Aux 2 Unit 10 Air Conditioning Terms Quiz

Correct Answer:
B) The energy required to lower the temperature of a space to a comfortable level

Explanation:
The cooling load is the amount of energy needed to reduce the indoor temperature to the desired level, offsetting heat gained from external sources like sunlight and internal sources such as occupants and equipment.

Correct Answer:
A) Heat that changes the temperature of a substance without changing its state

Explanation:
Sensible heat is the energy that causes a temperature change in a substance without a phase change. It is measurable by a thermometer.

Correct Answer:
B) The mass of water vapor per unit mass of dry air

Explanation:
Specific humidity is the ratio of the mass of water vapor to the total mass of the air parcel, including dry air, and is expressed in grams of water vapor per kilogram of dry air.

Correct Answer:
B) The heat needed to boil water

Explanation:
When water boils, it absorbs energy to change from liquid to vapor without a change in temperature, demonstrating latent heat.

Correct Answer:
C) The heat required for a substance to change its state without a temperature change

Explanation:
Latent heat is the energy absorbed or released during a phase change (e.g., water to vapor or ice to water) without a change in temperature.

Correct Answer:
A) The mass of water vapor in a unit volume of air

Explanation:
Absolute humidity is the measure of the total mass of water vapor present in a given volume of air, expressed in grams per cubic meter (g/m³).

Correct Answer:
C) The heat felt when a room is heated by a radiator

Explanation:
Heating a room with a radiator increases the air temperature without changing its phase, making it an example of sensible heat.

Correct Answer:
B) The weight of water vapor per kilogram of dry air

Explanation:
Specific humidity represents the mass of water vapor contained in a specific mass of dry air, useful for understanding moisture content in HVAC systems.

Correct Answer:
C) The amount of energy required to raise the temperature of a space to a desired level

Explanation:
The heating load refers to the energy needed to increase the indoor temperature to a set point, compensating for heat losses through walls, windows, and other structures.

Correct Answer:
B) Rapid snap-shut movement to seal the duct

Explanation:
Fire dampers are designed to close rapidly when activated to create an effective barrier that stops the spread of fire and smoke through the ductwork.

Correct Answer:
B) To prevent the spread of smoke and flames through ductwork during a fire

Explanation:
An automatic fire damper is designed to close and prevent the passage of fire and smoke through ductwork when a fire is detected, maintaining fire boundaries.

Correct Answer:
C) In vertical air ducts or ducts passing through fire-rated bulkheads and walls

Explanation:
Automatic fire dampers are installed in areas where ducts pass through walls, floors, or partitions that are designated as fire boundaries to prevent fire from spreading through these openings.

Correct Answer:
B) Pressure-controlled damper

Explanation:
A pressure-controlled damper automatically adjusts based on the pressure within the duct to maintain consistent airflow.

Correct Answer:
B) Butterfly damper

Explanation:
A butterfly damper is a common type of damper used to regulate airflow in HVAC systems by rotating a disc within the duct to control the flow rate.

Correct Answer:
C) By a fusible link or temperature sensor that releases when exposed to high heat

Explanation:
Automatic fire dampers are equipped with fusible links or temperature sensors that trigger the closing mechanism when exposed to high temperatures, indicating the presence of fire.

Correct Answer:
B) It has slats that can be adjusted to control the volume of airflow

Explanation:
Louvered dampers have adjustable slats that can be angled to control the flow of air, making them versatile for modulating airflow in HVAC systems.

Correct Answer:
C) To improve comfort and prevent mold growth

Explanation:
Controlling relative humidity is essential for maintaining comfort and preventing the growth of mold and mildew, which thrive in high-humidity environments.

Correct Answer:
B) An integrated building management system (BMS) with humidity sensors

Explanation:
A building management system with humidity sensors can monitor and control humidity levels automatically by adjusting system operations as needed.

Correct Answer:
C) Use the "Dry Mode" setting, if available

Explanation:
Many modern air conditioning units come with a "Dry Mode" setting that reduces humidity without excessively lowering the temperature, making it ideal for controlling humidity in moderate conditions.

Correct Answer:
B) It reheats the air after dehumidification to maintain temperature without adding moisture

Explanation:
The reheat coil warms the air after it has been dehumidified, allowing the system to maintain a comfortable temperature without raising humidity levels.

Correct Answer:
B) Using a humidifier or dehumidifier in conjunction with the system

Explanation:
A humidifier adds moisture to the air to increase relative humidity, while a dehumidifier removes moisture to decrease it. These devices help maintain optimal indoor humidity levels.

Correct Answer:
C) It may fail to remove enough humidity because it cools the space too quickly

Explanation:
An oversized system cools the air rapidly but may not run long enough to remove sufficient moisture, leading to higher indoor humidity levels.

Correct Answer:
B) Humidifier

Explanation:
A humidifier is specifically used to add moisture to the air when the relative humidity is low, ensuring a comfortable indoor environment.

Correct Answer:
B) By condensing moisture from the air as it cools, thereby reducing humidity

Explanation:
The cooling coil in an AC system cools the air below its dew point, causing moisture in the air to condense and reduce the relative humidity.

Correct Answer:
D) Decrease the airflow rate over the cooling coil

Explanation:
Reducing the airflow rate over the cooling coil allows the air to spend more time in contact with the coil, enhancing moisture removal and lowering humidity.

