HVAC 1-4
A latent heat change always causes a change in molecular spacing. True of False
True
A sensible heat change always causes a change in temperature True or False
True
There is a change of state in a substance whenever latent heat is added to it or removed from it. True or False
True
Heat produced by human bodies is an example of
chemical
A gas-fired furnace relies upon ...to take the heat of the flame through a metal of its heat exchanger to the air passing over it.
conduction
The three ways heat is transferred are called
conduction, convection, radiation
Materials that help heat move by conduction are called
conductors
The air which is circulated through an air conditioned space moves heat by
convection
The currents you see in a cup of hot coffee, tea or chocolate are caused by
convection
Heat is a form of
energy
As the temperature of any substance increases, the molecules which make it up vibrate
faster
Heat flows downhill. This means
it naturally flows from a warmer to a colder substance
List four forms of energy that turn into heat energy in air conditioned (cooled) spaces.
light, electrical, chemical, mechanical
Since man cannot destroy heat, when we say refrigeration "removes" heat, we are really saying it ......heat
moves/transfers
Sunlight is an example of
radiation
List two examples where mechanical refrigeration is used
refrigerator/ AC
Total heat is the sum of
sensible heat and latent heat
When we compare "heat content" to "heat transfer" which things are true?
-Heat content tells how much heat is contained in a substance -Heat transfer tells how much heat is moved from one substance to another
Mechanical refrigeration systems have all the components listed below except one.
A low side float value
One pound of refrigerant will take up the most space.
As a gas because it has the lowest density
Using the word "molecule" give a simple definition of density.
Density is a measurement of how packed molecules are from any substance
When heat is moved, the temperature of the substance it moved from:
Drops
Define latent heat
Energy of molecular separation/arrangement
Name two scales most commonly used to measure temperature
Fahrenheit and Centigrade
A thermometer can be used to measure a latent heat change. True or False
False
A livingroom in a house is kept at 70 F. When it is 20 F outdoors, which items below demonstrate heat flowing downhill?
Heat flows from the indoor air to the outside wall Heat flows from the outside wall to the outdoor air
Define sensible heat
Heat of molecular motion
When a substance changes state from a liquid to a gas, the spacing of its molecules.
Increase greatly
Hot food brought into space (Latent or Sensible)
Latent
Outside air brought in for ventilation (Latent or Sensible)
Latent
People perspiring and breathing in a space (Latent or Sensible)
Latent
To the refrigerant mechanic the most important type of heat
Latent, because the machinery moves most of its heat that way.
Which one of these is a good insulator and, therefore, a poor conductor?
Polystyrene
Define refrigeration
Refrigeration is cooling by the removal of heat.
There are 4 basic categories for the use of mechanical refrigeration. Which of these in NOT one of them?
Room air conditioner
Heat coming in through a hot roof (Latent or Sensible)
Sensible
Heat from electric appliances and motors (Latent or Sensible)
Sensible
Heat from lights (Latent or Sensible)
Sensible
Sun shinning in through a window (Latent or Sensible)
Sensible
What does temperature measure?
Sensible heat/ Speed of vibration of molecules in a substance
air conditioning is a form or refrigeration T or F
T
A cooling coil has 40 F refrigerant inside its tubes while 80 F air passes over it. Because heat flow "down hill" it will move from
The air into the coil surface
A cooling coil has 40 F refrigerant inside its tubes while 80 F air passes over it. Because heat flows "downhill" it will move from
The air into the coil surface
Define temperature
The density of heat in a substance
Define heat transfer
The movement of heat from one place to another
