Page 158 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Fundamental Concepts 131

loads computed are used to simulate the performance of a CHP plant and compute
associated economics. Several databases are in-built: Typical Meteorological Year (TMY)
data for 239 cities in the United States, commercial gas and electric rates for 160 U.S.
cities, performance and cost for HVAC equipment, performance and cost for power
generating equipment, and building design parameters. Various types of reports and
outputs in the form of tables and graphs allow easy interpretation and comparison of
results. Users can construct a base case and up to 25 alternative scenario for comparison.
Homer (2005) is a computer program developed by the National Renewable Energy
Laboratory (LBNL), meant to evaluate alternative off-grid and grid-connected system
options (such as wind, hydro, PV, traditional prime movers, batteries, and hydrogen)
for a variety of applications. It uses hourly simulations to evaluate a large number of
technology options as well as a large number of technology costs and energy resource
availability options. It allows results to be compared based on economic (net present
worth) and technical merits. The program also has in-built routines for sensitivity
analysis and optimization.

Emissions Calculation Tools
CHP Emission Calculator (EEA 2004) is a spreadsheet program which estimates the net
air pollution (NO , SO , CO , and mercury) from small CHP systems. On-site emissions
x x 2
from the CHP system, displaced emissions from on-site thermal production (e.g., from
a steam boiler) and displaced emissions from offsite electricity generation are all con-
sidered. Additional inputs allow the user to estimate power to heat ratios as well as
define specific operating and electricity-displaced scenarios. RETScreen (2006) described
earlier also has the ability to compute emission savings from installing CHP systems.

CHP Qualification Screening—Existing Facility
The purpose of the “qualification screening” phase is to determine if a CHP system
makes technical and economic sense. Qualification screening requires answering
specific questions before undertaking the engineering and economic analyses. As indi-
cated previously, this evaluation can be performed quickly (about 30 minutes) and the
required information is minimal. In order to assist the user, the U.S. EPA—Combined
Heat and Power Partnership developed a Web tool called “Is My Facility a Good Can-
didate for CHP?” which can be used for this purpose. A set of 12 questions is shown in
Table 8-3; if the answer is yes for three or more of these questions, the facility may be a
good candidate for CHP. If the site is found to be a good candidate for CHP, a feasibility
study Level 1 can be initiated.

Level 1 Feasibility Study—Existing Facility
The purpose of Level 1 feasibility study is to determine the technical applicability and
the economic benefits of the CHP for the facility under consideration. Unlike the quali-
fication screening, Level 1 feasibility study requires an experienced engineer or CHP
project developer with good understanding of the electrical, thermal, and cooling loads
and of equipment operation. The task of this individual will be to gather and analyze
the necessary information so that he can advise the owner(s) on whether it is worth-
while from an economic standpoint to pursue the CHP project analysis.