Refrigeration Load Calculation Part I
What's so funny!
I mean, why do I laugh every time I sit down to figure out what size refrigeration unit is needed to refrigerate and store a product? I'll tell you about the laughter in a moment but first I have the painful task of telling you a few physical constructs and constants.
Senior year in high school I had a diminutive, balding physics teacher who had an uncontrolled eye twitch. We twittered and tittered like small birds. "Blinky" we called him. In whispers behind our cupped hands which if said loudly enough and with enough daring would turn into blooming gales of laughter. From my now stately and advanced age I know that “Blinky” knew what was going on. He had the final laugh in the grade book. One day "Blinky”, talking about our illustrious fourth dimension decided to do away with the second as a means of measurement and to create a new measure that we would use for experimental purposes. That devil in rational scientific school teacher garb chose "an eye blink". A blanket of silence fell over the second floor end of the building physics classroom with its beakers and gauges and spring weights and rheostats now standing at rest. Afterward in the lunch room one flight down and to the right it became the stuff of ridicule, but in that precise eye blink we were stymied, stifled and without speech. I never really did like the guy, but I doff my hat (it would have to be my virtual hat) to him.
So, as "Blinky" would tell you 1 BTU is the amount of heat that must be applied to 1 Pound of Water from 59º to 60º Fahrenheit. An aside or a ramble in the halls of physical reality (something I usually do in parenthesis): the other term I always loved is Standard Air. Standard Air is dry air at 70º Fahrenheit and 14.696 pounds per square inch absolute (psia). See where a ramble takes you. Air (just the good old breathing stuff) exerts a pressure at sea level (every pain in the ass thing in science must be defined, qualified, filtered and explained to tears) on us of roughly 14.7 pounds per square inch and yet we still stand and walk around. It is less in mountains and more in valleys which indicates to me that it is indicative of how long a column of air there is that wighs us down. This really shouldn't surprise you too much. Put a couple two inch 100 pound weights on your head, now add about three inches more. See, science can be painful!
Now "Blinky's" amazing fact number two. You don't really make things cold, what you do is remove heat from them. And what is measurement of heat. Yay! A+, the BTU. Which does stand for British Thermal Unit. Being the patriot that I am I think we should convert to the ATU or American Thermal Unit or the USATU (Well they didn't call it the Great British Thermal Unit did they?) So problems come across my desk everyday. Hey, Joe, says customer, I need a walk-in cooler (or freezer) and how much does that cost? Now, I'm going to break down the rest of this entry into quanta of easy learning. Learn and think lessons, I’ll call them. General Topic: Where is the load in the load calculation?
Say, this is getting long so I am going to make it in at least two parts!