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Case Studies & White Papers:
Demand Based Static Pressure Reset Control for Laboratories, page 3.

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Closed Loop Control
As stated above, Demand Based Static Pressure Reset Control can only be achieved with a closed loop feedback control approach. An open loop system merely moves a valve to a preset position based on a factory calibrated flow rate and a spring compensates for static pressure changes. In an open loop system, merely knowing the valve position does not help to determine whether the static pressure in the duct is high, low or at the optimized setpoint.

By measuring airflow with a digital airflow system like vortex shedding and using that flow signal for feedback to control to an airflow setpoint, valve positions can be surveyed to determine if the static in the duct is too high. The BMS can now optimize the overall building system to operate at the lowest static pressure while maintaining a safe laboratory environment.

Also of importance is the type of airflow control valve being used since there are different designs in the marketplace. While a single blade damper does measure airflow the airflow measuring device that is typically used is very non-linear and operates best over about a 3:1 turndown in the center of the control output. It is most non-linear when in the upper or lower 30% of the device (near open or closed) which is the most important area when utilizing static pressure reset control.

Demand Based Static Pressure Reset Control is designed to make the valve operate near its open position. A single blade damper is non-linear and because of this, is subject to continual position hunting creating a dangerous situation in the lab and shorter lifespan of the actuator.

Summary
Through such organizations such as Labs21, the EPA, US Department of Energy Efficiency, Green Building Council and many others, owners and designers have been brought to the forefront of sustainable issues.

Laboratories are generally the largest users of energy in any facility. Many owners and engineers adopted VAV control systems for energy savings and are now looking at ways to save additional energy.

As stated above, lower static pressure system design can contribute greatly to sustainability goals and give the building owner a tremendous opportunity towards saving a large amount of energy dollars every year that the system is in operation. The AccuValve™ is a low pressure drop VAV control device. Its inherent design allows it to be utilized with Demand Based Static Pressure Control further reducing the static pressure in the system and maximizing energy efficiency.

The utilization of these airflow control valve technologies with the combined approach of Demand Based Static Pressure Control, offers the safest airflow control system (closed loop control) with the lowest operating cost.

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Tek-Air Systems, Inc.
41 Eagle Rd., Danbury, CT 06810
203-791-1400
www.tek-air.com

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