This document contains calculations for determining the sensible heat load of an office space. It includes calculations for solar heat gain through windows and walls/roof, transmission gains through doors, glass, partitions and the floor, infiltration from windows and doors, ventilated air, and internal occupancy heat loads. Sensible heat loads are calculated in watts for various building elements and occupancy. The total sensible heat load is the sum of loads from all sources. Psychrometric properties of indoor and outdoor air are also provided.

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4. CALCULATION SHEET
 Space used for Office : 27 x 17 x 4 m3
 = 1836 m3
 PSYCHROMETRIC PROPERTIES
CONDITION DBT WBT % RH DPT h W [kg/kg]
OUTDOOR 43 27 29 21.3 85 0.016
ROOM 25 18 50 15.7 50.85 0.010
DIFFERENCE 18 34.15 0.006
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5. EFFECTIVE ROOM SENSIBLE HEAT
SL.
NO
TYPE OF LOAD LOAD IN
WATT
1 SENSIBLE HEAT SOLAR HEAT GAIN THROUGH WINDOW
GLASS
W
2 SOLAR TRANSMISSION GAIN –WALLS & ROOF W
3 TRANSMISSION GAIN –OTHERS W
4 INTERNAL HEAT GAIN W
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6. A. ROOM SENSIBLE HEAT LOAD CALCULATION
1. SENSIBLE HEAT SOLAR HEAT GAIN THROUGH WINDOW GLASS
ITEM AREA (m2) /
QUANTITY
SOLAR HEAT GAIN
(W/m2)
CONVERSION /
MULTIPLICATION
FACTOR
LOAD IN
WATT (W)
EAST GLASS ---------- ------------------------ -------------- ----------
WEST GLASS m2 W/m2 -------------- W
NORTH
GLASS
m2 W/m2 -------------- W
SOUTH GLASS m2 W/m2 -------------- W
SKY LIGHT ------------ ----------- -------------- -------------
TOTAL W
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7. 2. SOLAR TRANSMISSION GAIN –WALLS & ROOF
ITEM AREA (m2) /
QUANTITY
EQUIVALENT
TEMP.DIFFERENCE
(Δ0C)
CONVERSION /
MULTIPLICATION
FACTOR (U)
W/m2/K
LOAD IN
WATT (W)
UA ΔT
EAST WALL ---------- ------------------------ -------------- ----------
WEST WALL m2 0C W/m2/K W
NORTH
WALL
m2 0C W/m2/K W
SOUTH
WALL
m2 0C W/m2/K W
ROOF SUN m2 0C W/m2/K W
TOTAL W
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8. 3. TRANSMISSION GAIN –OTHERS
ITEM AREA (m2) /
QUANTITY
TEMP.DIFFERENCE
(Δ0C)
CONVERSION /
MULTIPLICATION
FACTOR (U) W/m2/K
LOAD IN WATT (W)
UA ΔT
DOORS m2 0C W
ALL GLASS m2 0C W
PARTITION m2 0C W
FLOOR m2 0C W
INFILTRATED
LOAD
VENTILATED
LOAD
CMM
CMM
0C
0C
W
20.4x(cmm) x ΔT x B.F
= W
TOTAL W
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9. 4. INTERNAL HEAT GAIN
ITEM PERSON/ QUANTITY LOAD/PERSON
OR
QUANTITY
LOAD IN WATT (W)
PEOPLE W
POWER W
LIGHTS W
APPLAINS W
ADDITIONAL W
TOTAL W
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10. SOLAR HEAT GAIN THROUGH WALL/ROOF
 Solar heat gain through wall can be calculated using the
equation
 Q = U A Δ T
 Where ΔT = Equivalent temperature difference obtained
from Table
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11.  From Table 18.9 following values OF EQUIVALENT TEMPERTURE
DIFFERENCE in 0C are tabulated for walls & Roof
WALL 2 PM
WEST WALL 16.5
NORTH WALL 11.3
SOUTH WALL 17.4
ROOF 29.7
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12. HEAT LOAD CALCULATIONS
 To calculate heat load Q through Wall, roof & floor, We require U , the
overall heat transfer coefficient as
 Q = U x A x Δ T
 A. To calculate U for Outside wall:-
 The thermal conductivity K is available in Table 18.1

