Industrial Refrigeration Flashcards
What are the 2 most common types of compressors used in industrial refrigeration (ILM)
semi-hermetic open drive Reciprocating and open drive Screw
Describe the operation of a high side float
as the refrigerant level rises in the condensor, the valve to the evaporator opens more to allow more refrigerant to flow.
Describe the operation of a low side float
as the refrigerant level rises in the evaporator, it closes the inlet more to maintain a constant level of refrigerant to feed to the low pressure reciever
What is the purpose of an Oil Pot
To recover oil that has been carried past the oil separator and logged in the system. Oil and Ammonia are not miscible so it does not get carried back to the compressor like typical refrigeration systems.
Describe how refrigerant flows in a Gravity flooded evaporator
evaporator is flooded and the natural convection and proper liquid pressure circulate the refrigerant
Describe how refrigerant flows in a Liquid Overfeed Evaporator
Refrigerant is pumped either by a mechanical pump or through the use of differential pressure
What is a critical factor in determining the capacity of an evaporative condenser used in industrial refrigeration
Wet Bulb Temperature (key word is evaporative meaning it relies on ambient conditions)
What is the advantage of a flooded evaporator
it provides a large area for heat transfer to come in contact with the saturated liquid
What is the purpose of the oil in a screw compressor
it cools, seals and provides rotor silencing
what type of oil separator is used with a screw compressor
coalescing separator
Why are solenoid valves seldomely used in industrial refrigeration
the valve is unable to generate enough force in the coil to open
what is anhydrous ammonia
ammonia that is relatively free of water and other impurities
why are ammonia TXV’s specially designed
to slow the rate of wire drawing
What are wet return lines
lines between the evaporator outlet and the low pressure reciever that carry saturated vapour and liquid
Class T machine rooms must provide fire resistive construction for ___ hour(s)
1 hour
Dead man valve is a _____ valve
spring closing
ammonia leaks can be detected by using___
Litmus paper (turns pink during presence)
Ammonia offers ___ btu/lb latent heat of evaporation
575 btu/lb
ammonia levels of ___ppm is permissable
25 ppm for an 8 hour work day and 40 hour work week
ammonia levels of ___ ppm must be limited to no more than 15 minutes
35 ppm
ammonia levels of ___ ppm are considered IDLH (immediately Dangerous to Life and Health)
300 PPM
ammonia exposure of ___ to ____ ppm is fatal in a few breaths
1700 - 2000 ppm
Ammonia is harmful to the Ozone (true/false)
false, zero global warming potential and no ozone depletion
Ammonia is classified as a __ refrigerant (A or B, 1-3)
B2 refrigerant
What type of ice is produced in industrial refrigeration
Flaked and blocked ice used for the fishery industry, but NOT BAGGED ICE
What is the “return reverse” method used when piping lines on an ice rink
the concept that the first rung fed is the last to return refrigerant to promote even distribution
how many alarm stages are required in a class T room and at what levels do they activate
3 stages, 25 ppm, 50 ppm and 200 ppm
monitoring company is notified at 2nd and 3rd stage
a class T room exhaust fan and MUA will activate when ammonia levels reach ___ ppm or more
25 ppm
Class t room doors must open ______
outwards
Ammonia sensor in a Class T room must be located at ____ feet above finished floor
10 ft. must also be 10-30 cm from the cieling
Where must the exhaust fan pull air from in a Class T room
Cieling, not the wall
MUA supplies air to _____ part of a Class T room and is a(n) ____ fired MUA
supplies air at floor level and is indirect fired (but I wouldn’t nap in there
Monitors for Class T rooms are located where?
outside the room, if it is inactive, treat room as hazardous location
Eye wash stations for Class T rooms are typically located where
outside the room or in a flood room
Plaquard for a Class T room will be located where and with what information listed on it
outside the room on the door, it will include the service company, type of refrigerant and charge, type of oil used including the ammount
What switch is required outside the door of the Class T room and what does it control?
a switch to shut down all rotating equipment except MUA and EF. It must be
- 7 feet above finished floor
- in a red painted box with a breakable panel
- include an emergency stop with blow off valve to release refrigerant to atmosphere
What is the main purpose of a Class T room
to isolate the refrigerant charge from occupied areas
To neutralize ammonia, ___ water for every ___ of ammonia is required
1 gal of water (8.33 lbs) for every 1 lb of ammonia
refrigerant monitor must be tested every ____
every month
what is the minimum ammount ventilation required in a Class T room
0.5 cfm per sq ft and 15 air changes per hour
why do we not superheat Ammonia?
it gets too light and fluffy, lines of constant entropy go way out
formula for overfeed rate
overfeed rate = Liquid Mass out / Vapour mass out
eg. 100 lbs supplied to the evap, 75 lbs return as liquid, 25 lbs return as vapour
OVERFEED RATE = 3:1
formula for recirculation rate
recirculation rate = Liquid mass in/ vapour mass out
eg. 100 lbs supplied to the evap, 75 lbs return as liquid, 25 lbs return as vapour
CIRCULATION RATE = 4:1
what is another name for the low stage compressor
Booster compressor
Name 3 types of overfeed systems
Mechanical pump
Dump system
Double Pumper system
compression ratio
Absolute discharge/absolute suction
Interstage pressure formula
Sq root (absolute discharge x Absolute Suction)
What is the common temperature for the brine used on ice rinks
10-12 F
average approach on ice rink system
2 - 4 F degrees
Ice rink temperature settings for pro/amateur/and figure skating
21/24/26 F
how much slope is required on lines
.5” per 10 foot run
hydrostatically trapped liquid ammonia will increase ____ psi for each Degree F increase in temperature
100 - 150 psi
when labeling ammonia lines, identify the colors \_\_\_\_\_ liquid \_\_\_\_\_ vapor \_\_\_\_\_ low press (70 psi) \_\_\_\_\_ high press(70.1 psi or higher)
orange - liquid
blue - vapor
green - low pressure
red - high pressure
3 way valves fail to ____ path
90 degree bend route, not straight through
Black iron pipe
1.5” and smaller is ____
2” - 6” is _____
1.5” is SCHED 80
2” - 6” is SCHED 40
anything above 1.25” must be connected via____
Welding
1.25” may be connected via threads however what consideration must be made
threaded connections have weakened wall at the joints
supports must be attached to what and with what minimum size threaded rod
must be supported to building structure supports and with 3/8” rod minimum
number of supports is determined with what 2 factors in mind
within 2 ft of the walls and every 10 ft
eg. for a 100 ft run there are 2 by the ends, and 96 ft = 9 supports. 11 supports total for 100 ft run, not 10
how does one know when an oil pot should be drained?
when the oil pot is cold but not frosted
