01-PhoenixLaboratory.pdf

l a b o r a t o r y s o u r c e b o o k 5 t h e d i t i o n e n s u r i n g e n v i r o n m e n t a l i n t e g r i t y

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Phoenix Controls is a business of Honeywell International, Inc.

© 1999 Phoenix Controls 11/11 Printed in U.S.A.

MKT-0156 MPC-1677

A Thorough Understanding of Laboratory Environments As the setting for experimentation, testing or analysis, a laboratory is a specialized environment. Whether the laboratory is at a university, pharmaceutical or chemical facility, or in a medical or private research setting, its operation must be reliable. In every case, the laboratory airflow control system is vital to researchers' safety. It exhausts noxious fumes from the fume hoods, maintains correct room pressurization and creates a comfortable working environment.

Phoenix Controls has built its reputation on providing quality airflow controls for critical room environments.

We are recognized as an innovative leader in laboratory airflow controls. Since the company's founding in 1985, we have grown our installed base to more than one half million valves shipped, nearly 100,000 fumehoods under control on more than 22,500 projects in 42 different countries.

This sourcebook explores airflow system design issues that affect laboratories, reviews commonly used control applications and describes our airflow control system components.

Copyright 1999, 2000, 2003, 2006, 2009, Phoenix Controls

Accel, Phoenix, Phoenix Controls, Usage Based Controls, UBC, Celeris, Traccel, Zone Presence Sensor and ZPS are registered trademarks, and LabPro, MacroServer, MicroServer and Neutralizer are trademarks of

Honeywell International, Inc.

Phoenix Controls products are covered by one or more of the following U.S. patents:

5,251,665 5,304,093 5,385,505 D642894 5,545,086 and other patents pending.

The material in this document is for information purposes only and is subject to change without notice.

Phoenix Controls assumes no responsibility for any errors or for consequential damages that may result from the use or misrepresentation of any of the material in this publication.

Microsoft, Windows, and Excel are registered trademarks of Microsoft Corporation. BACnet is a trademark of

ASHRAE. Echelon, LON, LNS, LonMark, LonTalk, and LonWorks are registered trademarks of Echelon

Corporation. LonMark and the LonMark Logo are managed, granted, and used by LonMark International under a license granted by Echelon Corporation.

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DO NOT BLOCK

Access required after installation

Phoenix Controls Corporation

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PATENT NOS. 5,304,093 / 5,251,665 AND PATENTS PENDING

END VIEW

COVER TAB

Phoenix Controls Laboratory Sourcebook

Design Issues for Laboratory Airfl ow Systems

Accel® II Air Valve

Fume Hood Control Solutions

Room Level Control Solutions

Integration

System Components ............................................. 67Standard Operation

Flow Alarm

Emergency Exhaust Mute

Standby Operation

D e s ig n I s s u s fo r

L a b o ra to ry A ir fl o w

Phoenix Controls Laboratory Sourcebook 3

Table of Contents

Primary Objectives of Laboratory Airfl ow Systems 3

Determining Safe and Effi cient Face Velocity Levels 3

Design Issues for Laboratory Airfl ow

This chapter presents an overview of the key elements basic to the design of a laboratory airfl ow control system.

Primary Objectives of Laboratory Airfl ow

Systems With any control approach for laboratories, the ultimate objectives are:

Operator safety • –Capturing and containing fumes

Room pressurization • –Maintaining correct airfl ow direction

Ventilation • –Providing proper air changes

Comfort • –Providing proper temperature control

Historically, the standard method of controlling laboratory airfl ow was the constant volume (CV) approach. Next, two-state controls were used to gain effi ciency by reducing laboratory airfl ow under specifi c conditions, such as night setback. A more comprehensive method of laboratory airfl ow control is the variable air volume approach (VAV), in which sash positioning helps determine airfl ow rate. A fourth approach is Usage Based Controls® (UBC). With UBC, the airfl ow rate is maintained at safe minimum levels and increased only when needed by the presence of a user at a hood. When either the VAV or UBC options are used, safety and energy savings are optimized. Finally, providing accurate information about the space’s operation improves overall facility operation. Integration through the Phoenix Controls BACnet® portal provides effi cient and seamless method of data exchange.

Applications for each of these control methods are reviewed in Chapter 3.

Determining Safe and Effi cient Face Velocity

Levels

Fume containment is critical to the safety of laboratory workers. Several factors are involved with the proper containment of fumes, including face velocity, cross-drafts, and work practices.

Research and fi eld experience offer insight into effective face velocity settings for fume hoods.

