Case Studies & White Papers:
Variable Volume Ventilation at Ethyl Petroleum Research Facility

Tek-Air Job Profile

Project: Ethyl Petroleum Research Facility
Location: Richmond, Virginia
Design Engineer: Albert Khan Associates
Building Management System Contractor: Siebe DMS
Completed: 1994

Facility Design Goals
This new flagship research facility for a Fortune 500 chemical manufacturer is their first laboratory building designed to incorporate variable volume ventilation. Although the concern for efficiency was the primary factor driving variable volume design, Ethyl was not willing to compromise safety, comfort, noise reduction, reliability, and maintenance to achieve energy savings.



In an effort to reduce the initial capital cost of the ventilation system, an aggressive diversity factor was used in the design of the exhaust system. The supply air to and exhaust air from the smaller labs were designed with a 55% diversity. This required installation of fans capable of handling 55% maximum exhaust requirement if all fume hoods were left fully open.

These high diversities were accomplished by combining HOPEC (Hand Operated Positive Energy Conserving) combination sash fume hoods and variable volume face velocity controls. Because of the diversity factor, accurate control of the laboratory airflow was paramount. If too many fume hoods were left in the open position at any one time, the system would not have the reserve capacity to maintain safe face velocities. The high diversity mandated the ability to alert the lab workers to any low face velocity conditions.

Scope of Project
Tek-Air provided all airflow controls for approximately one hundred and seventy fume hoods in forty-four laboratories. The laboratory layouts ranged from one to twelve fume hoods per lab, with each lab also containing varied mixes of solvent sinks, canopy hoods, scavenger outlets, and snorkel exhausts.

Equipment Supplied
Fume Hood Face Velocity Controls: Tek-Air FVC-2000 stand-alone, direct digital controller with side wall sensor and room vent kit.
Supply Airflow Valve Assemblies: Composite assemblies consisting of Tek-Air Pneumavalve air valves, VorTek-SD airflow measuring devices, Titus reheat coils, Minco duct temperature sensors w/transmitter, lined-duct sound attenuator sections, industrial current-to-pressure transducers, and DEI ball-type reheat control valves with Belimo electronic actuators.
General Exhaust Valves: Composite assemblies consisting of Tek-Air Pneumavalve air valves, VorTek-SD airflow measuring devices, and industrial current-to-pressure transducers.
Fume Hood Exhaust Air Control Valves: Composite assemblies consisting of Tek-Air Pneumavalve air valves, VorTek-SD airflow measuring devices, and industrial current-to-pressure transducers.
Room Temperature Sensors: Space temperature sensor w/integral transmitter.
Laboratory Control Panels: Tek-Air Tek-Trak ll direct digital controllers in NEMA 1 enclosures, flush mounted in each lab.
Building Automation Interface: Tek-Air FVCNet Gateway.

BAS Interface
Ethyl had selected the Siebe DMS building management system for monitoring and controlling the non-laboratory areas of the facility. To integrate both systems into one console for the facility operators, Siebe and Tek-Air provided a direct digital link between systems. Data associated with the laboratories such as face velocity, air volume, temperature, and valve position are transferred to the Siebe system and displayed on the Ultivist Operator's Console.

Information moves throughout the Tek-Air system on two distinct networks. Each FVC-2000 fume hood controller communicates digitally with the Tek-Trak controller in the laboratory via a two-wire communications link referred to as the Local Lab Network. Tek-Trak controllers serving the individual rooms are networked together via the Global Lab Network which in turn is connected to the Siebe computer via the FVCNet Gateway link.

System Operation
Each lab fume hood in the facility was fitted with an FVC-2000 face velocity controller which measures actual face velocity and modulates a Pneumavalve air valve in the exhaust duct from the hood to maintain a constant face velocity, regardless of sash position. A Tek-Air VorTek airflow measuring transmitter, factory mounted in the valve inlet, measures the resultant hood exhaust airflow and reports the volume to the Tek-Trak lab control panel.

The laboratories with fewer hoods include Pneumavalves mounted in the general exhaust to modulate the air drawn from the room to supplement to the fume hood exhaust. A VorTek airflow measuring transmitter in the valve intake measures the general exhaust airflow and reports volume to the Tek-Trak panel. The total exhaust air volume is then computed in theTek-Trak controller by taking the sum of the individual exhaust air volumes from each of the fume hoods and the lab's general exhaust.

Supply air to the lab is controlled by a Pneumavalve air valve assembly. A VorTek airflow transmitter in the valve inlet measures the supply air volume and reports it to the Tek-Trak panel. The Tek-Trak modulates the Pneumavalve to synchronize the supply volume to the actual total exhaust, less a differential airflow volume. The differential volume is controlled so that the supply airflow is always less than the exhaust, creating a negative pressure in the lab.

In each lab the Tek-Trak controller is programmed to maintain the minimum supply volume required to guarantee the design minimum air change rate. When the hood sashes are lowered fully and the supply is at the minimum air change volume, there typically is insufficient exhaust to maintain a negative space pressurization. In these instances the Tek-Trak increases the flow through the Pneumavalve in the general exhaust, thereby providing the additional exhaust required to keep the supply/exhaust offset and maintain pressure.

A space temperature sensor in the lab reports to the Tek-Trak controller, which then resets the supply air discharge temperature setpoint up or down in response to an increase or decrease in the lab temperature. A duct temperature sensor in the discharge of the reheat coil reports to the Tek-Trak controller, which modulates the reheat coil valve to maintain the required supply air discharge temperature when the space is cold. If the lab is warm, the controller closes the reheat valve and then increases the volume of air supplied to the lab. This is achieved by first opening the general exhaust, thereby increasing the total exhaust. causing the tracking controls to increase the supply air to maintain the lab pressurization.

All airflow volumes, duct and space temperatures, hood face velocities, and low face velocity alarms are reported to the Siebe Central Computer. Lab temperature and airflow differential setpoints can be adjusted directly from the Siebe Central Computer.

Summary
The facility was occupied by the owner in the summer of 1994 and the laboratory control system has been operating since that date. The laboratories are successfully operating within the limits of diversity specified by the engineer. Sound levels in the laboratories are extremely low (even those with ten and twelve fume hoods), despite the absence of sound attenuation in ducts leaving the fume hoods.