Sensors are the foundation of any climate control system. They measure what is happening in your building and transmit that information to the control system. But which HVAC sensor suits which application? In this article, we discuss the main sensor types for temperature, humidity and pressure.
The sensor determines how accurately your system can regulate. The wrong choice leads to measurement deviations, which you notice directly in the indoor climate or on your energy bill. If you choose a sensor that responds too slowly, the control system will lag behind. If the measuring range is too narrow, you will get unreliable values at peak loads.
The environment also plays a role. Different requirements apply in a dusty production hall than in an office space. And signal loss can occur with long cable distances. Which HVAC sensor you choose therefore depends on the application, the circumstances and the desired measurement accuracy.
NTC sensors are relatively inexpensive and responsive. Resistance decreases with increasing temperature. They are widely used in standard room sensors. With longer cable lengths, the measured value may vary, however.
Pt1000 sensors are platinum-based and have a linear signal. This type is more stable over longer periods of time and less sensitive to cable length. Pt1000 is a logical choice when remote accuracy is important.
Which HVAC sensor you choose for temperature depends on your situation. For standard room measurements, NTC is usually sufficient. For critical applications or long cable runs, Pt1000 is the better option.
Humidity measurement is usually done with capacitive sensors. These record changes in electrical capacitance as humidity changes. They are compact and work reliably in most building applications.
In practice, you often see combination sensors that both temperature and relative humidity measure. That saves on wiring and installation time. Brands such as Thermokon and Produal offer versions for wall mounting, duct installation or outdoor installation.
When choosing, consider measurement range and accuracy. For offices or schools, a tolerance of ±2% to ±3% is often sufficient. In environments with more stringent requirements, a higher accuracy class may be required.
Pressure sensors in HVAC systems typically measure differential pressure. Think of the pressure difference across a filter or in an air duct. With that information, the system determines when a filter becomes dirty or how to control the fan.
Differential pressure transmitters are available in measurement ranges from a few pascals to thousands of pascals. For filter monitoring, ranges up to 500 Pa are often sufficient. Cleanrooms, on the other hand, require low ranges with high resolution, because the pressure differences there are small but must be measured accurately.
Which HVAC sensor you choose for pressure, depends on the application. In demand-controlled ventilation, an accurate differential pressure measurement is indispensable.
Several factors come into play in the selection process:
At Betec Controls we supply sensors and controllers from manufacturers such as Thermokon, Produal and HK Instruments. Whether you are looking for a room sensor or transmitters for a new construction project, we are happy to think with you. Many products are available directly from stock.
Need advice on which HVAC sensor is right for your installation? Get in touch or reach us by phone: 055 20 325 30.
For long cable distances, a Pt1000 is recommended. Due to the higher base resistance, the influence of cable resistance on the measurement is smaller than with NTC. An alternative is a sensor with 4-20mA output. This current signal is insensitive to cable resistance and thus the most robust option for longer distances.
Choose a sensor with an appropriate IP rating. For humid environments, IP65 is a good guideline. For dusty areas, the protection needed depends on the situation: in slightly dusty areas, IP54 may suffice, in more severe industrial environments IP65 or higher is recommended. Also pay attention to protection of the sensor element. Some humidity sensors have a sinter filter that stops contamination. For outdoor installation, a weather shelter is recommended.
It depends on the protocol your BAS supports. Most sensors are available with analog outputs (0-10V or 4-20mA) or digital communication via Modbus or BACnet. Check in advance which connections your controller accepts. If in doubt, our specialists will help you further.