Common industry guidelines range from 60-120 fpm (0.3-0.6 m/s). In many modern facilities, 100 fpm (0.5 m/s) is accepted as the standard for safe operation. The following research indicates that, in part, the presence and movement of an operator create the requirement for a 100 fpm face velocity.

The ASHRAE Symposium CH-99-09 on Laboratory Verifi cation and Testing offered the • paper, “Containment Testing for Occupied and Unoccupied Control of Fume Hoods.”

This research offers signifi cant fi ndings that unoccupied hoods—those with no people present—contain fumes while operating at the reduced face velocity of 60 fpm (0.3 m/s).

Occupied hoods, those with people present, required higher velocities to achieve proper containment. See Chapter 3 for details on Usage Based Controls (or hood occupancy control).

4 Phoenix Controls Laboratory Sourcebook

1Ljungvist, Bengt, “Some Observations on Aerodynamic Types of Fume Hoods,” Ventilation ’91, pp. 569-572.

• Research by Bengt Ljungvist from the University of Stockholm at the International Ventilation ‘91 conference has shown that the dynamic movement of an operator in front of a fume hood signifi cantly affects containment when compared to a still person or mannequin (see Figure 1-1).

There is some interest in operating hoods below the 60 fpm (0.3 m/s) level. Hoods with sash opening limits and deeper hoods have been tested for this concept. Often the ASHRAE 110-95 test is used to test hoods for containment. This is a static test where tracer gas is released in the fume hood and a non-moving mannequin is used to test the breathing zone.

The amount of tracer gas sensed at the mannequin determines the hood’s containment level.

If the level remains below the maximum threshold (e.g., 0.1 ppm), the hood may be deemed compliant.

Figure 1-1. Effects of operator movement on fume hood containment. The graph shows that the move ment of an operator has little effect on containment at 80-100 fpm, but movement has a disturbing effect at fl ows below 80 fpm. However, with no oper ator move ment, general containment down to 60 fpm is realized. (Ljungvist, 1991)1 .

Face Velocity (fpm)

O

O

O O O

60 100 140 160

Concentration (ppm)

Person Moving

Person Still

80 120

Figure 1-2. Tracer gas test setup. Both ASHRAE 110-95 and the DIN 12924 (a European standard) offer similar tracer gas test apparatus. Neither test is designed to account for active personnel movements. Sulphur

Hexaflouride

Probe

To Leakmeter

Occupied Hood

Mannequin

D s ig n I s s u s fo r

L a b o ra to ry A ir fl o w

Phoenix Controls Laboratory Sourcebook 5

This type of test does not assure containment under actual operating conditions. The static nature of the test does not take into account the dynamic conditions in a working laboratory.

The movement of people, high-supply air cross-drafts, and operator work habits are examples of everyday events that affect proper containment.

Although the ASHRAE and DIN test use a mannequin, containment under dynamic conditions is currently diffi cult to quantify. However, visual smoke tests under dynamic conditions do show cause for concern at low-face velocities. For example, walk-by and hand movement tests show improved containment at 100 fpm vs. 60 fpm.

This all leads to a design dilemma for many projects. On one side is the need for containment, thus sizing systems to meet the 100 fpm need. On the other side is the desire to reduce system capacity—often to meet budget constraints. However, it is possible to get both the safety from containment and the reduction in HVAC system capacity by taking diversity—that is, designing a system for less capacity than the sum of the peak demands. Sizing systems with diversity may be risky, however. Understanding diversity in laboratories becomes critical for safe designs that optimize savings (see discussion on Diversity on page 29).

Other factors that impact fume hood operator safety include speed of response of the airfl ow control system as well as accuracy and stability of control. These factors are explored in greater detail in Chapter 3, but are summarized below:

Speed of response • —the airfl ow control system must respond to changes in airfl ow command rapidly to ensure proper face velocity control. A system that can respond to changes in fl ow commands in less than 1 second assures that the operators safety is never compromised due to changes in sash position of fume hood occupancy.

Accuracy • —the airfl ow control system must have the precision of control to maintain proper face velocity regardless of sash position. Errors in airfl ow control can compromise operator safety. Airfl ow devices whose accuracy is expressed as a percent of range, introduce the possibility of signifi cantly high errors in face velocity.

Stability • —the airfl ow control system must provide consistent fl ow regardless of changes in duct static pressure and must respond precisely to changes in airfl ow command with little or no overshoot or undershoot

Figure 1-3. Airfl ow effi ciency by control method.