Correct Answer:
B) Low-pressure vapor

Explanation:
As the refrigerant absorbs heat in the evaporator, it changes from a low-pressure liquid to a low-pressure vapor.

Correct Answer:
C) Low-pressure liquid

Explanation:
The refrigerant enters the evaporator as a low-pressure liquid and absorbs heat to change into a low-pressure vapor.

Correct Answer:
C) To change from a vapor to a liquid state

Explanation:
The refrigerant releases heat in the condenser to condense from a high-pressure vapor to a high-pressure liquid.

Correct Answer:
C) Low-pressure liquid-vapor mixture

Explanation:
After passing through the expansion valve, the refrigerant is in a low-pressure, partially vaporized state, preparing it for heat absorption in the evaporator.

Correct Answer:
C) High-pressure vapor

Explanation:
After leaving the compressor, the refrigerant is in a high-pressure vapor state due to the compression process.

Correct Answer:
B) Its pressure and temperature increase

Explanation:
The compressor increases the pressure and temperature of the refrigerant as it compresses the low-pressure vapor into a high-pressure vapor.

Correct Answer:
B) To lower the pressure of the refrigerant and regulate its flow

Explanation:
The expansion valve reduces the pressure of the high-pressure liquid refrigerant and regulates its flow into the evaporator.

Correct Answer:
B) To transfer heat from a low-temperature region to a high-temperature region

Explanation:
The main purpose of the vapour-compression refrigeration cycle is to absorb heat from the evaporator (low-temperature region) and release it to the condenser (high-temperature region), effectively cooling the evaporated space.

Correct Answer:
C) High-pressure liquid

Explanation:
The refrigerant exits the condenser as a high-pressure liquid after releasing heat and condensing from a high-pressure vapor.

Correct Answer:
C) Both sensible and latent cooling

Explanation:
In the evaporator, the refrigerant absorbs both sensible heat (reducing air temperature) and latent heat (condensing water vapor in the air) to cool the air efficiently.

Correct Answer:
B) Low-pressure vapor

Explanation:
After absorbing heat in the evaporator, the refrigerant exits as a low-pressure vapor, ready to be compressed by the compressor.

Correct Answer:
B) Direct cooling with high efficiency and simple design

Explanation:
A DX system provides efficient cooling with a straightforward design, as the refrigerant directly cools the air without intermediate fluids.

Correct Answer:
B) To control and reduce the pressure and temperature of the refrigerant before it enters the evaporator

Explanation:
The expansion valve regulates the flow of refrigerant into the evaporator, reducing its pressure and temperature to allow effective heat absorption.

Correct Answer:
C) It absorbs heat and changes from a liquid to a vapor

Explanation:
In the evaporator, the refrigerant absorbs heat from the air being cooled, causing it to evaporate and change from a liquid to a vapor.

Correct Answer:
B) The air cooler directs warm air over the evaporator coils where the refrigerant absorbs heat

Explanation:
The air cooler channels warm air over the evaporator coils, enabling the refrigerant to absorb the heat and cool the air.

Correct Answer:
D) Cooling tower

Explanation:
A cooling tower is used in water-cooled systems, not in direct expansion systems. DX systems typically consist of an evaporator, compressor, condenser, and expansion valve.

Correct Answer:
B) The refrigerant directly absorbs heat from the air and changes phase in the evaporator

Explanation:
In a DX system, the refrigerant flows directly through the evaporator coils where it absorbs heat from the air, changing from liquid to vapor. This direct heat exchange eliminates the need for an intermediate fluid.

Correct Answer:
C) Chilled water

Explanation:
Chilled water is the intermediate medium that circulates between the chiller and the air handling unit, absorbing heat from the air in the AHU and carrying it to the chiller.

Correct Answer:
C) It circulates chilled water to absorb heat from the air and distribute cooled air

Explanation:
The air handling unit (AHU) takes chilled water from the chiller, uses it to cool the air that passes through, and then distributes the cooled air into the space.

Correct Answer:
C) Chiller

Explanation:
The chiller is the component that cools the water by using refrigerant. The chilled water is then circulated through the system to absorb heat from the air in the air handling units.

Correct Answer:
C) It allows for centralized cooling and better temperature control across large spaces

Explanation:
Indirect expansion systems are suitable for large installations because they can centralize the cooling process, distribute chilled water to different zones, and provide efficient temperature control.

Correct Answer:
B) To cool the air by circulating chilled water that transfers heat from the air to a refrigerant-cooled chiller

Explanation:
An indirect expansion system uses chilled water as an intermediate medium. The refrigerant cools the water in a chiller, and the chilled water is circulated to air handling units where it cools the air.

Correct Answer:
B) In the chiller's evaporator

Explanation:
The phase change from liquid to vapor occurs in the evaporator of the chiller, where the refrigerant absorbs heat from the chilled water, cooling the water in the process.

Correct Answer:
C) Expansion valve

Explanation:
The expansion valve regulates the flow and reduces the pressure of the refrigerant as it enters the evaporator, allowing it to absorb heat efficiently and change phase.

Correct Answer:
B) To cool the condenser water before it enters the condenser

Explanation:
In water-cooled chillers, the cooling tower is used to remove heat from the condenser water after it absorbs heat from the refrigerant, ensuring effective heat rejection.