Air conditioning
Marine Department,
(2018 / 2019)
Dr. M. Bassiouny
I) Moist air properties and psychrometric chart:
Using the Psychrometric chart, complete the following table.
State
Dry bulb
temp. (°C)
Wet bulb
temp. (°C)
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
26
21
38
13
Dew point
temp. (°C)
Humidity
ratio
(kgw/kga)
Relative
humidity
(%)
Specific
enthalpy
(kJ/kg)
40
95
21
0.01
16
0.85
4
4
80
16
30
35
27
70
0.012
40
27
10
50
24
0.02
35
Specific
volume
(m3/kg)
0.85
22
28
0.9
90
22
II) Moist air processes:
1. Air at 14 oC dbt and 90 % r.h is brought to 25 oC dbt by heating. If the air flow rate is 1500 m3/hr,
estimate the heating capacity in kW.
2. Air at 35 oC dbt and 26wbt is cooled and dehumidified by a direct expansion cooling coil till a
temperature 16 oC dbt. The air flow rate is 2000 m3/hr. Find the cooling capacity in tons-ref, Coil
SHF, Coil dew point, by-pass factor and amount of condensate in lit/min.
3. A chilled water spray system is used to cool and dehumidify 3600 kg/hr of air from 30 oC dbt and 21
o
C wbt to 10 oC dbt. Determine the cooling capacity in tons-ref, amount of condensate in lit/min,
apparatus SHF and dew point.
4. Air at 30 oC dbt and 40 % r.h is humidified partially to 90 % r.h with adiabatic air washer. Estimate
the amount of water required for humidification process in lit/min and the humidifying efficiency, if
the air flow rate is 3000 m3/hr.
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5. A cooling coil is used to cool 3600 kg/hr of air initially at 32 oC dbt and 40 % r.h. Find the cooling
capacity of the coil in tons-ref, if the final dbt is:
a) 13 oC
b) 21 oC.
6. A stream of outdoor air at 35 oC dbt and 28 oC wbt is mixed with return air at 25 oC dbt and 50 % r.h
in an air conditioning system. If the flow rates of the outside and return air are 900 and 1800 kg/hr,
estimate the condition of the air stream after mixing.
7. Moist air at 26 oC dbt and 19 oC wbt, passing through chilled water cooling coil (ADP = 10 oC). The
air is then reheated 4 oC through an electric heating coil. If the amount of moist air is 9000 m3/hr.
Represent the processes on the Psychrometric chart and then calculate the following:
a) Cooling coil capacity, in TR.
b) Heating capacity, in kW.
c) Coil BF, Coil SHR.
8. 1000 L/s outside fresh air at 35 oC dbt and 24 oC wbt is mixed with 5000 L/s return air at 24 oC dbt
and 50 % r.h. The mixture then passed over a cooling coil has a surface temperature 9 oC, and the
bypass factor (BF = 0.20). Represent the processes on Psychrometric chart, and then calculate the
followings:
a) Conditions of air off the coil (dbt & r.h).
b) Cooling coil capacity, in TR.
c) Coil sensible heat ratio (SHR).
d) Rate of coil dehumidification, in liter/min.
9. Air is to be brought to a final condition of 25 oC dbt and 50 % r.h from an initial condition of 5 oC dbt
and 90 % r.h by processes of preheating, partial adiabatic saturation to give 80 % r.h and reheating to
the final condition. If 10000 kg/hr of air are handled, find:
i. Capacity of preheater, in kW.
ii. Capacity of reheater, in kW.
iii. Water consumption in humidification process, in lit/min.
iv. Humidifying efficiency.
III) Air Conditioning processes:
Summer air conditioning:
1. The following data refer to design figure used in designing a summer air conditioning plant of a
theater employing chilled water spray. Theater capacity 1000 seats. Inside design condition is 25 oC
dbt and 50 % r.h. Outside design condition is 35 oC dbt and 26 oC wbt. Fresh air per person is 15
m3/hr. Supply air per person is 55 m3/hr. Temperature difference between supply and return air is 14
o
C. Calculate:
i. Room total load "RTH" in W.
ii. Room sensible heat factor "RSHF".
iii. Cooling capacity in tons-ref.
iv. Apparatus SHF.
