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The same formula is also used for mechanical ventilation and the ACR value is selected
based on to the choice of the ventilation system. In the first case the temperature of the air
is the value of the external temperature hour per hour, in the second case the value is
chose from the user by inserting a value of the inlet air temperature. In both parameters
are selected, the total amount of renewable air is the sum of the values.
Then, to calculate the heat gain due to infiltration, GA is multiplied for the specific heat and
the difference between the internal and external temperature for the considered hour. To
calculate the external temperatures during the day, referring to the ASHRAE code, hourly
temperatures given the hour (1-24) are depending by the peak temperature, the daily
range and multiplied by the coefficient p(τ).
THour  TPeak  p( )  Range
Hours
1
2
3
4
5
6
7
8
9
10
11
12
p(τ)
0.87
0.92
0.96
0.99
1
0.98
0.93
0.84
0.71
0.56
0.39
0.23
Hours
13
14
15
16
17
18
19
20
21
22
23
24
p(τ)
0.11
0.03
0
0.03
0.1
0.21
0.34
0.47
0.58
0.68
0.76
0.82
The internal gains are calculated by the sum of the number of the people, lighting and
equipment and are divided in sensible internal gain QS,Int and latent internal gain QL,Int. To
split these internal gains in the radiative and convective parts it is possible to assume:
N
QInt

Q N S , Int  Q N L, Int
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From the standard ISO 11855/2012 part 4, the formulas for the calculation of the total
heat loads acting toward the room are:
N
N
N
N
QConv
 0.15  QWall
 QVent
 QInt
N
N
N
N
N
QRad
 0.85  QWall
 QWind
 QSolar
 QInt
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