Many electrical contractors are finding additional revenue with the introduction of green technology. My definition of greening is taking whatever steps are necessary to reduce the energy consumed by a building or complex. Not only is that a desirable goal for the environment, but it is a way to significantly reduce operating expenses for owners and tenants, while, at the same time, generating revenue for the contractor.
The best way to achieve that goal is to use more efficient equipment to provide more output with less input. The push to use compact fluorescent lamps is a good example.
Another major avenue is to integrate a building’s energy-consuming systems. By doing that, whatever reduction in energy use achieved by using more efficient devices can be further improved—multiplied, in fact. Energy-efficient devices are essentially passive. They sit still and do the work regardless of its effectiveness. But building systems exist to do a job: lighting, cooling, heating and circulating breathable air, for example. The way each particular job is done is up to the control system.
Is the lighting control a simple on/off switch or a switch and dimmer combination? In that case, the decision of whether the lights should be on or off, on but dimmed, or on at maximum brightness is up to people who activate the switch or dimmer. That might work just fine—or not. It depends on what is in the mind of the person in control. The trouble is that people are different, some will think about minimizing the use of energy, and some won’t be bothered.
Then there is the question of what kind of illumination is needed. Are light switch operators thinking about controlling the lights so as to provide just what is needed to do a specific job? Does the lighting contribute to a mood, or should it focus on a given task, such as reading, assembling components, performing surgery or lighting a theatrical performance? Should there be the same amount of light in a room on a sunny or a cloudy day? Should the lights be on when the room is empty? Could people tolerate a somewhat lower light level on a hot day in order to use more air conditioning? For that matter, just what is the optimum light level?
If lighting is controlled by a closed-loop addressable system and there is a building management system that might use BACNET or Ethernet—the different systems can be programmed to interact with each—we then have the tools to begin exploring answers to these questions. The possibilities suddenly become wide open:
1. With a daylight harvesting system, illumination sensors cause the level of lighting to be adjusted for a constant level of area illumination. Energy will not be wasted adding to naturally available illumination. It can be used to enhance the lighting in cloudy or nighttime conditions or even vary as the sun moves across the sky. The daylight system could be programmed to adjust motorized window coverings to minimize glare or to adjust shutters to follow the sun, aiming sunlight into the room throughout the day.
2. The control system could allow individual users to adjust the task lighting they need for their work.
3. Occupancy sensors could change the lighting pattern according to whether a room is occupied. There could even be a grid of sensors that would enable the lighting program to energize only some of the room’s lights.
Heating and cooling
These days, even simple home thermostats can be used to adjust set points for different times of day and days of the week. Systems in larger buildings can easily be programmed that way as well and also can incorporate other energy-saving control features.
Closed-loop control can allow the heating or cooling system to be optimized, only allowing enough energy needed for the task. Temperature feedback to the control system could come from sensors placed throughout an area with the information averaged or entered into a more complex algorithm. In this case, the heat output of the system would be much more efficiently controlled than if it were based on a single thermostat.
The motor speed of an air circulator can be controlled based on the level of carbon dioxide in a room, as measured by gas sensors. Therefore, the rate of air circulated into the room will only be as much as needed for the number of occupants.
Although smart metering is largely viewed for providing more nuanced usage information to electrical utilities, it can be used within a building to identify the electrical energy costs of different systems at different locations, which leads me to the most important contribution integrated control systems can make towards reducing energy usage …
Fine tuning the system
When building systems are integrated and controlled, settings and control algorithms can be adjusted over time, using data fed back from energy measurements and from observations and comments from the people who use the building. The parameters are not set in stone.
BROWN is an electrical engineer, technical writer and editor. He serves as managing editor for SECURITY + LIFE SAFETY SYSTEMS magazine. For many years, he designed high-power electronics systems for industry, research laboratories and government. Reach him at firstname.lastname@example.org.