To calculate the two indicators PES and EFF, we need to determine the specific fuel consumption of CCHP system. Specific fuel consumption is the sum of fuel input for cogeneration unit and additional boiler. Its determination involves knowledge of cogeneration unit and boiler energy production, and cogeneration unit and boiler efficiency.
To exemplify, let us consider the illustrative exercise from the paragraphs above. Using data corresponding to the illustrative exercise, namely from Table 31 for monthly energy specific consumption of the mCCHP system in the case of cooling with mechanical compression chillers, and from Table 6 for monthly specific power and heat production of the panels, we can determine the energy production of the CHP and backup boiler. The results obtained for the mCCHP system with mechanical compression chiller are shown in Table 35, then PES = 73 % and EFF = 55 % for the whole CCHP system. Even though the PES is high, the efficiency is low indicating an excessive energy production.
|
Month |
Energy specific consumption of the mCCHP system |
Specific power and heat production of the PV and ST panels |
Specific power and heat production of the CHP unit |
Specific heat production of the boiler |
|||
|
(kWh/m2) |
(kWh/m2) |
ePV (kWh/m2) |
qTP (kWh/m2) |
ecg (kWh/m2) |
qcg (kWh/m2) |
qad (kWh/m2) |
|
|
January |
3.33 |
15.94 |
1.24 |
4.16 |
2.09 |
6.26 |
5.52 |
|
February |
3.33 |
13.77 |
1.76 |
5.90 |
1.57 |
4.71 |
3.16 |
|
March |
3.33 |
10.94 |
2.91 |
9.73 |
0.42 |
1.27 |
0.00 |
|
April |
3.47 |
6.23 |
4.04 |
13.53 |
0.00 |
0.00 |
0.00 |
|
May |
4.23 |
2.21 |
5.02 |
16.81 |
0.00 |
0.00 |
0.00 |
|
June |
4.62 |
1.25 |
5.47 |
18.32 |
0.00 |
0.00 |
0.00 |
|
July |
4.89 |
1.25 |
5.54 |
18.56 |
0.00 |
0.00 |
0.00 |
|
August |
4.89 |
1.25 |
4.86 |
16.27 |
0.03 |
0.10 |
0.00 |
|
September |
4.34 |
1.39 |
3.59 |
12.02 |
0.75 |
2.26 |
0.00 |
|
October |
3.56 |
5.94 |
2.51 |
8.40 |
1.05 |
3.15 |
0.00 |
|
November |
3.33 |
10.63 |
1.34 |
4.49 |
1.99 |
5.97 |
0.17 |
|
December |
3.33 |
14.21 |
1.01 |
3.37 |
2.32 |
6.97 |
3.87 |
|
46.65 |
85.01 |
39.26 |
131.57 |
10.24 |
30.71 |
12.71 |
A more detailed analysis made at monthly level shows the yearly evolution of the excessive electrical and thermal energy produced. Thus, based on the data recorded in Table 35 the electricity and heat excess production are shown in Figs. 31 and 32.
Excess energy is the difference between energy production (denoted with “load”) and useful energy (denoted with“ sys”).
|
|
|
q_load q_sys————- Poly. (q_load)——- Poly. (q_sys)
Month Fig. 32 Excess heat production |
In addition, these figures show the monthly useful and produced specific energies as well as their trend during the entire year.
Improving the performance indicators of the system is achieved by analyzing the specific energy production system components and through actions to reduce losses but especially by diminishing the excess energy produced.
Analysis of the monthly power and heat consumption, and monthly energy production of PV and ST panels (Table 35), highlights big excess heat produced by thermal panels in summer season and small excess production of photovoltaic panels.
Linking the renewable energy production with the energy consumption of residence could be done by changing the surface area of the thermal and photovoltaic panels. To find the concrete actions, which could lead to performance improving, two cases may be considered, namely, case of the CCHP system type off-grid and case of the CCHP system type on-grid. Finally, the results of these two cases shall be comparative analyzed in order to make a decision.
