National Building Controls Information Program, Task 8

Grant #: 03S-02
Principal Investigator: Michael Pate
Organization: Iowa State University
Mission Area: Energy Efficiency

Under funding received from the Iowa Energy Center via U.S. EPA, the PI and a Graduate Research Assistant completed the following activities.

A. Developed the Method of Test for performance testing of humidity sensors and had it externally reviewed. The Method of Test has been updated as it has been used.

B. Tested humidity sensors obtained from each of six different manufacturers (ACI, MAMAC, JCI, BAPI, Vaisala, and GE). The testing was done for three sensors from each manufacturer at three temperatures (15, 25, and 35 C) and five relative humidities (10, 30, 50,70, and 90). The following performance tests on humidity sensors were conducted:

a. Effect of sensor position inside the manifold
b. Analysis of deviations for each model
c. Comparison of sensor models
d. Hysteresis study of the humidity sensors
e. Linearity study of the humidity sensors
f. Repeatability study of the humidity sensors.

C. Re-tested the BAPI sensor at the ERS and ISU in order to eliminate the ambiguity in the relative humidity readings obtained at the ERS and ISU. The relative humidity readings were obtained using both the data acquisition system and a voltmeter for data validation.

D. A comprehensive report on the first phase of the humidity sensor performance testing is being prepared. The report includes appropriate plots and analysis of the effects of variables (e.g., temperature, model, etc.) on relative humidity readings.

Current Activities
The Method of Test will be modified to include the following activities. These activities will be performed by the GRA with guidance and assistance from the Principal Investigator and the Iowa Energy Center.

A . Determination of response time – Based on the first year results, response time varies with the type of sensor (capacitive or resistive) and manufacturer. A more detailed study of the sensor response times will be conducted.
B. Aging effect of humidity sensors – The humidity sensors will be tested in an actural building HVAC system. The testing will evaluate the effects of contamination and aging on the humidity sensors.
C. Velocity effect – The humidity sensors will be tested to assess the effect of airflow velocity on the sensor humidity readings.