Advanced Refrigeration mideterm
The design box temp for a low temp walk in freezer is between ______ & _______
0 to -20
The saturated amount of sub-cooling for air cooled equipment operating at design conditions using R22 using a TXV is
10
A ___________ evaporator is an evaporator that uses a fan to circulate air across an evaporator coil
Air- medium
A __________ evaporator is a type of air-medium evaporator hat consists of tubing only
Bare tube evaporator
Superheat cannot be determined by taking the difference between the temperatures at the inlet and outlet of the evaporator, explain.
Because of the pressure drop in the evaporator coil, you will get erratic readings
A _________________ system is piping that is used to transfer heat either to or from he earth
Geothermal ground loop
A _________ system is a water system that uses the temperature of the earth to heat or coil the water loop of a building
Geothermal ground loop system
__________ is the most common material used for backfill in geothermal systems
Grout
What is the state of the refrigerant in the liquid line entering the metering device
High pressure, high temp, sub-cooled liquid
A _________ is a device that adds moisture to air by causing water to evaporate
Humidifier
A low temp walk in freezer is operating normally at 0 degrees. The saturated evaporator temp should be ___________
-15
What are 4 ways to check for refrigeration shortage in a system without a sight glass in the liquid line
1) check for high superheat & low sub-cooling 2) check system amperage 3) system operates for longer periods of time between shutdowns 4) low suction pressure & low discharge pressure
What 3 locations can be used to obtain the suction pressure
1) external equalizer line 2) suction line 3) suction valve on compressor
List items to be checked when the superheat is abnormally high
1) lost bulb charge 2) ice,dirt or wax 3) superheat spring set too high 4) excessive pressure drop through evaporator 5) low on charge 6) liquid line restriction 7) undersized compressor 8) undersized TXV
Which check points are to be checked is superheat is found to be abnormally low
1) overcharged 2) lack of airflow 3) overfeeding TXV 4) valve seat leaking
The 5 major requirements for comfort are _____,______,______,______,_______
1) proper temperature 2) humidity 3) circulation 4) filtration 5) ventilation
List 4 steps required to determine superheat
1) take suction line temp 2) get bulb temp 3) convert bulb temp to saturated suction temp 4) difference between saturated suction temp and line temp is superheat
How should a check be made for a lost charge in the remote bulb
1) turn off system 2) disconnect remote bulb 3) place bulb in bucket of ice water 4) start up system 5) remove bulb from bucket and place in hand, if suction pressure increases rapidly bulb charge is ok
Name three special devices which can be used for sub cooling when the system has excessive vertical lift in the liquid line
1) water coils 2) Separate heat exchanger 3) Suction - liquid heat exchanger
Suction superheat at the evaporator outlet for a low temp walk in freezer should be between
1-5
The design temperature rise for a tester cooled condenser is
10 degrees
A water cooled unit using recirculating water operating a design conditions will have a saturated condensing temp of
105
A high efficiency condensing unit operating at design conditions using R22 will have a saturated condensing temp of
120
A standard efficiency condensing unit operating at design conditions using R22 will have a saturated condensing temp of
130
Standard efficiency air handling equipment operating at design conditions will have an air side temp difference across the evaporator of
16-20 (18)
A comfort cooling condensing unit operating normally using R22 should have a superheat value 18" from the compressor of _______
18 degrees
Medium-temperature applications with coil temps renting from ______________
20-40 degrees F
A medium temp walk in cooler is operating normally at 38 degrees. The saturated evaporator temp should be ___________
23 degrees F
Recent studies show that night setback of 2 degrees F reduces the overall efficiency of a geothermal heat pump system by ________%
25%
The design box temp range for a medium temp walk-in cooler is between ________ & _________
35 & 45
Design air handler air flow for comfort cooling is between _______&_______
350 & 450
Air velocity of _______ FPM in building spaces is considered ideal for comfort
40 FPM
Comfort is typically attained at normal cooling and heating temps with a relative humidity of about ______%
55%
Suction superheat at the evaporator outlet for a medium temp walk in cooler should be between
6-10
The design space temp range for comfort cooling is between ______ & _______
70 & 80
Design space temp conditions for comfort cooling is _________ with ________% RH
75, 55%
Suction superheat at the evaporator outlet for comfort cooling using a TXV should be between
8-12
Design entering water temperature for recirculating water cooled equipment is
85
Design entering air for condensers in Miami,FL is
95
What is an indication there may be wax at the valve seat
A sudden rise in suction pressure when the system shuts down
What are the indications of a TXV Valve seat leakage
After shutting system down a whistling or gurgling sound can be heard
A _________ is the quantity of heat required to raise the temps of 1 lb of water 1 degree C between 32-212
BTU
A ___________ evaporator is a heat exchanger hat uses enhanced flat plates that are brazed together to prevent leakage
Brazed plate evaporator
What is the first step in a systematic analysis of a TXV performance
Checking the systems superheat
On an externally adjusted TXV, turning the adjustment stem _______________, will increase the superheat setting
Clockwise
A ________________ is a type of geothermal ground loop system that draws ground water from a well directly into a building
Closed loop system
The types of ___________ systems include horizontal, vertical and surface water closed loop system
Closed loop systems
The term ____________ is used to describe the fact that most building zones in light commercial areas are not in the cooling mode at the same time
Diversity
Pressure drop due to the distributor ____________ reduce the capacity of the system