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2. A summer air conditioning machine, equipped with a chilled water spray for cooling and
dehumidification, is to maintain 22 oC dbt and 70 % r.h in a print shop which has an estimated
sensible heat gain 14,600 W and internal moisture gain 6.49 kg/hr. Assume all-return system and
calculate:
i. Room sensible heat factor "RSHF".
ii. Refrigeration capacity in tons-ref.
iii. Amount of supply air in m3/hr.
Assume: the latent heat of evaporation (LH = 2225 kJ/kg)
3. The following data refer to the summer air conditioning plant of a restaurant. Inside design conditions
are 26 oC dbt and 19 oC wbt while the outside design condition is 35 oC dbt and 25 oC wbt. Room
sensible heat is 40 kW and room latent load is 20 kW. Outside fresh air is 4600 m3/hr. Assume direct
expansion cooling coil and calculate:
i. Amount of air supply in m3/hr.
ii. Cooling capacity of coil in tons-ref.
iii. Coil SHF.
iv. Amount of condensate in lit/min.
4. The following data refer to summer air conditioning plant for a restaurant. Inside design condition 26
o
C dbt and 19 oC wbt. Outside design condition 34 oC dbt and 25 oC wbt. Internal sensible heat is 20
kW. Internal total heat is 28 kW. Outside air sensible heat is 5,166 W. Calculate:
i. The capacity of cooling coil in tons-ref.
ii. The quantity of supply air in m3/hr.
iii. The quantity of outside air in m3/hr.
iv. Amount of condensate in lit/min.
5. In a summer air conditioning system, the outside design condition is 36 oC dbt and 24 oC wbt
while the inside design condition is 24 oC dbt and 50 % r.h. . The internal sensible load is 108000
W and the internal moisture gain is 155.52 kg/hr. The fresh outside air is 25 % of the supply air
while the temperature difference between supply and return is 8 oC. If a DX-Coil and electric
reheater are used, calculate:
i. The amount of supply air in cmh.
ii. The cooling capacity of the coil in tons-ref.
iii. Coil SHF.
iv. The reheater capacity in kW.
v. Amount of condensate in lit/min.
vi. BF of the cooling coil.
vii. State the Conditioner Arrangement.
6. In an all-fresh outside air summer air conditioning system of a surgical room of a hospital, the
inside design condition is 24 oC dbt and 50 % r.h. While, the outside design condition is 35 oC
dbt and 26 oC. Heat transmission load = 9000 W, Solar radiation load = 3000 W, Lighting load
= 3400 W, number of persons = 20, SH and LH by each person are 80 W and 60 W
respectively and appliances SH and LH are 1000 W and 800 W respectively. Estimate:
i. Amount of supply air in cmh.
ii. Cooling capacity of the coil in tons-ref.
iii. Coil SHF.
iv. Amount of condensate in lit/min.
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7. The following information was obtained in designing the summer air conditioning plant in a print hall.
Inside design condition is 21 oC dbt and 70 % r.h. Outside design condition is 38 oC dbt and 28 oC
wbt. Amount of outside fresh air is 40 % of the total air supplied. Estimated internal sensible heat gain
is 175,000 W. Amount of internal moisture gain is 65 kg/hr. The temperature difference between
supply and return air is 6.5 oC. Determine:
i. State the suitable type of cooling equipment installed.
ii. The quantity of supply air in m3/hr.
iii. The refrigeration capacity in tons-ref.
8. An industrial process room has 14,600 W of sensible heat and 14,600 W of latent heat under design
condition. It is required to maintain 27 oC dbt and 50 % r.h inside the room. Outside air at 33 oC dbt
and 25 oC wbt, is to be cooled and dehumidified by a chilled water spray system. The air leaves the
spray system at 5 oC dbt. Calculate:
i. The amount of supply air in m3/hr.
ii. The reheater capacity in kW.
iii. The cooling capacity in tons-ref.
iv. Apparatus SHF.
