Page 113 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Packaged CHP Systems 91

80 Traditional CHP
70
Efficiency for year (%) 50
60

40
30
20
10
0
Continuous Sys 1: E+H Continuous Sys 2: E+C

FIGURE 5-1 Continuously operated CHP systems outperform traditional energy systems.

Second, consider the three packaged CHP systems when operated at customers
with seasonal thermal energy demands. These demands were assigned as indicted in
Table 5-2. Five-month seasonal periods were assigned to either heating or cooling, with
continuous demand for electricity. The table also indicates the periods of energy delivery
from the power grid, boiler, and electric chiller so that the total energy delivered by the
CHP and traditional approaches were equal. It was recognized that if an electric power–
only period was eliminated for a CHP system, the energy delivery efficiency would
improve. However, the corresponding utilization of the system (i.e., hours per year)
would reduce, adversely affecting the economic metric of number of “years for pay-
back.” This effect would be great for Systems 1 and 2 but less significant for System 3.
Figure 5-2 compares the yearly efficiency of delivering the electrical and thermal
energies for the three packaged CHP systems with traditional methods for the above
assumed use profiles. These results indicate that CHP systems with a single thermal
output may have only a slight performance advantage over traditional methods if not
all of the thermal output can be beneficially used by the facility; System 2: E + C appears
to have no advantage. Again, note that other factors such as “economic benefits” may
justify the selection of a single thermal output CHP system for a seasonal demand.
However, only System 3 distinguished itself as significantly outperforming traditional

CHP Packaged System 1: E + H 2: E + C 3: E + H + C
CHP operation Months with E + H 5 0 5
Months with E + C 0 5 5
Months with E only 7 7 2
Traditional operation Months of grid 12 12 12
Months of boiler 5 0 5
Months of chiller 0 5 5
TABLE 5-2 Operating Periods for Seasonal Demand