HVAC - Chapter 1 - Heat, Temperature and Pressure

1. The terms hot and cold are considered subjective because their meaning can vary from one individual to the next. True or False?

True. The perception of hot and cold is often based on an individual's prior exposure or experience.

2. In the HVACR industry, what is the primary reason why terms like hot and cold are considered too general and undefined? A) They are too emotionally charged. B) They lack the specificity needed for precise measurements and system operations. C) They are rarely experienced by technicians. D) They only apply to outdoor weather conditions.

B) They lack the specificity needed for precise measurements and system operations. The industry requires specific measurements like temperature readings for decision-making regarding system operation.

3. Which of the following instruments is mentioned as important for taking accurate temperature readings in heating, air-conditioning, and refrigeration systems? A) A barometer B) A refrigeration gauge manifold C) A thermocouple thermometer D) A Bourdon tube

C) A thermocouple thermometer. This specific instrument is depicted and mentioned for accurate temperature readings.

4. Heat and temperature are interchangeable terms and can be used to mean the same thing. True or False?

False. It is important to understand that heat and temperature are not the same thing and cannot be used interchangeably.

5. What essential information do system operating pressures, combined with various temperature readings, provide to an HVACR technician? A) The brand of the equipment. B) Details about the equipment's manufacturing date. C) Valuable information for properly evaluating and troubleshooting heating and cooling equipment. D) The estimated lifespan of the system.

C) Valuable information for properly evaluating and troubleshooting heating and cooling equipment. This combination is crucial for diagnosis and maintenance.

6. When transporting pressure vessels, what safety precaution is specifically advised? A) Transport them horizontally for stability. B) Ensure they are properly secured and transported vertically. C) Transport them uncapped for pressure release. D) Transport them only when empty.

B) Ensure they are properly secured and transported vertically. This is a direct safety guideline for pressure vessels.

7. What is temperature defined as? A) The total amount of heat contained in a substance. B) The level of heat intensity. C) The rate of molecular motion stopping. D) The absence of cold.

B) The level of heat intensity. Temperature indicates how intense the heat is, not the total quantity.

8. As more heat is transferred to a substance, what happens to the molecular motion within that substance? A) It decreases, and temperature decreases. B) It stops completely, reaching absolute zero. C) It increases, and its temperature increases. D) It remains constant.

C) It increases, and its temperature increases. Increased heat transfer leads to faster molecular motion and a rise in temperature.

9. Under standard atmospheric conditions, what is the boiling point of water in Fahrenheit? A) 100°F B) 203°F C) 212°F D) 167°F

C) 212°F. This is the common boiling point mentioned for standard conditions.

10. What is the approximate boiling point of water in Denver, Colorado, which is about 5600 feet above sea level? A) 212°F B) 203°F C) 167°F D) 32°F

B) 203°F. This is given as an example of how elevation affects boiling point.

11. Standard atmospheric conditions occur at sea level with a barometer reading of 29.92 inches of Mercury. True or False?

True. This specific reading at sea level is defined as a standard condition.

12. What is the theoretical temperature at which all molecular motion stops and no heat is present? A) 0°F B) 32°F C) -273°C D) Absolute zero

D) Absolute zero. This is the term for the theoretical lowest attainable temperature where molecular motion ceases.

13. What is the Fahrenheit equivalent of absolute zero? A) -460°F B) -273°F C) 0°F D) 32°F

A) -460°F. The Rankine scale, which starts at absolute zero, has 0°R equivalent to -460°F.

14. The International System of Units (SI) uses which temperature scale? A) Fahrenheit B) Rankine C) Celsius D) Kelvin

C) Celsius. The Celsius temperature scale is part of the International System of Units (SI) or metric system.

15. What is the formula for converting a Celsius temperature to Fahrenheit? A) °F = (°C + 32°) / 1.8 B) °F = (1.8 * °C) + 32° C) °F = (1.8 / °C) + 32° D) °F = (°C - 32°) * 1.8

B) °F = (1.8 * °C) + 32°. This formula is explicitly provided for the conversion.

16. If the Celsius temperature is 20°C, what is the equivalent Fahrenheit temperature? A) 36°F B) 52°F C) 68°F D) 86°F

C) 68°F. Using the formula (1.8 * 20) + 32 = 36 + 32 = 68.

