Refrigeration Basics for Engineers and Mechanics

Below is the most comprehensive article about the basics of refrigeration- written by a 50 year veteran in the chiller service industry-John Schaub.  This article covers everything from superheat and subcooling to thermal valves and capillary tubes.  It also explains ohms law and btu's.  To see where this came from click here:  www.chillers.com/schaub.htm 

Professional Refrigeration Troubleshooter

The following manuscript was written from my own experiences in the field. I have personally been involved in over 50,000 jobs in the field for over 50 years. I'm sure you have your own stories which may be similar.  The common and not so common knowledge of this industry is compiled in one place ...for your use on any job and for any situation.  Equations, rules of thumb...and guidelines to quote jobs and gather data to learn this industry, is all compiled for you in the below book......A few examples are given, but the rest are listing in my book.  This will be a great tool for anyone in the field and as must have for you or your technicians........

Chiller Warranty Service- Click here for details

"Common Knowledge"

Table of contents: Click on a topic or scroll down

* Refrigeration:

* Defined as the removal of heat. It may also be described as the transfer of heat by a mechanical means from one object or space to another

* Heat is energy. Something that can be neither created or destroyed - cannot be seen.

* 1 Calorie = 1 gram of water raised from 0 C to 1 C (centigrade)

* B.T.U. = British Thermal Unit (Heat required to raise 1 lb of water 1 degree F

* Rapidity of heat flow depends upon temperature difference.

* Ability of substance to absorb (give up) heat = capacity

* In order of heat capacity: 1. Aluminum, 2. Iron, 3. Copper, 4. Zinc, 5. Lead

* Heat capacity may be defined as: The amount of heat required to raise the temperature of 1 lb of substance 1 degree F.

* Specific heat of iron is: .113 Almost 9 times less than water

* Specific heat of ice is: .5

* B.T.U.'s = weight X specific heat X temperature difference. ( W. x S.H. x T.D).

* Heat Transfer:

* Radiation: Travels in straight lines ( The Sun)

* Conduction: By contact of molecules

* Convection: Through 3rd medium ( Air)

* Sensible: Heat that can be felt.

* Specific: Heat per unit of mass required to produce a degree rise in temperature.

* Latent: Change in state without a change in temperature.

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Beyond this you'll have to look at the book...for those hard to find equations and rule of thumb details for sizing and data gathering....thank you...CLICK HERE FOR BOOK DETAILS

* Refrigerant Effect = ..................................

* A refrigeration system is more effective with a .......................

* The addition of heat to a substance that exits as a solid will transform ............................................

* When physical heat is added to a substance without a change in temperature, it is called latent heat.

* To change 1 lb. of water from 212 F water to 212 F steam requires................................

** Note: Water reaches it's greatest density at ...........................F. This is why it freezes on the surface of any body of water.

* Total Heat: Sum of ...................................

* Heat will flow from a warmer to a .........................................

* Pressure: Atmospheric pressure is:...........................

* As the pressure decreased the boiling point also ....................................

* At double atmosphere, ( approx. 30 lb.) water boils at .......................... F.

* R-12 refrigerant boils at ................................... F .

** Superheat is ...................... heat.

* At expansion valve approx. ........% by volume is flash gas.

* Electrical Data:

* Split Phase = ................

* All 3 and 5 Hp units using 208 or 220 Volt circuits are built to operate effectively from ....... volts to...... volts.

* No spark is allowed to occur in the rotor of a hermetic system. Therefore ..............................................

* Underwriters have checked klixons on hermetic motors under locked rotor conditions for a period of .... days, ...... hours /day

* For each motor there is a starting capacitor which will give a motor the greatest torque. All capacitors are rated in ............................

* All capacitors are rated for so many ......... second starts per hour.

* Starting capacitors create .....................................

* Klixon type protectors will open on a ........, caused either by .................or ..............................

NOTE: What substance has the greatest resistance to a current flow? ANSWER: .......................................

Always use time ............ fuses for compressors, pumps and fan motors. (- Never ....... fuses)

* It is of vital importance to have the proper size fuses installed within the supply line in the event the compressor is in some way overloaded. The damage caused by a current overload is directly proportional to the size fuses ................................................

Always replace all fuses even if ...........................

* Compressors: (Open type)

* All have aluminum covered lead gaskets. (may be used again) When removing a motor, or for some reason disconnecting the terminal leads, always make sure the compressor shaft is .................................................................

* NOTE: If the aluminum gaskets have been replaced since this report. It is recommended that refrigeration oil .......................................

* Hermetics:

* Hermetic circuits (York) were brought out in 1952. It enabled the buyer to purchase refrigeration and air conditioning equipment more inexpensively.

* No hermetic is .....................................

* 2 types of Hermetics: ....... and ........................

* Refrigeration Notes:

* Limit the height of the condenser above the evaporator if possible. Reason: ..........................................

* Never put unit in room with .......................................

* When evacuating a unit, use ..................................

* Micron: = .......................

* Wet bulb thermometer used to check ....................

* Use dry nitrogen to remove .......................................

* Also use ..................... through lines when brazing. ( prevents ......................)

* Discharge check valves were installed to prevent ..............................................

* Recycling pump down to prevent excessive .......................................................

* Liquid Controllers:

* Thermal Expansion Valve:

* A thermal expansion valve is a metering device used to...................................................

* The liquid charge in the thermal bulb is enough so that ..........................................................

* In reference to liquid filled thermal bulbs, there is no more ........................................................

* Oil:

* Oil within a refrigeration system has but one function, and that is to......................................................

* Oil is pumped from..............................

Crankcase Heaters:

1. When buying make sure to get.............................................

2. Check surface temperature of heaters. Should be between .... F and ............ F.

3. Should have a ......................... watt rating. (on larger compressors)

* When using compressors in multiple, always make oil .......................................................

* If the velocity within a system is too low you will have ....................................................................................

NOTE: The length, size and pitch of suction line plus compressor unloading can effect .......................................................

* Air Conditioning:

* Defined as the change of the ..........................................................................

It is divided into two phases: Summer and Winter.

* Summer: To decrease the .....................................................

* Winter: To increase the ..............................................................

* Air is like a sponge. It can hold a certain amount of ................................................

* When it has absorbed all the ...........................................

* When the air contains less than the maximum amount of .........................................................

* The ability of air to .......................................................

* Fans:

*Air Motion and Distribution:

* Rules of Thumb:

* Formulas for Calculating System Tonnage:

* Formula Review:

* Book References:

* R.S.E.S Service Manual

* York Institute of Refrigeration

* York Service Manual

* Commercial and Industrial Refrigeration - Written By: C. Wesley Nelson, Printed By: McGraw- Hill Book Co. Inc. New York, NY

* Encyclopedia Britannica: Refrigeration and its application.

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