Thermoelectric Energy Harvesting
Before energy harvesting and self-powered sensors were available, integrators were limited to line-power and batteries when powering building automation system devices. The wires required for lighting and HVAC systems made it difficult to reach all the corners of buildings and batteries introduced maintenance issues into the equation that the building automation system (BAS) market has been unwilling to tolerate.
In the early 2000s, EnOcean introduced an energy harvesting wireless standard and technology that stemmed from a simple observation—where building sensor data resides, sufficient ambient energy exists to power sensors and radio communications. Since its inception, applications for self-powering wireless sensors and controls for building automation have steadily increased. Lighting and HVAC energy management systems provide a rich habitat for the development of sensor-driven systems that regulate the energy flow in buildings. A decade ago only a handful of energy harvesting wireless sensors existed. Now, system integrators have hundreds of self-powered sensor solutions at their disposal.
Thermoelectric power generation has been added to the mix of power sources available to OEMs and their customers. Thermoelectric energy harvesting widens the scope of applications to include those that operate in the dark. Pipes and ducts, for example, frequently exist in dark places that are not appropriate for light- or motion-based energy harvesting. Thermal energy harvesting can capture the power from the temperature differentials that are abundant in those dark spaces, enabling its use to power HVAC controls such as water valves, variable air volume vents (VAVs), and diffusers. In some cases, wireless sensor applications can power electronic circuits using temperature differentials as small as 2°C. By converting temperature differentials into usable power, this new class of sensors and switches can reduce energy consumption by as much as 40%
Capturing Energy in the Dark
Temperature differentials contain a lot of energy; cooling a drop of water by 2°C releases enough energy to power 20,000 RF transmissions when operating on the EnOcean Wireless Standard. Thermo-harvesting can power wireless sensors and a number of wireless actuators.
When EnOcean went to market in 2003 with its first series of energy harvesting wireless products, their devices were powered by energy produced by motion or from light. An alternative to solar panels for applications with limited light is a radio module that can be powered by other external power sources such as a thermoelectric generator, which is based on a standard Peltier element. Such an energy source can deliver enough energy to power ultra-low-power EnOcean RF modules. An energy storage device, such as a supercapacitor, provides a reservoir for harvested energy and provides the short-term burst current required by the radio module.
Sensors that are powered by differences in temperature enable a host of new applications across a number of markets in heating, ventilation, and air-conditioning; in process automation; in vehicles; and even on the human body. Virtually all tanks and pipes that carry fluids or gases exhibit at least temporary differences in temperature from their surroundings.
Basic Principle of Thermoelectric Energy Harvesting
EnOcean manufactures a family of sensor modules that enables the design of a compact, modular, energy-autonomous wireless sensor. Attached to the rear of the module is either the ECT 310 converter or a solar cell. Variants have either a whip or helical antenna and operate at 868 MHz (Europe) or 315 MHz (in the USA, Japan, China). Energy storage and energy management for a typical duration of four days without energy input are factory-integrated and three analog and three digital measuring inputs are implemented on a connector. The module also has a microcontroller for data processing, including a software stack for the wireless protocol (equipment profile of EEP 2.0 specification), and predefined firmware that the user can reprogram for a specific application, such as preprocessing sensor data.
Delivering Conditioned Air When and Where It Is Needed
Motion- and light-based energy harvesting have enabled OEMs to develop building automation solutions that overcome many of the limits inherent to wires and batteries. Members of the EnOcean Alliance, an international consortium of 200 companies, subscribe to the common goal of reducing building energy waste via energy harvesting and wireless control while maintaining true interoperability between respective Alliance member solutions. Now that thermoelectric energy harvesting is an option, OEMs in the Alliance can develop solutions for a host of new applications.
EnOcean developed the patented ultra-low-voltage DC/DC converter enabling low-cost standard Peltier elements to power batteryless EnOcean wireless modules by harvesting thermal energy. The module works on as little as 20 mV, corresponding to a temperature difference of about 2° K, and exhibits an efficiency of 30% for a 25 mV input voltage.
Summary
Harvesting ambient energy with energy-optimized wireless technologies enables a variety of wireless lighting and HVAC sensors and controls. These devices can be easily installed in almost any building, with minimal invasiveness, to help conserve energy and save costs. Tougher environmental standards and soaring fuel costs demand better ways to manage the energy use in buildings and that, in turn, requires technologies that allow such concepts to be speedily and efficiently implemented. Energy harvesting and wireless technologies are two of these technologies.
(Source www.sensorsmag.com, 01.06.2011)