Energy and Energy Production

Energy

the capacity to do work.

heat

the energy transfer driven by a temperature

1st law of thermodynamics

ΔE=Q+W

2nd law of thermodynamics

the quality of energy; state of entropy of entire universe will increase over time (until thermal death)

Exergy

the maximum useful work possible during process that brings the system into equilibrium (exergy=0) with a heat reservoir

heat transfer

conduction, convection, and radiation

convection

heat coming off people

radiation

doesn’t need a medium, needs a temperature difference

conduction

two solid thins touch each other and hotter one transfers heat to colder one

transpiration

sweating cools off the body, can’t drip off in order to cool

thermal comfort

that condition of mind that expresses satisfaction with the thermal environment and is assessed by the subjective evaluation

comfort

personal and relies on individual activity clothing, and physiological

clo

unit used to to express the thermal insulation provided by garments and clothing

dry bulb temperature

the temperature of air measured by a thermometer freely exposed to the air, but shielded from radiation and moisture

mean radiant temperature (MRT)

radiant environment for a point in space. a function of both the temperature and exposure angle of all objects that are in view of the body

Operative temperature

average of the air and mean radiant temperatures

air motion

greater air speeds may be used to increase the upper operative temperature if the occupants have control over the air speed

humidity

a general reference to the moisture content of the air

wet bulb temperature

measured by a thermometer with a wetted bulb rotated rapidly in the air to cause evaporation of its moisture as with sling psychrometer.

In dry air: the moisture readily evaporates and draws heat out of the thermometer to produce a lower temp reading called wet-bulb depression (low relative humidity)

in moist air: less evaporation when air is already moisture laden, results in small wet bulb depression and indicates high relative humidity

100% humidity

wet and dry bulb temps are equal

relative humidity

the ration of the actual density of water vapor in the air to the maximum density of water vaper that such air could contain, at the same temperature, if it were 100% saturated

RH=

actual water vapor density in air/water vapor density if air saturated