# Acr 120 Unit 35

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• 1.

### Comfort can be described as the gentle balance between___

• A.

Air cleanliness, air movement, temperature and humidity

• B.

Air velocity, air cleanliness, humidity and air movement

• C.

Air speed, air velocity, temperature and humidity

• D.

Acceleration, air cleanliness, filtration and humidity

A. Air cleanliness, air movement, temperature and humidity
Explanation
Comfort can be described as the gentle balance between air cleanliness, air movement, temperature, and humidity. This means that for an environment to be comfortable, the air should be clean, there should be proper air circulation, the temperature should be at a comfortable level, and the humidity should be within a comfortable range. All of these factors contribute to creating a pleasant and comfortable environment for individuals.

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• 2.

### Of the heat produced in the human body, which is by perspiration?

• A.

Conduction

• B.

Convection

• C.

• D.

Evaporation

D. Evaporation
Explanation
Evaporation is the process by which sweat on the skin's surface changes from a liquid to a gas, releasing heat in the process. This is the primary way in which the human body dissipates heat and regulates its temperature. Conduction, convection, and radiation are also involved in heat transfer, but they do not directly involve perspiration.

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• 3.

### If the dry-bulb temperature is 93F and the wet-bulb temperature is 60F, what ist he specific volume of the air?

• A.

14.0 ft3/lb

• B.

14.0 lb/ft3

• C.

10 lb/ft3

• D.

10 ft3/lb

A. 14.0 ft3/lb
Explanation
The specific volume of air can be determined using the psychrometric chart. The dry-bulb temperature of 93F and the wet-bulb temperature of 60F can be used to find the specific volume. By locating the intersection point of these two temperatures on the psychrometric chart, the specific volume can be read off as 14.0 ft3/lb.

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• 4.

### The generalized comfort chart can be used as a basis to_____.

• A.

Determine combinations of temperature and humidity to produce comfort in summer and winter

• B.

Study air and its properties

• C.

Determine the amount of fresh air make up necessary for comfort

• D.

None of the above

A. Determine combinations of temperature and humidity to produce comfort in summer and winter
Explanation
The generalized comfort chart can be used to determine combinations of temperature and humidity that will result in a comfortable environment during both summer and winter. It provides a basis for understanding the relationship between temperature and humidity and how they impact comfort. By referring to the chart, one can identify the ideal temperature and humidity levels that will create a comfortable indoor environment in different seasons.

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• 5.

### The density of air is the

• A.

Amount of moisture in the air

• B.

Amount of movement int he air per cubic foot

• C.

Weight of the air per cubic foot

• D.

Combination of the temperature and pressure of the air

C. Weight of the air per cubic foot
Explanation
The density of air refers to the weight of the air per cubic foot. It is a measure of how much mass is present in a given volume of air. The density of air is influenced by factors such as temperature and pressure, but ultimately it is the weight of the air that determines its density.

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• 6.

### The density of water is

• A.

61.3 lb/ft3

• B.

62.0 lb/ft3

• C.

62.3 lb/ft2

• D.

62.3 lb/ft3

D. 62.3 lb/ft3
Explanation
The correct answer is 62.3 lb/ft3. This is the density of water, which is a measure of how much mass is contained in a given volume. The density of water is commonly expressed in lb/ft3, and the value of 62.3 lb/ft3 is the accepted value for the density of water at standard conditions.

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• 7.

### What is the relative humidity if the dry-bulb temperature is 100F and the wet-bulb temperature is 65F

• A.

13%

• B.

33%

• C.

43%

• D.

63%

A. 13%
Explanation
The relative humidity can be determined by comparing the dry-bulb temperature (the air temperature) with the wet-bulb temperature (the temperature at which water evaporates from a wetted bulb). In this case, the dry-bulb temperature is 100F and the wet-bulb temperature is 65F. By comparing these temperatures, we can determine that the relative humidity is 13%.

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• 8.

### If the wet-bulb and dry-bulb temperature are both 80F, what is the humidity

• A.

0%

• B.

50%

• C.

75%

• D.

100%

D. 100%
Explanation
If both the wet-bulb and dry-bulb temperatures are the same at 80F, it means that the air is saturated with moisture and cannot hold any more water vapor. This indicates that the relative humidity is at its maximum level of 100%.

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• 9.

### The dry-bulb temperature is the

• A.

Same as the wet-bulb temperature

• B.

Total of the sensible and latent heat

• C.

Sensible heat level of the air

• D.

Sensible heat less the humidity

C. Sensible heat level of the air
Explanation
The dry-bulb temperature refers to the actual temperature of the air, without taking into account the effects of humidity. It represents the sensible heat level of the air, which is the heat that can be sensed or felt. This means that it does not include the latent heat, which is the heat associated with the moisture content in the air. Therefore, the correct answer is "sensible heat level of the air".

