Hvac day 44 study guide
a typical superheat___
8 to 12
Condensing units located outside that are required to operate year-round must have __.
D. head pressure control
Large or small compressors on parallel compressor racks, which are usually dedicated to the coldest cases, are called:
both A and C Satellite compressors and booster compressors
infrared electric eye senses the______ by infrared technology.
buildup of ice
two types of defrosts used with low temp fixtures are
electric and hot gas defrost
the formation of sweat around the doors on display cases is eliminated by
electric heaters under the surfaces
a txv controls refrigerant flow to the evap based on
evap suction line superheat
Cutting surfaces on an auger for a flake ice machine are called
flights
periodic way of getting rid of mineral buildup?
flush cycle
If the spring pressure of a water regulating valve is increased/decreased, the system head pressure will also ____.
increase/decrease
If a critically charged refrigeration system is over charged, which of the following is a likely result?
increased operating pressure
When the load on the evaporator increases, the TXV ______.
increases the flow of refrigerant
Condensing temperatures in an air-cooled condensing unit can be reduced by ____.
increasing the cfm through the condenser increasing the condensing surface area decreasing the temperature of the air entering the condenser(all of the above)
In a 2-ton capillary tube system, the unit does not develop full capacity. Head pressure is low, and suction pressure is high. What is the problem?
inefficient compressor
The discus valve design is more efficient than a flapper valve design because ____.
it allows a compressor design with less clearance volume
the advantage of using one large compressor for several refrigerated cases is
larger motors are more efficient
the pressure limited txv valve
limits the refrigerant flow rate to the compressor capacity
Three types of bin controls are
liquid filled thermostat bulb infrared eye sound waves
On an R-11 or R-123 system, the refrigerant removal process normally starts with the removal of _____.
liquid refrigerant
If a thermostatic expansion valve's thermal bulb came loose from the suction line at the outlet of the evaporator, which of the following could result?
liquid refrigerant would flow back to the compressor,bulb pressure would increase and the txv would open, the superheat in the evap would decrease
Why is it that many products that require medium - temperature refrigeration will not freeze at 30 degree F?
water freezes at 32 degrees F any other addtives will lower the freezing put
The shell and tube condenser is cleaned
with a brush after removing the end caps
can individual evaporators be defrosted one at a time?
yes
the primary function of an expansion device is to
.to produce a reduction in the pressure on the liquid refrigerant.. Regulate the flow of refrigerant into the evaporator.. Lower the boiling point of the refrigerant far enough below the temperature of the load to get the needed heat transfer. (all of the above)
For each 12,000 Btu/h capacity, a wastewater-cooled condensing unit uses approzimately __ GPM.
1.5
natural draft towers and spray ponds are designed to produce a difference in water and air temps at ___F
10
centrifugal chillers range in size from____ tons
10 to 10000
When sizing a cooling tower, the tower is sized to handle the cooling load of the conditioned area plus about ____% for heat of compression.Select one:a. 15b. 25c. 35d. 0
25
For each 12,000 Btu/h capacity, a water-cooled condensing unit and cooling tower combination will circulate approzimately __ GPM through the condenser.
3.0
Pure water freezes at
32*F
A typical chilled water system is designed to operate with a leaving water temperature off the chiller coil of___.
45F
The process of ice making usualy occurs in which temperature range?
5 - 20 degrees F
Most water-cooling towers can cool the water that supplies the condenser to a temperature within __ degrees F of the wet-bulb temperature of the ambient air.
7
forced draft cooling tower are designed to reduce the entering water temperature to within___F of the air wet bulb temperature
7
the temperature of the water coming into the cooling tower is ___ and leaving is___
95F in, 85 out
When one large compressor is used, what desirable feature should it have?
A three-way heat reclaim valve. pg 553
When the compressors are located in the equipment room, the piping is routed:
A) in floor chases or in plastic pipes under the floor. pg 564
In a wastewater cooled system, the difference between the condensing temperature of the refrigerant and the leaving water temperature is approximately __.
A. 10 degrees F
In a water-cooled condensing unit/cooling tower combination, the temperature difference of the water through the condenser will be approximately __.
A. 10 degrees F
In a high-temperture refrigeration unit, the boiling point of the refrigerant in the coil is normally __ lower than the cabinet temperature.
