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Case Studies & White Papers:
Tek-Air Provides HVAC Controls at Rensselaer Polytechnic

Tek-Air Job Profile

Project: Walker Laboratory
      Rensselaer Polytechnic Institute
Location: Troy, New York
Design Engineer: Harza Northeast
Completed: 1996

Facility Design Goals
This is a laboratory facility on the campus of a prestigious northeastern engineering institute. The variable volume design was driven by the University's dedication to energy efficiency without compromising safety, performance, and reliability.

Scope of Project
Tek-Air provided all HVAC controls for a total of ten laboratories. While some laboratories did not have fume hoods, others had as many as thirteen. Each lab incorporated both general exhausts and various snorkel exhausts.

Equipment Supplied
Laboratory Control Panels: Tek-Air, Tek-Trak II direct digital laboratory controllers in flushmount NEMA 1 enclosures, located in labs.
Fume Hood Face Velocity Controls: Tek-Air FVC-2000 stand-alone, direct digital controller with side wall sensor face-velocity and room vent kit.
Supply Airflow Valve Assemblies: Composite assemblies consisting of Tek-Air Pneumavalve air valves, VorTek-SD airflow measuring devices, and industrial current-to-pressure transducers.
General Exhaust Boxes: Composite assemblies consisting of Tek-Air Pneumavalve air valves, and industrial current-to-pressure transducers.
Fume Hood Exhaust Control Valves: Composite assemblies consisting of Tek-Air Pneumavalve air valves, exhaust flow sensor, VorTek-SD in hood exhaust duct, and Fairchild current-to-pressure transducers.
Room Temperature Sensors: Space temperature sensor with integral 4-20mA transmitter.
Building Automation Interface: Tek-Air FVCNet Gateway.

BAS Interface
A lab controller network allows the lab controllers to communicate to a Honeywell graphics central monitoring computer. The lab controller network terminates at a Tek-Air FVCNet Gateway communication adapter. The adapter translates Tek-Trak data to Honeywell-usable data via a standard protocol. The adapters connect to the central computer through standard RS232 communications cables. See diagram below:

System Operation
Each lab fume hood is fitted with a Tek-Air FVC-2000 face velocity controller. The controller senses changes in face velocity and controls exhaust volume from the hood to maintain a constant face velocity regardless of sash position. A Tek-Air VorTek transmitter measures total hood exhaust airflow in the hood exhaust duct branch and transmits volume data to the Tek-Trak lab control panel.

Several labs have fixed (unmeasured, uncontrolled) exhaust in the form of snorkel exhaust. The value of these fixed exhaust amounts is accounted for in the total exhaust measurement.

Labs are fitted with general exhaust valves which draw air from the room as a supplement to the fume hood exhausts. A VorTek in the inlet measures the flow and transmits its value to the Tek-Trak. Should the room total exhaust requirement exceed the total fume hood exhaust volume at any given time, the general exhaust valve is modulated open to satisfy the room's load.

Supply airflow to the lab is measured by a VorTek transmitter in the supply air Pneumavalve assembly inlet. Supply air volume is reported to the Tek-Trak panel which modulates that supply air volume to synchronize the supply air with the actual total exhaust, less a differential airflow value. The differential is controlled so that the supply airflow is always less than the exhaust airflow, thereby creating a negative pressure within the lab envelope.

The Tek-Trak controllers are programmed to maintain a minimum exhaust airflow which is based on minimum required room air change. Space temperature sensors report lab temperature to the Tek-Trak, which then resets the required supply air temperature setpoint in response to an increase or decrease in lab temperature. If the reheat is closed and the room temperature continues to increase, the controller will increase the total lab exhaust volume by opening the general exhaust. Consequently, the controller will increase the volume of supply air to maintain the pressurizing offset differential and the increase in supply air will cool the lab.

All airflow, temperature, face velocity, alarm, and setpoint values are reported via a direct digital link to the Honeywell graphic central computer system. Room temperature and airflow differential setpoints can be adjusted from the operators console.
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