Civil Engineering Reference
In-Depth Information
•
Performance analysis of different thermal comfort indices
. As mentioned pre-
viously, there exist in the literature several thermal comfort indices. In this topic
two of them have been used, the PMV index and the Givoni diagram. The PMV
index is one of the most extended thermal comfort indices and has been selected
because it takes into account not only indoor air temperature but also indoor relative
humidity, mean radiant temperature, indoor air velocity, etc. Moreover, the Givoni
diagram, which only depends on indoor air temperature and relative humidity, is
widely used in architecture to evaluate the performance of the building. However,
after an exhaustive analysis of the results obtained by the different developed con-
trol approaches, it can be observed that although a PMV index equal to zero was
reached (setpoint), the Givoni diagram showed the thermo-hygrometric data out
of the comfort zone mainly due to a low relative humidity. This behaviour is occa-
sioned by the HVAC system, since it dries the air in the room. At this point, it is
important to mention that, although the Givoni diagram suggests that the thermal
comfort is outside the comfort zone defined by it, as this thermal comfort has
been calculated based on the PMV index, its value is correct if the PMV index
framework is considered. The conclusion is that, since there are several ways to
estimate thermal comfort depending on different variables, in this case the PMV
index takes into account more variables than the Givoni diagram; the obtained
results by one index could produce few divergences if these results are seen from
the point of view of a different index.
Thus, to solve this problem two different solutions can be considered:
- The installation of a humidifier or any other mechanism that allows, together
with the HVAC system, to control both indoor air temperature and relative
humidity.
- To develop a control strategy able to optimise thermal comfort between the
zone recommended by international standards, i.e.
−
0
.
5
≤
PMV
≤
0
.
5, instead
of optimising with the optimal thermal comfort,
PMV
=
0.
To demonstrate the previous assumption, several simulations have been performed
along the winter period modifying the controller in such a way that it optimises
around a comfort zone and not to a single point. The results obtained can be
observed in Fig.
6.8
. It shows that at first, see the red rectangle labelled number
one, although the HVAC system was turned off, the thermo-hygrometric data was
inside the comfort zone, the HVAC system is connected mainly because of the
other parameters which influence the PMV index; after that, see the red rectangle
labelled number two, when the HVAC system is connected the thermo-hygrometric
data is displaced inside the comfort zone, but in this case it is able to maintain it
at an appropriate relative humidity level until the HVAC system is disconnected
again.
