Domestic Air Conditioning MCQ Quiz - Objective Question with Answer for Domestic Air Conditioning - Download Free PDF

Explanation:

Heat load:

• The heat that develops inside the conditioned space from various sources is known as heat load or cooling load.
• Without heat load calculation we are not able to select properly rated Air conditioning units.

Source of Heat load:

• Outside heat (Solar radiation)
• Inside generated heat
• Visitors Heat

Sensible Heat:

• The heat increases or decreases the temperature of the body.
• Sensible heat is heat transferred by a body or thermodynamic system that affects the temperature of the body or system, as well as some macroscopic variables of the body or system.
• It can be defined as a system that does not show the phase transition.

Latent Heat:

• The heat is absorbed or released during phase change.
• At a constant temperature, during phase transition, the amount of heat absorbed or released is called latent heat.
• It describes the changes that occur in the internal energy of the system.

Heat load addition in AC system:

• Sensible Heat - added by types of equipment like printer, oven, etc.
• Latent Heat - added by humans.

Explanation:

Anemometer:

• It is a device that is used for measuring the velocity of air.
• When a small propeller is located in an air stream, the air stream rotates the propeller due to the passage of air over the blades. If the propeller is coupled with the dial indicator, the dial indicated indicates the value of flow. This type of instrument is known as an anemometer.
• The anemometer is located at a right angle to the flow of the air stream.
• There are three types of anemometers:
  1. Rotating vane anemometer
  2. Hot wire anemometer
  3. Deflecting vane anemometer

Thus, option (1) is the correct answer.

Explanation:

Direct cool refrigerator:

• Direct Cool Single Door Refrigerators work on the natural circulation of cool air without any external aid, leading to instant cooling.
• However, this makes it impracticable to control the uneven distribution of cool air.
• Direct Cooling technology is limited to Single Door domestic refrigerators.
• One of the main disadvantages here is that the frost gets collected around the freezer box and you will defrost it regularly and sometimes even scrape the ice out of the freezer manually.

Wire mesh condenser:

• One of the commonly used condensers in domestic refrigerators is the wire-and-tube (wire mesh) condenser.
• In this type, the wire mesh is provided vertically on a frame.
• The fins are like a thin rod (2mm dia) evenly welded in proper intervals to the frame.
• The condenser coils will be clamped & soldered to the fins. The frame is fit at the back wall of the fridge, tighten the screws.
• The natural air passes through the fins (distributed) & the condenser coils get cool. The pollution of air, the condenser wire mesh will get a coating of fine dust.
• This dust over the condensing tubes will affect the heat transfer efficiency of the condenser which can be cleaned periodically.

Explanation:

System performance:

• It is the most important required factor applicable to all refrigerating and air conditioning systems/appliances.
• It is nothing but the ‘measured output’ of the system/ appliance during functioning.
• Refrigerant charge is playing a major role in system performance.
• Each and every system/appliance will require a particular charge quantity of refrigerant based on the application (high, medium, or low temperature) and size of the components (condenser, receiver, evaporator, accumulator, etc.)
• System performance can also be defined as the ability of the system/appliance to remove heat from the space being cooled.
• It is expressed in the unit Kcal/hr (metric) or KW (SI unit) which is found from the following formula.
• System capacity = (Mass flow of refrigerant) × (refrigerating effect)
• The performance of the system will be affected by many reasons, but due to installation wise also the performance may affect sometimes.
• Performance is a visual inspection of the unit.
• Check the installation of all connecting duct collars or divider plates which separate the return and discharge/supply air.
• Any leakage from the supply air to the return is a loss in capacity to the recreational vehicle and must be sealed.
• Continuing with the visual inspection, you must make sure the return air filter(s) and the evaporator and condenser coils are clean and undamaged.
• Turn the blower to high speed.
• Set the controls for maximum cooling.
• Clean and straighten the fins on both coils and clean the filter(s) as necessary before starting a cooling.
• Do not place a thermometer inside the air inlet door for the performance test of an air-conditioning system.

