Air Conditioning Systems

Describe a complete air-conditioning system in terms of functional components.

A complete air-conditioning system includes a means of refrigeration, one or more heat transfer units, air filters, a means of air distribution, an arrangement for piping the refrigerant and heating medium, and controls to regulate the proper capacity of these components.

Describe the relationship between wet-bulb, dry-bulb, and dew-point temperatures.

A definite relationship exists between the wet-bulb, dry-bulb, and dew-point temperatures. These relationships are as follows: • When the air is not saturated but contains some moisture, the dew-point temperature is lower than the dry-bulb temperature, and the wet-bulb temperature is in between. • As the amount of moisture in the air increases, the amount of evaporation (and, therefore, cooling) decreases. The difference between the temperatures becomes less. • When the air becomes saturated, all three temperatures are the same and the relative humidity is 100 percent.

Q12. What type of unit cools and heats by reversing its cycle?

A residential or commercial heat pump can reverse its system and remove heat from one place and put it into another. Using no fuel, the electric heat pump automatically heats or cools as determined by outside temperature.

Q13, The reversing valve changes the direction of hot gas from what component to what other component in the system?

A reversing valve is the key to heat pump operation. The compressor always pumps in one direction, so the reversing valve changes the hot-gas direction from the condenser to the evaporator as indicated by the setting on the thermostat.

Define a self-contained air-conditioning unit.

A self-contained air-conditioning unit is understood to be an air-conditioning unit that is complete with compressor, condenser, evaporator, controls, and casing.

Define "air conditioning" with respect to building space

Air conditioning is the simultaneous control of temperature, humidity, air movement, and the quality of air in a conditioned space or building. Conditioning the air in a space helps to maintains a predetermined temperature-humidity relationship to meet comfort or technical requirements. The intended use of the conditioned space is the determining factor for maintaining the temperature, humidity, air movement, and quality of air. This warming and cooling of the air is usually referred to as winter and summer air conditioning.

Name three methods to purify air in an air conditioner?

Air may be purified or cleaned by filters, air washing, or electricity. Filters are usually made of fibrous material, which collects the particles of dust and other foreign matter from the air as it passes through the filter. In some cases, the fibers are dry, while in others they have a viscous (sticky) coating. Filters usually have a large dust-holding capacity. When filters become dust-laden, they are either discarded or cleaned. Water sprays are used to recondition the air by washing and cleaning it. These sprays may also serve to humidify or dehumidify the air to some extent. Electrical precipitators remove the dust particles from the air. The air is first passed between plates where the dust particles are charged with electricity; then the air is passed through a second set of oppositely charged plates that attract and remove the dust particles. This method is by far the best method of air cleaning, but the most expensive and typically used In large air-conditioning systems,

Define an air-conditioning unit.

An air-conditioning unit is understood to consist of a heat transfer surface for heating and cooling, a fan for air circulation, and a means of cleaning the air, motor, drive, and casing.

Define an air-handling unit.

An air-handling unit consists of a fan, heat transfer surface, and casing.

Heat pumps operating below 45°F develop what problem on the outside coils?

As the outside temperature drops, the heat pump runs for longer periods until it eventually operates continually to satisfy the thermostat. The system "balance point" is when the heat pump capacity exactly matches the heating loss. The balance point varies between homes, depending on actual heat loss and the heat pump capacity. However, the balance point usually ranges between 15°F and 40°F. Either electric heat or fossil fuels provide the auxiliary heat

Q1. What is the term given to the net effects of temperature, humidity, and air motion?

Effective temperature is the term given to the net effects of the factors temperature, humidity, and air motion. These factors are interrelated in their effects on health and comfort. Effective temperature cannot be measured with a single instrument. A psychrometric chart aids in calculating the effective temperature when given sufficient known conditions relating to air temperatures and velocity

Q7. What are the two types of filter designs?

Filters may be designed as permanent or throwaway types. Permanent filters are usually cleaned. Throwaway filters are only one-time filters and are discarded when they become dust-laden.

Qll. Floor units are often referred to as what type of units.

Floor units are sometimes referred to as Package Units, as the entire system is located in the conditioned space.

Q3. What is the term for the amount of water vapor in a given volume of air? What is the difference between the terms "humidity" and "relative humidity".

Humidity is the amount of water vapor in a given volume of air. Relative humidity is the amount of water vapor in a given amount of air in comparison with the amount of water vapor the air would hold at a temperature if it were saturated. Relative humidity may be remembered as a fraction or percentage of water vapor in the air; that is, DOES HOLD divided by CAN HOLD

Define a remote air-handling unit.

R e m o t e air-handling unit or a remote air-conditioning unit is a unit located outside of the conditioned space that it serves.

Q4. What instrument is used to measure relative humidity? How does this instrument measure relative humidity?

Relative humidity is determined by using a sling psychrometer. A sling psychrometer consists of a wet-bulb thermometer and a dry-bulb thermometer. The wet-bulb thermometer is an ordinary thermometer similar to the dry-bulb thermometer, except that the bulb is enclosed in a wick that is wet with distilled water. The wet bulb is cooled as the moisture evaporates from it while it is being spun through the air. This action causes the wet-bulb thermometer to register a lower temperature than the dry-bulb thermometer. Tables and charts have been designed that use these two temperatures to arrive at a relative humidity for certain conditions.

Q9. What are the two types of self-contained air-conditioning units.

Self-contained air-conditioning units may be divided into two types: window-mounted and floor-mounted units. Window-mounted air-conditioning units usually range from 4,000 to 36,000 Btu per hour in capacity. Floor-mounted air-conditioning units range in size from 24,000 to 360,000 Btu per hour.

Q5. The point where water vapor condenses is called the dew point. True or False. What is "dew point temperature".

TRUE The dew point depends on the amount of water vapor in the air. The dew-point temperature of the air for the quantity of water vapor present is the temperature point at which the air is saturated and condensation of moisture in the air begins. If air at a certain temperature is not saturated (maximum water vapor at that temperature) and the temperature of that air falls, the dew point temperature is reached when the air becomes saturated and condensation begins.

Q2. The comfort line is the specific effective temperature at which most people feel comfortable. True or False

TRUE. The range of effective temperatures within which most people feel comfortable is called the COMFORT ZONE. Since winter and summer weather conditions are markedly different, the summer zone varies from the winter zone. The specific effective temperature within the zone at which most people feel comfortable is called the COMFORT LINE.

Q8. What is the primary factor that determines the temperature and humidity required for room comfort?

The velocity air circulation is the primary factor that determines what temperature and humidity are required to produce comfort. Experience shows that a high velocity of air produces a cooling effect on human beings. The increased velocity of air passing over the skin surfaces evaporates moisture at a greater rate; thereby, cooling the individual. However, air velocity does not produce a cooling effect on asurface that does not have exposed moisture. A fan does not cool the air, but merely increases its velocity. For this reason, circulation of air has a decided influence on comfort conditions. Air can be circulated by gravity or mechanical means

Q6. What condition exists when the dry-bulb, wet-bulb, and dew-point temperatures are the same?

When the air becomes saturated, all three temperatures are the same and the relative humidity is 100 percent.

Q10. Who normally operates a window air-conditioning un

Window units are normally operated by the user who should be properly instructed on their use.