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Heater & Chiller Sizing Calculator Instructions


Introduction

The Heater & Chiller Sizing Calculator estimates the minimum size (power) of heater and chiller required to keep an aquarium system within a specified temperature range. Note that the heater size predicted is the minimum size required during the tank's coolest period and that the chiller size predicted is the minimum size necessary during the tank's warmest period.

When considering the size of an aquarium heater or chiller, two values are important. The first is the equilibrium size: the size of heater or chiller needed to keep an aquarium system at a temperature. The other is the equilibrating size: the size of heater or chiller needed to bring an aquarium system to a temperature. The equilibrating size is always greater than or equal to the equilibrium size; how much greater depends on how quickly one would like to reach equilibrium.

This calculator reports both values. The equilibrating size is reported under During Startup and the equilibrium size is reported under After That.

Multi-Tank Systems

If you have a multi-tank system, add up the respective heating and chilling requirements of each individual tank to determine the overall requirements of the system. Note that a sufficiently high rate of turnover between the tanks is required for this approximation to be reasonable. Heat loss through plumbing is typically negligible, but you can treat particularly long stretches of pipe as separate tanks (i.e. 1"x1"x100') made from PVC with a PVC lid.

If you do this, do not enter your overall system evaporation rate as the evaporation rate for each tank. Instead, enter your overall evaporation rate as the rate for your largest tank and then calculate the other tanks with zero evaporation rate.

Description of Inputs

Aquarium Dimensions:
Aquarium Top:
Aquarium Bottom:
Aquarium Sides:
Water Chemistry:
Rate of Evaporation:
Desired Temperature Range:
Ambient Temperature Range:
Heat Contributed by Equipment:
Equilibration Time:

Limitations

Frequently Asked Questions (FAQ)

Your calculator underestimates the cooling effect of removing lids from an aquarium. I notice a much more substantial drop in temperature when I remove my lids than your calculator predicts.
The majority of heat loss that occurs as a result of removing an aquarium lid comes from evaporative cooling. This calculator does not estimate the effect of evaporative cooling; instead it requires it to be explicitly inputted. In order to get a reasonable estimate of how much removing an aquarium lid will contribute to heat loss, you must increase the evaporation rate that you input appropriately.
Your calculator overestimates the size of heater and chiller required for an aquarium. It calculates that an X-Watt heater is required for my system, but I have successfully been using a smaller heater for a number of years.
Keep in mind that the heater and chiller sizes reported here are sufficient for their individual respective worst-case scenarios. For example, the heater equilibrating size is calculated assuming that the room temperature is at the minimum ambient value, that the aquarium water has completely cooled down to this minimum ambient temperature, that the heat contributed by equipment remains at the minimum value, and that the water should be heated up to the minimum desired temperature.
Why does your calculator disagree with P.R. Escobal's heat-flow model in "Aquarium Systems Engineering"?
Dr. Escobal makes a number of assumptions in his model. He assumes that heat-loss by evaporation, radiation, and convection are insignificant. He also does not take into account the heat-gain by equipment and does not attempt to size the heater to accommodate the initial heating of the water (it is only sized to maintain the system's temperature).

In addition to these assumptions, he also makes two critical mistakes. The first is the assumption that the inside of an aquarium pane is at the temperature of the water and that the outside of the pane is at ambient temperature. In reality, the outside of the pane is usually at an intermediate temperature except in the case of very thick panes. This assumption results in heater sizes that are much larger than needed.

His second mistake is a simple unit conversion error. To convert from calories/second to watts, he multiplies by 0.23889 rather than dividing (see this thread for more details). In effect, this mistake masks his first by dramatically reducing the heater size. These two mistakes work together such that the model appears to work for some medium-sized aquariums.
Why does your calculator disagree with Stephen Spotte's heat-flow model in "Seawater Aquariums: The Captive Environment"?
Mr. Spotte makes a number of the same assumptions that Dr. Escobal does. Namely, that heat-loss by evaporation and radiation are irrelevant. He also does not account for heat-gain by equipment and does not attempt to size a heater to accommodate the initial heating of the water (it is only sized to maintain the system's temperature).

In addition to these he also makes two critical mistakes. First, he assumes that both the inside and outside of an aquarium pane are at the same temperature as the water. In reality, the outside of the pane is usually at an intermediate temperature between that of the water and ambient. This mistake negates the effect of the thickness of the pane. Indeed his model does not consider the thickness of any of the panes as a parameter. This mistake tends to overestimate the heat-loss by convection of the surrounding air along the outer surface of the aquarium, which partially makes up for the failure to consider heat-loss by radiation.

However, the real issue with the model is the catastrophic underestimations of the heat transfer coefficients. For example, the heat transfer coefficient used for the convection of air along a concrete surface is 0.000045 calories/(second*cm^2*C). This is only 2 Watts/(m^2*K), where as it should be between 10 - 50 Watts/(m^2*K) (depending on the speed of the air, which is not considered). This mistake results in extremely undersized heaters. For example, in the text he concludes that a 163-Watt heater is sufficient to keep a 900-gallon (10' x 6' x 3') aquarium built from 6" concrete 7F above ambient. The heat-flow model used here suggests a minimum heater size of 1,500 Watts to achieve that.



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