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• 10.

### The wet-bulb temperature

• A.

Is the same as the wet-bulb depression

• B.

Is the saturation pressure

• C.

Takes into account the moisture content of the air

• D.

Is always higher than the dry-bulb temperature

C. Takes into account the moisture content of the air
Explanation
The wet-bulb temperature is a measure of the lowest temperature that can be reached by evaporating water into the air. It takes into account the moisture content of the air because the rate of evaporation depends on the amount of moisture already present. As water evaporates from a wet surface, it cools down, and the wet-bulb temperature reflects this cooling effect. Therefore, the wet-bulb temperature provides a more accurate indication of the actual temperature and humidity of the air compared to the dry-bulb temperature.

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• 11.

### The wet-bulb depression is___

• A.

The difference between the dry-bulb and wet-bulb temperatures

• B.

The same as the wet-bulb temperatures

• C.

The same as the dry-bulb temperatures

• D.

When the air is saturated with moisture

A. The difference between the dry-bulb and wet-bulb temperatures
Explanation
The wet-bulb depression refers to the difference between the dry-bulb and wet-bulb temperatures. Dry-bulb temperature represents the actual air temperature, while wet-bulb temperature indicates the lowest temperature that can be achieved through the process of evaporative cooling. The wet-bulb depression is a measure of how much cooling potential there is in the air, with a larger difference indicating greater potential for evaporative cooling.

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• 12.

### What is the dew point temperature if the wet-bulb temperature is 65F and the dry-bulb temperature is 100F?

• A.

40F

• B.

50F

• C.

60F

• D.

70F

A. 40F
Explanation
The dew point temperature is the temperature at which air becomes saturated and condensation occurs. It represents the point at which the air is holding as much moisture as it can. In this case, the wet-bulb temperature of 65F indicates the temperature at which water evaporates from a wet surface, and the dry-bulb temperature of 100F represents the temperature of the air. The dew point temperature is lower than both of these temperatures. Therefore, the correct answer is 40F, as it is the only option that is lower than both the wet-bulb and dry-bulb temperatures.

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• 13.

### The dew point temperature is the

• A.

Temperature when the air is saturated with moisture

• B.

Temperature when the moisture begins to condense out of the air

• C.

Difference between the dry-bulb and wet-bulb temperatures

• D.

Temperature of the air at 50% relative humidity

C. Difference between the dry-bulb and wet-bulb temperatures
Explanation
The dew point temperature is the temperature when the moisture begins to condense out of the air. This means that when the air reaches its dew point temperature, it becomes saturated with moisture and can no longer hold all of the water vapor it contains. As a result, the excess moisture starts to condense into water droplets, forming dew or fog. The difference between the dry-bulb and wet-bulb temperatures, on the other hand, is a measure of the amount of moisture in the air but does not directly indicate the point at which condensation occurs.

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• 14.

### Infiltration is the term used when referring to the air entering a structure

• A.

Through an air make-up unit

• B.

Around doors and windows

• C.

Through ventilation

• D.

Because of street traffic

B. Around doors and windows
Explanation
Infiltration refers to the process of air entering a structure through openings such as doors and windows. These openings can allow outside air to enter the building, which can affect the indoor temperature and air quality. Infiltration can occur due to gaps, cracks, or poor sealing around doors and windows, allowing air to leak in or out of the building. Therefore, the correct answer is "around doors and windows".

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• 15.

### A fresh air intake is necessary to keep the indoor air from becoming

• A.

Too humid

• B.

Superheated

• C.

Oxygen starved and stagnant

• D.

Too dry

C. Oxygen starved and stagnant
Explanation
A fresh air intake is necessary to prevent the indoor air from becoming oxygen starved and stagnant. Without a fresh air supply, the oxygen levels in the room would decrease, leading to a lack of oxygen for people to breathe. Additionally, stagnant air can become stale and unpleasant, causing discomfort and potentially leading to health issues. Therefore, it is important to have a fresh air intake to maintain a healthy and comfortable indoor environment.

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• 16.

• A.

Option 1

• B.

Option 2

• C.

Option 3

• D.

Option 4

A. Option 1
• 17.

### The human body is comfortable when the heat produced in the body is equal to the heat lost to the surroundings

• A.

True

• B.

False

A. True
Explanation
The statement is true because the human body maintains a constant internal temperature through a process called thermoregulation. When the heat produced in the body matches the heat lost to the surroundings, the body is in a state of thermal equilibrium, which is considered comfortable. This balance is achieved through various mechanisms such as sweating, shivering, and adjusting blood flow to the skin. If the heat lost exceeds the heat produced, the body may feel cold, while if the heat produced exceeds the heat lost, the body may feel hot.

