Unit 4 | unit 4 air conditioning

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RAC

Unit - 4

Air Conditioning

Q1) Name the Psychometric properties and explain them.

A1)

Psychometric properties:

Dry Air: - The mixture of Nitrogen the oxygen neglecting water vapour is known as Dry Air.
Wet Air: - It is the mixture of Dry Air and Water Vapour is known as Wet Air.
Saturated Air: - It is the mixture of Dry Air and Water Vapour and it is said saturated when it diffused maximum amount of water vapour depends on absolute pressure and temperature
Dry Bulb Temperature: - It is the temperature recorded by ordinary thermometer with a clean, dry sensing element when bulb of thermometer is expose to air.
Wet Bulb Temperature: - it is the temperature recorded by ordinary thermometer when its bulb is covered by a wet cloth exposed to the air.
Dew Point Temperature: - It is the temperature of air recorded by ordinary thermometer when the mixture present in air start to condensed
Specific Humidity: - The mass of water vapour present in 1 kg of moist air it known as Specific Humidity.
Absolute Humidity: - It is defined as the mass of water vapour in unit volume of moist air is called as Absolute Humidity.
Relative Humidity: - It is defined as the ratio of actual mass of water vapour in unit volume of moist air to the mass of water vapour in the same volume of saturated Air at the same temperature and pressure.

Q2) What do you mean by Psychometric chart and explain the different psychometric processes.

A2)

Psychometric chart:

The properties of atmospheric air at a specified total pressure are presented in the form of easily readable charts called Psychrometric Chart.
The dry – bulb temperature are shown on the horizontal axis.
The specific humidity is shown on the vertical axis.

Different Psychometric processes:

Sensible Heating
Sensible Cooling
Dehumidification
Humidifying
Adiabatic Cooling
Chemical Dehumidification
Adiabatic Mixing (Moist Air & Water Vapor)

Sensible Heating: It is addition of heat to moist air without the addition of moisture. It follows a constant humidity ratio line on the psychrometric chart.
Sensible Cooling: It is the removal of heat from moist air without the removal of moisture. It also follows a constant W on the psychrometric chart.
Heating & Cooling process – addition or removal of sensible heat without change in absolute moisture content.

NOTE: RH changes as temperature changes.

4. Dehumidification: Dehumidification by cooling – in cooling coils temp of air reduces and the saturation point (dew point) is reached.

Further cooling results in reduction of absolute humidity.

5. Cooling and Dehumidifying: It is the removal of heat and moisture from moist air, it involves sensible and latent heat transfer.

6. Humidifying: It is the addition of moisture to moist air without the addition of heat.

7. Adiabatic or evaporative cooling: A psychrometric process which involves the cooling without heat loss or gain.

Sensible heat lost by air is converted to latent heat in the added water vapor.

8. Heating and Humidifying: It is the addition of heat and moisture to moist air, it also involves sensible and latent heat transfer.

Q3) What do you mean by Effective temperature and comfort chart.

A3)

Effective temperature and comfort chart

It is defined as the temperature of a still and saturated atmosphere which would, in the absence of radiation, produce the same effect as the temperature in question.

• The first comfort scale was produced by Houghton and Yaglou in 1923, working at the American Society of Heating and Ventilating Engineers.

• Their findings were plotted on a psychrometric chart, producing ‘equal comfort lines’.

• This new scale was named Effective Temperature (ET Scale).

• The different factors determining thermal comfort – air temperature, humidity and air movements are combined together into a single index – Effective temperature

• Effective temperature is the temperature in an environment with 100% humidity and no air movements which will induce the same level of thermal comfort as in the present situation

• For example, if the effective temperature is said to be 30°C, it means that the thermal comfort is equivalent to one is an environment with temperature 30°C, 100% humidity and no air movements

• But effective temperature does not take into consideration, the effect of radiant heat energy.

The comfort chart:

The Comfort Chart is a tool that helps operators determine how well air-handling equipment is providing thermal comfort for the building occupants or for a process within the facility.

Q4) What do you mean by Infiltration & ventilation.

A4)

Infiltration:

Infiltration is the unwanted and unintentional flow of air through a building’s fabric. It’s caused by gaps and cracks, typically at junctions between different building elements. Some are big, for example a visible gap between a window frame and ill-fitting openable casement, and some are small, such as an almost imperceptible flow of air where an external wall meets a ground floor.

Ventilation:

Ventilation is the deliberate movement of air to remove contaminants such as water vapour, airborne chemicals (VOCs), CO2, NOx, and odours from an indoor environment, and to keep everything feeling ‘fresh’. Kitchen and bathroom extractors and opening a window are simple forms of ventilation.

Q5) Define the following:

Internal heat gain
Apparatus dew point (ADP)

A5)

Internal heat gain

Internal heat gain is the sensible and latent heat emitted within an internal space from any source that is to be removed by air conditioning or ventilation, and/or results in an increase in the temperature and humidity within the space.

Apparatus dew point (ADP)

If the GSHF line is extended, it strikes the saturation curve known as apparatus dew point (ADP).

Q6) What do you mean by Air Washers?

A6)

Air Washers

An air washer may be thought of as an enclosure in which air is drawn or forced through a spray of water in order to cleanse, humidity, or dehumidify the air. Cleansing the air refers to the removal of airborne impurities such as dusts, gases, vapors, fumes, and smoke. The increase in water vapor in a given space is called humidification, and the decrease of water vapor in a given space is the process of dehumidification.

