What is the relationship between thermal comfort and metabolic heat? -
ANSWER Thermal comfort exists when the temperature and relative humidity
of a person's environment permit the person to lose, without conscious effort,
metabolic heat at the same rate he or she produces it. Because temperature and
humidity combine to make
Human beings feel good in their environment, and all these features have to be
adjusted by an AC system if human comfort is to be improved.
What occupant activity level do engineers select when designing an air-
conditioning system? - ANSWER Office building air-conditioning systems are
usually designed for occupants performing sedentary activities, which involve
occupants sitting or standing while working. Sedentary activity is the most
important condition because people who are sedentary tend to think about their
comfort or discomfort.
Upon what does the rate of exchange of fresh air for return air in an AC system
depend? ANS: The rate of exchange of fresh air for return air is based upon the
quantity of fresh air needed for every occupant over a period of time.
Define heat - ANS Heat is the energy transferred from one body to another. It
always flows from a body at higher heat to one at lower heat, until they reach
the same temperature.
What happens if the difference in temperature increases? - ANSWER As the
difference in temperature between two objects increases so does the rate of heat
transfer.
,What are the three methods of heat transfer? - ANSWER Conduction,
Convection, and Radiation
Conduction defines: ANS Conduction is the direct transfer of heat from one
body to another. The substances have to be in physical contact with each other
but there is no movement of the material itself.
Latent Heat Define latent heat - ANSWER Latent heat is energy transferred
which either results in the release or absorption of energy during a state change.
Latent heat cannot be sensed nor measured with a thermometer because it is
hidden within a substance.
Relative Humidity Define relative humidity - ANSWER RH (relative humidity)
refers to the amount of water vapour suspended in the air.
Does moist air have more or less density than dry air? - ANSWER Moist air
has less mass than dry air and is less dense than dry air.
What is the atmospheric pressure of air at sea level? - ANSWER At sea level,
atmospheric pressure exerts an average force of 14.7 pounds on each square
inch of surface 14.7 psi.
Describe Charles' law. - ANSWER Charles' law gives the reason why gas
volume rises if it is subjected to heat and why it reduces when it is subjected to
cold. With any given amount of gas, as the temperature rises, volume increases.
This is because the molecules have room to move further and spread out. As
pressure increases and the volume decreases, the temperature will rise because
compressing the gas makes the molecules
vibrate faster and collide into each other more often creating friction heat.
, Boyle's Law. - ANSWER Boyle's Law holds that, while holding the
temperature constant, as volume increases, the pressure decreases. If pressure
on a
certain quantity of gas is doubled, the volume space the gas needs will be
reduced by half. As pressure increases volume decreases.
How does the human body regulate its temperature? - ANSWER The body
dissipates heat by sending blood from internal organs to the skin where the heat
is thrown off into the surroundings by radiant heat loss, convective heat loss, or
evaporation. One method of perspiring and losing the heat through evaporation
involves an evaporative cooling process and is utilized in airconditioning
systems as well as human bodies.
What system produces the most heat within a building? - ANSWER Lighting
is the largest source of internal heat within buildings. The quantity of heat
produced by any light source depends primarily upon the wattage rating of the
lighting element. The number of watts of heat load that may be contributed to
the space by the lighting systems is as high as four watts per square foot. One
watt of electrical energy produces heat at the rate of 3.4 Btu/hour.
How do AC systems in office buildings compensate for this office equipment
heat gain? - ANSWER To offset this office equipment heat gain in modern
office buildings, the design of airconditioning systems has taken into account an
additional one to three watts per square foot.
What is pull-down load? - ANSWER Heat left over from the day before must
be removed the following morning when the air-conditioning system is
restarted. The leftover heat is called the pull-down load and must be added to
the instantaneous solar heat gain during the morning hours to determine the
cooling load for the airconditioning system.
ANSWER Thermal comfort exists when the temperature and relative humidity
of a person's environment permit the person to lose, without conscious effort,
metabolic heat at the same rate he or she produces it. Because temperature and
humidity combine to make
Human beings feel good in their environment, and all these features have to be
adjusted by an AC system if human comfort is to be improved.
What occupant activity level do engineers select when designing an air-
conditioning system? - ANSWER Office building air-conditioning systems are
usually designed for occupants performing sedentary activities, which involve
occupants sitting or standing while working. Sedentary activity is the most
important condition because people who are sedentary tend to think about their
comfort or discomfort.
Upon what does the rate of exchange of fresh air for return air in an AC system
depend? ANS: The rate of exchange of fresh air for return air is based upon the
quantity of fresh air needed for every occupant over a period of time.
Define heat - ANS Heat is the energy transferred from one body to another. It
always flows from a body at higher heat to one at lower heat, until they reach
the same temperature.
What happens if the difference in temperature increases? - ANSWER As the
difference in temperature between two objects increases so does the rate of heat
transfer.
,What are the three methods of heat transfer? - ANSWER Conduction,
Convection, and Radiation
Conduction defines: ANS Conduction is the direct transfer of heat from one
body to another. The substances have to be in physical contact with each other
but there is no movement of the material itself.
Latent Heat Define latent heat - ANSWER Latent heat is energy transferred
which either results in the release or absorption of energy during a state change.
Latent heat cannot be sensed nor measured with a thermometer because it is
hidden within a substance.
Relative Humidity Define relative humidity - ANSWER RH (relative humidity)
refers to the amount of water vapour suspended in the air.
Does moist air have more or less density than dry air? - ANSWER Moist air
has less mass than dry air and is less dense than dry air.
What is the atmospheric pressure of air at sea level? - ANSWER At sea level,
atmospheric pressure exerts an average force of 14.7 pounds on each square
inch of surface 14.7 psi.
Describe Charles' law. - ANSWER Charles' law gives the reason why gas
volume rises if it is subjected to heat and why it reduces when it is subjected to
cold. With any given amount of gas, as the temperature rises, volume increases.
This is because the molecules have room to move further and spread out. As
pressure increases and the volume decreases, the temperature will rise because
compressing the gas makes the molecules
vibrate faster and collide into each other more often creating friction heat.
, Boyle's Law. - ANSWER Boyle's Law holds that, while holding the
temperature constant, as volume increases, the pressure decreases. If pressure
on a
certain quantity of gas is doubled, the volume space the gas needs will be
reduced by half. As pressure increases volume decreases.
How does the human body regulate its temperature? - ANSWER The body
dissipates heat by sending blood from internal organs to the skin where the heat
is thrown off into the surroundings by radiant heat loss, convective heat loss, or
evaporation. One method of perspiring and losing the heat through evaporation
involves an evaporative cooling process and is utilized in airconditioning
systems as well as human bodies.
What system produces the most heat within a building? - ANSWER Lighting
is the largest source of internal heat within buildings. The quantity of heat
produced by any light source depends primarily upon the wattage rating of the
lighting element. The number of watts of heat load that may be contributed to
the space by the lighting systems is as high as four watts per square foot. One
watt of electrical energy produces heat at the rate of 3.4 Btu/hour.
How do AC systems in office buildings compensate for this office equipment
heat gain? - ANSWER To offset this office equipment heat gain in modern
office buildings, the design of airconditioning systems has taken into account an
additional one to three watts per square foot.
What is pull-down load? - ANSWER Heat left over from the day before must
be removed the following morning when the air-conditioning system is
restarted. The leftover heat is called the pull-down load and must be added to
the instantaneous solar heat gain during the morning hours to determine the
cooling load for the airconditioning system.
