On a single acting reciprocating compressor, what is the function of a dual control device?
It allows constant speed control and automatic start and stops
If a system were using an automatic expansion valve, what would the constant pressure be maintained at?
The evaporator
What is the main advantage of a cascade refrigeration system?
Capable of reaching very low temperature
Choose the statement below, which would prove false about lithium bromide used in absorption system.
It is non-corrosive
What is a sling psychrometer device used to measure?
Relative humidity
A system using an evaporative condenser operates most efficiently under what conditions?
When the wet-bulb temperature of air is low
The discharge gas from the compressor is what, in a wet-compression refrigeration system?
Saturated
If a refrigeration system were over charged with refrigerant, what conditions would occur?
Decrease in capacity and increase in head pressure
If a cooling tower circulated 4,300 GPM of water, what is the cooling capacity in tons?
1,433 tons
What condition would cause a system to not respond to an expansion valve adjustment?
Oil in the evaporator
In an absorption system, the generator receives what medium?
Strong liquor
Which would have the lease effect on the capacity of a water-cooled condenser?
The ambient air temperature
What is the volume occupied by a refrigerant under specified conditions of pressure and temperature?
Specific volume
What should a cooling tower water pH be maintained at?
8
The absolute Celsius scale is referred to by which temperature scale?
Kelvin
Which devices control the high side float?
Condenser and receiver
In Fahrenheit, what is the equivalent of -15 degrees Celsius?
5 degrees F
If you had a flooded evaporator, which type of metering device would you use?
Low side float
Choose the formula used to determine the number of cycles of concentration for a cooling tower?
Cycles = Tower water chlorides / Makeup water chlorides
What determines the low side pressure in a refrigeration system?
The amount if load on the system
Which seal is not used on a refrigeration system?
Mechanical
Which water chemistry test is used to determine cooling tower cycles of concentration?
Chlorides
Why is a rheostat used on a synchronous motor?
To vary the power factor to the load conditions
What would happen if you had a sudden drop in the temperature in the cooling tower of a lithium bromide absorption system?
Crystallization in the system
What is the function of a heat exchanger in an absorption system?
Allows the weak liquor to heat the strong liquor
Define the term "refrigerant reclaiming
Selling reprocessed refrigerant as "reclaimed refrigerant" ; Reprocessing the refrigerant into a new product that can be reused ; Chemically analyzing and distilling the refrigerant ; All of the above
Which phrase best describes the term "free air"?
Air at atmospheric conditions
How is the setting on a thermostatic expansion valve rated?
Degrees of superheat
Which statement describes the operation of a single acting compressor?
The refrigeration gas is compressed on only one side of the piston
Which of the following would cause a noisy compressor?
Lack of oil ; Dry damaged seal ; Loose drive coupling ; All of the above
When the evaporator load increases, what happens to the suction pressure of the system?
Flow remains constant with a corresponding pressure increase
Thermostatic expansion valves are rated in what units of measurement?
Tons of refrigeration
If a cooling tower has a pH of 7.8 it is considered
Slightly alkaline
Where would you find flash gas in an efficiently operating system?
The evaporator
The capacity of an evaporative condenser is determined by
The amount of heat the entering air can absorb ; The amount of air flowing over the coil ; The area of the refrigerant coil surface ; All of the above
The ratio between the actual pressures of the vapor to its saturation pressure in the atmosphere is known as
Relative Humidity
A cooling tower is circulating 2,850 GPM of water: What is the cooling capacity in tons?
950 tons
What conditions can cause high discharge pressure in a system?
Refrigerant overcharge ; An undersized condenser ; Insufficient cooling water to the condenser ; All of the above
What would frost on the suction line of a system using a high side float indicate?
Overcharged system
In an absorption system, what would cause the strength of the strong liquor to decrease?
Decrease in the load on the evaporator
What type of heat exchange occurs at the exterior sides of a cooling tower?
Convection
Which of the following statements is true regarding the compression ratio of a reciprocating compressor?
Ratio varies according to the conditions under which it operates
If the high side float were to fill with liquid and sink, what would be the result?
The evaporator would starve for refrigerant
In a refrigeration system, what part is considered the low side?
Between the compressor and evaporator
What function does the evaporator perform in a refrigeration system?
None of the above
Why is a horizontal shell and tube condenser more efficient than a vertical shell and tube condenser?
Has more than one pass
On a two-stage system, where should the booster compressor be located?
Between the evaporator and intercooler
What is the maximum amount of refrigerant allowed in a 120 lb. cylinder?
96 lbs.
One ton of refrigeration equals
The removal of 12,000 btu/hr
Which statement best defines the operation of a synchronous motor?
