Description

The transient responses of two types of temperature sensors—an RTD and a thermocouple—and of a stationary energy wheel exposed to a transient step change in temperature with no change in humidity are investigated. These responses are measured and correlated with exponential functions with two time constants. The first time constant of the RTD sensor in a humidity transmitter alone without the wheel is found to be about 70 s and the second time constant is about 6~12 min, while the time constants of the thermocouple alone are found to be about 5 s and 130 s. The response time (time for 90% of the change to occur) for the RTD sensor and thermocouple are 1200 s and 250 s, respectively. When these sensors are used downstream of an energy wheel to measure the transient temperature response of the energy wheel, the measured temperatures are also found to correlate with exponential functions with two time constants. The measured response of the sensors in this setup includes the combined effects of the wheel and sensor transient response characteristics. An analysis is presented to determine only the dynamic characteristics of the wheel matrix using only the measured responses of the sensor alone and sensor with a wheel upstream. It is found that the predicted response of the wheel alone gave time constants that were about 20 s and 170 s, giving a response time of 450 s. Since the response time of the wheel is less than the response time of the RTD sensor, the RTD sensor cannot be used to measure the transient characteristics of the wheel.

Citation: ASHRAE Trans. vol. 112, pt. 2, paper no. QC-06-008, p. 76-88

Product Details

Published:

2006

Number of Pages:

13

File Size:

1 file , 2.9 MB

Product Code(s):

D-28729