TITLE

Analysis of Air-conditioning Processes

OBJECTIVE OF THE EXPERIMENT

The objective of this experiment is to observe and understand the changes in air properties as it is treated in a basic air-conditioning unit.

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1.0 INTRODUCTION

Air-conditioning is a process of treating air for the comfort requirements of the occupants in the conditioned space. The properties of air can be modified by undergoing certain thermodynamic processes. The most basic of processes involved in an air-conditioning system are simple heating, steam humidification, simple humidification, simple cooling and dehumidification.

Besides that, air-conditioning also is very useful to maintain the surrounding environment of temperature and ambient to satisfy the temperature of human comfort, which is between 20°C to 25°C. Conventional air-condition is use to cool and to heat the surrounding environment, but in some country, air-condition may use both heating and cooling, with or without humidifying air. Also the industrial usage of air-condition is to reduce temperature of thermal produce machine.

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1

Q

2

Heating Element

1.1 THEORY/ BACKGROUND OF STUDY

Air conditioning process can be divided into 4 categories which is:

1. Simple heating (T)

2. Simple cooling (T)

3. Humidifying (+ moisture)

4. Dehumidifying (- moisture)

5. Adiabatic Mixing of Air Streams (Increase fresh air calculation)

Air conditioning processes can be modeled as steady flow processes:Mass conservation:Dry air : ma,i = mw,e Water : mw,i = mw,e or mai i = ma,ee

Energy conservation:Disregard kinetic and potential energy changes

Steady Flow Energy Balance Ei = Eo

Qi + Wi + mihi = Qe + We + mehe

Simple heating and cooling : 1. The amount of moisture for simple heating and cooling remains constant because no moisture is added or removed into the air stream. Therefore, the specific humidity at the inlet and the exit remains equal ( i = e ).

2.Heating method: the air stream flow inside a duct and passes resistance wires (heaters). Heat is added to the air stream, so the dry bulb temperature increases (Te > Ti).

Figure 1.11: Simple heating method process

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1

Q

2

Cooling Element

Humidifier

1

Q

2

Heating Element

3

From water tank

3.Cooling method: the air stream passes through cooling coil (evaporator tubes of a refrigeration system). Heat transfer occurs from the hotter air stream to the cooler refrigerant of chilled water flow , and the dry bulb temperatures decreases ( Te< Ti)

Conservation of mass: ma,1 = mw,2 and (1 = 2)

Conservation of energy : Q = ma (h2 - h1) q = h2 - h1

Figure 1.12: Simple cooling process method

Heating with humidification1.Simple heating processes produced low relative humidity (air is dry), because the moisture amount is constant (mv and constant) but the maximum moisture absorption capacity (mg) increases with temperature rise.

2.If the humidifying agent used is steam, this will result in additional heating (T3 > T2).

3.If water is sprayed, the stream will be partially cooled (T3 < T2)

Figure: 1.13 heating with humidification process

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1

Q

2

Heating Element

\

Mass conservationDry air mass balance: ma1 = ma2 =ma3 =ma

Water mass balance: ma11 = ma22 , (1 = 2) (heating section) ma22 + mw = ma33 ( humidifying section)

mw = ma(3 - 2)

Energy Balance: Qin + mah1 = ma h2 ( heating section) Qin = ma (h2 - h1)

Cooling with dehumidification:1.Dehumidification is process to remove excess water in the dry air by condensation. It is achieve by altering the cooling process.2. The air is allowed to cool at a longer period until it reaches its dew point (saturation state). Further cooling along the saturation state (100% relative humidity 0 will result in condensation of part of the moisture in the air.

Figure 1.14: Cooling with dehumidification process

Dry air mass balance: ma1 = ma2 = ma ma22 + mw = ma3

mw = ma(1 - 2)

Energy Balance: mhin = Qout + mhout Qout = m (h2 - h1) - mwhw

Adiabatic mixing of air streams.

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1.The mixing process is assuming adiabatic (no heat transfer with the surrounding).2.Two stream of air (treated air from air conditioning process ing and fresh outside air) is merging and exists as one single stream with combined properties.