1960s

1970s

1980s

1990s

Constant Volume

Two-state and Auxiliary Air

Variable Air Volume

Airflo w Effic iency

Usage Based Controls ®

Celeris®

2000s

The

Future

6 Phoenix Controls Laboratory Sourcebook

Room Pressurization: Net Negative Airfl ow

Another objective if a VAV laboratory control system is to provide net negative room pressurization. This is typically done by controlling the supply or make-up air into the room to match the total exhaust airfl ow minus some offset. This is shown in Figure 1-4 by the line marked “Room Supply Air.” The exhaust to supply air offset is the airfl ow that comes into the room from the corridor door, transfer grills, other spaces, etc.

Ventilation and Comfort

The total airfl ow rate for a laboratory is dictated by the highest of the:

Total amount of exhaust from the hoods •

Minimum ventilation rates •

Cooling required for heat loads •

The minimum ventilation rate of Air Changes per Hour (ACH) is established to provide dilution and evacuation of any vapors or fumes that might escape from the fume hoods. Typical air changes rates are 6 to 12 ACH but could go as high as 20 ACH.

At times, the amount of airfl ow commanded by the hoods is below the amount needed to cool or ventilate the room (e.g., when the hood sash is closed and room thermal load is high).

In these instances, the room’s supply air volume must be increased to provide the proper amount of air. The lab control system must also act to maintain the proper lab pressurization by exhausting this “excess” supply air. This is achieved by adding a general exhaust valve to the room. This valve is controlled by the laboratory VAV system to maintain the proper balance between the total supply and total exhaust of the room.

Figure 1-4. Volumetric tracking of VAV fume hood airfl ow to sash position. The hood exhaust air maintains a constant face velocity through the sash travel while the make-up air tracks the total exhaust— maintaining room pressurization and proper ventilation.

Door

T

Make-up Air

100-900 CFM

Offset Air

100 CFM

Exhaust

200-1000 CFM

Fume Hood

Fum e

Hoo d

Exh au st Air

Roo m

S up ply A ir (M ak e-up A ir)

Example:

9 to 1 Turndown Supply Air Tracking

Example:

5 to 1 Turndown

Closed Sash Position Open

Constant Volume Mode

Variable Volume Mode

A irf lo w

C

F M

Phoenix Controls Laboratory Sourcebook 7

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Phoenix Controls Corporation

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PATENT NOS. 5,304,093 / 5,251,665 AND PATENTS PENDING

END VIEW

COVER TAB

Airfl ow Control

This chapter offers a description of the Accel II Air Valves airfl ow control methodologies with a focus on how the Accel II Air Valves address the challenges of controlling these dynamic environments.

The accuracy and stability of the airfl ow control device plays a critical role in maintaining the proper face velocity on fume hoods for operator safety, as well as space pressurization for containment and ventilation as well as comfort control. Not only must these devices provide precision air fl ow control, they must function with other devices as part of a system to maintain the safety and integrity of the entire laboratory.

Phoenix Controls introduced the venturi valve as an airfl ow control device in the early 1980s.

With over half a million valves installed, the Accel® II venturi valve has changed the way people control their labs and set a new performance standard. This chapter compares different fl ow control techniques and how the Phoenix Controls Accel II valve may be confi gured for different applications.

VAV Box versus Accel II Air Valve

Traditional VAV controls and even industrial quality controls cannot handle many of the control requirements unique to laboratories for a number of reasons. A few of these reasons are detailed below.

VAV Boxes with Velocity Pressure Sensors

This approach fails to meet most of the important requirements unique to laboratories. This technology along with other approaches that put sensors into the airstream is susceptible to fouling by tissues, contaminants, etc. Additionally, these devices have an accurate control range of only 3 or perhaps 4 to 1, even with very accurate transducers. This is because the velocity pressure varies as the square of fl ow.

The table below illustrates how velocity pressure measuring systems get into trouble even with very accurate ± 1% full-scale transducers.

Flow Velocity

Pressure (VP)

VP Error %VP Error % Flow Error

100% 1.00" 0.01" 1% 0.5%

20% 0.04" 0.01" 25% 13%

10% 0.01" 0.01" 100% 100%

For simplicity, a 1" velocity pressure was assumed for full 100% fl ow. Furthermore, a 1" ±1% full-scale (±0.01") transducer was used for the best case or optimum match of the transducer to the required signal span. Usually the transducer has a larger span or full-scale range versus the signal range creating an even larger error than shown.

Table of Contents

VAV Box versus Accel II Air Valve 7

Performance 9

8 Phoenix Controls Laboratory Sourcebook

Other Flow Measuring Technologies

Orifi ce plates and fl ow cross measuring techniques rely on much the same principles – measuring low-level differential pressure values and calculating an inferred fl ow rate. Errors and delays may occur as the fl ow controller runs through a process of; measure, control and adjust. Because of the inherent delays in this process it may require several cycles which could result in over and under shoots as the fl ow controller hones in on the fl ow set point. Each time the static pressure, measured fl ow, or fl ow command changes this cycle repeats itself.