Starts on AC, operates on AC/DC
Which statement best defines the operation of the valves of a refrigeration compressor?
They are opened and closed by pressure difference
Where is oiling required on a centrifugal refrigeration system?
At the shaft end bearings
If water is leaving an efficiently operating induced draft cooling tower, what is the temperature of the water?
Between the wet bulb and the dry bulb temperature of the air
What determines the low side pressure in a refrigeration system?
The evaporator flow rate
What is the reason for sub-cooling the refrigerant?
To increase the refrigeration effect
Which statements below would not cause a noisy compressor?
Flash gas in the expansion valve
Which type of motor is typically used on condenser and evaporator blowers?
Squirrel cage motor
If a reciprocating compressor were run with the suction valve closed and the discharge valve open, what would occur?
Non-condensables would enter the compressor
What is the position of the suction and discharge valves when the piston is at top dead center?
Both closed
What is ohms law?
E = I x R
What is the maximum amount of refrigerant you can put in a 250 lb. cylinder?
200 lbs.
If you have a 90% efficient 25 hp motor, and you pay 11 cents per kWh, what would it cost to run the motor for 1 hour?
HP x .746 / Efficiency x cost/Kw = 2.28$
What is the liquid head of a brine with a specific gravity of 1.2 and a pumped pressure of 75 psi?
PSI x 2.31 / SG = 144.375
A cooling tower is circulating 35,819 lb. of water per minute, what is the cooling capacity in tons?
1,433 tons
What motor circuit is de-energized after the compressor comes up to speed?
Start winding
State Boyle's Law as a formula.
P1 x V1 = P2 x V2
How do unloaders unload the pistons on a reciprocating compressor?
They bypass discharge gas back into the compressor suction.
The volume of a refrigerant under a specific pressure and temperature is called?
Specific volume
In an automatic expansion valve system, constant pressure is maintained at the:
Evaporator inlet
A 788,00 btu/hr unit produces how man tons of cooling?
65.66 tons
How do the valves on a compressor operate?
By pressure
Convert 5 degrees F to degrees C.
-15
What does the capacity of an evaporative condenser depend on?
Entering air wet-bulb temperature
What is an advantage of a cascade refrigeration system?
Capable of very low temperatures
The evaporator absorbs heat from the air or brine because the liquid refrigerant entering the evaporator
Has a lower temperature than the air or brine
Baffles in a gravity coil evaporator are used
For condensation ; For proper air flow ; To prevent moisture carry over ; All of the above
An engine indicator diagram for a reciprocating compressor would most likely show the
Action of the compressor valve
What is the purpose of a stuffing box seal?
It prevents refrigerant leaks from the crankcase
Packing in the stuffing box is
Made of metal with oil running through
As capacity decreases in a reciprocating compressor
Suction pressure decreases
What would happen if you overcharge a system with refrigerant?
Decreased efficiency ; High head pressure ; Decreased capacity ; All of the above
Heat that increases the temperature of a refrigerant without a change of state is
Sensible heat
A condenser water pH of 10 is considered to be
Highly alkaline
What does an evaporator do?
Absorbs heat into a system
The static setting of a thermostatic expansion valve is rated in
Degrees of superheat
What would cause oil to foam in a compressor crankcase?
A sudden drop in pressure
A superheated refrigerant, such as R-12, enters a reciprocating compressor. After being compressed it leaves as a
Superheated gas
The main reason for insulating the suction piping of a compression-type refrigeration system is to
Prevent loss of refrigerating capacity
Which refrigerant usually has a condenser pressure of 1,050 PSI?
CO2
In a carbon dioxide system, the oil system is usually
A splash system for vertical compressors ; A high pressure system for horizontal compressors ; Both (A) and (B)
What is the main refrigeration principle used in the steam jet system?
If you reduce the pressure of water, the boiling point will be lowered
In an aqua ammonia system
Refrigerant is the ammonia, absorbent is the water
The oil trap on a refrigeration system is located
On the discharge line, as far from the compressor as possible
How many BTU's are removed from 2,000 lbs. of ice at 32 F to give you ice at 28 F?
32-28=4 ; 4x.5=2 ; 2x2,000=4,000 BTU's
Convert 5 degrees Fahrenheit to degrees Rankine?
5+460=465 degrees rankine
What type of pump is used to circulate brine through the system?
Centrifugal pump
Which compressor gives the least side thrust when operating?
A vertical reciprocating compressor
During the re-expansion portion of the compression cycle, what is the position of the suction and discharge valves?
Both valves are closed
What happens to the volumetric efficiency of a compressor when the horsepower decreases?
