Questions and Answers
What is heat which causes a change in temperature of a substance called?
Sensible heat
What is the heat added to a substance without a rise in temperature called?
Latent heat
What is heat added to the refrigerant in a vapor state after the evaporation process called?
Superheat
How does a scroll compressor move refrigerant?
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What is the movement of heat by way of fluid called?
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What is the movement of heat through a solid object called?
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What is the standard unit for measuring the quantity of heat in a substance?
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When does a refrigerant give up heat?
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Why must refrigerant in the suction line be slightly warmer than the saturation temperature?
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Why is it desirable for refrigerant in the suction line to be slightly superheated?
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What should the state of the refrigerant in the suction line be?
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What is the state of refrigerant entering the condenser?
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What does the evaporator do?
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Flammability is a thermodynamic property of refrigerant.
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What are the sequential steps in the vapor-compression process?
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If a 30 lb container of R-410A refrigerant has been stored overnight at 70 degrees F, the pressure in the cylinder should be approximately?
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In which unit are fan airflow pressures usually measured?
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What does zero Psia (pounds per square inch absolute) represent?
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What does zero Psig (pounds per square inch gauge) mean?
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What is the temperature at which moisture will start to condense from the air called?
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What does a compound pressure gauge measure?
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On which type of compressor is a mechanical shaft seal necessary?
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What is liquid slugging?
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What effect does the clearance space have in a reciprocating compressor?
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Centrifugal compressors are the most efficient type of air conditioning compressor.
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What is the correct order for the functions of a condenser?
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If refrigerant R-134a vapor enters the condenser at 124 psig and 100 degrees Fahrenheit, what will be its pressure when it leaves as a liquid, sub-cooled 20 degrees Fahrenheit?
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What are the three basic types of condensers?
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If 10 lbs of refrigerant passing through a water-cooled condenser loses 20 BTU of heat per pound, what will be the temperature of the water leaving the condenser if it enters at 80 degrees?
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What type of heat is removed from the refrigerant by the condenser?
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What is an energy recovery ventilator?
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Crankcase regulating valves can be used as a low ambient temperature control.
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When testing the efficiency of an air-cooled condenser, how much higher should the refrigerant condensing temperature be compared to the entering air temperature?
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What is the first function that a condenser must perform?
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Study Notes
Basic Concepts of Heat
- Sensible heat causes a change in temperature of a substance.
- Latent heat is added without a temperature rise; an example is the phase change of liquid refrigerant to gas.
- Superheat refers to the heat added to refrigerant vapor after the evaporation process.
Refrigeration Systems Components
- Scroll compressors move refrigerant using involute spirals.
- The evaporator transfers heat from the refrigerated space to the refrigerant.
Heat Transfer Methods
- Convection involves the movement of heat by a fluid, such as air.
- Radiation is the movement of heat through solid objects.
Refrigerant Properties
- The British Thermal Unit (BTU) measures the quantity of heat in a substance.
- Refrigerant condenses when it gives up heat; it is ideal for suction line refrigerant to be slightly warmer than the saturation temperature to prevent compressor slugging.
Refrigerant States
- Refrigerant in the suction line should be low pressure and low temperature vapor.
- High pressure and highly superheated vapor enter the condenser.
Vapor-Compression Cycle
- The cycle involves four steps: Compression, Condensation, Expansion, Vaporization.
- An effective condenser performs three key functions: De-Superheats, Condenses, and Sub-cools.
Gauge and Pressure Measurements
- Fan airflow pressures are measured in inches of water column.
- Zero PSIA denotes a pressure that cannot be further reduced, while Zero PSIG is equivalent to atmospheric pressure.
Thermal Properties
- Dew Point Temperature is where moisture begins to condense from the air.
- A compound pressure gauge measures both pressure and vacuum.
Mechanical Components and Issues
- Mechanical shaft seals are essential for open drive compressors.
- Liquid slugging occurs when liquid refrigerant enters the compressor clearance space, affecting compressor capacity.
Efficiency of Compressors
- Centrifugal compressors are recognized as more efficient compared to other types.
Condensation Processes
- When R-134a vapor enters the condenser at specific pressures and temperatures, it leaves as a sub-cooled liquid.
- Water-cooled condensers can cool 10 lbs of refrigerant by losing 20 BTUs of heat per pound.
Energy Conservation Technologies
- Energy recovery ventilators act as air-to-air heat exchangers to recover heat.
Operational Efficiency
- An air-cooled condenser's refrigerant condensing temperature should not exceed 30 degrees above the entering air temperature.
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Description
Test your knowledge on HVAC terminology with these flashcards covering key concepts like sensible heat, latent heat, and superheat. Perfect for students and professionals alike who want to reinforce their understanding of heating and cooling systems.
