Page 114 - Sustainable On-Site CHP Systems Design, Construction, and Operations

92 CHP B a s i c s

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

40
30
20
10
0
Sys 1: E+H Sys 2: E+C Sys 3: E+H+C

FIGURE 5-2 Packaged CHP system with added functionality outperforms traditional energy
system for seasonal demands.

methods for the year, because all of the available thermal output from the recovered
waste heat is fully utilized. The corresponding yearly fuel savings is 19 percent.
Hence, while any continuously operated CHP system outperforms traditional
methods to deliver the same energy, the added functionality available from a packaged
CHP system outperforms traditional methods for the numerous customers with sea-
sonal thermal energy demands.

Lower Adverse Environmental Impact
As discussed in Chaps. 1 and 7, a CHP system impacts the environment by emitting a
quantity of undesirable emissions—including carbon dioxide (CO ), carbon monoxide
2
(CO), unburned hydrocarbons (HC), and nitric oxides (NO )—that it exhausts. CO is a
x 2
greenhouse gas that relates directly to the quantity and composition of the fuel con-
sumed. Fuel savings and/or the use of lower carbon content fuel will reduce CO emis-
2
sions. Other emissions may result depending upon the efficiency of combustion features
used in the prime mover, with CO and HC representing incomplete combustion and
high levels of NO being formed in regions of excessive temperature.
x
Any CHP system that operates continuously achieves high system efficiency with a
corresponding decrease in fuel consumption when compared to traditional methods to
deliver the same energy. However, a CHP system that operates with seasonal thermal
energy demand constraints may not be able to reduce fuel consumption or CO . Figure 5-3
2
depicts the predicted yearly CO reduction for the three CHP systems analyzed above.
2
Since only System 3 achieved a distinct energy performance enhancement over traditional
energy delivery methods based on full utilization of the available thermal output, only a
functional compatible packaged CHP system achieves significant yearly CO reduction
2
with seasonal thermal demands. Better results are generally achieved when energy is pro-
duced from natural gas, the fuel of choice for many CHP systems. In reality, the CO reduc-
2
tion with CHP is even greater because 50 percent of traditional U.S. electrical power plants
burn coal and thereby produce greater CO per kilowatt than for natural gas.
2
A CHP system also produces low quantities of undesirable exhaust emissions of
CO, HC, and NO because the prime mover usually employs the latest combustion
x