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• 18.

### The rate at which water will evaporate from the wick on the wet-bulb thermometer is determined by the moisture content of the surrounding air.

• A.

True

• B.

False

A. True
Explanation
The explanation for the given correct answer is that the rate of evaporation depends on the moisture content of the surrounding air. When the air is dry, water evaporates more quickly from the wick on the wet-bulb thermometer. Conversely, when the air is humid, the evaporation rate slows down. Therefore, the statement "The rate at which water will evaporate from the wick on the wet-bulb thermometer is determined by the moisture content of the surrounding air" is true.

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• 19.

### Introduction of forced ventilation in the winter heating season helps to raise the humidity level.

• A.

True

• B.

False

B. False
Explanation
The introduction of forced ventilation in the winter heating season does not help to raise the humidity level. In fact, forced ventilation can often lead to a decrease in humidity as it brings in outside air which is typically drier.

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• 20.

### The average body temperature is _____ F

98.6
Explanation
The average body temperature is commonly believed to be 98.6 degrees Fahrenheit. This value has been widely accepted for many years and is based on studies conducted by German physician Carl Reinhold August Wunderlich in the 19th century. He measured the body temperatures of thousands of individuals and found that 98.6 degrees Fahrenheit was the average. However, more recent studies have suggested that the average body temperature may actually be slightly lower, around 97.5 to 97.9 degrees Fahrenheit. Nonetheless, 98.6 degrees Fahrenheit is still widely used as the reference point for normal body temperature.

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• 21.

### For the summer months, the average individual will be comfortable if the surrounding air is ______ with a relative humidity of 50%

75F
Explanation
During the summer months, an average individual will feel comfortable if the surrounding air temperature is 75Â°F with a relative humidity of 50%. This combination of temperature and humidity creates a pleasant and moderate environment that is neither too hot nor too humid. It strikes a balance between warmth and moisture, ensuring that individuals do not feel excessively hot or sweaty.

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• 22.

• A.

True

• B.

False

A. True
• 23.

### Air is primarily made up of ____ and oxygen

nitrogen
Explanation
Air is primarily made up of nitrogen and oxygen. Nitrogen is the most abundant gas in the Earth's atmosphere, making up about 78% of it. Oxygen is the second most abundant gas, constituting approximately 21% of the atmosphere. These two gases are essential for sustaining life on Earth. Nitrogen is an inert gas that plays a crucial role in various biological processes, while oxygen is vital for respiration and energy production in most living organisms.

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• 24.

### Air consists of approximately _____ % oxygen

21%
Explanation
Air consists of approximately 21% oxygen. This means that out of the total composition of air, 21% is oxygen. Oxygen is an essential component of air and is necessary for the survival of most living organisms. It plays a vital role in the process of respiration, where it is used by organisms to produce energy. The remaining percentage of air is made up of other gases such as nitrogen, carbon dioxide, and trace amounts of other gases.

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• 25.

### _______ grains of moisture equals one pound of water

7000
Explanation
One pound of water is equal to 7000 grains of moisture.

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• 26.

### The difference between wet-bulb and dry-bulb temperature is called ______

wet-bulb depression
Explanation
The difference between wet-bulb and dry-bulb temperature is referred to as wet-bulb depression. This term is used to describe the variance between the temperature measured by a dry-bulb thermometer and the temperature measured by a wet-bulb thermometer. The wet-bulb depression is an important parameter in meteorology and is used to determine relative humidity and other weather conditions.

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• 27.

### If the dry-bulb temperature is 76F and the wet-bulb temperature is 68F, the wet-bulb depression is ______ F

8
Explanation
The wet-bulb depression is the difference between the dry-bulb temperature and the wet-bulb temperature. In this case, the dry-bulb temperature is 76F and the wet-bulb temperature is 68F. Therefore, the wet-bulb depression is 8F.

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• 28.

### When the dry-bulb and wet-bulb temperatures are the same, the relative humidity of the air is ______ %

100
Explanation
When the dry-bulb and wet-bulb temperatures are the same, it means that the air is saturated with moisture and cannot hold any more water vapor. Therefore, the relative humidity of the air is 100%, indicating that the air is fully saturated with water vapor.

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• 29.

### _______ if air is the measure of heat content in btu per pound of air.

Enthalpy
Explanation
Enthalpy is the correct answer because it is a measure of the total heat content in a substance, including both its internal energy and the energy associated with its pressure and volume. In this context, if air is the measure of heat content in btu per pound of air, it is referring to the enthalpy of air. Enthalpy is commonly used in thermodynamics to analyze and calculate heat transfer processes.

