An example: You want to know what an estimated refrigeration load is, of the product only, of taking 10,000 lbs per hour production rate of cookie dough, from 65F down to 15F. Using a freezing point of 26 degrees, a specific heat of .75 above freezing, .35 below freezing, and 59 as latent, we have the following:
10,000 x Sp Heat above (.75) x temperature differential from 65 to freezing.
= 292,500 BTU’s
10,000 x Sp Heat below (.35) x temperature differential from 26 down to 15.
=38,500 BTU’s
10,000 x Latent (59).
=590,000 BTU’s
We can see where the high loads are in freezing a product, latent.
Adding up the above, we have 921,000 BTU’s (energy), or 76.75 tons of refrigeration needed, just for the product load only. It is therefore to your benefit to identify these numbers accurately, and not guess; as if we were to use water in the above example the latent load only would have been 120 tons of refrigeration.
There are other considerations in determining the full design load of a system, including infiltration loads, motors, lights and others. |