Building Automation: Choosing the Right Technologies Reaps Energy Efficiency Rewards
By Carlos Petty - September 2005 - Building Automation
Regardless of building type, energy use accounts for a significant portion of operating costs. Part of the challenge in reducing costs lies in improving equipment performance and reducing energy consumption without diminishing comfort, safety or security. Meeting that challenge has illustrated the need for increased system automation and system integration.
Identifying the appropriate technologies for particular building types and occupancies will reduce overall energy use. A successful building automation system design implements effective strategies to optimize these new control technologies.
Today’s design trends include:
- System-controlled daylighting.
- Digital addressable lighting interface-driven lighting networks.
- Variable frequency drives with direct communication interfaces.
- Permanent air quality monitoring demand-controlled ventilation.
- Electronic variable air volume box controllers.
- Automatic ventilation system shutdown.
- Communication via a structured cable plant.
- Electronic utility meters.
While often considered for new buildings, all of these technologies are applicable for retrofits as well.
The key to achieving the most energy savings in both situations is to take an integrated approach to the design of the structure and systems. Facility executives should consider integrating these new technologies as part of a whole system of building improvements. In addition, each technology has specific advantages in various building types.
On average, lighting accounts for about 25 percent of a building’s energy use. A major portion of this expense is unnecessary. Technologies developed during the past 10 years can help cut lighting costs by 30 to 60 percent while enhancing lighting quality and reducing environmental impact.
• Design for Daylighting. Daylighting is an architectural technique that permits a controlled amount of of natural light to enter a space to reduce or eliminate electric lighting when possible. A greater potential to save on electric energy is realized when daylighting techniques are used in conjunction with automatic lighting controls, automatic shade controls, photocell daylight dimmers near windows to control fluorescent fixtures, and occupancy sensors integrated into a building automation system.
In general, buildings that are typically designed with large expanses of glazing, including schools, retail stores and malls, atriums and warehouses with skylights, are prime candidates for integration of daylighting techniques with automatic lighting controls.
• DALI, the New Digital Standard. The digital addressable lighting interface (DALI) is a bi-directional, digital protocol developed by lighting manufacturers to control light source levels. The new protocol was initially applied to the control of linear and compact fluorescent lamps, followed by additional light sources, such as HID, LED and incandescent lamps. Using this new digital standard in lighting control makes it possible to combine the installation of existing 1-10v interfaces with the advances of intelligent lighting control. This system closes the gap between previous 1-10v technology and expensive bus systems. DALI-driven lighting networks can be connected to building automation systems.
Because DALI gives each lighting fixture a unique IP address, it is an ideal way to control lighting costs in new construction, and applications with shifting occupancies or round-the-clock operations, such as office buildings and hospitals.
The first priority of an HVAC system is to provide a comfortable, safe environment through efficient heating, cooling, humidity control and circulation of filtered fresh air. However, even a properly sized HVAC system can waste energy because of thermal losses in ducts; excessive HVAC demand because of inefficiencies in the building envelope, lighting or office equipment; and poor control strategies. New control technologies help overcome these deficiencies in today’s variable air volume (VAV) systems.
• Communicating with VFDs. Variable frequency drives (VFDs) have proven to substantially reduce fan and pump energy at part-load conditions. Primary/secondary pumping systems and HVAC equipment with VFDs controlled via a building automation system should be considered for use with high-efficiency HVAC equipment. Not only are they efficient at part-load operation, but they also reduce initial installation costs by 20 percent: If all communication between the building automation system and the VFD is accomplished with one pair of wires via RS-232, RS-485, BACnet, LonWork or driver from the automation system vendor, labor for field installation and commissioning is reduced.
VFDs are available with direct communication interfaces such as BACnet, allowing the building automation system to directly communicate with and control each drive, providing more information to the user.
Any building will benefit from VFDs, but the highest potential savings can be achieved in facilities with varying occupancies throughout the day or year, such as sports arenas, convention centers, hospitals, office buildings, laboratories — both in the mechanical system and individual fume hoods — and schools.
• Electronic VAV Box Controllers. In a VAV system, a VAV box in the occupied space regulates the amount of supply air delivered to the space based on its thermal requirements. Yet malfunctioning pneumatic VAV boxes can result in thermal discomfort while allowing the buildup of indoor air contaminants. Today’s electronic VAV box controllers provide temperature and air flow information directly to the building automation system, ensuring that minimum supply air ventilation settings are maintained during partial loads. That is why VAV box controllers generate the highest potential savings in hospitals, laboratories and office buildings when used in conjunction with VFDs.