A. 8-10 degrees F
In a wastewater systems, the water entering the condenser is 85 degree F and the water leaving the condenser is 105 degree F. Which of the following statements is a logical explanation for the above conditions?
A. reduced water flow through the condenser
When multiple lowside cabinets are used with a single condensing unit in EPR valve must be used on _________
All but the lowest temperature evaporator
The refrigerated cabinet temperature of a high-temperature refrigeration unit ranges from __.
C. 45 - 60 degress F
Harvesting in an ice cube maker using a water spray is done using __________
Compressor discharge gas
When hot gas defrost is used on low temperature system's with remote condensing units, the hot gas line is connected between the __________
Compressor discharge line to the distributor on the outlet of the TX valve
The two methods for rejecting heat from refrigerated cases are ______ and ______.
Condensing unit built inside the box or a remote condensing unit. pg 550
With the entering air to the condenser above 70 degree F, the temperature difference between the outdoor air and the condensing temperature on standard will be __.
D. 25 to 30
Medium-temperature refrigerated cabinet temperatures range from __.
D. 30 - 45 degrees F
When the compressor in a system using capillary tubes is sweating, it is a sign of __.
D. refrigerant overcharge, dirty evaporator, and evaporator blower motor problem.
In a wastewater systems, the water entering the condenser is 85 degree F and the water leaving the condenser is 90 degree F. Which of the following statements is a logical explanation for the above conditions?
D. water regulating valve stuck in the wide-open position, excess water flow through the condenser
If large amounts of ice are forming on a low temperature evaporator, what could possibly be the proplem
Defective evaporator fan motor, defective hot gas defrost solenoid valve
Formation of ice cubes in a ice maker producing slab ice is done using _______
Electric grid
The formation of sweat. The doors on display cases is eliminated by __________
Electric heaters under the surface
which of the following can be used to maintain the head pressure of a system with an air-cooled condenser?
Fan cycling, condenser flooding valve(HPR), damper or louvers(all of the above)
Hot gas is commonly used to free ice cubes after they have been formed. The process is called _________
Harvest
Fan coil units used in medium temperature cases are usually defrosted using _______
Hot gas heat
In a heat reclaim system, the vapor line carrying hot refrigerant vapor to the heating coil is connected to the ____________
Hot gas line
A condensing unit with four motor compressor assemblies manifoled together must provide the suction pressure for the _________
Lowest temperature evaporator
Explain how the oil separator, oil reservoir, pressure differential valve, and oil level regulators work.
Oil separator - located in the common discharge line, it separates oil from the refrigerant and pumps it to an oil reservoir.Oil reservoir - can be combined with the oil separator, it holds oil that was separated by the oil separator.Pressure differential valve - It is located in the oil reservoir and ensures that the oil reservoir is pressurized each time an oil regulator is opened.Oil level regulators - it senses the oil level in the compressor's crankcase and adds oil if necessary. It senses the oil level by means of a float.
The two broad categories of display cases are _____ and ____.
Open display and closed display pg 549
For a low-temperature refrigeration system with an evaporator saturation temperature of -40 degrees F, why might R-502 be used instead of R-12?
R-502 will keep the pressure positve. R--12 will will operate in a vacuum
How are conditions maintained in open display cases when there are high shelves?
Refrigerated air is heavy and settles to the bottom of the case. Air patterns are formed to created air curtains that keeps the cooler air from leaving the case and controlled. pg 550
If a system has a __ for a metering device, the __ will try to maintain evaporator superheat even with an excessive overcharge.
TXV, TXV
An advantage in using one condensing unit with several evaporators is _________
The condensing unit is larger and more efficient
If an air-cooled condenser is located on a 95 degree F roof and the condenser saturation temperature is 150 degree F, which of the following is a possible scenario?
The system is overcharged and the condenser is clogged.
What are mullion heaters?