17. What is the formula for converting a Fahrenheit temperature to Celsius? A) °C = (°F - 32°) / 1.8 B) °C = (°F + 32°) * 1.8 C) °C = (1.8 * °F) - 32° D) °C = (°F - 1.8) / 32°

A) °C = (°F - 32°) / 1.8. This formula is explicitly provided for the conversion.

18. If the Fahrenheit temperature is 50°F, what is the equivalent Celsius temperature? A) 10°C B) 18°C C) 32°C D) 41°C

A) 10°C. Using the formula (50 - 32) / 1.8 = 18 / 1.8 = 10.

19. The Fahrenheit absolute scale is known by what name? A) Kelvin scale B) Rankine scale C) Celsius scale D) Scientific scale

B) Rankine scale. This is the name given to the Fahrenheit absolute scale.

20. What is the first law of thermodynamics? A) Energy can be destroyed but not created. B) Heat flows from cold to warm substances. C) Energy can neither be created nor destroyed, but can be converted from one form to another. D) All molecular motion ceases at absolute zero.

C) Energy can neither be created nor destroyed, but can be converted from one form to another. This is the stated first law of thermodynamics.

21. What term describes the quantity of heat energy or heat content in a substance? A) Temperature B) Heat intensity C) British thermal unit (Btu) D) Molecular motion

C) British thermal unit (Btu). The Btu is used to describe the quantity of heat energy.

22. An air-conditioning system with a rated capacity of 24,000 Btu/h indicates its ability to do what? A) Add 24,000 Btu of heat energy to a structure every hour. B) Generate 24,000 Btu of electrical energy per hour. C) Remove 24,000 Btu of heat energy from a structure every hour. D) Maintain a temperature of 24,000°F.

C) Remove 24,000 Btu of heat energy from a structure every hour. The "Btu/h" rating indicates the rate of heat transfer (removal for AC).

23. How is one British thermal unit (Btu) defined? A) The amount of heat required to raise the temperature of 1 gallon of water 1°F. B) The amount of heat required to raise the temperature of 1 pound of water 1°C. C) The amount of heat required to raise the temperature of 1 pound of water 1°F. D) The amount of heat required to stop molecular motion in 1 pound of water.

C) The amount of heat required to raise the temperature of 1 pound of water 1°F. This is the precise definition of a Btu.

24. When a temperature difference exists between two substances, in which direction will heat naturally flow? A) From a cooler substance to a warmer substance. B) From a warmer substance to a cooler substance. C) In both directions simultaneously. D) Heat flow is random and unpredictable.

B) From a warmer substance to a cooler substance. This is a fundamental principle of heat transfer.

25. If you pour warm soda into a glass filled with ice, which statement accurately describes the heat transfer? A) The ice makes the soda cold. B) The soda makes the ice hot. C) Heat is created by the interaction. D) No heat transfer occurs.

B) The soda makes the ice hot. The warmer soda molecules transfer energy to the slower-moving ice molecules, causing the ice to warm (melt).

26. Temperature relates to the quantity of heat energy, similar to how the depth of water relates to the quantity of water. True or False?

False. Temperature relates to the level of heat intensity, not the quantity of heat energy, just as water depth relates to the level, not the quantity (gallons) of water.

27. Heat transfer by conduction occurs when energy travels from one molecule to another within a substance. True or False?

True. Conduction is described as the energy traveling from molecule to molecule.

28. Which of the following materials is mentioned as a very poor conductor of heat? A) Copper B) Steel C) Wood D) Glass

D) Glass. It is explicitly stated that glass is a very poor conductor of heat.

29. Why does a steel car fender feel colder than a wooden fence post on a cold morning, even if they are the same temperature? A) The fender is actually at a lower temperature. B) Steel is a better conductor of heat than wood, causing heat to leave the hand faster. C) Wood absorbs heat more quickly than steel. D) The fender radiates cold.

B) Steel is a better conductor of heat than wood, causing heat to leave the hand faster. The sensation of cold is the feeling of heat leaving the body.

30. Substances that are poor conductors of heat are generally also poor conductors of electricity. True or False?

True. This similarity is explicitly noted, with copper being a good conductor of both and glass being a poor conductor of both.

31. What type of heat transfer relies on a fluid flow, such as air or water, to move heat from one location to another? A) Conduction B) Radiation C) Convection D) Evaporation

C) Convection. Convection involves the movement of a fluid medium to transfer heat.