 Uoutside wall = 3.5 W/m2/K
o
i h
1
h
1
1








plaster
brick
concrete K
x
K
x
K
x
U
23
1
65
.
8
01251
.
0
73
.
1
2
.
0
32
.
1
1
.
0
7
1
1





U
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14.  B. Partition wall:

 U = 1.86 W/m2/K
i
i h
1
2
h
1
1






plaster
brick K
x
x
K
x
U
7
1
65
.
8
0125
.
0
2
32
.
1
33
.
0
7
1
1



 x
U
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15.  C. Roof:

 URoof = 2.13 W/m2/K
o
i h
1
h
1
1








asbestos
plaster
roof
concrete K
x
K
x
K
x
U
23
1
154
.
0
04
.
0
65
.
8
0125
.
0
9
2
.
0
7
1
1





U
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16.  D. floor

 UFloor = 6.05 W/m2/K
h
1
1
i concrete
floor
K
x
U



9
2
.
0
7
1
1


U
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17. Rates of solar heat gain through glass on June 21st in W/m2
TABLE 17.9D
DIRECTION 2PM
WEST GLASS 492
NORTH GLASS 91
SOUTH GLASS 32
The heat gain includes the direct + diffused solar radiation
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18. A. ROOM SENSIBLE HEAT LOAD CALCULATION
1. SENSIBLE HEAT SOLAR HEAT GAIN THROUGH WINDOW GLASS
ITEM AREA (m2) /
QUANTITY
SOLAR HEAT GAIN
(W/m2)
CONVERSION /
MULTIPLICATION
FACTOR
LOAD IN
WATT (W)
EAST GLASS ---------- ------------------------ -------------- ----------
WEST GLASS 12 m2 492 W/m2 -------------- 5900 W
NORTH
GLASS
3 m2 91 W/m2 -------------- 270 W
SOUTH GLASS 6 m2 32 W/m2 -------------- 190 W
SKY LIGHT ------------ ----------- -------------- -------------
TOTAL 6360 W
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19. 2. SOLAR TRANSMISSION GAIN –WALLS & ROOF
ITEM AREA (m2) /
QUANTITY
TEMP.DIFFERENCE
(Δ0C)
CONVERSION /
MULTIPLICATION
FACTOR (U)
W/m2/K
LOAD IN
WATT (W)
UA ΔT
EAST WALL ---------- ------------------------ -------------- ----------
WEST WALL 96 m2 16.5 0C 3.5 W/m2/K 5540 W
NORTH
WALL
34 m2 11.3 0C 3.5 W/m2/K 1345 W
SOUTH
WALL
34 m2 17.4 0C 3.5 W/m2/K 3590 W
ROOF SUN 459 m2 29.7 0C 2.13 W/m2/K 29035 W
TOTAL 39510 W
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20.  Two types of air circulated:
 1. Ventilated Air
 2. Infiltrated Air
 Load due to Infiltrated air is
 a. Through open door
 b. Exhaust fan
 c. Crack through Windows.
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21. INFILTRATION RATE FOR WINDOWS
 The flow of air due to wind over a building creates regions in which the static
pressure is higher or lower than the static pressure in the undisturbed area.
 The pressure is positive on the wind side resulting in the infiltration of air
 There are two methods of estimating the infiltration of air into conditioned space
due to wind action. They are
 i) Crack method
 ii) Air change method
 In crack method, the estimate is based on measured leakage characteristics
and width and length of cracks( perimeter) around windows or doors.
 The air change method assumes a certain number of air changes per hour for
each space depending on its usage.
 The crack method is generally regarded as more accurate and is used in the
case of windows.
 The air change method is more convenient to use for doors.
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22.  The leakage of air in this case is a function of the wind pressure ΔP which can
 be determined by knowing the wind velocity C using the equation
 ΔP = 0.00047 C2
 Where ΔP is in cm of water and c is the wind velocity in km/hr
 Here assuming wind velocity 15 km/hr,
 ΔP = 0.00047 x 152 = 0.11cm of water
 Using Table 18. 11 for Infiltration through double Huge windows in m2/h/m
 For weather-stripped, loose fit type Window, and for minimum ΔP = 0.25 ,
 Infiltration = 2.5 m3/h/m crack
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24.  Length of the crack:
 Length of the crack = No. of windows x perimeter
 = 7 x [ 2 ( 2+1.5) ]
 = 49 m
 Infiltration load in cmm:
 Infiltration load in cmm = Infiltration in m3/h/ length of crack x Length
of crack
= 2.5 x 49 /60
 = 2.04 cmm
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25. INFILTRATION DUE TO DOOR OPENING:
 Infiltration through door openings depends on the type of door, as well
as usage.
 Use Table 18.13- 18.15 for this.
 Here Door is on adjacent wall, wooden door for average use
 From the Table 18.13,
 Infiltration in cmm /m2 = 1.98
 Here No.of doors = 3
 Area of the door = 1.5 x 2 = 3m2
 Total infiltration rate = infiltration rate in cmm /m2 x area x No.of doors
 = 1.98 x 3 x 3
 = 17.8 cmm
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27.  Total load due to Infiltration:
 = Infiltration due to windows + Infiltration due to door openings
 = 2.04 cmm + 17.8 cmm
TOTAL INFILTRATION LOAD = 19.84 cmm
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28. VENTILATED AIR
 Ventilated is the fresh air coming from outside conditions.
 Total ventilation in cmm = No. of occupancy x ventilation rate
 Ventilation rate for different application can be obtained from Table 16.2
 Here application is for Office use
 From table 16.2 recommended cmm/person = 0.28-0.6
 VENTILATION LOAD = No.of occupancy x 0.28
 = 100 x0.28
 = 28 cmm


