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 viabilitychecks 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 notreflect several critical cost influences, however. Seasonal and diurnalvariations in electrical and thermal loads, as well as time-of-use utilitypricing structures, can have a dramatic impact on the economics. A moreaccurate economic assessment requires additional detailed data on elec-trical and thermal demand (e.g., hourly load data), which may not bereadily available for the specific facility under study. Recent develop-ments in CHP evaluation tools, however, can generate the needed hourlydata 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 tothe savings when evaluated on an hour-by-hour basis. It is observed thatthe simple, aggregated analysis forecasts much greater savings (i.e.,greater economic viability) than the more detailed hourly analysis. Thefindings confirm that the simpler tool produces results with a muchmore optimistic outlook, which, if taken by itself, might lead to errone-ous project decisions. The more rigorous approach, being more reflectiveof actual requirements and conditions, presents a more accurate eco-nomic comparison of the alternatives, which, in turn, leads to betterdecision risk management.