32. In convection, if fans, blowers, or pumps are used to move the fluid, it is classified as: A) Natural convection B) Forced convection C) Passive convection D) Radiant convection

B) Forced convection. Mechanical means like fans or pumps indicate forced convection.

33. A gas-fired furnace that uses a blower to distribute heated air to rooms is an example of what type of heat transfer? A) Natural convection B) Conduction C) Forced convection D) Radiation

C) Forced convection. The use of a blower classifies it as forced convection.

34. What phenomenon occurs in natural convection when heated air rises? A) It becomes denser and falls. B) It expands and becomes lighter than the surrounding unheated air. C) It creates a vacuum effect. D) It converts to latent heat.

B) It expands and becomes lighter than the surrounding unheated air. This density difference causes it to rise.

35. What is the only type of heat transfer that can travel through a vacuum? A) Conduction B) Convection C) Radiation D) Absorption

C) Radiation. Radiation does not require a medium and can travel through space.

36. How does heat transferred by radiation diminish with distance? A) It remains constant regardless of distance. B) It increases proportionally with distance. C) It diminishes by the inverse of the square of the distance traveled. D) It diminishes linearly with distance.

C) It diminishes by the inverse of the square of the distance traveled. This is known as the inverse-square-of-the-distance rule for radiant heat.

37. If you move your hand twice the distance away from an incandescent light bulb, what fraction of the original heat intensity will you feel? A) Half B) One-third C) One-fourth D) Double

C) One-fourth. According to the inverse-square-of-the-distance rule, doubling the distance reduces intensity by a factor of 4.

38. What type of heat is measured when it changes the temperature of a substance, which can be observed with a thermometer? A) Latent heat B) Specific heat C) Sensible heat D) Radiant heat

C) Sensible heat. Sensible heat is associated with measurable temperature changes.

39. Adding more heat to water that is already at its boiling point in an open container will cause its temperature to rise further. True or False?

False. Once water reaches its boiling point, adding more heat only makes it boil faster; it does not raise the temperature of the water.

40. What is latent heat also referred to as? A) Hidden heat B) Visible heat C) Active heat D) Surface heat

A) Hidden heat. Latent heat transfers are described as latent or hidden heat transfers.

41. What is the approximate latent heat of vaporization for water at atmospheric conditions? A) 144 Btu/lb B) 16 Btu/lb C) 970 Btu/lb D) 180 Btu/lb

C) 970 Btu/lb. This value is given for ease of calculation, rounded from 970.3 Btu/lb.

42. If 1 pound of water at 212°F is to be changed to 1 pound of steam at 212°F, how much heat energy must be added? A) 144 Btu B) 180 Btu C) 970 Btu D) 100 Btu

C) 970 Btu. This is the definition of the latent heat of vaporization for water.

43. What is the term for the amount of heat energy required to change a vapor into a liquid? A) Latent heat of vaporization B) Latent heat of fusion C) Latent heat of condensation D) Sensible heat

C) Latent heat of condensation. This is the specific term for converting vapor to liquid.

44. To change 1 pound of ice at 32°F to 1 pound of water at 32°F, how much heat energy must be added? A) 16 Btu B) 144 Btu C) 180 Btu D) 970 Btu

B) 144 Btu. This is the latent heat of fusion for water when melting ice.

45. How many Btu of heat energy are required to raise the temperature of 1 pound of ice from 0°F to 32°F? A) 0.5 Btu B) 16 Btu C) 32 Btu D) 144 Btu

B) 16 Btu. This is the sensible heat added during the first phase of the water heating example.

46. What can be concluded about the specific heat of ice based on the heat required to raise its temperature 1°F? A) It takes 1.0 Btu/lb/°F. B) It takes 0.5 Btu/lb/°F. C) It takes 2.0 Btu/lb/°F. D) It takes 16 Btu/lb/°F.

B) It takes 0.5 Btu/lb/°F. The text states it takes 0.5 Btu to raise 1 lb of ice 1°F (16 Btu for 32°F rise).

47. At which point in the water heating graph (Figure 1.14) is the substance 100% water, with 160 Btu of heat energy added? A) Point 1 B) Point 2 C) Point 3 D) Point 4

C) Point 3. At this point, the ice has melted to water (16 Btu + 144 Btu = 160 Btu total).