VENTILATION LOAD = 28 cmm
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30. OCCUPANCY LOAD
 The occupancy load ( both Sensible heat load (SHL) and Latent heat
load (LHL) is obtained form the Table 19.1
 Corresponds to the activity as office work and the DBT 250C, take the
average value between 240Cand 260C
 SHL = (80 + 70)/2 = 75 W
 LHL = (60 + 70)/2 = 65 W
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32. 3. TRANSMISSION GAIN –OTHERS
ITEM AREA (m2) /
QUANTITY
SOLAR HEAT GAIN
(W/m2) /
TEMP.DIFFERENCE
(Δ0C)
HUMIDITY DIFFERENCE
CONVERSION /
MULTIPLICATION
FACTOR (U) W/m2/K
LOAD IN WATT (W)
UA ΔT
DOORS 9 m2 180C 0.63 100 W
ALL GLASS 12+3+6 =
21 m2
18 0C 5.9 W/m2/K 2230 W
PARTITION 108+28 =131
m2
*15.5 0C 1.86 W/m2/K 3930 W
FLOOR 459 m2 ** 2.5 0C 6.05 W/m2/K 36940 W
INFILTRATED
LOAD
VENTILATED
LOAD
19.8 CMM
28CMM
18 0C
18 0C
20.4 ***
20.4
7270 W
20.4x(cmm) x ΔT x B.F
= 20.4x 28x18x0.15
=1542 W
TOTAL 20470 W
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33.  * Assume a temperature difference of 2.50C across the floor,
 ΔT for Partition = 18-2.5 = 15.5 0C
 ** Assume a temperature difference of 2.50C across the floor
 *** 20.4 is the conversion factor from cmm into W for Infiltration
W
60
C
x
x
cmm p
T
Q
on
Infiltrati s 