The volumetric efficiency increases
Why is a horizontal shell and tube heat exchanger more efficient that a vertical shell and tube exchanger?
It has more than one pass
With an increased load to the evaporator coil, a TXV will
Allow more refrigerant to enter the coil
What are the three terminals on a single phase compressor?
Primary, secondary, ground
When do high pressure safety devices close their contacts?
When the pressure is below the high pressure cut out setting
What is the range of the resistance in a compressor motor winding?
Between 0-10 ohms
What does the internal overload of a compressor sense?
Excessive amperage in the compressor motor
What compressor uses a damper to control capacity?
Centrifugal compressors
With all things being equal, what system will remove the most heat?
An R-717 system (Ammonia)
When is liquid injection into the suction line necessary to cool a compressor?
When the compressor is running unloaded
How should properly installed refrigeration lines be pitched?
They should be pitched towards the direction of flow
Where would you find the greatest possible pressure drop?
The condenser
What type of control is used for loading and unloading a compressor automatically?
A pressure switch
When installing refrigeration lines, when is it recommended to install oil traps?
When suction lines rise 8 inches or more
When evaporator pressure goes down
The load goes down
What is the license required in an ammonia plant rated between 24-65 tons of toxic refrigerant?
Blue Seal
What substance is the absorbent in an ammonia absorption system?
Water
What is the formula for total force?
Diameter x Diameter x .7854 x Pressure
What is the total force on a 4 inch piston with a cylinder pressure of 100 psig?
1,256.64 lbs. of total force
What is the latent heat of vaporization?
970.3 btu/lb
What is the latent heat of fusion?
144 btu/lb
Why would you pre-cool air in an ice-making plant?
To prevent airline freeze up
The counter-flow principle is an important feature of what type of system?
Double-piped water cooled condenser
In the absence of automatic unloaders, the motor starting load can be minimized by using
A back pressure valve
Change 80 degrees celsius to degrees fahrenheit
80x1.8=144 ; 144+32=176f
Can copper and brass be used on ammonia refrigeration systems?
No, ammonia is extremely corrosive to brass and copper
If the specific gravity of calcium chloride brine is increased from 1.29 to 1.30, what happens to the freezing point?
It rises
Where are oil separators located in an ammonia system?
On the discharge line close to the compressor
What does a low side float prevent?
Over filling of the flooded evaporator
What is the capacity of a 100 ton refrigeration unit?
20,000 btu/min
What is the purpose of a water jacket on a system?
To prevent thermal shock and to remove heat
What is the definition of compression ratio?
Ratio of the absolute discharge pressure to the absolute suction pressure
Refrigerant recycling is defined as
Cleaning refrigerant of dirt and contaminates
How many tons of refrigerant is required to prevent 2,000 lbs of ice from melting in 24 hours?
1 ton
Before starting new refrigeration equipment, what must you do?
Have it inspected
The static setting of a thermostatic expansion valve is
Degrees of superheat
600,000 btu/hr equals ____ tons of refrigeration?
50 tons
What would indicated that your expansion valve is leaking?
Suction line would begin to frost up
On a liquid level site glass, what precaution is used for safety from leakage?
Ball checks
What formula is used to determine tower water chlorides?
Tower water chlorides / Make up water chlorides
The relationship between the actual performance of a compressor and its calculated performance is
Volumetric efficiency
Where would you locate a sub-cooler or pre-cooler?
Before the expansion valve in the liquid line
What does it mean when a refrigerant is anhydrous?
Absence of water
What value is the latent heat of fusion for water?
144 btu/lb
Where is the booster compressor of a 2-stage refrigeration system located?
Between the evaporator and the intercooler
Name three methods of heat transfer.
Conduction, convection, radiation
What will cause high head pressure?
A dirty condenser ; Air and non-condensables in the system
What 1 values are needed to calculate the amount of refrigeration required?
The btu's to be removed and the time required to compress the refrigerant
Give the specific heat for the following: Water, Steam, Ice
1, .5, 1
A refrigerant cylinder has a 125 lb. capacity. How many lbs. can be stored in it?
100 lbs.
In a shell and tube heat exchanger, where is the refrigerant located?
Located in shell
What is the latent heat of ammonia at 5 degrees fahrenheit?
565 btu/lb.
What is the pressure at 5 degrees fahrenheit of ammonia?
19.6 psig
What are the 4 steps of a mechanical refrigeration system?
Evaporation, Expansion, Compression, and Condensation
Define british thermal unit.
The amount of heat necessary to raise 1 lb. of water 1 degree of fahrenheit
What refrigerant sublimates at 14.7 psia?