48. Between which two points in the water heating graph is 180 Btu of sensible heat added to raise water from 32°F to 212°F? A) Point 1 to Point 2 B) Point 2 to Point 3 C) Point 3 to Point 4 D) Point 4 to Point 5

C) Point 3 to Point 4. This phase represents the sensible heating of liquid water.

49. What is the total heat energy added to 1 pound of water to go from ice at 0°F to water at 212°F? A) 160 Btu B) 340 Btu C) 970 Btu D) 1310 Btu

B) 340 Btu. This is the sum of heat from 0°F ice to 32°F ice (16 Btu), 32°F ice to 32°F water (144 Btu), and 32°F water to 212°F water (180 Btu), totaling 16+144+180 = 340 Btu.

50. What state is water in at Point 5 on the heat/temperature graph (Figure 1.14)? A) Ice B) Liquid water C) Saturated liquid D) 100% saturated vapor

D) 100% saturated vapor. Point 5 represents the state where all the water has converted to vapor.

51. What term is used for water vapor with a temperature above the boiling point of 212°F? A) Latent vapor B) Superheated vapor C) Compressed vapor D) Saturated liquid

B) Superheated vapor. Any vapor above its boiling point is called superheated.

52. What is specific heat defined as? A) The total heat content of a substance. B) The amount of heat necessary to raise the temperature of 1 pound of a substance 1°F. C) The rate of heat transfer through a substance. D) The temperature at which a substance changes state.

B) The amount of heat necessary to raise the temperature of 1 pound of a substance 1°F. This is the definition provided for specific heat.

53. What is the specific heat of pure water? A) 0.5 Btu/lb/°F B) 1.0 Btu/lb/°F C) 0.24 Btu/lb/°F D) 0.116 Btu/lb/°F

B) 1.0 Btu/lb/°F. This value is given in the specific heat table for water.

54. If 1 Btu of heat energy is added to 1 pound of ice, what will be the resulting temperature rise? A) 1°F B) 0.5°F C) 2°F D) 0°F

C) 2°F. The text states that adding 1 Btu to 1 lb of ice results in a 2°F rise because its specific heat is 0.5 Btu/lb/°F.

55. What is the specific heat of steel? A) 0.214 Btu/lb/°F B) 0.129 Btu/lb/°F C) 0.116 Btu/lb/°F D) 0.50 Btu/lb/°F

C) 0.116 Btu/lb/°F. This value is listed for steel in the specific heat table.

56. To calculate the quantity of heat needed (Q) for a substance, which formula is provided? A) Q = W / (Specific Heat * ΔT) B) Q = W * Specific Heat * ΔT C) Q = (W + Specific Heat) * ΔT D) Q = ΔT / (W * Specific Heat)

B) Q = W * Specific Heat * ΔT. This formula is provided for determining the total heat required.

57. A manufacturing plant wants to heat 1000 pounds of steel per hour from 0°F to 70°F. How much heat (in Btu/h) must be added? A) 1000 Btu/h B) 7000 Btu/h C) 8120 Btu/h D) 11600 Btu/h

C) 8120 Btu/h. Using Q = 1000 lb/h * 0.116 Btu/lb/°F * (70°F - 0°F) = 8120 Btu/h.

58. What is pressure defined as? A) Volume per unit of area. B) Mass per unit of volume. C) Force per unit of area. D) Weight per unit of time.

C) Force per unit of area. This is the direct definition of pressure.

59. If a 100-pound weight rests on a surface that is 100 square inches, what is the pressure exerted? A) 100 psi B) 10 psi C) 1 psi D) 0.1 psi

C) 1 psi. Pressure = Force / Area = 100 lb / 100 in² = 1 psi.

60. What is the weight of 1 cubic foot of water? A) 1 pound B) 7.48 pounds C) 62.4 pounds D) 100 pounds

C) 62.4 pounds. Water weighs 62.4 pounds per cubic foot.

61. If 1 cubic foot of water (62.4 lb) is in a container with a base area of 144 square inches, what is the pressure at the bottom in psi? A) 1 psi B) 0.433 psi C) 62.4 psi D) 144 psi

B) 0.433 psi. Pressure = 62.4 lb / 144 in² = 0.433 psi.

62. What is the approximate atmospheric pressure at sea level in pounds per square inch (psi)? A) 0 psi B) 1 psi C) 14.696 psi D) 29.92 psi

C) 14.696 psi. This is given as the standard atmospheric pressure at sea level.

