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Demand-Controlled Ventilation: A Design Guide June 2003 This guide is intended

Demand-Controlled Ventilation: A Design Guide June 2003 This guide is intended to assist those implementing demand-controlled ventilation (DCV) systems. It was written by Marty Stipe, P.E. with the Oregon Office of Energy. Funding for the guide was provided by the Northwest Energy Efficiency Alliance. Demand-Controlled Ventilation Guide 1 Demand-Controlled Ventilation: A Design Guide Editor's Note: This guide is intended to assist those implementing demand-controlled ventilation (DCV) systems. It was written by Marty Stipe, P.E. with the Oregon Office of Energy in June 2003. Funding for the guide was provided by the Northwest Energy Efficiency Alliance. Introduction Ventilation is required so that the human occupants in buildings are provided with fresh air. The purpose is to provide oxygen and dilute other gases such as CO2 and human odors. ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) is a technical organization in the United States that recommends the systems and procedures for ventilation equipment. It has focused on two basic methods. The "dilution method" is used most frequently where pollutants are diluted by fresh air. Demand- controlled ventilation (DCV) is considered a dilution method. The second method, called the "Indoor Air Quality (IAQ) Procedure," is used to identify and remove specific contaminants. The IAQ method is not addressed in this guide. The concept of automatic ventilation control based on occupant demand has been known for over 20 years. The barrier to widespread implementation was not having a cost- effective, simple, and reliable sensor. Early sensors did not provide the reliability that was needed in many applications. In addition, the cost for the sensors was high. They were used in specialized applications primarily for indoor air quality purposes. Other methods were also explored. For example, as computers became used more in theater operations, the operators began to use the computers to track ticket sales to control ventilation rates. In recent years, advances in sensor technology have shown that demand-controlled ventilation is now both feasible and cost-effective. Interpretations of the ASHRAE guidelines indicate that demand-controlled ventilation is acceptable when properly designed and installed. What is a demand-controlled ventilation (DCV) system? Demand-controlled ventilation adjusts outside ventilation air based on the number of occupants and the ventilation demands that those occupants create. DCV is part of a building's ventilation system control strategy. It may include hardware, software, and control strategy and is an integral part of a building's ventilation design. Demand-Controlled Ventilation Guide 2 Which spaces would benefit from DCV? Large assembly spaces such as gymnasiums, auditoriums, lecture halls, conference rooms, churches, and theaters are good candidates for DCV. These spaces are designed for large numbers of people with high outside air requirements. However, the spaces are frequently only partially occupied. It is expected that, in the future, most spaces with ventilation air capacities of at least 1,500 cubic feet per minute (CFM) and serving areas having an average occupant load factor of 20 or less will be designed with DCV features. How will the space benefit? DCV is a ventilation control strategy that provides just the right amount of outside air that is needed by the occupants. Active control of the ventilation system can provide the opportunity to control indoor air quality. It can save energy. Figure 1 shows the ventilation savings potential (area in gold) for a typical application where DCV replaces fixed scheduled ventilation. Figure 1 - Comparison of ventilation rates for different system designs What are the typical components for each type of system? Many of the components that are used in controlling outside air may already be in place. These existing components could include an economizer or air makeup unit with modulating dampers. The additional components would be control sensors to communicate either directly with the economizer or with a central computer. The extra components might include carbon dioxide (CO2) sensors, occupancy sensors, or turnstile counters. Programming, while not a physical component, is a critical element of system operation. What is the Design Guide? Good communication among those implementing DCV systems is critical to a successful project. The building owner, architect and engineer, installer, commissioning agent and 0% 20% 40% 60% 80% 11:00 AM 12:00 P M 1:00 P M 2:00 P M 3:00 P M 4:00 P M 5:00 P M 6:00 P M 7:00 P M 8:00 P M 9:00 P M 10:00 P M 11:00 P M 12:00 AM 1:00 AM 2:00 AM % Of Design Ventilation - Scheduled % Of Design Ventilation - DCV % Of Design Occupancy Demand-Controlled Ventilation Guide 3 building inspector have different perspectives, but should work together to produce a good ventilation system. This guide is organized into multiple sections that focus on the needs of a particular group. The sections are: · Building Owners · Architects and Engineers · Installers · Building Inspectors and Commissioning Agents · Case Studies For Business Owners What is a demand-controlled ventilation system? A demand-controlled ventilation (DCV) system controls the amount of outside air brought into the building. It should provide the amount of outside air the human occupants need, and no more. This accomplishes two things. First, it saves energy by not heating or cooling unnecessary quantities of outside air. Second, it can provide assurance that sufficient outside air is being supplied to the occupants. Fixed ventilation systems provide constant, sufficient fresh air, but do so at the cost of heating or cooling excess air. Scheduled ventilation can provide fresh air at the correct rates at the right time, but run the risk of under or over-ventilation if schedule changes are not made at the appropriate times. How much money will a DCV system save me? The savings will vary greatly depending upon the building. However, energy savings are calculated to be as high as 60 percent for spaces that are lightly used but designed for large numbers of people (for example, gymnasiums). Also, buildings in predominantly heating climates such as the Pacific Northwest will get most of their savings during the heating season. How does a DCV system work? The system will use one or more sensors or systems to determine how many people are in a space. The ventilation system, typically part of the heating and cooling system, will adjust a damper to let more or less outside air into the building depending on what the sensor detects. For theaters, ticket sales or turnstile counters will provide the occupancy number. For gymnasiums, CO2 sensors will detect the presence of people. What do I have to do? First, it is important to work with the architect and designer to make sure they know how you will use the building. This will help them design appropriate systems. Future use of the building should also be considered. Some larger systems will contain most of the ventilation equipment due to building code requirements. There would be some Demand-Controlled Ventilation Guide 4 additional sensors and controls to provide the demand-control features. It is important to commission the system to assure that the sensors are properly integrated. Once installed, the system will run automatically. Annual building maintenance should include a check of system performance. The designer or builder should provide a procedure for the building owner on proper maintenance procedures. What will the tenants think of the DCV system? The tenants should not notice anything unusual. Proper ventilation should prevent the spaces from becoming stuffy, which should reduce complaints. It has been reported that the presence of a monitor actually improves tenant confidence in the quality of the air. Respond to serious tenant concerns by consulting with an air quality specialist and mechanical systems engineer. How does the DCV system manage new building odors? In new construction, there may be additional sources of odors. New furniture, carpeting, paint, office equipment, or other commercial processes may add contaminants that overwhelm the designed ventilation or occupants' perceptions. Sensors will not likely detect these unusual odors unless they are specifically designed to do so. In these cases, the ventilation should be increased until the situation is resolved. Discuss with the designer and builder the options for modifying initial ventilation requirements. Has anyone used a DCV system before? Yes. Adoption of this technology was promoted as early as the 1970s. However, sensor technology made significant improvements in the 1990s. Infrared and CO2 sensors are now being used in creative, successful applications (see Case Studies). Schools are using CO2 sensors to monitor classroom air quality conditions, large department stores are using CO2 sensors to save energy, and large office buildings are retrofitting their ventilation systems to take advantage of both energy conservation and fresh air benefits. For Architects and Engineers What is a demand-controlled ventilation system? Demand-controlled ventilation is a control strategy that adjusts the amount of outside air based on the number of occupants and the ventilation demands that those occupants create. This strategy is used to both control energy costs as well as assure sufficient ventilation. How will a demand-controlled ventilation system impact the occupants' living/working environment? The occupants should perceive little or no difference in their environment. A properly designed, installed, uploads/Geographie/ dcv-guide.pdf