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
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
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.