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• 30.

### When fresh air is introduced through the air handling system, the process is called ______.

ventilation
Explanation
Ventilation refers to the process of introducing fresh air into a space through an air handling system. This helps to remove stale air, odors, and pollutants, and maintain a healthy and comfortable indoor environment. Ventilation is essential for ensuring proper air circulation, controlling humidity levels, and preventing the buildup of harmful substances.

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• 31.

### How can the cost of heating a home in the winter be lowered, and still have comfortable conditions in the home?

raising humidity level and lowering the thermostat setting
Explanation
By raising the humidity level, the air in the home becomes more humid, which can make it feel warmer. This allows for the thermostat to be set at a lower temperature while still maintaining comfortable conditions. Lowering the thermostat setting directly reduces the amount of energy needed for heating, resulting in lower heating costs. Combining these two strategies can effectively lower the cost of heating a home in the winter while still ensuring a comfortable living environment.

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• 32.

### How does air movement improve comfort?

humans sweat, moving air increases evaporative effect, making it seem cooler
Explanation
Moving air improves comfort because humans sweat, and the movement of air increases the evaporative effect. When sweat evaporates from our skin, it cools us down. Therefore, when there is moving air, it helps to enhance the evaporation process, making us feel cooler and more comfortable.

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• 33.

### Explain how a wet-bulb thermometer works.

Uses humidity in the air with water to get a reading of the surrounding ambient air.
Explanation
A wet-bulb thermometer works by utilizing the principle of evaporative cooling. It consists of a thermometer with a moistened wick or cloth wrapped around its bulb. As the moisture on the wick evaporates, it absorbs heat from the surrounding air, causing the temperature on the thermometer to drop. This drop in temperature, known as the wet-bulb temperature, is a measure of the cooling effect of evaporation and provides an indication of the humidity in the air. By comparing the wet-bulb temperature with the dry-bulb temperature (measured by a regular thermometer), one can determine the relative humidity and other important weather parameters.

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• 34.

### What will happen if a technician uses a sling psychrometer that has a perfectly dry wick on the wet-bulb thermometer?

both thermometers will read the dry bulb temp
Explanation
If a technician uses a sling psychrometer with a perfectly dry wick on the wet-bulb thermometer, it means that there will be no moisture available to evaporate from the wick. As a result, the wet-bulb thermometer will not be able to measure the cooling effect of evaporation accurately. In this case, both thermometers will read the dry bulb temperature, which is the temperature of the surrounding air.

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• 35.

### The air leaving an evaporator has a dry-bulb temperature of 85F and a wet-bulb temperature of 65F.  The air entering the evaporator has a dry-bulb temperature of 95F and a wet-bulb temperature of 75F.  How many grains of moisture per pound of dry air were removed by the evaporator?

40 grains of moisture per pound of dry air
Explanation
The dry-bulb temperature represents the actual temperature of the air, while the wet-bulb temperature represents the lowest temperature that can be achieved through evaporative cooling. The difference between the dry-bulb and wet-bulb temperatures indicates the amount of moisture in the air. In this case, the air entering the evaporator has a higher dry-bulb temperature and a higher wet-bulb temperature compared to the air leaving the evaporator. This means that the evaporator has removed moisture from the air, resulting in a decrease in the wet-bulb temperature. Therefore, the correct answer is 40 grains of moisture per pound of dry air.

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• 36.

### Under what conditions can the wet-bulb temperature be higher than the dry-bulb temperature?

Never, there is something wrong with the sling phsychrometer
Explanation
The wet-bulb temperature is always lower than or equal to the dry-bulb temperature. This is because the wet-bulb temperature is measured by evaporating water from a wetted wick around the bulb of the thermometer, which causes cooling due to the process of evaporation. Therefore, it is not possible for the wet-bulb temperature to be higher than the dry-bulb temperature. If this occurs, it indicates a malfunction or error in the sling psychrometer.

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• 37.

### Why must the thermometers in a sling psychrometer be swung in order to obtain the readings?

To obtain the necessary evaporation rate of moisture of the wet-bulb thermometer
Explanation
When the sling psychrometer is swung, air is forced over the wet-bulb thermometer, causing moisture on the bulb to evaporate. The evaporation process cools down the wet-bulb thermometer, which in turn provides a lower temperature reading. By comparing the temperature readings of the wet-bulb and dry-bulb thermometers, the evaporation rate of moisture can be determined. Swinging the psychrometer ensures a continuous flow of air over the wet-bulb thermometer, allowing for accurate and consistent readings.

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• Mar 21, 2023
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