emissivity*StefanBoltzmann*(Degrees Kelvin)**4, where StefanBoltzmann = 5.670*10**(-8) Watts / (m**2*K**4)

Black / Gray body radiation heat transfer depends primarily on absolute temperature differences between the bodies and the emissivity of the bodies. The emissivity is spectrally oriented based on the wavelength of the radiation. Since most of the visible light exits the tank, infrared radiation is where the heat is coming from, which is also probably very usefull to the coral.

I would "guess" that the heat is getting in through conduction or convection somehow. I have seen fluorescent ballasts get so hot as to start smoking. Convecting any heat generated by the ballasts away from the tank would be a good thing.

Look for the refrigerator with the best efficiency, or COPR. Then find one that will eliminate heat at some rate above the maximum you think will ever be necessary. If you need 200 watts or 682 BTU / Hour heat eliminated, then anything larger than 682 BTU / Hr will cycle on and off to maintain the temperature of your tank between the high / low temperature set points.

The other thing that might be important is a way to control the flow rate of the tank water through the chiller / refrigerator. Slowing the flow rate down will lower the chiller exit temperature of the water that enters the tank. You don't want your fish to catch a cold when they swim by this flow, so some adjustment in this area may be required. Or maybe you can dump the cold water into the filter pump where it will be well mixed with warm water before coming back into the tank.

Chris. T.

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O5O
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These use electronic ballasts. Essentially zero temperature rise.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

temperature.

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And your house AC will have to run longer to remove the additional moisture from the air. What kind of lamps do you use for illumination? If they are incandescent, perhaps a change to fluorescent might help reduce the heat load.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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Software Engineering is like looking for a black cat in a dark room.
Systems Engineering is like looking for a black cat in a dark room
  in which there is no cat.
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Reply to
Paul Hovnanian P.E.

riment

ature.

You can extract an exponential time constant from any three successive measurements of an exponential decay - it helps the accuracy if the spacing is of the order of the time constant.

The expression is [T(time) - T(infinity)]=3D [T(begin) - T(infinity)] exp(-k.time)

T(begin) is just your first measurement, and you can use the next two two set up two simultaneous equations which you can solve for T(infinity) and the time constant k.

If you have more than three measurments, you have to use a non-linear less-squares curve fitting algorithm to extract the best-fit values for T(begin), T(infinity) and k,

There are a couple of good procedures for non-linear curve fitting - Marquandt 's has been around since 1963, as has the fairly similar Fletcher-Powell procedure that I coded up in Fortran 4 back in 1967 for my Ph.D. project. In recent years I've mostly used a copy of the shareware program NLREG which I bought when it was cheap

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=3D2004+113768

Sure, but how much did you increase the evaporation rate? 2 US gallons a day of evaporation is 190W of cooling. If you work out the new evaporation rate, you will be able to equate the extra heat loss with the drop in temperature, giving you a much better handle on the thermal resistance of the fish tank to ambient in watts per degree Kelin, or Btu's per degree Fahrenheit ....

You could do better at exploiting the information you've got.

--=20 Bill Sloman, Nijmegen

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bill.sloman

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No matter how the heat is removed from the tank, be it by a chiller or by evaporation, that heat will have to be pumped by the air conditioner in both cases. The difference with the chiller is that the electrical input of the chiller will also get converted to heat and will have to be removed by the air conditioner. Hopefully the electrical input of the chiller would be several times (maybe 4x ?) less than the heat pumping capacity so perhaps isn't such a big deal.

If you didn't want the heat pumped by the chiller and the electrical input power of the chiller to have to be pumped again by the AC then you'd have to put the chiller in a non airconditioned room (garage?) and run insulated pipes to the tank, but this is likely to be quite impractical. Whether it would improve energy efficiency may be doubtful in any case, because the chiller may not run as efficiently in a high ambient temperature and long runs of pipe may cause loss of efficiency.

Evaporation from the tank could be deliberately increased with a fan and a small fountain above the surface of the water, but I would be a little concerned that if a lot of water is added and allowed to evaporate, salts and impurities from the water being added could accumulate in the tank over time and after a few weeks the fish might not like it. This depends a lot on the quality of the water being added.

Chris

Reply to
Chris Jones

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