CO2
What main substance should be kept out of refrigeration oil?
Moisture
How often should you have your relief valves re-certified on an ammonia system?
Every 5 years
When is the best time to purge an ammonia plant with a 250 lb. drum?
During operation
Which temperature scale refers to the absolute celsius scale?
Kelvin temperature scale
Where is the scale trap located?
Between the compressor and evaporator
On a 10 ft. refrigeration line, what is the correct pitch?
1/4 inch
The specific gravity of brine is measured
To determine how much calcium chloride it contains
How often do you inspect safety valves?
Annually
Name the 4 parts of a refrigeration system
Compressor, Condenser, Metering Device, Evaporator
What is the total force exerted on a 2 inch piston with a cylinder pressure of 130 psi?
408 lb.s of total force
What is the formula for total dynamic head?
TDH=Hs+Hp+Hf+Hv
If power is removed from a solenoid valve and it opens, it is said to be what type of valve?
Normally open solenoid valve
An NH3 compressor low side compound gauge is usually calibrated to read from
30" vacuum to 250 psig
On an ammonia compression system, compression ratio can be described as
The ratio of absolute discharge pressure to absolute suction pressure
What is the absorbent in an ammonia refrigeration system?
Water (R-718)
Which of the following would no cause high head pressure?
Refrigerant undercharge
If a compound gauge reads 15" Hg, what is its equivalent in psig?
7.5
Calculate the rpm's of a four pole motor rated at 150 HP, 120 volts, and 60 cycles.
1,800 rpm
On a synchronous motor, as the DC amperage increases, the AC amperage
Decreases
On a reciprocating compressor, the unloaders unload the compressor by
Keeping the suction valves open
Which of the following is a false statement concerning the ASHRAE standard 34 Classification of refrigerants?
None of the Above
What is the lowest recommended temperature for use with calcium chloride brine?
-41.8 degrees Fahrenheit
Which type of compressor can be used with a steam turbine as a prime mover?
Centrifugal
What schedule of piping is required for the liquid refrigerant lines in an NH3 system?
Schedule 80
Which is a false statement about the operation of a shell and tube condenser?
Water normally circulates through the shell
In an ammonia absorption system, the analyzer can be described as an
Open type heat exchanger
In a refrigeration system, where would you find the king valve on the receiver?
Between the receiver and the expansion valve
What increase above normal condenser temperature could indicate scale formation?
3 degrees Fahrenheit
A refrigeration plant that has NH3 as a refrigerant requires licensed engineers if the capacity is
Over 24 tons
What is the principle difference between a lithium bromide/H2O absorption system and an NH3/H2O absorption system?
The pressure range of the cycle
One possible problem caused by air leaking into a refrigeration system is
Overheat the condenser
What is the term used for the type of heat that increases the temperature of a substance without causing a change of state?
Sensible heat
How many btu's must be removed to lower the temperature of 2,000 lbs. of ice from 32 degrees Fahrenheit to 29 degrees Fahrenheit?
3,000 btu's
What is refrigerant R-718?
Water
What is the max fill for industrial refrigeration condensers and receivers?
90% of total volume
As suction pressure increases, horsepower decreases. What happens to the compressor capacity?
Capacity increases
Which of the following conditions would not cause high discharge pressure in the system?
Undercharge
Water being pumped at 85 psig has a liquid head of what?
196.35 feet of total head
What is the maximum amount of refrigerant in pounds allowed in a 3,000 lb. receiver?
3,000 lbs. x 90% = 2,700 lbs
Convert 373 degrees Rankine to Kelvin.
373x1.8=207.22 Kelvin
What is the metric unit of heat measurement and its definition?
1 calorie is the amount of heat necessary to raise 1 gram of water 1 degree celsius
What is the English unit of heat measurement and its definition?
1 btu is the amount of heat necessary to raise 1 lb. of water 1 degree Fahrenheit
What part of an absorption system is considered an axillary?
Analyzer
When a compressor is turned on what motor winding is energized?
Start
On this semi-hermetic compressor, where is the oil pump located?
Right side (compressor end shaft)
What is the pressure at 86 degrees Fahrenheit of ammonia?
154.5 psig
How many pounds of refrigerant can you put in a 3,000 lb. receiver?
2,700 lbs.
Ammonia and R-123 are both considered ______ refrigerants?
Group B
The flash point of refrigeration oil is
The temperature at which oil vapor will flash when exposed to flames
The fire point of a refrigerant oil is the temperature at which
Oil will continue to burn
Viscosity is
Coefficient of internal friction
Floc point is the temperature at which
Wax is first noticed separating from the oil
Pour point is the
Lowest temperature that oil will flow
The perfect gas law expressed as a formula is
PV=MRT
What type of compressor uses a slide valve for capacity control?
