Instrument uncertainty effect on calculation of absolute humidity using dewpoint,wet bulb,and relative humidity sensors

摘要

As part of a national program, NREL is currently characterizing the state-of-the-art in desiccant dehumidifiers,the key component of desiccant cooling systems.The experimental data will provide industry and end users with independent performance evaluation and assess the energy savings potential of the technology.Accurate determination of humidity ratio is critical to this work and an understanding of the capabilities of the available instrumentation is central to its proper application.This paper compares the minimum theoreticla random error in humidity ratio calculation for three common measurement methods to give a sense of the relative maximum accuracy possible for each method assumign systematic errors can be made negligible.A series of experiments are also conducted to illustrate the capabilities of relative humidity sensors as compared to dewpoint sensors in measiuring the grain depression of desiccant dehumidifiers.These tests support the results of the uncertainty analysis.At generally available instrument accuracies,uncertainty in calculated humidity ratio for dewpoiont sensors is determined to be approximately constant at 2