Functional Design of the mCCHP-RES System - Design for Micro-Combined Cooling, Heating and Power Systems - page 293

10 8 J is obtained, to which an average diurnal power
of P collector = 5.18 kW does correspond.
B. Load model

interval, an energy of 4 : 48

The thermal load differs depending on the season (winter/summer). In winter
regime, the thermal load includes two components:

the power necessary to the residence;

￿

the power consumed for heating the domestic water. The graph of this power in
a 24 h interval is given by Fig. 22 . If the power given by the graph presented in
Fig. 22 is integrated, the energy consumed in this circuit, equal to 1

￿

: 98 10 8 J, is

obtained.

In summer regime the main component of the thermal load is the power nec-
essary for the air conditioning. The second component, for the domestic water
circuit, is considered the same as in the case of winter regime.
Both powers are independent variables, which play the role of disturbances in
the control loop of the thermal agent temperature in the accumulation tank.

C. Energetic balance checking

In both operating regimes, winter/summer, the main components of the load are
given by the power necessary for the residence heating and the one necessary for
the air conditioning equipment. The values of the powers mentioned before are
obtained with WTB and STB energetic balances, for the two regimes.
In winter regime, the thermal balance of the residence indicates that the power
necessary to compensate the heat losses through transmission and ventilation is
14.8 [kW]. If the average power consumed by the domestic water circuit is added, it
results a total average consumed power equal to P s = 17.1 kW.
In the summer regime, the thermal balance of the residence provides a necessary
power of about 30 kW for the air conditioning. The total average power necessary
in this case, together with the consumption of the domestic water circuit, is

32.3 kW.
With these data, the necessary power of the pellet boiler may be chosen, the tank
being controlled by the temperature controller. The selection criterion is the max-
imum value of the average load. Based on this value, of 32.3 kW, a boiler with a
nominal power of 30 kW is chosen. In this case, the average thermal power, in kW,
available in summer regime, is P t ¼ 3 [kW].

The difference between the available average thermal power and the average
thermal load may seem excessive, especially in winter regime. It is important to
notice that the instantaneous values of the consumed power in the domestic water
circuit are much higher than the average value. Under these conditions, there may
be intervals in which the instantaneous value of the load exceeds sensitively the
instantaneous value of the produced thermal power. Thus, only the simulation of the
system in dynamic regime may show whether the deviation of the collector tem-
perature from the setpoint value remains into an admissible limits interval.

30 þ P collector þ P St ; t [ 32 :