Powerpoint notes pg. 1+2 Flashcards
Compressors are essentially ______ pumps
vapour
What can damage the compressor?
too much liquid
Vapour comes in as _____ temp, _____ pressure and leaves as _____ temp, _____ pressure
low, low,
high, high
How does a compressor raise temperature and pressure?
by decreasing volume and compressing
In a reciprocating compressor, the refrigerant vapour enters the cylinder when the pressure in the cylinder is _____ that of the suction line
below
In a reciprocating compressor, refrigerant vapour is discharged from the cylinder when pressure in the cylinder is ______ than the discharge line
greater
what term describes the space 1lb of gas occupies at a certain temperature and pressure?
specific volume
Increase in pressure means ________ in specific volume
decrease
______ _____rate is based on the density number in lbs in a cubic foot of gas
mass flow
________ _____ _____ is determined by the compressor type and design
volumetric flow rate
A compressor that delivers a constant volume of gas under a constant speed is called
positive displacement
How is capacity measured?
but/hr
capacity increases as mass flow rate increases resulting from a decrease in _______ _______
specific volume
capacity increases as specific volume decreases resulting from an increase in ____\_____
sst/pressure
Capacity increases as volumetric flow rate increases resulting from an increase in ____ _________
comp. displacement
Capacity increases as compression ratios decreases resulting from a decrease in _______ _______
specific volume
What are the main parts of a reciprocating compressor?
crankshaft crank throw eccentric piston connecting rods cylinder
Mass flow rate =
Volumetric flow rate/specific volume
name two types of reciprocating compressor crankshafts
crank throw and eccentric
What is the purpose of the shaft seal?
keeps refrigerant in and air out
What type of compressor is the centrifugal?
non-positive displacement compressor
Reciprocating compressors have pistons that when moving down pull air __ through the intake and when moving up push high pressure air ___ the exhaust valve
in, out
Three types of valves in a reciprocating compressor
Reed valve, ring valve, discuss valve
Methods of cooling for reciprocating compressors?
Air cooled, water cooled, refrigerant vapour cooled
How do Hermetic reciprocating compressors look?
round and covered
how do reciprocating semi-hermetic compressors look?
bolts everywhere
Hermetic cooling method of cooling?
primary method of vapour
Semi-hermetic primary method of cooling?
vapour/air/water
Open drives primary methods of cooling?
air/water/oil
Oil pressure in a refrigeration compressor is the difference between ______ pressure and ___ _____ pressure
crankcase pressure and oil pump pressure
Net oil pressure =
oil pump discharge pressure - oil pump inlet pressure/crankcase pressure
On what side of the compressor is the oil pump located?
low side
Since the oil pump is on the low side of the compressor, the crankcase is the _ starting point for the oil pump
0
Most systems operate at the design load less than ___ percent of the time due to variations in lighting, occupancy, ambient temp
20
operating below design load is to rebalance at a lower ______ temp and pressure
evaporator
lower evap pressure means lower suction pressure and this lower pressure means less _________ _______
compressor capacity
operating at lower evap temp could result in:
frosted coils, poor oil return, poor humidity control, and short cycling
Capacity control methods ; (3)
on/off, speed control, multiple compressors
Name three types of mechanical unloaders? (Capacity control method)
cylinder bypass
suction cutoff
hydraulic
what are mechanical unloaders operated by? (3)
pressure, electrically, or hydraulics
what are mechanical unloaders controlled by?
temperature or suction pressure
(Capacity control method) Refrigerant hot gas bypass to ______ line and ________ inlet
suction line
evaporator inlet
Rotary compressors capacity control?
speed control on/off
Rotary compressors are _______ shaped
cylinder
Scroll compressors have ___ % less moving parts, and are ___% more efficient
70% less
20% more
scroll compressors have one fixed ____ and one vibrating against it
scroll
three structural type of compressors
hermetic , semi hermetic , open drive
how does a scroll compressor compress the vapour?
volume decreases as vapour flows from the outside of the scroll toward the middle
positive displacement uses a decrease in _______ in order to compress
volume
diffuser slows down the refrigerant and converts _______ energy into _______ pressure
kinetic energy
static pressure
what creates the pressure differential?
speeding up and slowing down