Does not
A ____________ evaporator is a heat exchanger in which refrigerant boils from a partial liquid/has mixture to 100% gas before the refrigerant leaves the evaporator
Dry-type evaporator
How can a suspicion of wax in a TXV be checked
Encase the valve in dry ice during disassembly . Check for wax at valve seat & pin
What type of TXV must be installed with a distributor of he centrifugal type, the venturi type, or the pressure drop type
Externally equalized TXV
Rapid cooling of the distributor by submerging in water after soldering the tubing is permissible
False
The best method for keeping the air in building spaces comfortable is to adjust the air circulation to maintain building temps
False
The major problem with dry-type evaporators is that liquid refrigerant may easily get into the compressor and cause severe damage
False
Thermostat cycling should always be used to reset heat pumps after an operational fault
False
Discomfort is the condition that occurs when a person cannot sense a difference between themselves and the surrounding air
False; they can sense the difference
A ____________ evaporator is a heat exchanger in which a float or other device ensures that the entire evaporator is full of liquid refrigerant
Flooded evaporator
What is the state of the refrigerant in the discharge line entering the condenser
High pressure, high temp, super heated vapor
A _____________ is a condition where the evaporator pressure, temperature and superheat values are higher than normal because of application conditions
Hot pull down
_________ is the amount of moisture, or water vapor in the air
Humidity
When multiple heat pumps are in heating mode, heat is extracted from the ____________
Hydronic loop
A _____________ control system is a grouping of electrical devices that control water temps and flow in a hydronic loop and geothermal loop
Hydronic loop control system
A decrease in the superheat setting of a cross-charged TXV will ___________ the MOP of the valve
Increase
When changing the superheat on an internally adjusted TXV, compressing the spring will ____________ the superheat
Increase
If too much refrigerant is fed to the evaporator he superheat will be ____________
Low
The _____________ side of a mechanical refrigeration system consists of an expansion device, evaporator, suction line and a number of accessories
Low pressure side
What is the state of the refrigerant in the suction line leaving the evaporator
Low pressure, low pressure, superheated vapor
__________ loop systems are most common in residential and light commercial applications
Open
A cooling tower can be of the __________ or _________ type
Open or closed loop
Soldering of the TXV to the distributor is to be done one the _____________ of the distributor
Outside
Name the three fundamental pressures that control the operation of the TXV
P1 - bulb pressure P2 - evaporator pressure P3 - spring pressure
Which type of distributor uses a nozzle to control the capacity of the distributor
Pressure drop type distributor
Why is pressure drop important to the operation of a gas-charged TXV
Provides a higher temperature at the diaphragm and prevents loss of control
____________________ is the amount of moisture in air compared to the amount of moisture the air would hold at the same temperature when air is saturated
Relative humidity
One part of the liquid line being colder than another indicates a _______________
Restriction
_____________ is sensible heat added to refrigerant after it has changed state from a liquid to a gas
Superheat
A __________ loop system is a type of geothermal loop system that circulates water through a loop heat exchanger in a lake or pond in order to exchange thermal energy
Surface water closed loop system
State the function of the TXV in the simplest of terms
To cause a drastic pressure drop across he valve & to supply the evaporator with enough refrigerant to satisfy all given load conditions
What is the purpose of a refrigerant distributor
To distribute a somewhat even amount of liquid refrigerant to each circuit. To increase refrigerant velocity through the evaporator causing a "scrubbing effect" returning oil to the compressor
Why should distributor tubes be of equal length
To ensure maximum distribution efficiency to each evaporator circuit
Evaporation is the process that occurs when a liquid changes to a vapor by absorbing heat
True
Heat sinks are needed for water source and geothermal heat pump systems
True
Humidity is always present in the air
True
Humidity level is controlled by humidifiers and dehumidifiers
True
Low temperature evaporators operate at a temperature below freezing
True
Make up air is air that is used to replace air that is discharged as exhaust
True
Most air conditioning systems use a centrifugal fan to circulate return room air across an evaporator
True
Pressure drop in the distributor does not reduce the capacity of the system
True
The external equalizer line must be installed beyond the point where f the greatest pressure drop
True
The major difference between water source and air source heat pumps is that water is used in the refrigerant heat exchangers of water source heat pumps
True
The short term effect of a loop performance is the change in ground temperature that occurs over many years
True
_____________ evaporators are used is water source heat pumps
Tube-in-tube
A ____________ evaporator is a type of water medium heat exchanger that consists of a small tube inside of a larger tube
Tube-in-tube evaporator
A __________ loop system is a type of geothermal ground loop system in which U—tube ground loops that circulate water inserted into holes drilled perpendicular to the surface
Vertical closed loop system
____________ evaporator is an evaporator that uses a pump to circulate water across its coil to give up heat to the refrigerant
Water medium evaporator
A ___________ control is a tstat that controls system fans, reversing valves and expansion device when the hydronic loop controls are activated
Water source heat pump
What should be done to see if the remote bulb of a gas charged TXV has lost control
Wrap the bulb with a tag saturated in warm water
A properly operating evaporator contains ______________ refrigerant
boiling saturated (80/20)