Explanation:

Leak testing methods: 

Electronic leak detectors:

• This type is highly sensitive and operated by batteries.
• The refrigerant is sensed by a plug-in element exposed to air drawn through a probe or tube.
• Its pressure will be indicated by a flashing lamp and audible ‘bleep or buzz’ or a meter reading, each increasing in speed or intensity as more refrigerant passes over the element.
• The best way of checking the leak of the split A/C condenser installed unit is with an electronic leak detector.
• The halide torch and electronic leak detector are difficult to use around urethane insulation.
• Since urethane uses refrigerant as the expander such detection devices show a leak trace all the time.
• In this case, the soap bubble test is best.

• It is applicable for ammonia refrigerant vapor.
• When it is exposed to air containing ammonia vapor, it gives off a white cloud of ammonium chloride or ammonium sulfite.
• The drawback of this method, it cannot be used to pinpoint leaks.

• This is also applicable to ammonia.
• When it is exposed to ammonia vapor, moist red litmus paper will turn blue.
• The drawback of this method, it cannot be used with any halogen family refrigerants.

• This method is followed in most common areas on pipes and fittings.
• Soapy water (mixture of soap and water) will indicate the locations of leaks by the formation of bubbles escaping the gas/vapor/air.
• The drawback of this method is applicable to the pressure of the system more than atmospheric pressure (1.01325 bar).
• When test solutions are applied to low temperature, low pressure (below atmospheric level) suction lines could cause considerable damage; due to which the test solution could be drawn into the system.

• This kind of leak detection is used to locate fluro-carbon refrigerant leaks by the fuel like propane, butane, or methylated spirits which is filled into the fuel tank.
• The fuel tank supplies pressurized fuel at a steady and controlled pressure and a jet admits the fuel to a burner.
• When lit, the burner flame is supported by oxygen in the air which is drawn through a tube used as a sensing probe.
• The probe is passed slowly over the joints or surfaces being leak tested.
• If any fluro-carbon refrigerants are drawn into the tube, the color of the lamp flame will change to green or blue depending on the quantity of gas passed over the burner element.

Concept:

Air Conditioning:

• Air conditioning is the simultaneous control of temperature, velocity, purity, and humidity of the air.
• The objective of this system is to provide the environment with the required temperature and humidity, for human comfort and health.
• 50% RH and 22°C to 25°C dry bulb temperature are found to provide comfort.

Vapour Compression Cycle

• The vapour-compression cycle is a process used to extract heat from a box or a room that underlies most refrigeration and air conditioning techniques.
• It consists of four separate stages:
  1. Compression(1-2)
  2. Condensation(2-3)
  3. Expansion(3-4)
  4. Evaporation (4-1)

In room AC there is no duct provided. The conditioned air is directly supplied to the enclosed space without duct.

As much lower temperature is to be maintained in the domestic refrigerator, so its COP is always low compare to window AC.

COP = T_L/(T_H-T_L)

In the split air conditioner, there are two units

Outdoor unit: This contains the important components of the air conditioner like the compressor, condenser coil and also the expansion coil. There is also a fan in the outside unit which blows the air over condenser coil. As compressor is maximum noise making part and its located outside so there is no noise inside the house.

Indoor unit: It is the indoor unit that produces the cooling effect inside the room. It houses the Evaporator coil, blower and motor, air filter, control panel, supply and return air grills.

In the split air conditioner there are two units

Outdoor unit: This contains the important components of the air conditioner like the compressor, condenser coil and also the expansion coil. There is also a fan in the outside unit which blows the air over condenser coil. As compressor is maximum noise making part and its located outside so there is no noise inside the house.

The part marked as A is transmitter.

Transmitter: Sends signals to the indoor unit

Display: Displays the current settings. Each section is shown with all its displays ON for the purpose of explanation

In the room A.C, the vapour compression cycle is utilised. In this cycle, the refrigerant vapours are compressed in the compressor and then sent to the condenser for phase change. After passing through the condenser, it is expanded in the expansion valve and then passed through the evaporator to produce a cooling effect.

In Evaporator: As the liquid refrigerant flows through the evaporator, it absorbs heat and changes from the liquid state to a saturated vapour.

In Compressor: Due to the work done on it during compression, the gas further superheated. Therefore the temperature of the discharge gas will be much higher than the saturation temperature of vapour corresponding to discharge pressure.

In Condenser: In the condenser, the temperature of the superheated vapour has to be brought down to its saturation temperature before it can be condensed into a liquid.