USE OF TIME-A GGREGATED DATA IN E CONOMIC SCREENING A NALYSES OF COMBINED H EAT AND P OWER SYSTEMS

Abstract

Combined heat and power (CHP) projects (also known as cogen-
eration projects) usually undergo a series of assessments and viability
checks before any commitment is made. A screening analysis, with elec-
trical and thermal loads characterized on an annual basis, may be per-
formed initially to quickly determine the economic viability of the pro-
posed project. Screening analyses using time-aggregated data do not
reflect several critical cost influences, however. Seasonal and diurnal
variations in electrical and thermal loads, as well as time-of-use utility
pricing structures, can have a dramatic impact on the economics. A more
accurate economic assessment requires additional detailed data on elec-
trical and thermal demand (e.g., hourly load data), which may not be
readily available for the specific facility under study. Recent develop-
ments in CHP evaluation tools, however, can generate the needed hourly
data through the use of historical data libraries and building simulation.
This article utilizes model-generated hourly load data for four po-
tential CHP applications and compares the calculated cost savings of a CHP system when evaluated on a time-aggregated (i.e., annual) basis to
the savings when evaluated on an hour-by-hour basis. It is observed that
the simple, aggregated analysis forecasts much greater savings (i.e.,
greater economic viability) than the more detailed hourly analysis. The
findings confirm that the simpler tool produces results with a much
more optimistic outlook, which, if taken by itself, might lead to errone-
ous project decisions. The more rigorous approach, being more reflective
of actual requirements and conditions, presents a more accurate eco-
nomic comparison of the alternatives, which, in turn, leads to better
decision risk management.