A Unique Solution—The Phoenix Accel® II Venturi Valve

The Phoenix Controls Accel II venturi valves com bine a mechanical pressure independent regulator with a high-speed position/airfl ow controller to meet the unique requirements of laboratory airfl ow. These valves can be used in VAV, as well as constant volume and two-state applications.

Flow Control

Variable fl ow control is accomplished by using a pivot arm to repositioning the shaft and cone assembly to achieve the desired fl ow set point. Each and every valve that ships from the Phoenix Controls manufacturing facility is characterized on a sophisticated NIST traceable air station where shaft position is correlated to actual valve fl ow.

For constant volume valves, the air station delivers the desired air fl ow and the pivot arm locked in place at the fi xed set point.

For 2-state valves, the air station delivers the desired minimum and maximum fl ows and the actuator is mechanically clamped at the fl ow set points.

For VAV valves, a precision potentiometer is attached to the pivot arm and each valve is ramped through its entire fl ow range at a fi xed static pressure and a characterization curve of resistance versus fl ow is captured and downloaded to the valve mounted controller. The valve mounted controller precisely measures and controls the shaft position through a variety of actuation options and develops a precise fl ow feedback value. The known relationship of pivot arm position to fl ow allows the controller to rapidly drive the cone and shaft a specifi c orifi ce opening with little or no overshoot.

Figure 2-1. Cutaway view of a venturi valve.

Phoenix Controls Laboratory Sourcebook 9 ir fl o w C o n tr o l

Performance

Accuracy

All Phoenix Controls valves maintain a fi xed fl ow of air by adjusting to changes in static pressure.

Each valve has a cone assembly with an internal stainless steel spring. The custom engineered springs were selected based on passing one million cycles of full-defl ection testing. The cone assembly adjusts the open area of the venturi to system pressure as described below so that the fl ow set point is maintained continuously and instantaneously.

Pressure independent over a 0.6"-3.0" WC (150-750 Pa) drop across valve (medium pressure).

Low Pressure valves are independent over a 0.3"-3.0" WC (75-750 Pa) drop across valve.

This specialized characterization process and the precision mechanical components allow the Accel II valve to deliver unparalleled accuracy of +/- 5% of reading over the entire operating range.

3" WC

(750 Pa)

Figure 2-3. The effects of high static pressure on a venturi valve cone. As static pressure increases force on the cone, the spring compresses and the cone moves into the venturi, reducing the open area. Higher pressure and the smaller opening combine to maintain fl ow set point.

1" WC

(250 Pa)

Figure 2-2. The effects of low static pressure on a venturi valve cone. When there is low static pressure, less force is applied to the cone, which allows the spring within the cone to expand and push the cone away from the venturi.

The combination of low pressure and a large open area provides the desired fl ow.

10 Phoenix Controls Laboratory Sourcebook

Speed of Response

The Accel II valve is available with three actuation options: pneumatic; high-speed electric and normal-speed electric.

The high speed pneumatic and electric options will reposition the pivot arm to within 90% of the commanded position within one second.

The normal-speed electric actuator has the ability to drive the pivot arm over the entire operating range in less then 60 seconds. Subtle fl ow command changes are obviously accomplished in signifi cantly less time.

The valve works on the simple principle of metering airfl ow versus an air velocity measurement and control approach. Because pressure independence is de-coupled from the fl ow control with the Accel II valve, the two functions do not compete with one another as with fl ow sensing techniques. Flow sensing attempts to compensate for variations in measured fl ow due to both changes in fl ow command and static pressure which suggests the system is frequently repositioning.

The Accel II valves require no additional straight duct runs before or after valve for accurate control. They are available in fl ows from 35-5,000 CFM (60-8,480 m3/hr).

Accel II Valve Confi gurations

Applications require that each valve be built to with stand unique environments. The Accel II valves are available in three construction types and three valve designs.