63. An instrument called a barometer is used to measure what? A) Gauge pressure B) Absolute pressure C) Atmospheric pressure D) Internal system pressure

C) Atmospheric pressure. The barometer is specifically mentioned for measuring atmospheric pressure.

64. At sea level, a mercury barometer at 70°F will typically show the mercury column falling to what height? A) 0 inches B) 14.696 inches C) 29.92 inches D) 36 inches

C) 29.92 inches. This is the standard reading for a mercury barometer at sea level.

65. If a barometer is located at a higher elevation, such as on a mountain, what will happen to the mercury column height? A) It will rise. B) It will remain constant. C) It will start to fall. D) It will fluctuate rapidly.

C) It will start to fall. Atmospheric pressure decreases with elevation, so the mercury column will fall.

66. A low-pressure weather system is often associated with cloudy, rainy, or snowy conditions. True or False?

True. Weather forecasters link low-pressure systems with changing, often wet, weather.

67. What is the name of the tube mechanism typically found inside mechanical pressure gauges that links to a needle to measure pressure? A) Pitot tube B) Venturi tube C) Bourdon tube D) Mercury tube

C) Bourdon tube. The Bourdon tube is described as the mechanism for measuring pressure in closed systems.

68. What type of gauge reads pressures both above and below atmospheric pressure? A) High-side gauge B) Vacuum gauge C) Compound gauge D) Digital gauge

C) Compound gauge. This gauge is specifically named as reading both above and below atmospheric pressure.

69. When common pressure gauges are opened to the atmosphere, what pressure should they read if properly calibrated? A) 14.7 psi B) 29.92 in. Hg C) 0 psi D) 100 psi

C) 0 psi. Gauges designed to read psig (pounds-per-square-inch gauge pressure) use atmospheric pressure as their reference point of zero.

70. To convert a gauge reading in psig to absolute pressure (psia), what value must be added to the gauge reading? A) 0 psi B) 14.7 psi C) 30 psi D) 29.92 psi

B) 14.7 psi. The formula psia = psig + 14.7 is provided, using a rounded atmospheric pressure value.

71. If a pressure gauge reads 50 psig, what is the equivalent absolute pressure (psia)? (Use 15 psi for atmospheric pressure for calculation ease as suggested in the text). A) 35 psia B) 50 psia C) 65 psia D) 75 psia

C) 65 psia. 50 psig + 15 psi (atmospheric) = 65 psia.

72. If a gauge pressure is below 0 psig (in a vacuum), what formula is provided to convert a vacuum reading in inches of Mercury to psia? A) psia = (30 in. Hg + vacuum reading in in. Hg) / 2 B) psia = (30 in. Hg - vacuum reading in in. Hg) / 2 C) psia = 2 * (30 in. Hg - vacuum reading in in. Hg) D) psia = vacuum reading in in. Hg / 2

B) psia = (30 in. Hg - vacuum reading in in. Hg) / 2. This is the specific formula given for converting vacuum readings to psia.

73. A pressure reading of 20 in. Hg (vacuum) is equivalent to what absolute pressure in psia? A) 5 psia B) 10 psia C) 15 psia D) 20 psia

A) 5 psia. Using the formula: (30 - 20) / 2 = 10 / 2 = 5 psia.

74. What does a vacuum cause on human skin? A) Frostbite B) Burns C) A blood blister D) No effect

C) A blood blister. This specific bodily injury is mentioned as a result of a vacuum.

75. What is the conversion factor mentioned for converting 1 psi to inches of Mercury (in. Hg)? A) 1 psi = 1 in. Hg B) 1 psi = 2.036 in. Hg C) 1 psi = 14.696 in. Hg D) 1 psi = 29.92 in. Hg

B) 1 psi = 2.036 in. Hg. This specific conversion factor is derived and stated.

76. What is the freezing point of water in Celsius? A) 32°C B) 0°C C) -17.8°C D) -273°C

B) 0°C. This is the standard freezing point of water on the Celsius scale.

77. What is the average human body temperature in Fahrenheit? A) 70°F B) 98.6°F C) 100°F D) 212°F

B) 98.6°F. This value is indicated on one of the temperature conversion figures.

