Unit 35 Comfort and Psychrometrics
Psychrometric chart
A chart that shows the relationship of temperature, pressure, and humidity in the air
weight, pounds or grains, 7000, 1
Absolute and Relative Humidity Moisture content in air is measured by _____________ and expressed in ____________________ (____________ grains = _____ lb) per pound of air
moisture
Absolute and Relative Humidity There is ______________ in the air at all times, even in a desert
humidity
Absolute and Relative Humidity Water, in the form of low-pressure vapor, is suspended in the air and called ______________
grains per pound, pounds of water per pound of air
Absolute and Relative Humidity Defined Absolute and Relative Humidity Defined Expressed in either ________________________ or _____________________________________
Relative humidity:
Absolute and Relative Humidity Defined the relationship between the weight of water vapor in a pound of air compared to the weight it could hold at a 100% saturated condition
psychrometric chart
Building Air-Conditioning Specifications May also use the ____________________________
number, type
Building Air-Conditioning Specifications National code requirements for buildings where the public works are based on _____________ of people in the building and the __________ of use
outdoor air dampers
Building Air-Conditioning Specifications Technicians may get specific instructions for adjusting _________________________ to induce the correct amount of outdoor air into building
pleasant feeling
Comfort Describe a delicate balance of______________________ in the body produced by its surroundings
temperature, humidity, air movement, air cleanliness
Comfort Involves __________________, _________________, ________________________, and _____________________
circulatory, respiratory
Comfort The human body adjusts to conditions for comfort and protection using the ___________________ and ___________________ systems
dew point temperature, condensate line
Dew Point Temperature Air can be dehumidified by passing it over a surface that is below the ___________________________ of the air, such as an air-conditioning coil Condensed moisture drains out the air _______________________
condense
Dew Point Temperature Temperature at which moisture begins to ___________________ out of the air, collecting as water on cold surfaces
sling, digital, electronic, relative humidity, wet-bulb depression, saturated with moisture
Dry-Bulb and Wet-Bulb Temperatures Both obtained simultaneously with __________ or _______________ or _________________ psychrometer The closer the readings, the higher the ___________________ The difference is called the ___________________________ At 100% relative humidity, the air is ______________________
Dry-bulb:
Dry-Bulb and Wet-Bulb Temperatures Two types of temperature readings: sensible-heat level of air
Wet-bulb:
Dry-Bulb and Wet-Bulb Temperatures accounts for moisture in air
sensible, latent-heat
Enthalpy Enthalpy is the total heat content of air and has both ________________- and ___________________ components
heat content expressed in Btu per pound of air
Enthalpy Enthalpy of air is measure of __________________________________________
Enthalpy, wet-bulb
Enthalpy ________________ and __________________ temperatures are closely related
correct rate
Food Energy and the Body The body must transfer heat to its surroundings at the ___________________ to be comfortable
overheat
Food Energy and the Body The body needs to dissipate some heat to its surroundings or it will _________________
food, fatty tissue, waste, heat, body functioning
Food Energy and the Body The body uses __________ to produce energy Some energy is stored as _________________; some leaves as _____________; some leaves as __________; some is used to keep the ______________________
Ventilation, oxygen-starved, infiltration
Fresh Air, Infiltration, and Ventilation Fresh air intake (_________________): inducing a small amount of air from outside into the conditioner to keep the air from becoming ____________________ and stagnant and to dilute indoor pollutants Energy-efficient homes can be built so tightly that _________________ (random air leaking into a structure) does not provide enough fresh air
25%, Considerable load, winter, summer
Fresh Air, Infiltration, and Ventilation: Pollution Problems A minimum ________ air change per hour of the entire structure is desirable __________________________ on conditioning systems Calculate using different formulas for ______________ and ______________
more, people, activities
Fresh Air, Infiltration, and Ventilation: Pollution Problems Office buildings have the same pollution problems as homes, except with ____________ sources of pollution, because they hold more _____________, and different and varied _______________
conduction, convection, radiation, Evaporation
Heat Transfer to and from the Body The body gives off and absorbs heat by ________________, ___________________, and ________________ ________________________ of perspiration may be considered a fourth way
75, 50%, season, location, clothing, body metabolism
Heat Transfer to and from the Body The body is comfortable at rest in surroundings of ______ degrees F and _______ humidity with slight air movement Comfort conditions vary with ________________, ________________, _______________, and ______________________
Comfort
People are said to be comfortable when they are not aware of the ambient air surrounding them. They do not feel cool or warm or sweaty
plotted
Plotting on the Psychrometric Chart Conditions of air can be ______________ as it is being conditioned by following progression of lines across chart
heat, humidify, cool, dehumidify
Plotting on the Psychrometric Chart When an airstream enters air-conditioning equipment, the conditions of the air can be plotted on a chart The most common winter application is to __________ and ______________ The most common summer application is to __________ and _________________
weight, occupies space, 0.075lb/ft cubed
Psychrometrics Air has ______________ and _______________________ Air weighs about ____________________ at standard atmospheric pressure
air, properties
Psychrometrics The study of ______ and its __________________
weight, density
Psychrometrics To calculate the weight of air in a room: Multiply the room volume by the ______________ of a cubic foot of air Number of cubic feet per pound can be calculate by taking the reciprocal of the ______________ of the air
several different gases, 78%, 21%, 1%, superheated, exerts pressure, sum
Superheated Gases in Air Air is made of ____________________________ _______ nitrogen, _____ oxygen, _____ other gases Theses gases are ___________________ Each gas ________________________ independently of the others and the total pressure of a gas mixture is the ________ of each gas
lower, higher
Superheated Gases in Air Water will evaporate if water vapor pressure in air is ____________ than otherwise, and condense if it is _____________
one comfort situation with another
The Comfort Chart Can be used to compare _______________________________________
summer, winter
The Comfort Chart Different charts for _______________ and _____________
temperature, humidity
The Comfort Chart Shows different combinations of ______________________ and __________________
middle, more
The Comfort Chart The closer the plot falls to the ______________ of the chart, the __________ people will be comfortable at that condition
psychrometric chart
The Comfort Chart The complete graph is referred to as a ____________________________
Knowing any two conditions of air allows us to find the others:
The Psychrometric Chart Dry-bulb temperature, wet-bulb temperature, dew point temperature, total heat content of 1 lb of air, moisture content of 1 lb of air, relative humidity, and specific volume of air
graphical representation
The Psychrometric Chart Provides a ___________________________ of air and its properties
Dew point temperature
The exact temperature at which moisture begins to form
Psychrometrics
The study of air and its properties, particularly the moisture content
