Chapter hvac engineering Fundamentals: Part 1 Introduction

8.3.1.2
Humidity sensors.
Many hygroscopic (moisture-absorbing) ma-
terials can be used as relative-humidity sensors. Such materials ab-
sorb or lose moisture until a balance is reached with the surrounding
air. A change in material moisture content causes a dimensional
change, and this change can be used as an input signal to a controller.
Commonly used materials include human hair, wood, biwood combi-
nations similar in action to a bimetal temperature sensor, organic
films, and some fabrics, especially certain synthetic fabrics. All these
have the drawbacks of slow response and large hysteresis effects.
Design Procedures: Part 6
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