78. What is the approximate temperature of liquid nitrogen in Fahrenheit? A) 0°F B) -109°F C) -321°F D) -460°F

C) -321°F. This specific temperature is shown on the Fahrenheit and Celsius equivalent temperatures chart.

79. The boiling temperature of R-410A at 0 psig is listed as approximately: A) 32°F B) -109°F C) -50°F D) 1483°C

C) -50°F (implied from -45.5C which is close to -50F) The chart shows -45.5°C which converts to approximately -50°F. The actual source lists -50°F next to -45.5°C.

80. The lowest value on absolute temperature scales is zero, representing where molecular motion starts. True or False?

False. Absolute temperature scales use zero as their lowest value, where molecular motion stops.

81. A homeowner needs a furnace for a house that loses, on average, 75,000 Btu of heat per hour. What should the furnace's rating be? A) Greater than 75,000 Btu/h. B) Exactly 75,000 Btu/h. C) Less than 75,000 Btu/h. D) Rating is irrelevant; efficiency is key.

B) Exactly 75,000 Btu/h. The text states the selected furnace should be rated at 75,000 Btu/h to keep the house warm.

82. The sensation of cold is actually the feeling we experience when heat is: A) Entering our body. B) Being created in our body. C) Leaving our body. D) Staying constant in our body.

C) Leaving our body. The text explains that the sensation of cold is the feeling of heat being transferred away from the body.

83. When a person gets a fever and experiences chills, this is partly due to an elevated body temperature that: A) Decreases the rate of heat transfer from the body. B) Stops all heat transfer from the body. C) Increases the rate of heat transfer from the body. D) Converts sensible heat to latent heat.

C) Increases the rate of heat transfer from the body. The higher body temperature drives a faster heat loss, leading to the sensation of chills.

84. What is the total quantity of heat needed to raise 10 pounds of water from 70°F to 170°F? A) 100 Btu B) 170 Btu C) 1000 Btu D) 1700 Btu

C) 1000 Btu. The example calculates this as (170-70) degrees * 10 pounds = 100 * 10 = 1000 Btu.

85. Why will a larger tank of water, heated to the same temperature as a smaller tank, cool down much slower? A) It has a higher temperature. B) It has less surface area for heat loss. C) It contains much more heat energy stored within it. D) Its specific heat is higher.

C) It contains much more heat energy stored within it. The greater quantity of heat energy leads to slower cooling.

86. What is the purpose of snowshoes when walking across snow? A) To increase the pressure pushing down. B) To lower the pressure pushing down by increasing the base area. C) To melt the snow. D) To absorb heat from the snow.

B) To lower the pressure pushing down by increasing the base area. By spreading weight over a larger area, the pressure is reduced, preventing sinking.

87. If a barometer is placed inside a closed jar and the air in the jar is removed, what will happen to the mercury column? A) It will rise to its maximum height. B) It will fall to the level of the puddle at the bottom. C) It will remain at 29.92 inches. D) It will oscillate rapidly.

B) It will fall to the level of the puddle at the bottom. Without atmospheric pressure pushing on the puddle, the mercury in the tube is no longer supported.

88. What can happen if pressure above atmospheric levels pierces the skin? A) It can cause a blood blister. B) It can result in skin and flesh damage. C) It can inflict damage by blowing air that lifts small objects like filings. D) It will cause instant freezing.

C) It can inflict damage by blowing air that lifts small objects like filings. This is given as a specific safety concern for high pressure.

89. What is the approximate specific heat of lean beef? A) 0.50 Btu/lb/°F B) 0.77 Btu/lb/°F C) 0.94 Btu/lb/°F D) 1.00 Btu/lb/°F

B) 0.77 Btu/lb/°F. This value is listed in the specific heat table.

90. The concept of "cold" is numerically expressed as a negative value in relation to no heat. True or False?

False. Cold is an expression of comparison with no numerical value, referred to as a "level of heat absence."

91. What is the total heat energy absorbed when 1 lb of water is heated from 70°F to 71°F? A) 100 Btu B) 10 Btu C) 1 Btu D) 0.5 Btu

C) 1 Btu. This is the definition of the British thermal unit.

92. What is the purpose of "standard conditions" in the context of water boiling points and pressure? A) To establish absolute temperatures. B) To provide a consistent reference for practical applications and calculations. C) To determine equipment performance ratings. D) To describe subjective experiences of hot and cold.