Indoor Air Quality Issues
Indoor air quality (IAQ) is a significant concern for both facility executives and occupants. Poor IAQ is associated with a range of issues, from complaints about odors to respiratory illness, absenteeism and loss of productivity. It is difficult to identify a single reason for IAQ complaints because of the variety of possible sources and causes, as well as individual sensitivities. Poor IAQ may be caused by poor or uncontrolled ventilation, overcrowding, cigarette smoke, microbiological contamination, intake of outside air pollutants, off-gassing from interior finishes and furnishings and problems with the mechanical system.
• Permanent IAQ Monitoring. A permanent IAQ monitoring system is the first step toward understanding and addressing IAQ issues. Duct- and wall-mounted sensors allow the building automation system to monitor carbon dioxide and carbon monoxide and adjust these to meet ANSI/ASHRAE Standard 62-1999, “Ventilation for Acceptable Indoor Air Quality.” This is particularly valuable in office buildings, hospitals, laboratories and schools, especially in buildings with art rooms and science laboratories.
• Saving Energy with Demand-Controlled Ventilation. In buildings designed for large occupancies, such as convention centers, museums, malls, sports arenas, and hotels with conference centers or ballrooms, energy is typically wasted when these spaces are not at capacity. In these types of buildings, especially, applying a concept known as demand-controlled ventilation saves energy. Demand-controlled ventilation works by continuously monitoring carbon dioxide concentrations as per ANSI/ASHRAE Standard 62-1999 to sense occupancy and adjusting fan speeds accordingly.
Preparing for Terrorist Threats
Since 9/11, there has been heightened concerns about the potential for terrorists attacks to use airborne chemical, biological or radiological agents. Thus, mechanical equipment is becoming an important part of building-wide security. HVAC systems are being designed with automatic exhaust and purge system functions, along with low-leakage dampers installed at all outdoor air intakes, to minimize the potential introduction of airborne agents into any part of the building.
These HVAC security functions are being integrated with the building automation system, providing for automatic shutdown of the ventilation system if a chemical, biological or radiological agent is detected outside the building. This strategy requires direct two-way communications with each dedicated security-related monitoring system. Redundant fan and damper control functions via a dedicated building automation system workstation should be located within the building’s security office. The system should be powered by emergency back-up power. This type of security system should be implemented in all new public spaces, especially office buildings, hospitals, schools, retail/malls, hotels and theaters/auditoriums.
Reducing Communication Cabling Costs
Many buildings that are supported by a building automation system, security system, lighting system or elevator monitoring system, use separate communication cabling. These buildings should be designed to support multiple pathways, communications closets and equipment rooms. Each system is installed and commissioned by multiple contractors, resulting in high initial costs.
New building automation system design trends include the ability to communicate on a common communication infrastructure or structured cable plant. An engineered structured cable plant allows several building systems, such as security, lighting control and building automation, to share a single IT infrastructure. At the same time, each system communicates in a secure, independent manner.
This new strategy takes advantage of the fact that data communications for many systems share the same communication protocol, such as the TCP/IP standard (IEEE standard 802.3). New direct digital control panels that reside on local area networks can also connect to the Internet using static IP addresses. As more building systems are designed to integrate with others, less cabling will be required, reducing initial installation costs and yearly maintenance.
Buildings with extensive IT infrastructures, such as data centers and hospitals, reap the most savings from a structured cable plant.
Measuring Building-Wide Energy Efficiency
Measurement of building-wide utilities is becoming an accepted part of facility operations as a result of the growing interest in and development of sustainable design. For example, the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED-EB ) rating system for existing buildings requires utility measurement for energy efficiency in order to achieve LEED certification.
Electronic meters are now available to measure electricity, natural gas and steam. Some of these meters are capable of connecting to an existing LAN or directly to the Internet, and they support TCP/IP, SMTP, DNS, Modbus, HTTP, FTP and XML communication protocols. They can be assigned a static IP address or can receive one by a DHCP request.
These are especially valuable in new construction, as well as any building with a central plant, such as hospitals and laboratories.
Many of the latest energy-efficiency automation measures and strategies can be used across different building types and occupancies. However, effectively integrating these technologies and optimizing their performance in a new or existing building automation system requires both design expertise and a comprehensive commissioning process. Using this approach, facility executives can reduce energy costs while ensuring the comfort, safety and security of building occupants.
Carlos Petty is an Associate Partner and Group Manager in the New York City Office of Syska Hennessy Group, a national consulting, engineering, technology and construction firm.