They are heaters made of resistance-type wire that runs just under the surface of the cabinet. They keep moisture from forming on the sides of the refrigeration cabinet. pg 568
the copper connecting the evap, metering device to the condensing unit is called
a line set
Water levels can be sensed and controlled by what
a probe located in the water reservoir
the condenser in a refrigeration system
a. desuperheats the vapor from the compressor b. condenses the vapor from the compressor c. subcools the liquid refrigerant before it leaves the condenser d. all of the above ANSWER : D
Overheated oil may turn to carbon and create ____ in the system.
acid
the first step in starting a chilled water system is to
activate the chilled water circulating system
when multiple evaps with multi circuits are used with a single condensing unit, an EPR valve must be used on
all but the lowest temp evaporator
mineral deposits in the water portion of a water-cooled condenser act as
an insulator
how does a rack system work?
applies two or more compressors to a common suction header, a common discharge header and a common receiver
if the blower on a cooling tower breaks down on a hot day, the___
approach temperature will increase and water supplied to the condensers will be warmer
the reduction gears are usually made of fibrous material designed to strip or break if the___ starts to bind up
auger
Sanitizing gets rid of
bacteria
the panels on a walk in cooler are held together by
can action locks
secondary fluids will not what through the system?
change
When a system with a water-cooled condenser cycles off, the water regulating valve should
close since the head pressure is lower
the purpose of an externally equalized thermostatic expansion valve is to
compensate for excessive evaporator pressure drop
The heat that the cooling tower must reject from the water in the chiller is the cooling load of the conditioned area plus the heat of ____.
compression
When hot gas defrost is used on a low temperature system with remote condensing units, the hot gas line is connected between the
compressor discharge line to the distributor on the outlet of the tx valve
Connecting rods connect the piston to the
crankshaft
liquid entering the compression chamber of a reciprocating compressor can lead to
damaged valves and piston rings
if large amounts of ice are forming on a low temp evaporator what could possibly be the problem
defective evap fan motor or defective hot gas defrost solenoid valve
on a direct drive compressor the _____ is used to insure proper alignment in the flexible coupling?
dial indicator
a capillary tube controls the refrigerant flow into the evap by its size in
diameter and length
The approach of a cooling tower is the __.
difference in temperature between the entering air wet-bulb temperature and the sump water temperature
In a 2-ton TX valve system, the unit does not develop full capacity. Head pressure is high, suction pressure is slightly above normal, and subcooling is superheat is normal, and subcooling is above normal. What is the problem?
dirty condenser
the pulley on the compressor is called the
driven pulley
sediment from the troth of an ice machine during the flush cycle we use a
dump
when multiple evaps are manifolded together to a common suction line, what must be done?
each evap must have its own expansion valve
difference between even and uneven parallel compressor systems?
even have compressors of equal sizes and are made for refrigeration loads that are relatively constant or have known increases and decreases in capacity ex 0, 10, 20, 30 for 3 compressors uneven or odd are systems with widely varying loads. ex 0, 5, 10, 15, 20, 25, 30 for 3 compressors
T/F: A thermostatic expansion valve's capacity will drop if the pressure drop across the valve increases.
false
T/F: Bubbles in the sight glass always indicate refrigerant shortage.
false
T/F: High compression ratios will lead to lower compressor discharge temperatures.
false
balanced port txv are used to
feed refrigerant at a normal rate with low condenser entering air temps
is used to connect the the compressor shaft and motor shaft together
flexible coupling
what is the most prone to failure than any other part in the ice flaker
gear motor
the cross liquid charge bulb at the txv contains fluid that
has different characteristics from the system fluid
A refrigeration system is operating with a vapor charged thermostatic expansion valve. The thermal bulb is sensing a suction line temperature that is higher than the temperature that allows liquid to be present in the bulb. Any additional increases in the vapor load will _____.
have no effect on the position of the needle (pin) in the seat
An air-cooled R-12 refrigeration system is operating normally with a suction pressure of 25 psig and a head pressure of 136 psig. Which of the follwing represents a possible set of operating pressures if the condenser fan motor burns out?
high side 180 psig, low side 35 psig
The three temperature ranges for refrigeration systems are ______, _______ and _______.
