by Jim Newman and Travis Sheehan — It used to be that a sophisticated building had pneumatic controls managing the heating and cooling systems and banks of switches for the lights. If you wanted to know the overall energy performance of your building, you looked at your utility bills. While those days may not be completely over, modern building systems are managed through a generally complex assortment of sensors, controllers, software, and communications protocols. Modern building control systems handle more complicated equipment as well as more complicated tasks, including the provision of energy reporting and performance diagnostics.
Energy reporting has grown in importance because of a combination of corporate reporting needs and municipal regulation in the US. Many building managers expect that they can get energy use information from their building control systems. Unfortunately, standard building control systems are not built for collecting and distributing building energy use data, and even more sophisticated energy management systems may be of limited value for energy use reporting. To understand what information might be available from a building control system, we have outlined the basic part of these systems and how they communicate, with a focus on where energy use data might be found.
Controlling Building Systems and Tracking Performance
Building Control Systems (or Building Management Systems) are comprised of sensors, controllers, a communications infrastructure, and some computing resources. In general, the sensors send signals through the communications infrastructure to the computing resources, which decide on a control action, which is communicated back to the controllers. This structure can be more complex — with many types of sensors, a distributed communications infrastructure, and controllers capable of complex control sequences, or it can be pretty simple — a thermostat with a temperature sensor that calls for heating or cooling. Typical systems control heating and cooling, lighting, and security systems. These systems typically do not interact with process loads such as servers or heavy equipment, although specialized systems of various sorts will also manage such loads.
Tracking the overall use of energy or water in a building is typically done with meters of various sorts. At the most basic level, the meters are read by the utility and that information is available to building operators in the form of a bill. The more sophisticated energy monitoring systems in larger, newer buildings use meters that report data more frequently, either directly to the utility or directly to building operators. These meter systems use a different communication protocol from the building control systems, leading to a more arms-length relationship between building system monitoring and control and overall energy use monitoring.
90% of buildings in the US have hard-wired control systems. There are several communications protocols used in these systems, ranging from BACnet, an open system developed by ASHRAE to LONTalk, a proprietary protocol developed by the Echelon Corporation, as well as a number of other lesser-used systems. Compatibility of devices on any system is the real issue when talking about communication protocols. A building will likely need a number of different types of sensors and controls, working with equipment from multiple manufacturers and communicating appropriately.
With the BACnet communication protocol, some devices claim to be “BACnet compatible”, but the term is misleading. Often, there needs to be an intermediary ‘gateway’ between the device and the BACnet network. A more direct specification is defined as ‘native BACnet’, meaning the device requires no gateway and can be connected directly to the BACnet network. Still, some manufacturer use native BACnet specifications for new products, but not for older products, and devices from different manufacturers may not speak the same ‘native BACnet’ to each other.
LonTalk, a proprietary protocol developed by Echelon Corp., has been adopted by a wide range of manufacturers and accepted as a part of ANSI/EIA709.1-b. LonTalk supports devices branded as LonWorks. To further the uptake of the protocol, LonMark Interoperability Association formed as a group of manufacturers that define implementation guidelines for LonWorks devices. LonMark creates profiles for each class of devices, specifying baseline profiles for each type of object- all thermostats will report out the same base data, making it much easier to integrate devices and equipment from different manufacturers in a building automation network.
Wireless protocols are the new kid on the block. However, these wireless communications protocols, such as ZigBee or the EnOcean system are primarily overlays on the older and more established communications protocols. Wireless protocols primarily allow devices and sensors to talk to each other and then pass information to “collectors” which communicate via a wired BACnet or LONTalk network. ZigBee is essentially an interpreter of BACnet into the wireless language. What kind of data is ZigBee good at transferring? That depends on its bandwidth. ZigBee operates at a maximum data rate of 250Kbps, about the download rate of your old telephone connected modem. This is good for applications such as thermostats, light switches, and wireless sensors, but not more data-intensive uses.
Control versus Monitoring — Talking Different Languages
While much has been written about the natural relationship between the Smart Building and Green Building movements, the intersection of actual systems are less clear. The types of information, ways of communicating that information, and uses of information are quite different. Controlling building systems requires simple information from many sensors and a large number of devices that can act based on sensor input. Even a large and complicated building is essentially following this model. Energy use tracking requires large amounts of detailed information from a small number of sensors (or meters) that is collected, stored, and analyzed in depth. Because of the differences in data and uses, the basic systems for communicating this information are quite different. The idea that a building manager might be able to gather energy use data from their building management system to fulfill reporting needs is unlikely without a very sophisticated system in place. Fortunately, energy monitoring is a much easier task than managing building systems, and simple solutions can be highly effective.
The basic components of a monitoring system are meters, data logging and storage, analysis tools, and display or reporting. Meters and data loggers communicate over protocols such as the open Modbus RS485 or simple proprietary protocols. Once the data is collected, then a more standard connection via internet protocols is used for connecting to display and reporting systems. Energy management systems that perform complex analyses, such as load shedding calculations or energy conservation analysis do this work at the analysis level. The most sophisticated systems have built-in mechanisms to generate control feedback based on such analyses, however, this feedback is necessarily simple in nature.
The costs associated with installing and managing a performance monitoring system have been dropping over the last several years. Because of the simplicity of the systems and because of the low cost barriers, performance monitoring systems have gained in value for building managers. Many organizations now require building energy and water use reporting as part of their overall sustainability reporting initiatives. In addition, a growing list of municipalities are requiring mandatory energy and water reporting for buildings over 50,000 square feet. Make sure that your building can cost effectively meet these requirements without getting bogged down in expensive and complicated system evaluations.