B) To provide a consistent reference for practical applications and calculations. Understanding standard conditions is important because they will be applied to actual practice.

93. If an absolute pressure reading is 6 psia, what is its equivalent vacuum reading in inches of Mercury? A) 12 in. Hg B) 18 in. Hg C) 24 in. Hg D) 30 in. Hg

B) 18 in. Hg. Using the formula In. Hg = 30 in. Hg - 2(psia) = 30 - 2(6) = 30 - 12 = 18 in. Hg.

94. What is the boiling point of pure water at sea level in Kelvin? A) 100 K B) 273 K C) 373 K D) 492 K

C) 373 K. The boiling point of water is 100°C, and 100°C is equivalent to 373K.

95. In the heat/temperature graph for water, at Point 1, the heat content (as read on the horizontal axis) is zero. What is the state and temperature of the water at this point? A) Ice at 32°F B) Water at 0°F C) Ice at 0°F D) Steam at 212°F

C) Ice at 0°F. Point 1 represents the starting point where ice is at 0°F and no heat has been added.

96. How much heat energy (Btu) is absorbed when 1 pound of water changes from 32°F water to 212°F water? A) 16 Btu B) 144 Btu C) 180 Btu D) 970 Btu

C) 180 Btu. This is the sensible heat added to raise the temperature of liquid water from freezing to boiling.

97. What is the approximate surface temperature of dry ice in Fahrenheit? A) 0°F B) -109°F C) -252°F D) -460°F

B) -109°F. This temperature is specified on the Fahrenheit and Celsius equivalent temperatures chart.

98. Why are performance ratings of HVACR equipment often established using absolute temperatures? A) To make them easily comparable among different manufacturers. B) Because absolute temperatures are easier to measure. C) To relate them directly to atmospheric pressure. D) To indicate the total heat content.

A) To make them easily comparable among different manufacturers. Performance ratings are established using absolute temperatures to allow for easy comparison.

99. When considering the rate of heat transfer, what is the impact of a greater temperature difference between two substances? A) It slows down the heat transfer rate. B) It has no effect on the heat transfer rate. C) It increases the heat transfer rate. D) It causes heat to flow from cold to warm.

C) It increases the heat transfer rate. The greater the temperature difference, the greater the heat transfer rate.

100. If a 20,000-gallon swimming pool needs to be heated from 70°F to 80°F in 5 hours, and the appliance is 100% efficient, what size heater is required (in Btu/h)? Assume 1 gallon of water weighs 8.33 pounds. A) 332,000 Btu/h B) 166,000 Btu/h C) 830,000 Btu/h D) 1,660,000 Btu/h

C) 332,000 Btu/h is the required heat, but the question asks for Btu/h over 5 hours, so 332,000 / 5 = 166,000 Btu/h. Correction: the question asks for the heater size in Btu/h, which is a rate. Total heat needed: Q = (20,000 gal * 8.33 lb/gal) * 1 Btu/lb/°F * (80-70)°F = 166,600 lb * 10 °F = 1,666,000 Btu. This heat needs to be transferred in 5 hours. So, rate = 1,666,000 Btu / 5 hours = 333,200 Btu/h. The closest answer is 332,000 Btu/h. Let's re-verify the provided example in the source (Q23) which is directly applicable. Q23 asks: "What size heater will be required to heat the water in a swimming pool from 70°F to 80°F in 5 hours if the appliance is 100% efficient and the pool holds 20,000 gallons of water?" Answer D is 1,660,000 Btu/h. However, in the options for my question, 332,000 Btu/h is given. Let's re-calculate to match the source's provided Q23 answer. 20,000 gallons * 8.33 lb/gal = 166,600 lbs of water. Temperature change = 80°F - 70°F = 10°F. Total Btu needed = 166,600 lbs * 1 Btu/lb/°F * 10°F = 1,666,000 Btu. This total heat is needed over 5 hours. Heater size (rate) = 1,666,000 Btu / 5 hours = 333,200 Btu/h. Option C is 332,000 Btu/h. This is the correct rate. The source's Q23 answer (1,660,000 Btu/h) is the total Btu needed, not the Btu/h rate. This means Q23 in the source has a problematic answer option. I should use the correct calculated rate. So, the answer is 332,000 Btu/h.1. The terms hot and cold are considered subjective because their meaning can vary from one individual to the next. True or False?