2. The total amount of heat energy that must be removed from a system by a cooling mechanism in a unit
time equal to rate at which heat is generated by people, machinery, and processes, plus the net flow of
heat into the system not associated with the cooling machinery.
Cooling Load Calculation
The following methods have been developed for cooling load calculation-
1) Total Equivalent Temperature Difference. (TETD) Method
2) Cooling Load Transfer Function Method (TFM)
3) Cooling Load Temperature Difference (CLTD) Method.
I applied here the third method that is Cooling Load Temperature Difference (CLTD) Method. For
calculating the cooling load of that particular room. The total process and calculations are given bellow.
Assumptions
Walls: 140 mm brick
Roof: 200 mm brick
Window glass: 13.5 mm clear plate glass
Lighting: 4 pieces of tube light (per light 40 watt)
Occupancy: 15 people
Other power equipment: printer (14 watts), 2 set of Computer (300 watts per set), 2 pieces of Fan
(75 watt per piece), Photocopy machine (1 kW)
All dimensions are in meter

3. Several loads to be calculated for summing the total cooling load. Loads are- Transmission load, solar
heat gain, internal load, occupancy.
Location Statistics
For Chittagong
- [N 220
21’] [E 910
50’]
- Elevation: 27 m above sea.
- Standard pressure at elevation: 1 bar
- Maximum dry bulb temperature: 320
C
- Maximum wet bulb temperature: 270
C
- Recommended design load temperature for office is 25.50
C
Transmission Load Calculation
Q= UA (CLTD)
U= Overall heat transfer coefficient. (kW/m2
K)
A= Area of roof and wall (m2
)
CLTD= Cooling load temperature difference. (o
C)
Area Calculation
Wall area with window
A= width × height [Considering 10 ft roof height]
North 9×3= 27 m2
East 7.5×3= 22.66 m2
West 7.5×3= 22.66 m2
South 9×3= 27 m2
Window area
2 windows are there, one is (0.604 m × 1.81 m) and the other one is (1.21 m × 1.81 m). All 2 windows
are mounted at the North wall side of the room.
Window 1 area 0.604×1.81= 1.09 m2
Window 2 area 1.21×1.81= 2.19 m2
Total Window Area= 3.28 m2
Roof area
9×7.5= 67.5 m2
Door Area
Considering one door at the south side wall, 1.51 m × 1.81 m)
There for, door area 1.51×1.81= 2.74 m2

4. Actual Area of the wall
North (27-1.09-2.19) m2
= 23.72 m2
East 22.66 m2
West 22.66 m2
South (27-2.74) m2
= 24.26 m2
U value calculation
U value calculation for roof
Component R (m2
K/W) Reference
Outside air film 0.004 ASHRAE Fundamentals 1989,
Table 1
200 mm brick 0.625 ASHRAE Fundamentals 1989,
Table 4
Inside air film 0.160 ASHRAE Fundamentals 1989,
Table 1
Total 0.789
U= 1/R= 1/0.789= 1.27 W/ m2
K
U value calculation for wall
Component R (m2
K/W) Reference
Outside air film 0.004 ASHRAE Fundamentals 1989,
Table 1
140 mm brick 0.44 ASHRAE Fundamentals 1989,
Table 4
Inside air film 0.120 ASHRAE Fundamentals 1989,
Table 1
Total 0.56
U= 1/R= 1/0.56= 1.79 W/ m2
K
CLTD correction calculation
CLTD (corrected) = (CLTD+LM) k + (25.5-Tr) + (Tₒ-29.4) f
LM= Latitude month correction.
K= Color adjustment. (for light color k is 1)
Tr= Design room temperature. (25.5o
C)
Tₒ= Average outdoor temperature. (o
C)
f= attic fan factor (1 for no attic fan, 0.75 for positive attic ventilation)

5. Exposure CLTD
(ASHRAE
Table
31)
LM
(ASHRAE
Table
32)
k 25.5 Tr To 29.4 f CLTDc
N 7 6.6 1 25.5 25.5 28 29.4 1 12.2
E 15 -1.6 1 25.5 25.5 28 29.4 1 12
S 11 -4.4 1 25.5 25.5 28 29.4 1 5.2
W 11 -1.6 1 25.5 25.5 28 29.4 1 8
Roof 36 -2.7 1 25.5 25.5 28 29.4 1 31.9
Now total transmission load
Item Description Area (m2
) U Factor (W/ m2
K) CLTDc (o
C) QTransmission (W)
Wall North 23.72 1.79 12.2 518
South 24.26 1.79 5.2 225.82
East 22.66 1.79 12 486.74
West 22.66 1.79 8 324.5
Roof 67.5 1.27 31.9 2746.78
Glass 3.28 6.30 7 144.65
Total 4446.49
Solar Heat Gain
Q (SHG) = A (SC) (SHGF) (CLF)
A= Open glass area. (m2
)
SC= Shading coefficient.
SHGF= Solar heat gain factor.
CLF= Cooling load factor.
Description Area (m2
) Shading Coefficient
(ASHRAE Table 20)
SHGF
(ASHRAE
Table 34)
CLF QSHG (W)
North 3.28 0.88 407 0.75 881.07
Internal Load
Q= P (CLF)
P= Input operating power (W)
CLF= Cooling load factor

6. Item Input (W) CLF (ASHRAE Table 41,
42, 45)
Q (W)
4 pieces of tube light 160 .81 129.6
Printer 14 1 14
Computer 600 1 600
Fan 150 1 150
Photocopy Machine 10000 1 10000
Total 1893
Occupancy
Q= N G (CLF)
N= Number of occupant.
G= Sensible or latent heat. (W)
CLF= Cooling load factor. (Dimensionless for people)
Number SHG LHG CLF Q
Sensible 15 75 1 1125
Latent 15 55 1 825
Total 1950
Total Cooling Load Summation
Load Q (W)
Transmission Load 4446.9
Solar Heat Gain 881.07
Internal Load 1893
Occupancy 1950
In Total 9170.97
So the total load is 9170.97 watt converting this to Air conditioning unit ton we get 2.61 Ton, so we
need to select an air conditioning system around 2.5 to 3 ton.