Q7) What do you mean by Bypass factor?

A7)

By pass factor

Bypass factor is an important coil characteristic on moisture removal performance. Its value depends on:

• Number of rows/fins per inch

• Velocity of air

Bypass Factor of the coil:

When air streams across the cooling, portion of air may not come into contact with the coil surface.
BPF = un-contacted air flow/ total flow

BPF is normally selected at 0.1 for offshore cooling and dehumidification

Q8) What do you mean by Sensible Heat Factor and write its important factors.

A8)

Sensible heat factor (SHF)

SHF: The heat added during psychometric process may be split into sensible heat and latent heat. The ratio of sensible heat to total heat is called sensible heat factor,

SHF = SHSH+LH

Where, SH = sensible heat and LH = latent heat

Importance of SHF factor:

Total heat is comprised of sensible heat and latent heat.

SHF (Sensible Heat Factor) is the ratio between the sensible and the total heat.

The factor comes handy for the ‘building specifications’ point of view. The factor is greatly influenced by the relative humidity and the working conditions of the air coolers.

By SHF the latent and sensible cooling or heating loads on a building can be estimated. It’s the basic ratio and yet the a very important one whenever cooling load is estimated for a room.

Q9) What do you mean by Thermal Analysis?

A9)

Thermal Analysis (TA)is a group of techniques that study the properties of materials as they change with temperature Thermal analysis.

Includes several different methods. These are distinguished from one another by the property which is measured.

Thermogravimetric analysis (TGA): mass
Differential thermal analysis (DTA): temperature difference
Differential scanning calorimetry (DSC): heat difference

Q10) Define Air conditioning and write its application.

A10)

Air conditioning is the process of treating air so as to control its temperature, humidity, cleanliness.

Applications:

1. Promoting the human comfort.

2. In manufacturing areas such as for tablets, capsules and sterile products.

3. Testing chambers

4. Maintenance of animals and equipment

Q11) Define air washers.

A11)

Q12) Explain cooling tower and heat efficiency.

A12)

The cooling tower is one of the most important devices in chemical industries for example when the hot water come from heat exchanger, we use the cooling tower to cool it. The purpose of cooling tower is to cool relatively warm water by contacting with unsaturated air. The evaporation of water mainly provides cooling.

Cooling tower performance depends on four factors:

(1) Range

(2) Heat load

(3) Ambient wet-bulb temperature or relative humidity and

(4) Approach.

Range is the temperature difference between the hot water inlet and cold-water outlet at the tower.

Cooling tower efficiency is limited by the ambient wet bulb temperature. Ideally, cold water temperature will be equal to the wet-bulb temperature which is practically impossible to achieve. Hence, cooling tower efficiency will be in between 70 to 75%.

Humidification efficiency was evaluated by:

(a) Measuring the water content of the inspiratory air on perfusion with different gas flows,

(b) Measuring the water loss of a lung model, and

The humidification efficiency of HHs is a function of gas flow and design characteristics.

Q13) Write short note on Thermal analysis of human body.

A13)

Thermal Analysis (TA)is a group of techniques that study the properties of materials as they change with temperature Thermal analysis. Includes several different methods. These are distinguished from one another by the property which is measured.

Thermogravimetric analysis (TGA): mass
Differential thermal analysis (DTA): temperature difference
Differential scanning calorimetry (DSC): heat difference

Concepts of Thermal Analysis:

Temperature: A measure of kinetic energy of molecular motion.

Temperature Scales:

• Newton (1701): freezing point of water 0, human body 12

• Fahrenheit (1714): freezing point of water mixed with NaCl 0, human body 96, freezing point of water 32, boiling point of water 212

• Celsius (1742): freezing point of water 0, boiling point of water 100

• Kelvin (1848): absolute zero is the temperature at which molecular energy is a minimum and it corresponds to a temperature of -273.15°C.

Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation.

Q14) Explain inside and outside design conditions.

A14)

Indoor Design Conditions:

Indoor air quality

Air contaminants
Air cleaning

2. Acoustic requirements

3. Pressurization requirements

4. Outdoor Design Conditions:

Weather data required for load calculation
Temperature & humidity
Wind speed, sky clearness, ground reflectance etc.

ASHRAE Fundamentals 2001:

– Design severity based on 0.4%, 1%, & 2% level annually (8760h)

– For example, at 1% level, the value is exceeded in 0.01x8760h = 87.6 h in a year

Q15) Explain window air conditioner.

A15)

Window air conditioner is now and again called room air conditioner as well. It is the most effective shape of a zircon machine and is hooked up on home windows or walls.

Front Panel

The front panel is the only this is visible via way of means of the person from within the room in which it's miles hooked up and has a person interfaced manipulate be it electronically or mechanically.

Indoor Side Components

The indoor elements of a window air conditioner include: Cooling Coil with an air clear out hooked up on it. The cooling coil is in which the warmth change occur among the refrigerant with inside the machine and the air with inside the room.

Outdoor Side Components

The out of doors facet elements include: Compressor is used to compress the refrigerant. Condenser Coil is used to reject warmth from the refrigeration to the out of doors air.

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