Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.1

Inquiry

Exhaust Stack Damper Control System Our project is a research laboratory building for a State University Campus. Approximately 60% of the total building square footage is dedicated laboratory space. The laboratory space includes 23 wet labs, 73 fume hoods, one cleanroom, 16 laser labs and 10 microscopy labs. Our design team has developed a unique stack damper control system that maintains minimum stack velocity optimizing plume height, provides dilution of hazardous exhaust to acceptable levels, minimizes energy consumption using variable frequency drives on exhaust fans, and because fan rpm is matched to load requirements, sound levels are minimized. We feel that this exhaust damper design is uniquely qualified for consideration as an Innovative Design Credit 1.2 because the design: 1. Minimizes the risk of re-entrainment of chemical laden fumes into the building. 2. Minimizes the risk of adverse effects to the surrounding vegetation and animal life. 3. Minimizes energy consumption. 4. Limits noise generated by the building mechanical systems. INTENT Comply with ANSI Standard Z9.5, which recommends an exhaust stack discharge velocity of at least 3,000 feet per minute, without nullifying energy savings derived at reduced exhaust airflows. REQUIREMENTS & SUBMITTALS Design a manifold central exhaust system incorporating a damper arrangement that functions to vary the discharge velocity through the exhaust discharge stack(s) to comply with ANSI Standard Z9.5. 1. Provide drawings & cut sheets highlighting exhaust damper control system & system components. 2. Provide P&ID & sequence of system operation. Identify various modes of operation & resultant discharge stack velocities. STRATEGIES By varying the overall cross-sectional area of the exhaust discharge stack(s) due to changes in airflow, the discharge velocity can be controlled to a desired setpoint. Damper operation should be designed to control stack discharge velocity over the entire range of exhaust airflows. Discharge velocity should be controlled as close to 3,000 feet per minute as practical so as not to add excessive static pressure drop to the exhaust system, thereby increasing fan energy usage. At excessively high discharge velocities, noise may create a nuisance. The exhaust damper control system will be used in lieu of a fan system that blends outside air with fume hood exhaust, forcing the fan(s) to operate at constant maximum airflow. Dilution isn\'t a factor when using the damper control system considering the large amount of fume hood exhaust even at the minimum exhaust airflow. Plume height is a function of discharge velocity & of discharge mass flow rate. When using modulating stack damper control in labs with small exhaust demand, stack quantity must be considered so that plume height isn\'t compromised at low airflows when overall exhaust is spread over a number of stacks. TECHNOLOGIES Exhaust discharge velocity can be controlled by altering the overall cross-sectional area of the exhaust discharge stacks in response to changes in airflow as sensed by duct mounted airflow monitors. This control can be achieved by modulating a damper located in each discharge stack or by sequencing on/off dampers in multiple stacks. In modulating damper systems, the damper characteristics must not disrupt the velocity profile of the exhaust air stream at the discharge of the stack or plume development is compromised. Both types of damper control system allow the central exhaust fans to operate across the range of exhaust airflows. The adjustable frequency drives control the fans to operate at their optimum point along the system curve, lowering horsepower usage and saving energy. SUBMITTALS 1. Exhaust Stack Discharge Damper Control P&ID 2. Patent for a control sequence for maintaining constant exhaust discharge velocity.