Refrigeration Basics Quiz

Ten questions on heat, pressure and the units the trade runs on. Pick an answer to see whether you are right and why. Related reading: The Code: pressure and temperature.

1. Heat always flows:

   1. From cold to hot
   2. From hot to cold
   3. Upward only
   4. Only through metal

   Heat moves from a warmer substance to a colder one. An air conditioner works by making the refrigerant colder than the indoor air, then hotter than the outdoor air.

2. One British thermal unit (BTU) is the heat needed to:

   1. Raise 1 pound of water by 1°F
   2. Raise 1 gallon of water by 1°F
   3. Melt 1 pound of ice
   4. Boil 1 pound of water

   The BTU is defined as the heat that changes the temperature of one pound of water by one degree Fahrenheit.

3. One ton of cooling capacity equals:

   1. 1,000 BTU per hour
   2. 12,000 BTU per hour
   3. 24,000 BTU per hour
   4. 288,000 BTU per hour

   A ton is the heat needed to melt a ton of ice in 24 hours, 288,000 BTU, which works out to 12,000 BTU per hour.

4. Sensible heat is heat that:

   1. Changes the state of a substance without changing its temperature
   2. Changes temperature and can be measured with a thermometer
   3. Exists only in humid air
   4. Is removed by the filter

   Sensible heat shows up as a change in temperature. Latent heat changes the state of a substance, such as water vapor condensing on a coil, without changing its temperature.

5. When water vapor condenses on a cold evaporator coil, the heat removed is:

   1. Sensible heat
   2. Latent heat
   3. Radiant heat
   4. Heat of compression

   Removing moisture means condensing water vapor, which is a change of state. That is latent heat, and it is why air conditioners dehumidify.

6. At sea-level atmospheric pressure, water boils at:

   1. 100°F
   2. 180°F
   3. 212°F
   4. 250°F

   Water boils at 212°F at 14.7 psia. Lower the pressure and it boils at a lower temperature, which is why a deep vacuum removes moisture.

7. Atmospheric pressure at sea level is about:

   1. 0 psia
   2. 14.7 psia
   3. 29.92 psig
   4. 100 psia

   Standard atmospheric pressure is 14.7 pounds per square inch absolute, or 29.92 inches of mercury. A gauge reading of 0 psig is about 14.7 psia.

8. Which kind of heat transfer moves heat through a solid, such as the wall of a copper tube?

   1. Conduction
   2. Convection
   3. Radiation
   4. Evaporation

   Conduction moves heat through a material by direct contact. Convection moves it with a moving fluid such as air, and radiation moves it as infrared energy.

9. Why does an air conditioner use a refrigerant instead of plain water?

   1. Refrigerants are cheaper
   2. Refrigerants boil at low temperatures at practical pressures, so they can absorb heat from room-temperature air
   3. Water cannot carry heat
   4. Refrigerants do not need a compressor

   To absorb heat from 75°F air, the working fluid has to boil well below that. Refrigerants do this at pressures that copper tubing and compressors can handle.

10. Superheated vapor is vapor that is:

    1. At its saturation temperature
    2. Hotter than its saturation temperature at that pressure
    3. Mixed with liquid
    4. Below atmospheric pressure

    Once all the liquid has boiled, any more heat raises the vapor's temperature above saturation. That extra temperature is superheat.