Download HVAC Study Guide: Questions and Answers and more Exams Refrigeration and Air Conditioning in PDF only on Docsity!
501 HVAC study guide
Questions and Answers | New
One | Grade A+
50 degrees centigrade equals Ans: 122 degrees F. (1.8 x C + 32F). An evaporator, generator, absorber, is a Ans: component of an absorption water chiller. A British Thermal Unit is Ans: the amount of heat required to change, one pound of water one degree Fahrenheit. A centrifugal compressor is Ans: basically a large capacity unit that handles large volumes of refrigerant. A common type of refrigerant control device used on centrifugal systems is? Ans: a high side float.
A compressor raises the pressure and lowers the temperature of the refrigerant. true or false? Ans: false. A condition that would be the least likely cause of head pressure problems is? Ans: a cooling tower sized larger than necessary. A control can be which of the following? Ans: all of the above, electrical, mechanical, electrical and mechanical. A cooling system for drinking fountains which uses an air-cooled condenser, a shortage of refrigerant would be indicated by? Ans: a cold liquid line. A current magnetic relay opens and closes its contacts based on the blank. Ans: current in the run winding. A desirable physical property of a refrigerant is? Ans: high stability.
A helicopter is lifting an 800-pound unit at a rate of two hundred feet per minute. How much horsepower of work energy is the helicopter using in the process? Ans: 4.848 hp. A horizontal direction to the left on the psychometric chart represents? Ans: Cooling the air. A liquid material exerts a pressure or force blank Ans: outward and downward. A material used as an active element of a relative-humidity meter or humidistat is? Ans: Horsehair. A micron gauge is used to measure blank. Ans: absolute pressures below 1 mm Hg. A motor's speed is determined by blank. Ans: number of motor poles.
A normally operating water-cooled condenser is operating with a 10° differential between water in and water out. If the amount of 85°F water going through the condenser is reduced, which of the following is a possible temperature of the water leaving the condenser? Ans: 105°F. A psychrometric chart is a graphic representation of what Ans: thermodynamic properties. A pump out unit is used to? Ans: ordinarily transfer refrigerant from the machine to an external source. A refrigerant gives up heat when it does what? Ans: Condenses. A rotary compressor is a type of? Ans: positive displacement compressor. A sensing bulb for a thermo expansion valve should not be installed, Ans: on a fitting, in a trap or a pocket, or on the bottom of the line.
Ans: first check the evaporator coil, condensate pan, tubing for signs of oil leaks, the electrical wiring. A thermometer indicates what? Ans: Sensible heat. A thermometer is a measuring instrument which indicates what? Ans: sensible heat. A ton of refrigeration is? Ans: 12,000 BTUs per pound. A ton of refrigeration is equal to blank. Ans: 288,000 Btu/ 24 - hr. A typical evaporator operating temperature in an air-conditioning system is blank Ans: 40°F. A typical superheat for an evaporator operating under normal conditions would be blank. Ans: 8 to 12°F.
A vapor material exerts a pressure or force blank. Ans: in all directions. Abnormally high suction pressures are found? Ans: in cases where we have defective compressor valves. Abnormally low suction pressure is caused by? Ans: dirty or restricted chiller tubes. Absolute pressures below atmospheric are measured in what? Ans: Inches of mercury. Absorption refrigeration is a process of refrigeration which the necessary energy for its operation is derived directly from heat. true or false? Ans: true. Air flow thru a duct has its highest velocity near the? Ans: center of the duct.
An example of an axial flow type of fan is a? Ans: propeller fan. An example of a power consuming device would be a blank while an example of a non- power consuming device would be a blank? Ans: light bulb, single-pole single-throw switch. An NC system which application of heat in the secondary process being applied in either preconditioned air or recirculated air in a room is a? Ans: terminal reheat system. An oil safety switch is operated by? Ans: the difference between oil pressure and crankcase pressure. As the refrigerant temperature increases? Ans: the rate of heat transfer decreases. At a constant pressure, the volume of a gas varies as to the absolute temperature and at a constant volume the pressure of the gas varies directly with the absolute temperature. This is known as blank. Ans: Charles' Law.
