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KMC Sensors: Sensing Your Needs

Sensors and Their Relatives

In today’s buildings, sensors are essential devices in maintaining efficient operation and healthy, comfortable environments for occupants. “Sensors” are used in diverse HVAC and Building Automation System applications and are closely related to several other types of devices.

• Sensors measure a physical characteristic of an environment and provide a signal corresponding to those properties. Sensors may be stand-alone or integrated within a control device (e.g., a thermostat).
• Transmitters are also sensors, but take the relatively small (and passive) sensor signal (e.g., the resistance of a thermistor in response to a temperature) and convert it into an active voltage (e.g., 0–5 VDC) or active current (e.g., 4–20 mA). Boosting the signal allows greater distance between the sensor and the controller.
• Transducers convert one kind of energy into another. The physics may be different, but they can function as sensors. In building automation, transducers may convert pressure into voltage or current (or vice versa) or voltage signals into current signals (or vice versa).
• In building automation applications, many sensors, transmitters, and transducers perform essentially the same function, sensing a physical characteristic and providing a signal to an external control device. Thermostats, on the other hand, contain a sensor integrated with a control device. Thermostats may be as simple as a bimetallic switch or be sophisticated digital devices. FlexStats, for example integrate a native BACnet controller with a temperature sensor and optional humidity, motion, and/or CO2 sensors.

In building automation systems, sensors monitor air (temperature, humidity, CO2 levels, CO levels, smoke, flow rate or pressure), water (temperature or pressure), or even motion/occupancy of people.

Temperature and Humidity

Temperature sensors are the most familiar and most common types of sensors in building automation. The compact STE-6000 series room temperature sensors offer various setpoint, override, and display options. The STE-1400 series contains a variety of temperature sensors for a multitude of applications, including the temperature of air inside rooms, inside ducts, and outdoors, as well as the temperature of the heating/cooling water inside pipes.

Depending on the climate, however, temperature alone doesn’t tell the whole story about human comfort. A (dry bulb) sensor temperature of 72° would feel very different to us at 10% relative humidity than it would at 90% relative humidity. Too much or too little humidity can be uncomfortable for people or even damaging to materials. KMC’s THE-1xxx series humidity sensors can measure humidity in rooms or ducts. KMD-1x8x NetSensors and FlexStats with the optional humidity sensor measure and display room temperature as well as humidity.

Carbon Dioxide and Motion

How much ventilation and conditioning of the air is needed for a space depends on how many people are occupying that space...if any at all. For spaces with variable occupancy (such as meeting rooms, classrooms, theaters, gyms, retail stores, and hotels), considerable energy savings can be obtained by determining the actual, real-time level of occupancy (compared to the “worst-case” design occupancy) and reducing the ventilation and conditioning accordingly (to just the right amount but no more).

Motion sensors can determine a simple yes-or-no occupancy state. KMD-12x1 NetSensors and FlexStats with the optional motion sensor (with an effective range of up to 33 feet) provide a convenient means of concluding if anybody’s home inside a room.

Motion sensors can only determine whether or not at least one person is in a particular space, but the ventilation needs of a few people are very different from the needs of a few dozen or a few hundred people. A complementary and more sophisticated approach to occupancy determination senses the gas that people breathe out. By measuring the levels of CO₂, Demand Control Ventilation (DCV) estimates the amount of occupancy and required (healthy) levels of ventilation and adjusts the ventilation accordingly. SAE-1011/1012/1062 CO₂ detectors provide CO₂ measurements in rooms or ducts to external controllers. FlexStats with the CO₂ sensor option integrate demand control ventilation with temperature and optional humidity control.

Carbon Monoxide and Smoke

Excessive levels of CO or combustion particulates mean not just discomfort, but danger! SAE-1100 series CO detectors watch for this deadly and invisible gas. Also, where there’s smoke, there’s fire, and early detection is critically important. CAE-1003/1103

Flow and Pressure

Although behind the scenes, the amount of and pressure of air and/or water flow are important factors in the efficiency of HVAC operation. SSS-1000 series and SSE-1000/2000 series flow sensors help determine how much air is flowing in the system. The various TPE-1xxx series pressure transducers provide pressure readings of air or water.

Sensor Models

See this sensor model comparison chart to find the sensing and mounting types you are looking for.

Sample Model Series	Sensing Types							Mounting Types
	Temperature	Humidity	Motion	CO2	CO	Smoke	Flow and Pressure	Wall	Duct and Other
FlexStat	X	X	X	X				X
NetSensor	X	X	X					X
CAE-1003/1103						X			X
SAE-1000				X				X	X
SAE-1100					X			X	X
SSE-1000/2000	X						X		X
SSS-1000							X		X
STE-1400	X							X	X
STE-5200/5300	X							X
STE-6000	X							X
THE-1xxx	X	X						X	X
TPE-1xxx							X	X	X
For details on these and other sensors, see their data sheets as well as the KMC product catalogs.

Additional Resources

KMC Sensors Brochure (SB-057)

Like a Breath of Fresh Air: Using CO2 Sensors with Demand Control Ventilation  

Motion Sensors for More Efficient Control

Benefits of Controls in Green Buildings

Why Green Buildings Are Good

Thinking about Thermostats

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