The hygrostat is a central part of Acetec desiccant dehumidifiers and controls when to dehumidify - neither too much nor too little. By measuring the relative humidity, it ensures that the unit starts and stops at the right times to maintain a stable climate and low energy consumption.
When setting a desired relative humidity, At its setpoint, the hygrostat continuously measures the moisture content of the air. If the level rises above the set value, dehumidification starts, and when the air has become sufficiently dry, the unit returns to standby mode.
To prevent the dehumidifier from switching on and off too often, there is a built-in control interval, hysteresis. This means that the dehumidifier does not react immediately to every small change in humidity.
Example: If the setpoint is set to 62%, the dehumidifier is activated when the humidity rises to approximately 64% and switches off again at 60%. This provides stable control without unnecessary start and stop cycles, depending on the model's control range.
There are several types of hygrostats, and they differ in technology, sensitivity and reliability. The choice affects the accuracy of humidity control, especially in colder environments.
The classic hair humidifier uses a hair strand that reacts to moisture by stretching or contracting. The movement is controlled by a simple switch that activates or stops dehumidification.
The technology works, but is sensitive to temperature changes and can give misleading results in cold spaces. In contrast, this type of hygrostats is commonly used indoors, in warm spaces, for simple applications.
Digital hygrostats use electronic sensors to measure humidity and control the dehumidifier with high precision. The most reliable models have an accuracy of around ±2 % RH, making them suitable even in cooler environments such as crawl spaces and cold attics.
The hygrostats used in Acetec dehumidifiers are based on sensors with high measurement accuracy, low long-term drift and fast response time. They react to changes in moisture level within seconds and are temperature compensated to maintain accuracy even with large temperature fluctuations. The sensor is also factory calibrated and protected against dust and condensation, making the system both durable and virtually maintenance-free.
Our hygrostats are designed to work stably even at low temperatures, which is important in a Nordic climate.
It is easy to confuse the concepts hygrometer and hygrostat, but they have different purposes.
In hygrometer is a pure measuring instruments which shows how humid the air is, for example in per cent relative humidity (% RH). It is used to monitor the climate, but does not affect anything itself.
A hygrostat, on the other hand, is a steering component. It also measures humidity, but uses the measurement to control other equipment - like a dehumidifier, fan or ventilation unit. When the humidity exceeds the set value, it activates connected equipment, and when the level drops, it switches off.
In short: the hygrometer displays the value, while the hygrostat acts on it.
More advanced hygrostats take into account more than just humidity. Our EvoDry RCF dehumidifiers, for example EvoDry RCF 20 G1, uses governance based on air humidity and temperature, which allows it to work in a more demand-driven and energy-efficient way.
As mould grows more slowly at low temperatures, the control can allow slightly higher relative humidity during cold periods, such as winter. This means that the dehumidifier does not have to run unnecessarily, saving both energy and operating hours.
In a crawl space or cold attic, you should have a desiccant dehumidifier that takes these factors into account.
To get an accurate measurement, the hygrostat should be placed where the air is representative of the whole space. Avoid placing a stand-alone sensor directly against walls, near floors, vents or in direct sunlight. Many dehumidifiers have the hygrostat built in, but there are also models with wired or wireless sensors for more flexible placement.
A stand-alone hygrometer can be placed in another part of the room, for example at the opposite end, to provide an independent control measurement of the humidity and verify that the climate is even further away from the dehumidifier's built-in hygrostat.
Dirt and dust can affect measurements, especially in digital sensors. Cleaning the dehumidifier regularly, for example with light vacuuming, and changing the filter at the inlet twice a year will ensure that it works efficiently and reliably. All sensors may start to show small deviations over time, so it is good to compare the values with a separate hygrometer once a year.
