Civil Engineering Reference
In-Depth Information
of the wind, and the type and quality of windows and doors. First of all, it is nec-
essary to estimate the amount of air intake from the outside. To do that, a method
based on air renovation rates is used. More specifically, this method consists in
estimating the air flow due to infiltrations,
q
inf
(m
3
/s), as the product between
the volume of air in the room
V
a
(m
3
) and the renovation rate, i.e. the number of
times this air is renovated in an hour
n
ren
[ren/s], as shown in Eq.
4.32
.
n
ren
3600
V
a
q
inf
=
(4.32)
After several experimental tests, it can be observed that one of the most influential
parameters within infiltrations is the wind velocity. Moreover, from those tests it
could be inferred that in this case, wind direction is not an influential parameter
mainly due to the typical shape of the building. Therefore, in this case, the reno-
vation rate (
n
ren
) has been modelled as a constant value that depends from wind
velocity, see Eq.
4.33
.
c
l
wind
,
v
a
out
<
c
lim
wind
n
ren
=
(4.33)
c
h
wind
,
v
a
out
≥
c
lim
wind
where
c
l
wind
and
c
h
wind
are the renovation rates for low and high outdoor air veloc-
ities (ren/h), respectively.
v
a
out
is the outdoor air velocity (m/s), and,
c
lim
wind
is the
limit velocity between low and high velocities (m/s). Hence, once air flow due to
infiltrations has been estimated, the heat gain occasioned by infiltrations can be
calculated as shown in Eq.
4.34
.
Q
inf
=
q
inf
ρ
a
in
C
p
a
in
(
T
a
out
−
T
a
in
)
(4.34)
6.
Heat Gain owned to Internal Gains
(
Q
iGain
)
Internal gains can suppose a considerable percentage of total heat gain in amodern
building (ASHRAE
2009
). Besides, themain internal gains inside a building come
from people and electrical appliances. Therefore, the total heat gain due to people
(
Q
p
) and electrical appliances (
Q
ea
), is estimated as shown in Eq.
4.35
.
Q
iGain
=
N
p
Q
p
+
Q
ea
(4.35)
where
N
p
represents the number of people (
−
).
•
People
.
The presence of humans in a certain environment entails the increment of
sensible heat as a function of their physical activity. It is usual to take this
increment as a constant value as a function of the physical activity of the
person (ASHRAE
2009
). However, it causes abrupt changes in indoor air
temperature each time a person goes into the room. To solve this situation,
the person has been considered as a heat source, which provides heat to the
environment by means of three processes: respiration, evaporation through the
