# Local 290 HVAC Term 6

 Define Refrigeration: Refrigeration is cooling by the removal of heat Heat is a form of __ energy As the temperature of any substance increases, the molecules which make it up vibrate: Faster One pound of refrigerant will take up the most space: As a gas because it has the lowest density Name the two most commonly used scales to measure temperature: Fahrenheit and Centigrade A cooling coil has 40 degree refrigerant inside its tubes while 80 degree air passes over it. Because heat flows "downhill", it will move from: The coil surface into the air The three ways heat is transferred are called ___, ___, ___ Conduction, convection, and radiation Which one of these is a good insulator and, therefore a poor conductor? Polystyrene T or F: A sensible heat change always causes a change in temperature? True T or F: A latent heat change always causes a change in molecular activity? True T or F: A thermometer can be used to measure latent heat change? False T or F: There is a change of state in a substance whenever latent heat is added to it or removed from it? True Total Heat= Sensible Heat + Latent Heat Temperature cannot measure total heat because: It cannot measure latent heat, which is part of total heat BTU stands for ___ ___ ___ British Thermal Unit A BTU is the amount of heat required to raise 1 pound of ___ ___F. water 1 degree Define Specific Heat: It is the amount of heat required to raise 1 pound of a substance 1 degree Fahrenheit. The total heat (in BTU) which a pound of any substance contains is called its ___ Enthalpy In terms of refrigeration language, the water we drink is: Subcooled The amount of heat transfer and rate of heat transfer are different because: Amount deals with "how much" while rate deals with "how fast" 1 ton of refrigeration capacity or cooling load is: 12,000 Btuh 3 1/2 tons= ___Btuh 42,000 48,000 Btuh=___tons 4 Define Pressure: Its force per unit of area Which of the following expresses pressure? Pounds per square inch Pressure in an operating refrigeration system is most often measured in ___ psig Pressure is measure in ___ when evacuating a system before it is charged with Freon. In., Hg., Vac. What will the gauge pressure reading be for:  14.7 psia ___ 0 psig What will the gauge pressure reading be for:  Standard atmospheric pressure ___ 14.7 psig What will the gauge pressure reading be for:  54.7 PSIA ___ 40 psig As pressure rises saturation temperature ___ rises A body has a negative charge when it: Contains an excess or electrons The force acting between two bodies dis-similarly charged: is referred to as an electrostatic field In electrical circuits, the time of doing work is expressed in: Watts The device used in circuits to prevent damage from overloads is called a: Fuse If the resistance is held constant, what happens to power if the current is doubled? Power is multiplied by 4 Soft iron is most suitable for use in a: temporary magnet Around a magnet, the external lines of force: leave the magnet from the north pole and enter the south pole When a conductor moves across a magnetic field: A voltage is induced in the conductor When voltage is applied to a conductor, free electrons: Are impelled along the conductor Which of the following is considered to be the best conductor? Silver Electrically operated devices in gas burning equipment use the electricity producing principle of: Dissimilar metals heated If a circuit is constructed so as to allow the electrons to follow only one possible path, the circuit is called a(n): Series circuit In a series circuit, the total current is: the same through all parts of the circuit T or F: Primary load devices are located in the line voltage circuit? True Most common control circuits operate from ___ volts AC 24 High voltages, such as 120v or 240v household supplies, are always dangerous. Under certain conditions, however, even low ___ can be lethal voltages What items listed below are considered load devices? Compressor, indoor fan motor, outdoor fan motor T or F: The indoor fan motor is located in the low voltage circuit? False Thermal overload devices respond to the heat generated by ___ flow. excessive current T or F: The low pressure and high pressure switch are normally in series with the compressor contactor? True OFM is abbreviated for ___ Outdoor fan motor IFM is abbreviated for ___ Indoor fan motor On a loss of refrigerant the low pressure switch closes or opens to de-energize the compressor circuit? Opens As the warm air from the room passes over the evaporator what happens to the refrigerant temperature? It rises As superheat at the evaporator outlet increases, what does the metering device do in response? It opens T or F: Heat is transferred from the indoor air to the outdoor air by the refrigerant? True T or F: Heat flows from cold to warm? False T or F: Sensible heat can measured with a thermometer? True Most of the heat transfer in a mechanical refrigeration system takes place because the ___ changes state. refrigerant On an air cooled condenser the fan motor fails, which switch will protect the compressor? High Pressure Switch T or F: The solenoid uses magnetism to open the valve? True T or F: The solenoid coil is considered an electrical load in the circuit? True In a circuit with two solenoids the correct wiring method would be to wire in a series or parallel circuit? Parallel The ___ valve regulates and controls the supply ___ to the burners. gas, gas T or F: A metering device at the evaporator maintains sub-cooling of the refrigerant? False T or F: Head pressure is read at the evaporator? False T or F: Capillary tubes are used as metering devices True T or F: Thermostatic expansion valves automatically adjust flow of refrigerant according to the superheat sensed? True AuthorTWilson88 ID292865 Card SetLocal 290 HVAC Term 6 DescriptionInfo that will be on the test Updated2015-01-13T05:19:13Z Show Answers