At the evaporator a temperature of '10 degrees Fahrenheit, which of the following refrigerants would have the lowest, coil pressure Ans: R-12. At what location or locations in a refrigeration system does the saturation pressure correspond to the saturation temperature? Ans: evaporator and condenser By design, which of the following air ducts will allow 250 cfm to flow with a velocity of 500 ft/min? Ans: 9" × 8". Can the performance of a fan at various speeds and air densities be predicted? Ans: Yes, thru fan curves or calculations. Calculations involving heat loads of people take into consideration heat due to? Ans: latent heat and sensible heat. Centrifugal chillers range in size from blank tons?
Compression ratio is the ratio? Ans: of absolute suction pressure and absolute discharge pressure. Compressor failure is often blamed on flooding. Which of the following are causes of flooding? Ans: Oversized expansion valve. Condensing units draw the most amperage when the suction pressure is? Ans: 30 psi. Conductance is a term used to denote heat flow thru? Ans: non-homogeneous materials. Conduction heat? Ans: is transferred by contact. Conductivity is defined as the amount of heat in BTUs flowing thru a piece of? Ans: homogeneous, material, one inch thick, in one hour per square foot, per degree Fahrenheit.
Convection heat is transferred by Ans: movement of fluid, water or air. Copper is the most common used tubing in Ans: commercial refrigeration. Dewpoint refers to the temperature in which air reaches its? Ans: saturation point. Dirty filters are detected by? Ans: checking the air pressure drop across the filter from the suction side to the discharge side. Double duct systems are affectively a constant volume system. True. or false. Ans: true. Drier desiccant cannot be chemically reactivated due to? Ans: oil or acid in the desiccant. Dry bulb temperature is room temperature taken by?
Enthalpy refers to? Ans: heat content of a refrigerant. (Both latent and sensible). Enthalpy refers to the? Ans: Measure of heat content of a substance. Equipment capacity for conditioning systems usually is determined by? Ans: peak load requirements. Evaporator pressure regulators (EPR) regulate the evaporator pressure. True or false? Ans: true. Excessive combustion noise is most likely caused by? Ans: improper burner adjustment. Fifty degrees C. is equal to how many degrees of F.? Ans: 122. For a substance to be used as a refrigerant, which of the following qualities would be considered to be the most important?
Ans: Low boiling point. For comfort cooling, a range of blank % relative humidity would be desirable. Ans: 30 - 50%. Friction losses of pressure in ducted systems occur? Ans: in elbows, along duct walls, with increase in air speed. Gas is normally charged in a refrigeration system at? Ans: the suction side of the compressor. Generally speaking, to calculate the required CFM for cooling applications, multiply the total cooling loads. Ans: times 400CFM per ton. Heat exchangers in a refrigeration system? Ans: sub cools the refrigerant. Heat flows by means of what? Ans: conduction, convection, radiation.
Heat will continue to flow between two bodies until they have the same?. Ans: Temperature Heating and cooling load calculations take the? Ans: sensible heat and the latent heat into consideration. High temperature refrigeration is that produced by blank. Ans: an air-conditioning system. How many Btu's are required to change five pounds of ice at 20°F to steam at 220°F? Ans: 6,520 Btu/h. How many Btus are required to change one pound of ice at 20°F to steam at 220°F? Ans: 1,304 Btu/h. How many BTUs of heat must be removed from one hundred pounds of water to cool it from 60 degrees F. to 40 degrees F.? Ans: 2000 BTUs.
How many btu's of heat must be removed from one thousand pounds of water to cool it from 80 degrees Fahrenheit to 40 degrees Fahrenheit?. Ans: 40, How many degrees superheater is necessary to assure that the refrigerant is fully vaporized at the suction line near the compressor? Ans: 20 degrees Fahrenheit. How many poles are there in a 120 volt, sixty· Hz. motor that turns 1200 RPM? Ans: 6. How many watts of electrical power are equal to 1 horsepower? Ans: 746. Humidity may be removed by lowering the? Ans: Dew point. If a heat pump runs but there is insufficient cooling and slightly low suction pressure the most probable cause is? Ans: a partially iced coil.
