Transient Humidity Measurements for Flow Through an Energy Wheel

摘要

In this paper, the transient characteristics of a humidity sensor and an energy wheel were investigated during a step change in humidity with no change in temperature. The transient response of the humidity sensor subject to a step change in relative humidity was measured and correlated with exponential functions with two time constants. The first time constant of the humidity sensor was found to be about 3 seconds, while the second time constant was found to be about 100 seconds. When the same sensor was used downstream of a desiccant-coated energy wheel to measure the transient response of the energy wheel, the measured humidity was found to correlate with exponential functions, albeit with longer time constants than those found for the humidity sensor (e.g., about 7 seconds and 120 seconds). In this case, the measured response of the sensor includes the combined effects of the wheel and sensor response characteristics. An analysis is presented to determine only the wheel dynamic characteristics from the measured responses of the sensor alone and the response of sensor with a wheel upstream. It was found that the predicted response of the wheel alone gave time constants that were about 6 seconds and 140 seconds. The time constants during desorption were smaller than the time constants during adsorption processes for the sensor, but not for the energy wheel, where the reverse was true.