9. A chilled water spray system is to cool and dehumidify air which is to be supplied to a lecture room
having 250 seats. Assuming that the only sources of direct heat and moisture gains are the persons and
lights. The inside design condition is 24 oC dbt and 50 % r.h. All of the air handled is to be taken from
the outside. Outside design condition is 35 oC dbt and 24 oC wbt. The room is provided with 15,000 W
of lighting. Sensible and latent heat generated by each person are assumed to be 100 W and 60 W
respectively. Calculate:
i. The amount of supply air in kg/hr.
ii. The cooling capacity in tons-ref.
iii. The apparatus SHF.
10. A commission data of A/C unit using cooling coil, serve a space has 38000W total heat are as follow:
Air inlet conditions to the coil: 28 oC DBT/19 oC WBT, supply airflow rate: 5600 m3/hr, coil surface
temperature: 9oC, coil by-pass factor: 0.112. The ambient conditions are 35 oC DBT/26 oC WBT.
Determine:
i. The state in the conditioned space (DBT/R.H)
ii. The total capacity of cooling coil (Tons-Ref.)
iii. Space SHF.
iv. Percentage of fresh air.
Summer air conditioning using evaporative cooling:
1. In a summer air conditioning system employing cooling, outside air at 35 oC dbt and 17 oC wbt is first
precooled. The air is then adiabatically saturated to 100 % r.h by passing through an air washer. The
space condition is to be maintained at 26 oC dbt and 19 oC wbt. The estimated internal sensible and
latent loads are 30,000 W and 10,000 W respectively. Calculate:
i. The temperature to which the air is precooled.
ii. The amount of supply air in m3/hr.
iii. The precooler cooling capacity in tons-ref.
iv. The water consumption of the humidification in lit/min.
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2. In a summer air conditioning system employing evaporative cooling. Equal masses of fresh air and
return air after mixing are first precooled and then adiabatically humidified to 100 % by an air washer.
Outside design condition is 35 oC dbt and 17 oC wbt. Inside design condition is 26 oC dbt and 20 oC
wbt. Internal sensible heat is 30,000 W while the internal latent heat is 15,800 W. Find:
i. The quantity of air supply in m3/hr.
ii. The precooler capacity in tons-ref.
iii. The water consumption in lit/min.
iv. The spray water temperature.
Winter air conditioning:
1. A building is to be heated by passing air over a heating coil. The air temperature at heater outlet is 44
o
C. Air is then humidified using steam humidifier to satisfy the required inside design condition. The
building heat loss is 10,000 W when the inside design condition is 22 oC dbt and 50 % r.h and outside
design condition is 10 oC dbt and 5 oC wbt. One-fourth of the air supplied is to be taken from the
outside. Calculate :
i. The amount of air supply in m3/hr.
ii. The heater capacity in kW.
iii. The humidifier capacity in kg/hr.
iv. The heating capacity required to generate steam in kW.
2. The air in a factory must be maintained at 21 oC dbt and 15 oC wbt. For ventilation, a minimum of
3,400 m3/hr of outside air must be handled. The outside design condition is 10 oC dbt and 5 oC wbt.
The net heat loss from the factory is 58,500 W. The mixture of outside and return air passes through a
heating coil and air washer. The supply air dbt is 38 oC. Calculate:
i. The quantity of air supply in m3/hr.
ii. The capacity of heater in kW.
iii. The amount of make-up water in lit/min.
3. In a winter air conditioning system, the outside design condition is 10 oC dbt and 7 oC wbt while
the inside design condition is 25 oC dbt and 50% r.h.. The amount of heat loss is 25000 W. The
outside fresh air is 20% of the supply air. The temperature difference between supply and return is
8 oC. If the system includes electric heater and steam humidifier, estimate:
i. The amount of supply air in m3/hr.
ii. The electric heater capacity in kW.
iii. The steam humidifier capacity in kg/hr.
iv. The heating capacity required to generate steam in kW.
