EKS-HUM-028 / Condensation, measurement and control
Humidistat
湿度控制器
A humidistat is a humidity-responsive controller that switches or modulates equipment according to a humidity input and control setting.
- Aliases
- humidity controller, humidity switch
QUANTITY, SYMBOL AND UNIT
Quantity / objectHumidity-responsive controller
UnitNot applicable
Definition
A humidistat is a humidity-responsive controller that switches or modulates equipment according to a humidity input and control setting.
It may combine sensing and control in one device or receive a signal from a separate sensor. In dehumidification service it can start, stop or modulate equipment around a selected condition, subject to dead band, sensor location, process lag and controller logic.
Relations and distinctions
Humidistat and hygrometer
A humidistat is selected for control action; a hygrometer is selected to measure and report a defined humidity quantity. One device can include both functions, but their performance claims differ.
Humidistat and setpoint
The humidistat is the device or control function; the setpoint is one parameter used by its logic.
Engineering meaning
- Confirm whether the input is local RH, return-air RH, dew point or another humidity quantity.
- Review sensor position, dead band, relay rating, fail state, alarm logic and the equipment's minimum cycling limits.
Common misconceptions
MisconceptionA humidistat set to 50% RH is equivalent to a calibrated room-wide RH measurement system.
Accurate explanationIt controls from its own input and location; calibration, spatial representation and reporting performance must be verified separately.
Application boundaries
- A built-in sensor may measure air inside the unit rather than the protected room or enclosure.
- The humidistat cannot compensate for insufficient dehumidification capacity, poor air distribution or an unsuitable sensor location.
Supporting sources
-
ASHRAE / SRC-ASHRAE-F17-CH07
ASHRAE Handbook - Fundamentals, Chapter 7: Fundamentals of Control ↗
2017 IP edition / Chapter 7, control-loop terminology, lines 13–20
Supports: A humidistat is an example of a hardware controller; The controller compares the sensed controlled variable with the set point and signals corrective action; Humidity is a possible controlled variable -
ASHRAE / SRC-ASHRAE-S20-CH25
ASHRAE Handbook - HVAC Systems and Equipment, Chapter 25: Mechanical Dehumidifiers and Related Components ↗
2020 SI edition / Chapter 25, humidistat operation and sensor location, lines 113–126
Supports: An adjustable humidistat can cycle a dehumidifier to maintain a selected RH; Humidistat setting affects run cycles; Sensor location inside a dehumidifier may differ from the surrounding room condition
Maintenance record
Humidistat
- Maintained by
- Yakeclimate Engineering Team
- Authoritative sources verified
- August 3, 2026
- Terminology checked
- August 3, 2026
- Last updated
- August 3, 2026