high, medium, and low
what is the special valve used in a refrigerated air drier
hot gas bypass valve
Most ice cube machines harvest by using
hot gas defrost
in a heat reclaim system the vapor line carrying hot refrigerant vapor to the heating coil is connect to the
hot gas line
the advantage of multiple compressors or parallel compressor rack operating several refrigerated cases is
if one compressor is defective the others can carry the load until repairs are made
a chiller field control circuit___
is often called a interlock system is a circuit that starts the control procedure before the compressor starts ensures that the appropriate fans and pumps are started in the proper sequence(all the above)
the shaft seal on an open drive compressor
keeps the refrigerant vapor in and atmosphere out of the compressor
a scroll compressor does not have___?
large clearance volume
three disadvantages are
large leaks will result in the failure of multiple remote units, one motor burnout can result in the formation of acid in the entire system, cleanup
Exactly matching the refrigeration load with the capacity of refrigeration compressors is referred to as:
load matching
five advantages of a rack system
load matching, diversification, flexibility, higher efficiencies, lower operating costs
Will the gauge readings be high or low with a system using a capillary tube that has a low refrigerant charge?
low
Low suction pressures, iced coils, short- cycling, and inefficient cooling can also result from_____
low head pressures
A low refrigerant charge will cause a __ suction pressure, which will __ the compression ratio.
low suction and increase compression
the purpose of a capillary tube is to
lower the boiling point of the refrigerant, regulate the refrigerant flow into the evap, and lower the pressure of the liquid refrigerant
a condensing unit with four motor compressor assemblies manifolded together must provide the suction pressure for the
lowest temp evaporator
The water quality required to maintain the water level in the sump is called __.
make-up
Water-cooled chillers must have water treatment to
minimize mineral and algae deposits
When using cleaning and sanitizing can you mix them?
no
a extrusion head can be added to the auger of a flake ice machine to make____ or ____ ice
nugget, cubed
What type of defrost is normally used for medium-temperature applications?
off cycle defrost
In a 2-ton TX valve system, the unit does not develop full capacity. Head pressure is high, suction pressure is slightly above normal, superheat is normal, and subcooling is above normal. What is the problem?
overcharged
In a 2-ton capillary tube system, the unit does not develop full capacity. Head pressure is high, suction pressure is high, and there is no superheat. What is the problem?
overcharged
another phrase for a rack
parallel compressor system
it is recommended that at least twice a year the ____ should be removed from the water reservoir and cleaned
probe
in a water cooled condenser a regulating valve is used to control the
refrigerant condensing temperature
If the power element of a TX valve loses its charge, the___.
refrigerant flow to the coil will stop
blowdown system for a cooling tower
relieves the concentration of sediment in the sump
To start the harvest, it can be done by___
reverse acting and bridge sensor
cleaning an ice machine with an approved ice machine cleaner gets rid of
scale and minerals
A bolted together motor-compressor assembly is sometimes referred to as___
semi-hermetic
Two types of shaft seals used for centrifugal pumps are
stuffing box and mechanical types
the______ valves in a reciprocating compressor open and close depending on the difference in pressure across them
suction and discharge
If the thermal bulb assembly develops a leak, what will occur?
the bulb pressure will reduce and the valve will close
when using hot gas defrost what must be on?
the compressor
an advantage in using one condensing unit with several evaps is
the condensing unit is larger and more efficient
a display case is considered to be self-contained when:
the evap and condensing units are located within the case
where are eprs installed?
the outlets of evaps
T/F: Becuase of the low refrigerant flow rate through the compressor and the system being undercharged, the 100% satured vapor point in the condenser will be very low in the condenser, causing low condenser subcooling.
true
T/F: Dirty condenser coils are often the cause for inefficient condensers.
true
T/F: If the evaporator and compressor are starved of refrigerant, the condenser will also be starved.
true
T/F: Low density vapors entering the compressor will mean low refrigerant flow through the compressor.
true
T/F: Since many new replacement refrigerants are being used throughout the industry, a techician should rely on system temperatures to ease the troubleshooting process.
true
T/F: The best place for a liquid line sight glass is at the inlet of the expansion device.
true
In a 2-ton capillary tube system, the unit does not develop full capacity. Head pressure is low and suction pressure is low. What is the problem?
under charged
The clearance volume of a compressor cylinder is the ____.
volume of the space between the bottom of the valve plate and the top of the piston at top dead center
A water regulating valve helps to maintain a system's head pressure by modulating the flow of ____ through the condenser.
water