4. In a winter air conditioning system, the outside design condition is 10 oC dbt and 5 oC wbt
while the inside design condition is 24 oC dbt and 50 % r.h.. The amount of heat loss is 18000
W while the temperature of supply air is 34 oC dbt. The system includes electric preheater,
steam humidifier then reheater. Assume all-fresh outside air. If the reheater capacity is 1/3 the
preheater capacity, calculate:
i. Amount of supply air in kg/s.
ii. Preheater capacity in kW.
iii. Reheater capacity in kW.
iv. Steam humdifier capacity in kg/hr.
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5. During a test on a winter air conditioning system including mixing plenum, main heater and steam
humidifier, the following data is obtained: Outside air condition is 10 oC dbt and 7 oC wbt. Inside air
condition is 23 oC dbt and 50 % r.h. Air heater capacity is 64.25 kW. Water consumption in humidifier
is 0.3 lit/min. Supply air dbt is 32 oC. Estimate:
i. The heating capacity required to generate steam in kW.
ii. Amount of fresh air in cmh.
iii. Outside load (OATH) in W.
iv. Heat loss from space in W.
v. Amount of supply air in cmh.
Industrial humidification:
1. The waving hall in a textile factory is maintained at 29 oC dbt and 80 % r.h when the outside condition
is 35 oC dbt and 40 % r.h. The internal heat gain is 45,000 W. An adiabatic air washer is installed.
Calculate:
i. The amount of supply air in m3/hr.
ii. The water consumption in lit/min.
iii. The percentage of fresh air.
2. A twisting hall in textile factory has 1000 kW as motors, and light loads, if the inside design
conditions must maintained at 27 oC dbt and 65 % r.h. The outside design conditions in summer are 40
o
C dbt & 23 oC wbt, while in winter are 10 oC dbt & 8 oC wbt.
Provide the suitable industrial air conditioning systems using an air washer with humidification rate of
500 kgw/hr. for both summer and winter.
Draw the Psychrometric cycle for both summer and winter uses and determine:
i. The amount of supply air in m3/hr.
ii. The air-mixing ratio.
iii. The Pre-cooler and the Pre-heater capacities, in kW.
3. In an industrial air humidification plant, the amount of supply air is 6800 m3/hr. The inside design
condition is 26 oC dbt and 70 % r.h while the outside design condition is 35 oC dbt and 17 oC wbt.
Estimate the individual capacities of the plant devices and the internal heat gain in the following cases:
i. All fresh outside air.
ii. Outside air is 50 % of the supply air.
iii. Outside air is 25 % of the supply air.
Repeat the problem, if the outside design condition is 10 oC dbt and 5 oC wbt with the same amount of
supply air.
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Supplementary problems:
1. Figure (1) shows the arrangement of a summer air conditioning plant. Assume that equal masses of
outside and return air enter the cooling coil. The amount of supply air to the room is 6,800 kg/hr.
Calculate:
i. The cooling capacity of coil in tons-ref.
ii. The reheater capacity in kW.
2. Figure (2) shows the arrangement of a summer air conditioning plant. The amount of air supplied to
the space is 9,100 kg/hr. Space RSHF is 0.65. Assume 25 % fresh air enters the chilled water spray
chamber while 75 % is return air. Determine:
i. The condition of supply air.
ii. The masses of by-pass, return and fresh air in kg/hr.
iii. The room total load in W.
iv. The refrigeration capacity in tons-ref.
v. The capacity of reheater in kW.
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3. The drawing given in Figure (3) shows the arrangement of a summer air conditioning plant. Assume
that equal masses of outside air and return air enter the chilled water spray system. The total air
supplied to the space is 13,600 kg/hr. Calculate:
i. RSHF.
ii. Total internal load in W.
iii. The amount of fresh air in kg/hr.
iv. The cooling capacity in tons-ref.
v. The capacity of reheater in kW.
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IV) Cooling load calculations and Duct design:
1. A restaurant in Alexandria [38 oC dbt & 25 oC wbt] with dimensions (30 m X 20 m X 4 m height).
The heat transmission from all walls and ceiling and the solar heat are neglected. If the number of
persons is 200 (Sensible load per person = 60 W, Latent load per person = 70 W), light load is 20
W/m2, Fresh air is 7 L/s for each person, equipment heat = 3000 W, and each meal heat ( Sensible
load = 40 W & Latent heat = 55 W).