Screw compressor
What type of device is used for capacity control on a screw compressor?
Slide valve
The temperature at which vapor at 100% humidity begins to condense back into a liquid is called
Dew point
The lowest temperature that can be obtained by evaporating water into the atmosphere is known as the
Wet bulb temperature
The relationship of the actual humidity of moisture vapor in the atmosphere to the maximum that air could hold at that temperature and pressure is called
Relative humidity
The relationship between a compressors theoretical and actual pumping capacity is called
Volumetric efficiency
The counter flow principal is an important feature of what type of condenser?
Double piped condenser
The lowest recommended temperature for use with calcium chloride brine is
-41.8 Fahrenheit
In an ammonia absorption system, the flow of ammonia goes from
Evaporator to absorber
In an ammonia absorption system, the analyzer can best be described as an
Open type heat exchanger
Where would you find the king valve in an industrial refrigeration unit?
Between the receiver and the expansion valve
If the load on the evaporator increases
Suction pressure increases, HP decreases
Assume an ammonia compression system is replaced with an ammonia dry compression system in a particular plant. If the capacity remains the same, the dry compression system will
Reduce the danger of damage to the compressor
The ideal cooling tower temperature of a lithium bromide absorption system should be 85 degrees Fahrenheit. What would be the result if the cooling tower temperature dropped to 78 degrees Fahrenheit?
Crystallization in the system
An ammonia plant rated at 10 tons produces how much ice?
Slightly less than 10 tons of ice
What cools the motor in a semi hermetic reciprocating compressor?
The refrigerant suction gas
In a single acting compressor
Refrigerant gas is compressed on only one side of the piston
The temperature at which moisture in the air begins to condense is known as
Dew point
When a reciprocating compressor discharge line is cool, it could indicate
The evaporator coils have frozen
The rate at which the viscosity of the oil changes as its temperature changes is called
Viscosity index
As the specific gravity of calcium chloride increases
The density increases
Condenser water having a pH of 10 would be considered
Alkaline
Which of the following would be a false statement concerning rotary pumps?
They need priming before start up
Which of the following does not increase compressor surging?
Decreasing the compression ratio speed
Heat transfer that occurs primarily by conduction is used for what type of process?
Indirect contact
The stuffing box bore on a pump is 4" and the pump shaft is 3 1/4". What size packing should be used?
3/8
On a single phase compressor, what are the three contacts?
Primary, secondary, ground
What do you call the sum of the friction head, velocity head, and the pressure head?
Dynamic head
Which compressor does not require lubrication?
Rotary lobe
When discussing a reciprocating compressor what does the term swept volume refer to?
The volume that is swept as the piston or pistons are moved from top dead center to bottom dead center
What is the purpose of wear rings on a centrifugal pump?
Increase efficiency
Which of the following is a false statement regarding the ASHRAE standard classification of refrigerants?
R-717 is not a group B2 refrigerant
What effect would oil in the evaporator have on a refrigeration system?
A decrease in suction pressure
Which of the following conditions would cause a low head pressure condition?
Refrigerant undercharge
This determines the low side pressure in a refrigeration system.
The amount of liquid in a system
In a system using a high side float, the following would control its operation.
The condenser and receiver
Using a high side float metering device, what would frost on the suction line mean?
System undercharge
Which of the following compressors does not require inlet or discharge valves?
Axial flow
Which of the following compressors does not require lubrication?
Axial flow
In a refrigeration system what function does the evaporator perform?
None of the above
The strong liquor in an absorption system is developed in the
Generator
What is the maximum amount of refrigerant that can be stored in a 125 lb. cylinder?
100 lbs.
As the condensing temperature of a centrifugal system decreases, the power required by the compressor
Decreases
On a centrifugal compressor, where is oiling required?
None of the above
What is the flow cycle in an absorption refrigeration system?
From the condenser to the evaporator to the absorber to the generator
The quantity of energy absorbed by a unit mass of refrigerant in the evaporator is called
Refrigeration effect
In an absorption refrigeration system, where does the vapor turn into a liquid?
Generator
The weak liquor in an absorption system develops in the
Absorber
The amount of water vapor that can be absorbed by the atmosphere under it's current conditions is called
Relative humidity
If the specific gravity of calcium brine is increased from 1.29 to 1.30, the freezing point would
Rise
Why is specific gravity of brine measured?
To determine how much calcium chloride it contains
Moisture content is measured in what unit?
% Humidity
In the absence of automatic unloaders, the motor starting load can be minimized by using
A back pressure valve