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Formula for Sizing Chillers


There is a formula for sizing chillers for any application that takes little effort to know exactly what size chiller you need. This only works if the tank is setup and all heat producing equipment (lighting, powerheads, pumps, etc) are installed.

Turn on all the equipment and give it a chance to warm up to full operating temperature. Also you want to test at the hottest part of the day (hottest temp inside your house). I would suggest running at least an hour before beginning the test. If necessary put bags of ice in the sump or in the tank to cool the water down to the desired temp. Remove the ice and give it another 10 minutes or so to stabilize. Check the water temperature and write it down and try to be as accurate as possible. Leave everything running and in exactly 1 hr check the water temp. This will give you your total temperature rise over 1 hr.

Next calculate the water volume as closely as possible in the entire system. Its ok if you don't take out the volume of the rock or only deduct a little for it. This will equate to a slightly larger chiller than you need which is ok.

Here is the formula

8.34 (weight of a gallon of water) x number of gallons in system x temperature rise over 1 hr = BTU load per hour

I would suggest to add 20% to this number of a cushion, you never want to size your chiller for exactly what you need then the chiller will not shut off while under a load. Chillers aren't designed to run this way and it will surely reduce the life of it.

Here is an example of 100 gallon tank, 50 gallon sump, with a 2 degree temperature rise.

8.34 (weight of water) x 150 (volume of tank) x 2 (rise in temp) = 2,500 BTU

+ 20% (2,500 btu x .20)


3,000 BTU

Chillers are sold in 1/10th, 1/4, 1/3, 1/2, 3/4, 1, 1.5, 2, and 3 hp for aquarium use. 1hp is basically equal to 12,000 BTU.....so 3,006 BTU is 1/4 hp.

Here is the problem that I can warn you about. Most chiller (especially aquarium chillers) do not put out their hp rating so you have to be careful. This is because aquarium chillers use titanium heat exchangers which are less efficient at heat exchange. You can try finding the actual BTU output from the chiller manufacturer or you can use the general formula of it losing approximately 30%. So this means that that a 1/4 hp chiller actually outputs around 2000 BTU. This means that for the example above we would go with a 1/3 hp or 1/2 hp unit.

Some tips....

Oversizing chillers is not a problem, a properly sized chiller and an oversized chiller will use the same amount of power to cool your tank. The larger chiller uses more power while its on but has a shorter run time.

If you are using a chiller in a hot area this could further reduce the BTU. If the area gets over 95 degrees then it will start reducing BTU....and over 100 degrees the BTU's really start to drop off. Losing another 20-30% is completely possible,

Always place your chiller in where it can get adequate airflow, don't shove it up against a wall or put it under the tank stand, it needs to have free air movement to work efficiently.

Keep in mind that the chiller is removing heat from the aquarium and is exchanging that heat in to the air that it blows out of the back of the unit. It also makes its own heat just operating. Some of the heat that the aquarium absorbs is directly through the glass unless the room is colder than the tank. If you place your chiller beside your aquarium and it makes the room hot this is counter productive. The heat that is being pulled out of the aquarium comes out the chiller, heats the room, making the tank absorb more heat, making the chiller run more, making the room hotter.......makes a cycle of building heat that doesn't stop until the lights shut off.

If the temp of your tank will get to warm over an hour you can do a shorter test of 30 minutes (slightly less accurate), just double the results for BTU per hour.

Hope this helps and didn’t blow anyone's mind lol.

Hydro (http://www.austinree...20-all-wysiwyg/)

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