Thursday, June 4, 2015

0 Tubing

Most tubing used in refrigeration and air conditioning is made of copper. However, some aluminum and steel tubing is being used. Instructions in this chapter will deal principally with copper tubing. All tubing to be used in air conditioning and refrigeration work is carefully processed to be sure that it is clean and dry inside and it must be kept sealed at the ends to be sure that it remains clean and dry in handling.
Most copper tubing used in air conditioning and refrigeration work is known as ACR tubing. This designation indicates that the tubing is intended for air conditioning and refrigeration and that it has been processed to give the desired characteristics. ACR tubing is charged with gaseous nitrogen to keep out air and eliminate oxidation when soldering and silver brazing fittings to the tubing. This tubing should have the ends plugged immediately after cutting a length from the piece.
Another type of copper tubing used in heating and plumbing is called nominal size tubing.
Copper tubing is available in both soft and hard types. Both hard and soft copper tubing is available in two wall thicknesses, K and L. Most ACR tubing used at present is the L thickness.

Wednesday, November 5, 2014


The refrigeration serviceman's job consists mainly of performing rather basic mechanical operations using common tools and materials. There are three basic principles which should guide the serviceman:

1, Know what needs to be done.

2, Select the proper tools and materials.

3, Keep all refrigeration mechanisms clean and dry.

This chapter is carefully planned to give the refrigeration and air conditioning serviceman the necessary basic knowledge concerning tools and materials used in this industry. In addition, directions are given concerning the selection of proper tools and materials and the correct and safe handling of tools used in the many types of refrigeration work.

Wednesday, January 22, 2014

0 Evaporator - Cooling Coil

In this text the word evaporator is used to indicate the coil or surface in which liquid refrigerant boils or evaporates and picks up heat. In some trade literature the word cooling coil is used to indicate the area in which cooling takes place. The correct technical terminology is evapo­rator coil.

0 Review, Abbreviations, Symbols

Btu    =       British thermal unit

Btuh     =         British thermal units per hour

F.         =        Degrees Fahrenheit

C.        =       Degrees Centigrade

FA        =       Degrees Fahrenheit Absolute

CA       =       Degrees Centigrade Absolute

        =         Degrees Rankin = degrees abso­lute F.

K°          =           Degrees Kelvin = degrees abso­lute C.

P          =        pounds = lbs.

psi     =       pounds per square inch = lbs. per sq. in.

i       =        inches = in.

f       =        foot or feet = ft.

si       =        square inch = sq. in.

sf       =          square feet or foot = sq. ft. r = radius of circle

r        =         radius of circle

 π         =          3.1416 (a constant use in deter­ mining the area of a circle)

pcf          =       pounds per cubic foot = lbs. per Cu. ft.

Hg         =        inches of mercury vacuum     =        specific gravity       =        specific heat

hp           =

w             =      
Watts      =         foot-pounds
ton       =        ton of refrigeration effect

lb./cft.  =       pounds per cubic foot

psig     =         pounds per square inch gauge

psi       =         pounds per square inch = lbs. per sq. in.

psia        =       pounds per square inch absolute
                  = pounds per square inch gauge
                   plus atmospheric pressure of
            14.7 lbs. or 15 lbs. per sq. in.

Po      =       Old absolute pressure

Pn      =       New absolute pressure

Vo      =      Old Volume

Vn      =      New Volume

To      =      Old absolute temperature

Tn      =     New absolute temperature

        =      Infinity

Monday, December 23, 2013

0 Degree Days

Degree days is a term used to indicate the heating or cooling needed for any certain day.
It is calculated from a temperature of 65 degrees. (It should be noted that the standard conditions temperature is 68 de­grees.) The degree day is computed by tak­ing the mean of the highest temperature and the lowest temperature for a day and sub­tracting it from 65.

Example: The lowest recorded temperature for a certain day was 28 F. (degrees)
The highest recorded temperature for the same day was 36 F. (degrees)

The mean temperature for the day was

28 + 36
2        - 31 degrees
65 -32 = 33 degree days.

Degree days may be added by weeks, months or for a season to give a comparison of ­the heating needs for different years.

Saturday, December 14, 2013

0 Temperature Humidity index

The term "temperature humidity index" (THI) is a number which aims to establish the degree of discomfort of the average individual due to the ambient temperature and the relative humidity.
It is indicated by a number. The THI is calculated by a mathematical formula as follows: THI = .4 of the sum of the wet and dry bulb temperature plus 15.
Example No. 1. On a certain day the wet bulb temperature was 70 degrees and the dry bulb temperature was 80 degrees.
The THI = .4 x (70 +80) + 15
= .4 x (150) + 15
= 60 + 15
= 75
From this it may be seen that the relative humidity as indicated by the wet bulb temperature is quite important in establishing the temperature humidity index.
Example No. 2. On a certain day the dry bulb temperature was 80 degrees and the wet bulb temperature was 75 degrees.
The TI-11 = .4 x (80 + 75) + 15
= .4 x (155) + 15
= 62 + 15
= 77
In example No. 1, the relative humidity was 61% and in example No. 2 it was 79%. The dry bulb or ambient temperature was the same on both days, however, the THI is two points higher on the second day due to the higher humidity.

Wednesday, December 11, 2013

0 Humidity Measurement (Hygrometer)

Relative humidity is measured by a hygrometer. A hygrometer consists of two identical thermometers. The bulb of one is uncovered and dry, (dry bulb). The bulb of the other thermometer is covered with a wick and it is kept moist, (wet bulb). The two thermometers will not read alike. The bulb of the wet bulb thermometer will be cooled slightly by the evaporation of the moisture from the wick surrounding the bulb. Consequently, this thermometer will read lower than the dry bulb thermometer.
The lower the humidity the more rapidly the moisture on the wet bulb will evaporate and this rapid evaporation will cool the wet bulb to a much lower temperature than the dry bulb.
If the humidity is high, approaching 100%, the difference between the dry bulb temperature and the wet bulb temperature will be very slight, one degree or less.
To determine the relative humidity, the operator records the difference between the dry bulb and wet bulb temperatures and refers to established tables which indicate the relative humidity for the air being tested. An in­strument for measuring relative humidity using a wet and a dry bulb thermometer is called a psychrometer.
Hygrometers using moisture absorbing wood, hair and other substances are being used, however the wet and dry bulb ther­mometer (psychrometer) is simple, re­liable and easy to operate.

Refrigeration and AC Copyright © 2011