An air handling unit (AHU) with direct expansion (DX) cooling coil used to provide the air
conditioning for the restaurant at [24 oC dbt and 50 % RH). Calculate:
a) The cooling coil capacity (C.C in T.R), percentage (%) fresh air, Coil sensible heat ratio,
and the total air supply (Vs in L/s)
b) Route and size the supply round duct using ten (10) supply air outlets (round diffuser)
(Take ΔP/L = Pa/m)
3. The figure shows a classroom of dimensions 28.5 m length X 16 m width X 5 m height and have the
following design data:
• Outside design conditions: 37 oC dbt & 25 oC wbt.
• Inside design consitions: 24 oC & 50 % RH.
• Number of students: 2.0 square meters per student.
• Heat of student: 70 W sensible, 60 W latent.
• Fresh air required for each student: 8 L/s.
• Light intensity: 30 units, 4 lamps /unit, and each lamp 60 Watt.
• The overall heat transfer coefficient (U) for walls: 2.25 and for windows: 3.20 W/m2.oC
• Equipment: one data show & one computer: 400 Watt.
• Neglect ceiling, floor and sun heat gain.
a) Calculate: The space cooling load in T.R, the amount of total supply air in m3/hr, the
percentage of fresh air, and the space SHR.
b) Design a suitable summer air conditioning system for the classroom with proper cooling &
dehumidification device, represent the cycle on the psychometric chart and then calculate
the capactities of the summer cooling equipment.
For the classroom, distribute eight (8) ceiling outlets (diffusers) for the supply air, and then route the
supply duct network.
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c) Size the supply duct using the equal friction method. (Maximum duct depth must not
exceed 400 mm).
d) Calculate the total fan pressure drop (internal pressure drop = 250 Pa, diffuser pressure
drop 25 Pa, and return duct pressure drop = 45 Pa).
e) Calculate the fan motor power in kW. (ηm = 0.75)
GIVEN: Equivalent Lengths (Elbow 90 = 6 mt, Elbow 45 = 4 mt, reducer = 4 mt, Tee (main) = 1.5 mt,
Tee 90 (branch) = 15 mt)
4. The figure shows a sporting hall with the following design data:
• Dimensions: 80 m length X 30 m width X 6 m height and have the
• Outside design conditions: 40 oC dbt & 27 oC wbt.
• Inside design consitions: 24 oC & 50 % RH.
• Number of people (fans): 500.
• Heat of person: 120 W sensible, 160 W latent.
• Fresh air required for each student: 8 L/s.
• Light intensity: 40 Watt per square meter.
• The overall heat transfer coefficient (U) for walls: 0.325 W/m2.oC, and for ceiling: 0.0325
W/m2.oC
• Equipment: 1500 Watt
• Additional temperature difference due to the sun effect on ceiling: 10 oC. neglect sun gain on
the walls.
a) Calculate: The cooling load in T.R, the amount of total supply air in m3/hr, the percentage
of fresh air, and the space SHR.
b) Select two (2) air conditioning units for the hall with proper cooling& dehumidification
device, represent the cycle on the psychometric chart and then calculate the capacity of the
cooling equipment.
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5. The lecture room shown in figure has 30 m length X 20 m width X 4 m height and has the following
design data:
• Summer outside design conditions: 38 oC dbt & 25 oC wbt.
• Winter outside design conditions: 8 oC dbt & 7 oC wbt
• Inside design consitions: 22 oC & 50 % RH.
• Number of students: 350
• Heat liberated from each student: 60 W sensible, 50 W latent.
• Fresh air required for each student: 10 L/s.
• Equipment load (data show, PC, etc…): 2000 W
• Solar heat gain on roof (∆Ts = 12 oC)
• Light intensity: 20 Watts per square meter floor area.
• The overall heat transfer coefficient (U) for walls: 1.6, for roof: 0.58 and for windows: 3.18
W/m2.oC
a) Calculate the summer and the winter loads, the amount of supply air, the percentage of
fresh air, and the space SHR.
b) Calculate the capacities of all round year air conditioning components.
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