Section 28 Air Movement and Measurement

Vocabulary flashcards covering the composition of the atmosphere and the five primary atmospheric layers from Chapter 28: Air Movement and Measurement.

Nitrogen

The atmospheric gas that composes the majority of the Earth's atmosphere.

Oxygen

The gas that makes up approximately $23\%$ of the atmosphere by weight.

Carbon dioxide

A gas that makes up $0.03\%$ to $0.04\%$ of the atmosphere and is absorbed by growing plants.

Troposphere

The lowest layer of the atmosphere closest to Earth's surface (layer E), extending up to approximately $12.5\text{ miles}$.

Stratosphere

The layer of the atmosphere (layer D) located directly above the troposphere, spanning from approximately $12.5\text{ miles}$ to $32\text{ miles}$.

Mesosphere

The layer of the atmosphere (layer C) situated between the stratosphere and the thermosphere, extending from approximately $32\text{ miles}$ to $53\text{ miles}$.

Thermosphere

The layer of the atmosphere (layer B) situated above the mesosphere, extending from approximately $53\text{ miles}$ to $435\text{ miles}$.

Exosphere

The outermost layer of the atmosphere (layer A), extending beyond approximately $435\text{ miles}$.

A gas that is very light and present in small amounts is .

Hydrogen

According to Bernoulli's principle, the velocity of air decreases the pressure.

Increasing

One pound of air at standard conditions ($14.7\,\text{psia}$ [$101\,\text{kPa}$], $69.8^\circ\text{F}$ [$21^\circ\text{C}$]) occupies $\text{ft}^3$.

$$13.343$$

By dividing the weight of air by the volume it occupies, you can calculate the of the air.

Density

When measuring very low temperatures, thermocouple thermometers or are used.

Resistance temperature detectors (RTDs)

True or False? The amount of moisture that a set volume of air can hold depends on air temperature.

True

True or False? Since dry air prevents rapid evaporation of moisture from a surface, the surface does not cool as quickly as it would with moist air.

False

The amount of moisture in an air sample compared to the total amount of moisture the same sample would hold if it were completely saturated at the same temperature defines the term .

Relative humidity

Point A to B

A line showing how much additional moisture $75^\circ\text{F}$ ($23.9^\circ\text{C}$) air could hold.

Point A to E

A line representing an increase of only dry-bulb temperature.

Point C

A point showing a saturated condition with the least total grains of moisture per pound of air.

Point B

A point showing a saturated condition with the most total grains of moisture per pound of air.

Point A

A point containing $65\text{ grains}$ of moisture per pound of air at $75^\circ\text{F}$ ($23.9^\circ\text{C}$).

Point D to C

A line representing what happens when saturated air at $55^\circ\text{F}$ ($12.8^\circ\text{C}$) is cooled to a saturated temperature of $40^\circ\text{F}$ ($4.4^\circ\text{C}$).

Point A to D

A line representing how moist air at $75^\circ\text{F}$ ($23.9^\circ\text{C}$) is cooled to a saturated temperature of $55^\circ\text{F}$ ($12.8^\circ\text{C}$) with $65\text{ grains}$ of moisture per pound of air.

An instrument that measures moisture in the air is a ****.

Hygrometer

Desiccants are substances that absorb **** from the air.

Moisture

In the heating season, humidity controls are typically set to **** the conditioned air.

Add humidity to

In the cooling season, humidity controls are typically set to ____ the conditioned air.

Remove humidity from

True or False? Wet-bulb temperature will be higher than dry-bulb temperature at $100\%$ humidity.

False

How warm the combination of humidity and temperature feels to an occupant of a space is ____ temperature.

Equivalent

The low temperature for a certain day was $39^\circ\text{F}$. The high temperature for the same day was $58^\circ\text{F}$. What was the number of heating degree days in Fahrenheit?

$$16.5\text{ heating degree days}$$

A(n) ____ chart is a graph of the properties of air.

