New Trends - Comfort Control in Buildings - page 229

regulate impulse temperature as a function of the water flow and fan velocity. For
the buildings that fulfil these requirements the comfort control results presented in
Sects. 5.4 , 5.5 and 5.6 will be of particular interest since they are obtained inside
a room with the main features listed previously. On the other hand, for most of
the buildings Sect. 5.3 can be considered the typical example of results that are
obtained from a commercial HVAC controller where only one degree of freedom,
the fancoil air velocity, is available even though the controlled variable is the PMV
index instead of the indoor temperature. A few sensors are needed to retune the
control system to control thermal comfort through the PMV index, a bigger cost
is necessary to obtain similar results as the ones presented in Sects. 5.4 , 5.5 and
5.6 . Thus, depending on the managed budget, building technicians must choose
one or another solution.

• Influence of people on indoor air temperature . International standards establish

that the amount of heat added to a certain environment by a person is directly
related to the physical activity this person is performing. However, to quantify this
contribution a fixed relationship is normally used. Moreover, it represents an abrupt
static increment on indoor air temperature which is not true, since this contribution
has a smoother shape as a function of both the indoor air temperature, and the core
temperature of the person. Therefore, to solve this situation it is recommended to
develop models (as the one developed in Chap. 4 ) based on energy/mass balances
between the person, considering it as a whole entity, and the environment.

• Influence of indoor air velocity . Indoor air velocity is a decisive factor since, as

a function of the selected index, for example the PMV index, it has great influence
and besides, it presents very fast dynamics when compared to the variable to be
controlled. However, from the results obtained by the nonlinear control approach
developed in Chap. 5 , the main conclusion is that this variable can be established
as a constant value if the impulse of the HVAC system is located in a position
where it does not directly affect any user of the room. On the contrary, it would
be advisable to use a filtered value of this variable for control purposes.

• Selection of an appropriate control approach . As pointed out previously, to

select an appropriate control approach, a key factor is the available resources that
will allow us to obtain both more or less accurate models of the room (as a function
of the size of the sensors network) and degrees of freedom to reach a tradeoff
between comfort and energy consumption (provided by the number of actuators
and their characteristics). More specifically, it is recommended to have an accurate
model (as the first principles model developed in Chap. 4 ) which includes as inputs
different disturbances, such as the number of people inside the room, since it will
allow one to develop appropriate NMPC strategies, and thus will react faster than
other strategies to these disturbances removing the steady-state error and, at the
same time, being able to look for a tradeoff between comfort and energy saving
since both concepts can be implicitly included in the cost function to optimise.
Nevertheless, if only a temperature sensor is available, the best option that will
allow us to maintain thermal comfort and minimise energy consumption will be a
linear MPC since, as in the previous case, it can integrate both concepts inside the
cost function.