HVACR #32
Cooling Capacity Formula's
CC = RE x W x 60 W = Mass Flow Rate
The two main designs of ___ compressors are stationary-vane and movable-vane.
rotary
A(n) ____________________ compressor consists of a motor-driven shaft that turns a plate with a spiral of metal on it.
scroll
The piston ____________________ is a measurement of the distance a piston moves up or down in a cylinder.
stroke
Reciprocating compressors use ____________________ to direct refrigerant flow into the compressor during the suction stroke and out of the compressor during the discharge stroke.
valves
Refrigerant flow rate can be expressed either as weight (mass) or ___ of refrigerant.
volume
Most manufacturers recommend a compression ratio of no greater than ___.
10:1
CR = Pd/Ps
CR = Compression ratio Pd = Discharge absolute pressure (psia) Ps = Suction absolute pressure (psia)
Compressor Ratio Formula
CR = Pd/Ps
___ and screw compressors are used in large commercial and industrial refrigeration systems.
Centrifugal
A compression stroke is the downward movement of a piston in a cylinder. T or F
False
____________________ compressors have a motor overheating challenge, due to design.
Hermetic
____________________ flow rate is the rate of refrigerant flow in pounds per minute.
Mass
Volumetric Flow Rate
Q = W * V
Q = W * V
Q = volumetric flow rate(in cfm) W = mass flow rate V = specific volume
Refrigerant Effect Formula
RE = Hv - Hl Hv = Heat vapor Hl = Heat liquid
___ compressors are also known as positive displacement compressors because a specific amount of vapor is displaced, or moved, with each stroke of the compressor.
Reciprocating
___ compressors are most popular in air conditioning applications.
Reciprocating
___ compressors condense refrigerant vapor by moving a piston up and down inside of a cylinder.
Reciprocating
____________________ valves can flex as they open, and they close based on a difference in pressure.
Reed
____________________ compressors are used in small domestic applications such as refrigerators, freezers, and window air conditioning units.
Rotary
A fully welded hermetic compressor cannot be opened and serviced in the field.
True
An electric motor used in a hermetic compressor must have electrical connections extending through the housing in order to provide power to the motor. T or F
True
Compressors used in refrigeration systems can be classified by housing type, model, and application. T or F
True
In addition to the housing, a compressor can be distinguished by how the motor is connected to the pump.
True
Reciprocating compressors come in two-, four-, six-, eight-, or twelve-cylinder models, depending on tonnage requirements.
True
Smaller-tonnage compressors often use fully welded hermetic housings.
True
The term "housing type" refers to the type of metal shell containing the compressor such as fully welded hermetic, semihermetic, and open-drive.
True
Traditionally, scroll compressor designs have been introduced in small- and medium-size residential and commercial applications. T or F
True
Compressor Volumetric Capacity
Vc = V * N * RPM/1728in3
Vc = V * N * RPM/1728in3
Vc = volumetric capacity of compressor(in cfm) V = volume of 1 cylinder(in in3) n = number of cylinders Nc = speed of compressor(in rpm) 1728 = constant (to convert cu in. to cu ft)
____________________ flow rate is the rate of refrigerant flow expressed in cubic feet per minute.
Volumetric
Mass Flow Rate
W = CC/RE * 60 Answer written as LBS/Min
The two general categories of ____________________ are antifriction and plain.
bearings
The types of refrigeration compressors based on mechanical action are reciprocating, scroll, rotary, screw, and ____________________ compressors.
centrifugal
One major difference between compressors is the construction of the ____________________.
compressor housings
A(n) ____________________ is a reciprocating compressor component that transmits the circular turning motion of a prime mover to piston rods and then to pistons, producing an up-and-down motion.
crankshaft
The housing for hermetic and semihermetic compressors contains the compressor and the ____________________.
electric motor
A ___ is a device that reduces transmitted vibrations and noise.
muffler
In a(n) ____________________-drive system, the motor is cooled by ambient air instead or refrigerant, as in a hermetic system.
open
A ___ is a short pipe in the discharge line of a compressor that is larger in diameter than the largest suction piping to the compressor.
pulsation chamber
Several valve types are used in reciprocating compressors such as reed valves and ___ valves.
ring
