Hey guys, sup.

I have noticed many people on the forums talking about how their chillers don’t preform. Here is a super simple formula you can use to calculate the cooling capacity needed for a project to make sure you aren’t undersizing.

Take the specific heat of your solvent in BTU/lb F – you can find it in this link - Butane - Thermophysical Properties (we are using butane in this example which is equal it .39 BTU/lb F)

Multiple by pounds of solvent desired to be cooled – here, we use 100 lbs

Multiple by your temperature differential - here, we are going from 80F to -40 F

Divide your desired target temp time into hours for your time multiple (i.e. 15 min would be a BTU/hr multiple of 4). In this case we want to take 100lbs of butane from 80F to -40F in 15 min.

Then convert the BTU to Kw@ your desired temp. Here is a simple converter link - BTU/hr to kilowatts (kW) conversion

Once you have the answer in Kw reduce by your estimated drop do to loss. (normally 20-30% or below for a jacketed vessel and non-vacuum insulated lines). To do this we add 20% to our cooling capacity by multiplying by 1.20. Hot environment about 70 degrees? Add more. Non vacuum insulated vessels? Add way more. Conditions are paramount.

So, in our example 100lbs of butane cooled from 80f to -40f in 15 min would be -

.39 (specific heat) * 100 (lbs of butane) * 120 (degrees of change) * 4 (multiple of 1 hr (15min)) = 18,720 BTU/hr @-40F

Same thing but in one hour instead of 15 min = 4,680 BTU/hr @-40F

Convert 18,720 BTU/hr to Kw - 5.48Kw @ -40F

Add losses from thermal fluid, hoses, jacket, and shell. (20-30%)

Add the difference 1+.20 (added 20% over power for losses)

5.48KW*1.20 = 6.57KW @ -40F

Remember that cooling capacities of chillers generally drop as they get cooler. The deeper you go, the more expensive it gets. Be sure to check your chillers cooling curve before spec’ing a chiller.

Alternatively, you can just call me. Questions and comments welcome. I hope this helps.