Psychrometric

What do the red lines represent in the following chart?

Constant dry-bulb temperature

What do the red lines represent in the following chart?

Constant wet bulb temperature

What do the red lines represent in the following chart?

Constant specific humidity levels

What do the red lines represent in the following chart

Constant relative humidity

What do the red lines represent in the following chart

Constant specific volumes

The quantity of moisture air can hold decreases at its temperature increases?

True

Most people are comfortable in an atmosphere with the relative humidity between **** and the temperature between 70°F and 85°F

30% and 70%

The combined effect of dry-bulb temperature, wet-bulb temperature, and air movement that provides an equal sensation of warmth and cold describes the term _.

Effective temperature

In the wintertime, air-conditioned buildings are usually kept at temperatures approximately _ the outside temperature.

$68^\circ\text{F}\text{ to }72^\circ\text{F}$ ($20^\circ\text{C}\text{ to }22.2^\circ\text{C}$) above

True or False? At comfortable temperatures, there is no sensation of either warmth or cold.

True

True or False? In extreme heat, the body attempts to cool down by shifting direct circulation to the extremities.

True

True or False? In extreme cold, the body attempts to warm itself by increasing surface blood flow.

False

True or False? Because glass is a rather poor conductor of heat, greenhouses and other buildings with a lot of glass rarely get hot on sunny days.

False

True or False? Black absorbs more heat than white.

True

True or False? Polished metal does not radiate heat effectively.

True

When heat rays strike a surface of the same _ as the radiating body, there is no increase or decrease of heat in the body being struck by the radiation.

Temperature

Water vapor condenses into droplets when its temperature drops to the _.

Dew point

True or False? Vapor barriers prevent water vapor from passing from warm to cold surfaces.

True

True or False? Vapor barriers should be installed on the cold side of a heated space.

False

Reducing heat conductivity with _ helps maintain desired air-conditioning temperatures more economically.

Insulation

What forecast term on the Beaufort Scale is used to describe a wind velocity of 8-12 mph?

Gentle

What forecast term on the Beaufort Scale is used to describe wind effects of breaking twigs off trees and generally impeding progress?

Gale

True or False? Air movement in wind velocity increases the heat loss of a heated structure, thereby impacting the efficiency of a heating system.

True

True or False? The calculated heat load for a structure should include the maximum wind velocity expected for the area.

True

During the winter months, the _ is used to describe the combined effect of temperature and wind speed.

Windchill index

True or False? The exposure time required for frostbite to occur becomes shorter as wind speed decreases.

False

The volume of air flowing through a duct is calculated in _.

Cubic feet per minute

An anemometer using a small propeller and electronic circuitry to calculate velocity is a _ anemometer.

Vane

True or False? With an anemometer that can be placed over an entire duct grille, a technician can calculate the number of Btus going into the space through each grille by multiplying the volume of airflow by the appropriate temperature factor.

True

An anemometer using current conducted through tungsten to calculate velocity is a _ anemometer.

Hot-wire

An anemometer using incoming air to deflect a vane at different angles to calculate velocity is a _ anemometer.

Swinging vane

A pitot tube and manometer used for ductwork airflow in HVAC most often measure value in _.

Inches of water

If the air is in motion when a technician is measuring airflow using a pitot tube and manometer, the _.

Fluid in the manometer is pushed toward the static pressure side

True or False? Velocity pressure is exerted when the airflow is slowed or stopped.

False

True or False? To obtain correct velocity values, a technician should take several readings in various parts of the duct and then average the readings.

True

A pitot tube should be used only where the duct is very _.

Long

The process of _ requires oxygen from the air, which is necessary for the operation of fuel-burning furnaces, stoves, water heaters, and fireplaces.

Combustion

The process of cold air drops and warm air rises resulting in a gradual difference in air temperature from floor to ceiling is known as _.

Stratification