Getting the most out of your system

An important characteristic of an intelligent building is its ability to sense ambient conditions and react to them. This ability resides in the building’s control systems, the primary purpose of which is to direct the performance of building systems and processes. These building systems include fire and life safety, lighting, energy management, security and access control, and other systems depending on the nature of the building and the functions that it houses.

No matter how simple or complex a control system is, it only has three basic functions: sensing, processing and directing. Sensing involves the ability to detect current conditions. Processing takes the sensing data about current conditions, compares it with the desired conditions and then devises a strategy for changing current conditions to desired conditions. Directing initiates action to physically change the existing conditions to the desired conditions.

To illustrate these three basic control system functions, consider a simple residential thermostat. The occupant of the house sets the thermostat to the desired temperature and the thermostat senses the ambient temperature. The thermostat continually compares the ambient temperature it senses with the desired temperature, and when the two are not the same, it develops a strategy for changing the actual temperature to the desired temperature.

In this case, the control strategy is simple. If the actual temperature is below the desired temperature, the furnace needs to come on. If the actual temperature is above the desired temperature, the air conditioner needs to come on. The thermostat then accomplishes the directing function by closing a set of contacts and causing either the furnace or air conditioner to come on.

The three control functions can either be centralized or distributed. In the case of the simple residential thermostat, everything is centralized. All three control functions take place in the thermostat itself. In commercial/industrial/institutional (CII) buildings, the sensing function is often performed remotely and the data relayed back to a stand-alone control panel or the central control station where the processing and directing functions take place depending on system architecture. In either case, there are only a finite number of sensors, and their placement is critical to the success for the control function. In fact, the fixed number and location of sensors often requires “averaging” system response that can lead to large variations in the controlled variable such as temperature. For example, a single thermostat in one room of a house can result in large temperature variations throughout the house as conditions change from room to room.

Control system problems and limitations can often be traced to the sensing function. The processing and directing functions of the control system are performed by increasingly powerful microprocessors that are capable of receiving and processing data from an almost unlimited number of sensors. Similarly, advances in power electronics and networking are making it easy to individually monitor and control each piece of mechanical and electrical in a building. For example, today it is possible to individually address and control each building luminaire. The constraint is the sensing function and advances in microelectromechanical sensor (MEMS) technology may be the answer.

Motes are an emerging MEMS technology that may have a lot of advantages for the building industry. Motes combine radio frequency, networking and data processing technologies into a single tiny package that can sense, process and communicate. Sensors can be integral or separate and can sense temperature, humidity, moisture, light, sound, vibration, pressure, stress, weight or any other measurable physical quantity. Motes use the TinyOS operating system and can operate on their own or self-organize into ad hoc networks that allow the exchange of data and communication between motes. Motes were developed by collaboration between the University of California Berkeley and Intel and are manufactured and sold by firms including Crossbow Technology Inc.

Like their size, the cost of motes is decreasing, which makes them economically viable for a variety of applications. They are powered by batteries that can last one to two years. However, research is being done into ways of powering motes indefinitely such as the conversion of ambient vibration or light into sufficient electrical energy. Motes could be built into building materials such as ceiling tile or equipment such as circuit breakers and fuses to provide the owner with vast monitoring capability at minimal cost. Similarly, because of their size and ability to operate wirelessly they would be ideal for older buildings, particularly historical buildings. Electrical contractors should keep their eye on this technology as a way of meeting customers’ need for expanded monitoring and control of building and production systems.

For more information on motes, contact Intel Corp. at www.intel.com/research/ print/motes.htm or Crossbow Technology Inc. at www.xbow.com. EC

GLAVINICH is an associate professor in the Department of Civil, Environmental and Architectural Engineering at The University of Kansas and is a frequent instructor for NECA’s Management Education Institute. He can be reached at 785.864.3435 or [email protected].