W
(cmm)
20.4
60
1.0216
x
1.2
x
cmm
T
T
Q
on
Infiltrati s




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34. 4. INTERNAL HEAT GAIN
ITEM AREA (m2) /
QUANTITY
SOLAR HEAT GAIN
(W/m2) /
TEMP.DIFFERENCE
(Δ0C)
HUMIDITY DIFFERENCE
CONVERSION /
MULTIPLICATION
FACTOR (U)
W/m2/K
LOAD IN
WATT (W)
UA ΔT
PEOPLE 100 -------------- 75W/PERSON 7500 W
POWER --------- -------------- -------------- ---------
LIGHTS 15,000 W -------------- 1.25* 18750 W
APPLAINS -------------- -------------- -------------- --------------
ADDITIONAL -------------- -------------- -------------- ------------
TOTAL 26250 W
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35.  *Lighting load :Electric lights generates sensible heat w]equal to the
amount of the electric power consumed.
 Most of the energy is liberated as heat, and the rest as light which also
eventually becomes heat after multiple reflections.
 As rough calculation, one may use the lighting load equal to 33.5 W/m2
to produce a lighting standard of 540 lumens/m2 in an office space;
20W/m2 is minimum.
 After wattage is known, the calculation of the heat gain is done as
follows
 Fluorescent : Q = Total watts x 1.25
 Incandescent : Q = Total watts
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36. EFFECTIVE ROOM SENSIBLE HEAT
SL.
NO
TYPE OF LOAD LOAD IN WATT
1 SENSIBLE HEAT SOLAR HEAT GAIN THROUGH WINDOW
GLASS
6360 W
2 SOLAR TRANSMISSION GAIN –WALLS & ROOF 39510 W
3 TRANSMISSION GAIN –OTHERS 20470 W
4 INTERNAL HEAT GAIN 26250 W
SUB TOTAL 1 92690 W
5 STORAGE LOAD( HERE NEGLECTED) ---------------
6 SAFTEY FACTOR - 5% OF THE SUB TOTAL 4635 W
SUB TOTAL 2 97325 W
7 FAN POWER FOR SUPPLY DUCT(5%)+ LEAKAGE LOSS(0.5%) OF
SUB TOTAL- 2
5352 W
EFFECTIVE ROOM SENSIBLE HEAT 10422 W
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37. B.LATENT HEAT LOAD CALCULATION
ITEM AREA (m2) /
QUANTITY
SOLAR HEAT GAIN
(W/m2) /
TEMP.DIFFERENCE
(Δ0C)
HUMIDITY
DIFFERENCE
CONVERSION /
MULTIPLICATION
FACTOR (U) W/m2/K
LOAD IN WATT (W)
INFILTRATION
VENTILATED
LOAD
19.8cmm
28 CMM
0.006 kg/kg
0.006 kg/kg
50,000*
50,000*
75940 W
50, 000 x(cmm) x
Δw x B.F
=1260 W
PEOPLE 100 -------------- 65 W 6500 W
STEAM
APPLAINCES
--------- -------------- ------------ -----------
ADDITIONAL
VAPOUR
TRANS.
--------------- -------------- -------------- --------------
SUB TOTAL 11,440 W
W
(cmm)
50,000
60
2500
x
1.2
x
cmm
*






L
Q
Load
Heat
Latent

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38. EFFECTIVE ROOM LATENT HEAT
ITEM
AREA (m2) /
QUANTITY
SOLAR HEAT GAIN
(W/m2) /
TEMP.DIFFERENCE
(Δ0C)
HUMIDITY DIFFERENCE
CONVERSION /
MULTIPLICATION
FACTOR (U) W/m2/K
LOAD IN WATT
(W)
SUB TOTAL 1 11,440 W
SAFTETY FACTOR – 5 % OF THE SUB TOTAL 570 W
SUB TOTAL 2 12010 W
SUPPLY DUCT LEAKAGE LOSS(0.5%) OF SUB TOTAL- 2 60 W
EFFECTIVE ROOM LATENT HEAT LOAD 13,330 W
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39. EFFECTIVE ROOM TOTAL HEAT LOAD
= ROOM SHL + ROOM LHL
= 104,425 + 13,330
= 117, 755 W
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40. C.OUTDOOR AIR TOTAL HEAT LOAD
(ON EQUIPMENT)
ITEM AREA (m2) /
QUANTITY
SOLAR HEAT GAIN
(W/m2) /
TEMP.DIFFERENCE
(Δ0C)
HUMIDITY DIFFERENCE
CONVERSION /
MULTIPLICATION
FACTOR (U)
W/m2/K
LOAD IN WATT
(W)
SENSIBLE
HEAT
28 cmm 180C 20x (1-0.15) 8740 W
LATENT
HEAT
28cmm 0.006 kg/kg 50,000x(1-0.15) 7140 W
RETURN --------- -------------- ----------- ---------
EFFECTIVE OUTDOOR HEAT 15880 W
GRANT TOTAL
HEAT
EFFECTIVE ROOM TOTAL HEAT
+ EFFECTIVE OUTDOOR HEAT
133635 W
OR
38 T.R
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