- As accurately as possible, calculate how much water is in your hydroponic system.
- During the hottest part of the day, turn everything in your garden that produces heat on. The goal is to let the room get to max temperature.
- Now, chill your system down to your desired temp (often 60-70F). Do this with sealed bags of ice or frozen two liter bottles so you won’t be adding extra water to your system.
- Once you reach your desired water temperature, remove the ice from the system and circulate the water.
- Start a timer and write down the starting temperature.
- One hour later, write down the current temperature.
- Subtract your starting temp from your 1 hour temp and write it down - this is your temperature differential.
- Now, use the following formula to calculate the BTUs you need:
Gallons of Water X 8.34 (weight of a gallon of water) X Temperature Differential
Now you know how many BTUs you need to adequately chill your system.
Example Reservoir Calculation
If you have a 75 gallon system, your max temperature is 80F, your desired temperature is 65F, and after an hour the water temperature is 70F…
75 X 8.34 X 5 = 3,127.5
Here are your conversions to the standard sizes that water chillers are sold in:
Tons
BTUs
1/10 ton
1,200 BTU
1/4 ton
3,000 BTU
1/2 ton
6,000 BTU
1 ton
12,000 BTU
It’s recommended to give yourself a bit of a cushion, especially when buying a low-end chiller. Typically, they won’t put out their actual power rating, so I would recommend adding about 25% to your total BTUs when deciding.
That means in the example above, you would want to boost up to the ½ ton chiller just to be safe.
