ERBIL TECHNICAL ENGINEERING COLLEGE

FACULTY OF MECHANICAL AND ENERGY ENGINEERING

Air conditioning

Heating and humidification

Experiment number: 3

Group: B

Submitted to: Mrs. Bayan

Lecturer: Mr. Bashir E. Karim

Submitted by: Mahdi Karim

Date of submission: November 13. 2022

Objective

The objectives of this experiment are:

• To study the psychrometric chart process of moist air.

• To study and investigate the Cooling and de-humidification process

• To estimate the average heat transfer from moist air.

Introduction
Cooling is typically done by using a refrigeration system evaporator coil directly or with
an intermediate fluid’s help. De-humidification is achieved by using cooling coils at
temperatures below the dew point temperature of the air sample. :

The apparatus is shown in figure (1).

Figure (1): Schematic of (ET 620 Real Air-conditioning and Ventilation System).

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Operating Instructions and Procedure
Start up the test rig as recommended in the rig’s manual. Stat-up is followed
by running the fan at a certain speed at a uniform rate. The air carries the
humidity, which can be measured using the psychrometric chart. Set the
equipment to supply a given quantity of fresh air, which can vary for getting
different readings. The vapor-compression system (the cooling equipment) is
used for cooling/de-humidification. The de-humidification occurs due to
moisture condensation on the evaporator tubes when the air reaches the dew
point temperature. Some time is given until steady conditions are obtained,
as observed by the steadiness of various temperature readings. The system
reaches a steady state usually takes about 25-35 minutes. Follow the on-
screen menus and store the readings of all air temperature and relative
humidity.

The following measurements are taken:

• Read the dry-bulb temperature and relative humidity at the air inlet
and outlet along the air path.
• Measure air velocity and cross-sectional area of the duct.
• Measure the mass of condensation and the time for condensation.

Theory and calculation:

The cooling and de-humidification process is generally used in summer to
cool and dehumidify the air. The air will be cooled when it passes through
the cooling coil, and the air is dehumidified when the surface temperature of
the cooling coil is lower than the dew point temperature of the air. That is
called condensation.

This experiment will be conducted on the (ET 620 Real Air-conditioning

and Ventilation System). The rig has a refrigeration system for cooling and
dehumidifying air through a cooling coil.

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Liquid refrigerant inlet Vapor refrigerant outlet

Rh=30%
Supply air Condensate Incoming Air
A

B A
Rh=100%
TB=35℃

Rh=75% TADP=10℃
TA=35℃

Rh=30%
⸰B

C
Condensate removal

TB=10℃ TC=15℃ TA=35℃

Heat and mass balance

Dry air mass balance

ṁ a@A = ṁ a@B

Water mass balance

ṁ v@A = ṁ v@B + 𝑚̇ 𝑤

ṁ a@A𝑊𝐴 = ṁ a@B𝑊𝐵 + 𝑚̇ 𝑤

Heat balance

𝑚̇ 𝑎ℎ𝐴 = 𝑄̇𝑜𝑢𝑡 + 𝑚̇ 𝑎ℎ𝐵 + 𝑚̇ 𝑤 ℎ𝑤

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The capacity of the cooling coil

𝑄̇𝑐𝑜𝑜𝑖𝑙𝑛𝑔 𝑐𝑜𝑖𝑙 = 𝑚̇ 𝑎(ℎ𝐴 − ℎ𝐵) − 𝑚̇ 𝑤 ℎ𝑤

1. Air mass flow rate

𝑉̇
𝑚̇𝑎 = 1
𝑣
𝑚̇𝑎=mass flow rate of air, (kg/s)

𝑉̇ =volume flow rate of air, (𝑚̇3/𝑠)

𝑣=specific volume of air at inlet temperature (𝑚̇3/𝑘𝑔)

𝑉̇ (𝑚̇3/𝑠) =air velocity (m/s) * cross-sectional area of channel (𝑚̇2)

