The EnEV 2014 (Energy Saving Ordinance) sets requirements for the degree of automation of a building. The annual primary energy requirement and the energy performance certificate of a property are calculated on this basis, among others. The energy performance certificate influences the value of a property for potential buyers or tenants. Since January 1, 2016, the second stage of the EnEV has also stipulated a further 25% reduction in the primary energy requirement for new buildings. For existing buildings, the mandatory energy performance certificate is particularly relevant when selling.

However, the EnEV does not contain any decision criteria for the right building automation system. The legislator makes no recommendations here, meaning that building owners have to consider the various options themselves: According to the classic state of the art, either a wired or a battery-operated wireless solution is available.

Wire versus radio

Wired networking is considered to be particularly reliable and low-maintenance. However, automation systems require extensive cabling; every switch and every sensor is connected to a central control system via a cable. In addition to complex planning, a rigid system structure and kilometers of cables, this results in a high fire load.

In recent years, wireless technologies have become increasingly popular as a flexible alternative. Here, the sensors that supply the necessary data and execute control commands can be placed at the appropriate measuring points without cabling. The freely positionable components also accommodate flexible office concepts. If the office structure changes, the switches and sensors simply move with it.

A major disadvantage of this technology is that the components are powered by batteries: These have to be changed regularly and can cause failures.

Radio without batteries

Modern systems work with battery-free wireless components that use the energy provided by their immediate surroundings. Three main sources have become established in building automation: kinetic, solar-based and thermal energy.

Kinetic energy

Motion is a reliable source of energy for various switches. Inside the switch housing, an electromechanical energy converter (Eco 200) converts the push of a button into electrical energy and makes it available immediately after actuation. Similar to a bicycle dynamo, a small, powerful magnet drives a magnetic flux that closes in a U-shaped core through two magnetically conductive armature plates. An induction coil is wound around this core. The core itself is movable and can assume two positions in which it touches the opposite armature plates. This leads to a sudden change in the magnetic field and thus to a voltage pulse in the induction coil.

With an energy level of 120 µWs, each actuation is sufficient for three radio telegrams. At room temperature, the transducer enables more than 1,000,000 switching cycles. This principle of kinetic energy harvesting can be used for light or blind switches. There are also battery-free sensors that warn of water damage. Swelling disks at the bottom of the sensor expand as soon as they come into contact with a liquid. This movement triggers the electromechanical transducer and thus a radio signal. Based on this signal, the valve in the pipe closes and the homeowner receives a corresponding message on their smartphone.

Solar-based energy

In battery-free switches and sensors, small energy converters generate the energy for wireless communication. An electromechanical converter, for example, uses the movement of a keystroke; other sources are light and temperature differences.

© EnOcean

Miniaturized solar modules can use the low light intensity of indoor light to supply wireless modules with power. Solar-powered sensor modules such as the 'STM 330' are very energy-efficient: if a temperature reading is to be transmitted every 15 minutes, for example, a charging time of just 3.6 hours a day at 200 lux is sufficient for uninterrupted operation. The solar cell generates a voltage of 3 V at 200 lux. An additional PAS (Poly Acenic Semiconductor) charging capacitor provides an energy reserve that bridges periods with a lack of ambient energy. With a fully charged energy store, the module is fully functional for about a week in complete darkness.

Light energy enables a large number of energy self-sufficient sensors, such as window contacts, temperature, gas and humidity sensors, as well as light sensors and presence detectors.

Thermal energy

The combination of a thermal converter and a voltage amplifier can convert temperature differences of just 2 °C into usable current.

© EnOcean

Temperature differences, for example between a radiator and its surroundings, provide a lot of energy. This is not only sufficient for sensors, but also for actuators. The 'harvesting' takes place via a Peltier element together with a DC/DC converter (ECT 310). In this combination, an input voltage from 20 mV - which corresponds to a temperature difference of around 2 °C - can be converted into a usable output voltage greater than 3 V. The greater the temperature difference, the more energy the DC/DC converter supplies.

This principle is currently used primarily in radiator actuators. Here, the energy harvested is sufficient for both radio communication and valve stroke changes. Together with a solar-powered room sensor, a completely energy self-sufficient wireless individual room control system can be implemented.

Energy-saving radio

In building automation, the battery-free wireless components use the international standard ISO/IEC 14543-3-1X (868 MHz). It is optimized for the transmission of data with the lowest possible energy consumption. The telegrams are only 1 ms long. To rule out transmission errors and collisions, the short telegram is randomly repeated twice. This means that numerous wireless switches and sensors can be installed in a very small space and operated in parallel. Each module has a unique 32-bit identification number that prevents overlaps with other wireless sensors. Inside the building, the range of the wireless sensors is typically a maximum of 30 m.

Building automation with radio-based components can be implemented with different system architectures depending on requirements. Decentralized automation can serve as the basis, in which the battery-free wireless sensors are taught directly to the corresponding receivers (actuators).

By using sensors that record various parameters - for example light intensity, temperature, presence - different functions can be mapped with one device. By connecting the radio-based components to a central web server, building operators can consolidate, visualize and control the automation at a central location. Gateways can also integrate the wireless components into other systems such as BACnet or KNX.

Flexible control for a flexible working environment

The Squaire at Frankfurt Airport is a building that utilizes the advantages of battery-free wireless solutions for the automation of various trades. Under the name 'New Work City', the 140,000 m² building offers a working environment that combines concentrated work, meetings and quiet zones as well as restaurants, services and shopping facilities under one roof. The rooms are designed to adapt to individual requirements and work processes. It must be possible to reconfigure office spaces flexibly without having to work on the electrical installation or reprogram the automation solution.

The horizontal high-rise building 'The Squaire' - one of the most spectacular buildings in Europe with flexible office and room design.

© Roland Horn

The Squaire is divided into six sections along the main axis, each with its own component server. This makes it possible to separate entire parts of the building from each other in terms of tenant-specific and communication technology, without the operator losing overall operation and monitoring.

The switches on the various floors are connected to each of the six component servers via a fiber optic ring; there are two switches per floor and component. The ring-shaped architecture ensures a high level of security: if a connection is interrupted, the second path within the ring still ensures that the data arrives at its destination.

Several system distributors are connected to the switches, in each of which a '750-841' controller from Wago is installed to control the individual components. In addition to the controller, the system distributors also contain the various terminals via which the controller controls the individual components such as lights and blinds. Each system distributor with a controller also contains an extension terminal block that extends the internal terminal bus.

Up to seven additional system distributors can be connected as slaves at intervals of 15 m. A single controller can therefore be used to automate a building section with a length of over 100 m.

The controller controls the heating and cooling, the lighting, the windows and the blinds via the terminals in the system distributors. In the central main systems of the building, pumps, valves, frequency converters for the fans, outdoor lighting and heating and cooling distributors, among other things, have to be controlled. Sub-bus systems such as Modbus RTU, DALI, MP-Bus and KNX are used for this.

The lighting, heating and shading of the rooms are controlled using battery-free switches and the 'SR04' temperature sensors from Thermokon. If the office structure changes, the EnOcean-based devices can be relocated at any time. They and the layout of the rooms can then be reassigned with just a few mouse clicks. At the same time, there is no need to change the batteries in the devices, which would be very time-consuming with a total of 18,000 units.

Communication between the room automation controllers and the building management system takes place via the floor switches. The slave boxes receive the EnOcean telegrams from the wireless sensors and control the room automation components such as lighting, windows, blinds and valves.

Author:
Frank Schmidt is Chief Technology Officer at EnOcean in Oberhaching.