Dry air mass balance : ma1 + ma2 = ma3

Water mass balance : ma11 + ma22 = ma33

Energy balance : ma1h1 + ma2h2 = ma3h3

Eliminating ma3 :

ma1

ma2=

ω2+ωh

ω3+ω2=

h2−h3

h3−h1

2.0 LAB’S APPARATUS

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Figures below shows the apparatus or equipment used in this experiment.

Figure 2.1: Air Conditioning Laboratory Unit ( P.A. Hilton)

Figure 2.2: Control Panel

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Control Panel Cooling

Area

Figure 2.3: Computer Linked Air Conditioning Unit (P.A. Hilton)

Figure 2.4: Container

Figure 2.5: Stop watch

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3.0 PROCEDURES

Start the unit by having the suction fan running and the screen displaying the Master Menu. Program 1 shows the process data displayed on a schematic layout of the system. Program 2 displays the properties of the treated air on the psychometric chart.

A) No Process

Print the data and psychometric chart to read the initial properties of the air as it enters the air-conditioning unit.

B) Sensible Heating

Switch on a 1kW pre-heater and print the data. Then, switch on the 0.5 kW re-heater and print the data and chart. For this process, calculate the temperatures rise of the air at the exit.

C) Steam Humidification

Switch all water heaters to boil the water. When steam is produced, switch only 3 kW of heat to maintain the steam. Print the data and chart when the conditions are stable. Then, calculate the amount of steam introduced the change in relative humidity and the corresponding rise of temperature.

D) Cooling and Dehumidification

Switch on the compressor of the refrigeration system. Cool the air until 18°C to 20°C (stable temperature), and then print the data and chart. Calculate the heat rate and amount of moisture removed from the air. Lastly, the time for the drain water filled up the measuring cylinder about 100 ml from 0 ml was recorded using stopwatch.

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4.0 DATA & RESULTS

This table below shows the data and result obtained for Air-conditioning processes which is No process, Sensible heating, Steam humidification, cooling and dehumidification experiment.

Experiment

Reading

No process Sensible heating (kW) Steam

humidification

Cooling and dehumidification

1.0 1.5 20 100T1 (TA d) 27.5 27.7 28.2 28.6 31.0 31.2T2 (TA w) 23.4 23.8 24.2 25.0 25.4 25.6T3 (TB d) 28.1 38.2 40.1 33.9 31.4 31.6T4 (TB w) 24.4 28.7 29.5 34.4 26.4 26.4T5 (TC d) 27.5 36.0 39.2 33.3 18.6 18.5T6 (TC w) 23.2 26.3 27.4 33.4 17.9 17.9T7 (TD d) 27.4 34.9 42.9 33.5 19.2 18.9T8 (TD w) 23.6 26.4 28.4 33.8 18.7 18.6T9 (T 1) X X X X 11.3 12.1T10 (T 2) X X X X 69.0 79.0T11 (T 3) X X X X 46.3 47.9T12 (T4) X X X X 6.9 7.7

Qp X 1001.2 1002.1 X XQr X 0.00 532.9 X XQb X X 2740.6 X

Pevap(P1) X X X 23.9 223.3Pcond(P3) X X X 1159.7 1223.4

ma 214.8 209.6 200.0 219.6 219.9mr X X X

Time(s) X X X 0 459.59Drain Water (m) X X X 100 ml

Table 1.0: Data and result obtained for Air-conditioning processes

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5.0 DISSCUSSIONS

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6.0 CONCLUSIONS

7.0 REFERENCES

There are several resources that had been referred to in order to finish this report:

1. MEC551 Thermal Engineering, McGraw Hill Companies, 2011.

2. R. K. Rajput, Laxmi Publication, Thermal Engineering, Apr 1, 2010.

3. J. Selwin Rajudurai, New Age International, Thermodynamic and Thermal Engineering, Jan

1, 2003.

4. http://www.me.eng.kmutt.ac.th/MEE362_files/Air-conditioning-Unit.pdf

5. http://www.autopedia.co.uk/motoring-information/169-how-to-how-does-it-work/air-

conditioning-how-it-works-theory

6. http://encyclopedia2.com/Air+Conditioning

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8.0 APPENDICES

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