2. Bypass factor of the cooling coil

TB−TC
BF= 2
TA−TC

3. Total cooling load in coil

Qcooling coil = ṁ a ( hA − hB) − 𝑚̇ 𝑤 ℎ𝑤 3

hw = hf@TADP enthalpy of water at TADP of coil

4. Amount of water condensate by cooling coil

mw = ma (WA − WB ) 4

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 Table (1) observed data

Inlet air temperature before cooling coil TA 35℃

A
Inlet air relative humidity before cooling coil RhA 30%
Air temperature after cooling coil TB 15 ℃
B
Air relative humidity after cooling coil RhB 75%
Apparatus dew point temperature ADP 10℃
Amount of water condensate 0.6 kg during 30 minutes
Duct dimension (0.4 m*0.2 m )
Inlet air velocity 4 m/s

Calculation:
𝒌𝒋
𝒉𝑨 = 𝟔𝟐. 𝟒 𝑻𝑨 = 𝟑𝟓𝒄 𝑻𝑩 = 15𝐶 𝑻𝑪 = 10 𝐶
𝒌𝑮
𝒌𝒋
𝒉𝑩 = 𝟑𝟓. 𝟓 𝑽 = 𝟎. 𝟖𝟖𝟏
𝒎𝟑
Wa=0.0105 Wb=0.008
𝒌𝑮 𝒌𝒈

1. Air mass flow rate

𝑽 = (𝟎. 𝟒 × 𝟎. 𝟐) × 𝟒 = 𝟎. 𝟑𝟐𝒎𝟑

𝑉 0.32 𝑘𝑔
𝑚̇𝑎 = = = 0.3613
𝑣 0.881 𝑠

2-Bypass factor of the cooling coil

𝑇𝐵 − 𝑇𝐶 15 − 10
𝐵𝐹 = = = 0.2
𝑇𝐴 − 𝑇𝑐 35 − 10

3.Amount of water condensate by cooling coil

mw = ma (WA − WB )
𝑘𝑔
𝑚̇𝑤 = 0.3613(0.0105 − 0.008) =0.001039
𝑠
4.Total cooling load in coil
Qcooling coil = ṁ a ( hA − hB) − 𝑚̇ 𝑤 ℎ𝑤
Qcooling coil =0.3613(62.4-35.5)-0.001039(42)=9.675Kw
 Discussion

This test examined the cooling and dehumidification process dually, previously cooling has
been studied, however in this experiment dehumidification has been combined to it. Using
psychometric chart, the properties of air were found, including enthalpy and humidity ratio, also the
effects of dehumidification on the process was investigated.

The outcome of the experiment is that while heating and humidification, the expected result would
be connivance while predicting the outcome. the properties was measured at the inlet, furthermore,
the properties at the outlet of the system. The capacity of the cooling coil was 10 kw, practically it
was found to be lower than that, approximately 9.67 kW which means the full rate of the coil has
not been transferred to the coil as had to be. Reasons might include the time required for the
refrigerant to travel was not enough. In addition to the defect in the sensor responsible for the coil,
which might have given errors. Last but not least, the intensity of the air contacting the coil, which
can be named as the bypass factor, as it indicates the amount of air contacting the coil, which can be
interpreted as there is no fully contact between the air and the cooling coil. That indicates that there
are a certain amount of air having no contact with the coil, that is a major reason for having lower
value of the cooling process. Coming to the dehumidification results, when air passes through a
cold coil its condensates, and losses some mass of water vapor.

Finally mentioning the major losses of the experiment, first and foremost, the device was at indoor,
which in practice, it is designed to be at outdoor (its suction), meaning fresh air is to be fed, that
results in errors and losses. In addition, losses through the duct were inevitable, as it is a matter of
fact, this phenomenon happens. Last but not least, observing the properties on psychometric chart,
since it was gained by human being and observers, accuracy have been a crucial issue. The filters
used in the process caused the air to be reflected and some of it might have not gone through it to
finish up near the heating coil. The speedometer might read the speed of the air inaccurately, last
but not least, the room temperature, the result will be inconvenience. Also, the air had to be sucked
over and over again as a loop. Therefore, the outcome ends up indivertibly. In order to conduct a
better experiment, further studies should consider the following:

• Using fresh air and fed into the system.

• Designing a coil to minimize the bypass factor. .

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