Its all an excersize in energy Lee. Bottom line, the temperature of the tank will be determined by the sum of the energy going in, the energy going out, and then a resulting difference from ambient. All tanks have input energy in the form of powerheads and lights, and in the winter months, heaters provide extra energy input. There is really only one significant method of heat leaving the tank, and that is through evaporation. There are other modes of heat loss but they are negligable compared to evaporation.
Now, when water evaporates, 540 calories (0.627 watts) of energy are removed with every gram/mL of water that is actually evaporated. Now, consider a tank that looses 1 liter of water per day to evaporation. 1L = 1000mL and therefore 627 watt hours of heat are removed from the tank through evaporation. That's not a lot of energy for a 24 hour period. Thats only a little over 26 watts per hour of heat removed. Now when you've got hundreds of watts of light over the tank, you're putting more heat into the system than you're removing from evaporation. Consequently, the temperature of the tank water rises above ambient.
Now lets say you add some fans in the hood and evaporate 5L of water per day. Now you're removing 3135 watt hours per day or 130watts of energy per hour. Now all of a sudden you're making up for the fact that your lights are inputting a large amount of heat into the tank by increasing the heat energy out, and your tank's temperature will not be that far above ambient. And when you consider the cost of fans and the running cost of fans, they are incomprehensibly more cost-efficient than buying and running a chiller.
I realize the glass may be shielding some of the heat the lights are generating away from the water, but there is plenty generated in the tank itself via infrared radiation that you can't feel. Please trust me when I say your heater is not malfunctioning and the problem is the high powered lights over a closed water volume. You are one of many. And the solution, fans pointed at the surface for more evaporation. I know it might be a pain to keep up with the evaporative loss, but would you rather have some extra evaporation, or would you rather have dead livestock or empty pockets?
Now, when water evaporates, 540 calories (0.627 watts) of energy are removed with every gram/mL of water that is actually evaporated. Now, consider a tank that looses 1 liter of water per day to evaporation. 1L = 1000mL and therefore 627 watt hours of heat are removed from the tank through evaporation. That's not a lot of energy for a 24 hour period. Thats only a little over 26 watts per hour of heat removed. Now when you've got hundreds of watts of light over the tank, you're putting more heat into the system than you're removing from evaporation. Consequently, the temperature of the tank water rises above ambient.
Now lets say you add some fans in the hood and evaporate 5L of water per day. Now you're removing 3135 watt hours per day or 130watts of energy per hour. Now all of a sudden you're making up for the fact that your lights are inputting a large amount of heat into the tank by increasing the heat energy out, and your tank's temperature will not be that far above ambient. And when you consider the cost of fans and the running cost of fans, they are incomprehensibly more cost-efficient than buying and running a chiller.
I realize the glass may be shielding some of the heat the lights are generating away from the water, but there is plenty generated in the tank itself via infrared radiation that you can't feel. Please trust me when I say your heater is not malfunctioning and the problem is the high powered lights over a closed water volume. You are one of many. And the solution, fans pointed at the surface for more evaporation. I know it might be a pain to keep up with the evaporative loss, but would you rather have some extra evaporation, or would you rather have dead livestock or empty pockets?
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