NOx Emissions Impacts from Widespread Deployment of CHP in ...

NOx Emissions Report
Optimal Thermal Utilization.” This is because Case 3 is designed to obtain maximum
work from the input fuel, it results in a faster payback than either the “Case 1: Maximum
Electrical Demand” or “Case 2: Maximum Thermal Demand.”
Because the CHP system is designed to serve the building’s thermal loads, Case 3
operation results in a relatively smaller system compared to Cases 1 and 2. The impact of
this is that Case 3 CHP systems offset far less grid electricity. Because the bulk of the
NOx savings from CHP is achieved by offsetting grid electricity, the net effect is that
much less NOx savings is achievable using the Case 3 strategy. In fact, empirical data
shows that Case 3 provides a reasonable and consistent lower bound of NOx savings
from CHP.
Case 1 operation is desirable for some organizations like hospitals that are highly
motivated to secure reliable electricity supplies. Because the generator is sized to meet
the peak electrical load, Case 1 design and operation provides backup power to the whole
facility in case of a general grid outage. Due to the relatively large prime mover used in
the CHP system, Case I operation tends to result in the greatest aggregate NOx reductions
at the regional level. For the same reason, it also leads to greater on-site NOx emissions
as compared to the base non-CHP case. The goal was to approximate a NOx savings
number that is closer to an upper bound. Empirical data shows that Case 1 provides a
reasonable and consistent upper bound of NOx savings achievable with CHP.
Table 2-3: Potential NOx Emission Impacts from CHP – Existing Sites HGB Region
Commercial Sector
On-site
NOx Change
(tons/day)
Off-site
NOx Change
(tons/day)
Total
NOx Change
(tons/day)
Case 1: Maximum Electrical Load 0.8 -10.1 -9.4
Case 3: Optimal Thermal Utilization 0.0 -2.9 -2.9
The overall NOx impact from CHP in the commercial and institution building sector was
determined by multiplying the modeled NOx results for each of the prototypical building
types by the estimated number of buildings in the region. The summary data is shown in
Table 2-3, where Cases 1 and 3 provide the upper and lower bounds of NOx impacts. As
an intermediate case, the Case 2: Maximum Thermal Utilization is not considered in the
final analysis.
Widespread implementation of CHP into the five commercial and institutional building
sectors is estimated to result in an overall NOx reduction in HGB of between 2.9 - 9.4
tons per day. A reduction in NOx production by wholesale electricity generators affecting
the HGB region is found to dramatically offset a small increase in NOx at the sites where
CHP is developed. Given the high potential for CHP development using the optimal
thermal utilization strategy, the 2.9 tons per day NOx reductions estimated for Case 3 is
likely to provide a conservative, but realistic estimate of NOx emissions benefits within
HGB in the commercial sector.
18