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March 6, 2018

5 HVAC sensors you need to know about

An HVAC installation has so many components your customers simply don’t see. They will choose diffusers, grilles, and vents that blend tastefully with their home design, but other HVAC equipment is usually hidden away in a basement or on a roof. And even more invisible are the sensors that make everything run smoothly.

As energy efficiency and indoor air quality become more important, and your customers opt for Internet of Things (IoT) capability, sensors are becoming a bigger part of HVAC. Some, like pressure sensors, are most useful to HVAC techs. Others, like occupancy sensors, will be used directly by your customers.

The most common sensor used in HVAC is, of course, the thermostat. One of the first uses of a thermostat to regulate temperature was around 1620 when Cornelis Drebbel invented a mercury thermostat to regulate the temperature in a chicken incubator.

Modern thermostat control began in textile mills in the 1830s when Andrew Ure, a chemist, invented the bimetallic thermostat. A bimetallic thermostat is made of a strip of two different metals fused together. Their different expansion rates cause the strip to bend. This mechanical reaction can be used to trigger other events, like switching on heat or air conditioning.

Today, thermostats are usually digital and use semiconductor devices such as thermistors or resistance temperature detectors (RTDs). Thermistors and RTDs both measure temperature based on resistance. A thermistor is typically made of a ceramic or polymer, whereas an RTD is made of pure metal.

The sensors available for HVAC today go far beyond the thermostat. Sensors are used to keep equipment running smoothly and safely, to improve energy efficiency and to preserve human health.

Pressure sensors

Pressure sensors are used in compressors, boilers, coolers, heat recovery systems, burner control, and variable air volume systems. They monitor rooms and filters for drops in pressure which may indicate that the system needs maintenance. Monitoring pressure is also useful for optimizing air flow, heating and cooling.

Duct smoke detectors

Ducts can move toxic gasses, smoke, and even flames from one area to another. Duct smoke detectors are used primarily to prevent the HVAC system from spreading smoke through a building. Duct smoke detectors may be required by regulations and building codes. For example, some call for smoke detectors to be installed in return ducts for air conditioning units over 2000 CFM.

Occupancy sensors

At their most basic, occupancy sensors identify the presence of a person in a room. Occupancy sensors can help your customers improve their energy efficiency, particularly when used in combination with zoned HVAC.

There are two main types of occupancy sensors, PIR and ultrasonic.  PIR, passive infrared, sensors measure heat and motion. They work via line of sight, so the sensors have to be aimed at where inhabitants will be and are best used in open rooms. Ultrasonic sensors send out a high-frequency sound wave. If it bounces back with a change, the system is triggered.

Ultrasonic waves can pass through solid objects, so they can pick up smaller movements and are more sensitive than PIR sensors.  

Sensors and indoor air quality

Sensors that measure indoor air quality (IAQ) are becoming increasingly important. The basic IAQ sensor is a carbon sensor, which detects carbon levels in the air. Carbon levels are an indicator of air circulation, and poor air circulation increases the chances that other contaminants could be present. Carbon dioxide sensors use either infrared light or a chemical process to measure levels of CO2.

Sensors are also used to detect volatile organic compounds (VOCs). VOC sensors use a process called photoionization. Ionization is the changing of an atom’s charge. VOC sensors can ionize particles with ultraviolet light and measure electron levels. These measures allow them to detect toxic or combustible gases.

Gateway technology and sensors

Many of your customers legacy HVAC systems have a lot of life left in them. And while they would benefit from sensor technology that goes beyond the basic thermostat, they don’t want to replace a system that is functioning well. This is where gateway technology comes in. Gateway technology basically provides a bridge between the legacy equipment and any other IoT device, allowing your customers to use sensors that may not have been available when their system was installed.

This is by no means an exhaustive list of the sensors used in HVAC, but a sampling of some of the more important applications. As sensor technology advances, you can expect to see more of them, both embedded into HVAC system and offered as independent devices.

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