Construction

16 ga. spun aluminum valve body with continuous welded seam •

Composite Tefl on • ® shaft bearings

Spring grade stainless steel spring and polyester or PPS slider assembly •

Supply valves* insulated with 3/8" (9.5 mm) fl exible closed-cell polyethyl ene. •

Operating Range

32-122 °F (0-50 °C) ambient 10-90% non-condensing RH •

Valve Construction

Class A: • Body and cone-uncoated aluminum; Shaft-uncoated 316 stainless steel

Class B: • Body and cone with phenolic coating; PFA coated stainless steel shaft (for standard fume hood applications)

Class C: • Body, cone and hardware with phenolic coating. PFA coated stainless steel shaft (for highly corrosive fume hood applications)

Valve Designs

A • - Conical Shape Diffuser (Standard Accel II Valve)

S • - Standard Shut-off Valve

L • - Low Leakage Shut-off Valve

Phoenix Controls Laboratory Sourcebook 11 ir fl o w C o n tr o l

Valve Types

With the internal pressure independent cone assem bly in operation, airfl ow can be regulated by posi tioning the shaft/cone assembly. The following types of Accel II valves are available:

Two-state: • The valve’s actuator positions the shaft to two dis tinct airfl ows. Mechanical clamps assure precise min imum and maximum airfl ows via a factory preset.

0-20 psi

Potentiometer on 'B' control type provides position output signal

VAV: • Closed loop control of airfl ow via flow feed back to command.

The shaft is positioned using direct potentiometer mea surement to produce a l inear ized factor y characterized feedback.

Potentiometer

Shut-off: • There are two confi gurations of shut-off valve, standard and low-leakage. The standard shut-off provides a metal-on-metal seal between the valve body and cone assembly which allows on the order of 5 cfm (8 l/s) at 4" of static pressure.

The low-leakage shut-off valve adds a gasket to the cone assembly which reduces the leakage rate past the cone to less then 0.010 cfm (0.005 l/s) at 4" of static pressure.

The shut-off valves provide 2-state or VAV control under normal conditions and may be commanded to shut-off via a local input or network command.

Constant Volume: • The valve’s shaft is adjusted and then locked into a specific position, which provides the scheduled air flow via factory calibration.

Position at low pressure

Pivot arm locked

12 Phoenix Controls Laboratory Sourcebook

Feature/Option Constant

Volume

Two-position Upgradable

Variable Air Valve

Analog Variable Air Volume Celeris Traccel

Control type C

Fixed Flow

P Two-state (0/20 psi)

B Base

Upgradable

A Analog (0-10 V)

E Analog (0-10V)

L Digital

N* Digital

M Digital

L Digital

Actuator Type None Pneumatic Pneumatic Pneumatic High-speed electric Low-speed electric Pneumatic

High-speed electric

Low-speed electric

Fail safe Fixed NO/NC NO/NC NO/NC NO/NC or last position

Last position

NO/NC

NO/NC,

last position

Last position

Flow feedback signal

— — Option

Flow alarm via feedback circuit

Flow alarm via pressure switch Option Option Option Option Option Option Option Option Option

Field-adjustable fl ow

Factory-insulated valve body

(supply)

Option

Low-noise diffuser construction†

Single 14-inch

Without Flow

Feedback

Without Flow

Feedback N/A N/A

Dual 14-inch N/A N/A N/A N/A

Standard Shut-off N/A N/A N/A N/A N/A

Low-Leakage

Shut-off* N/A N/A N/A N/A N/A

Medium Pressure

.6 to 3" WC

(150 to 750 Pa)

Low Pressure

.3 to 3" WC

(75 to 750 Pa)

Single valve body

Dual valve body

Triple valve body** N/A N/A N/A N/A N/A N/A

Quad valve body** N/A N/A N/A N/A N/A N/A

* Not available in the 14-inch valve size.

** 12-inch valve only.

NOTES:

All valves include pressure-independent, factory-calibrated position controllers, and are available in fl ows from 35-10,000 CFM (60-16,900 m3/hr).

Accel II valves are designed to reduce sound over all frequencies, but signifi cantly target the lower bands (125-500 Hz) to help eliminate the need for silencers.

Phoenix Controls Laboratory Sourcebook 13 ir fl o w C o n tr o l

Valve Sizes, and Operating Ranges

Accel II valves are available in four specifi c model sizes: 8, 10, 12 and 14" (for actual fl ow, refer to the chart below). In order to increase fl ow capacity, multiple valves may be assembled to operate as a unit.

For complete information on valve dimensions and weights, see various valve Product Data Sheets.

Standard Valves

Celeris/Traccel/Analog

Flow and Operating Range CFM (m3/h)

Shut-off Valves - For both Standard “S” and Low-

Leakage “L” Celeris/Traccel only

Flow and Operating Range CFM (m3/h)

Designation Size Single Dual Triple*** Quad*** Single Dual Triple Quad

Medium Pressure

0.6-3" WC

(150-750 Pa)

08" 35-700 (60-1185)

— — — 35-600 (60-1015)

10" 50-1000 (85-1695)

100-2000 (170-3390)

— — 50-850 (85-1440)

100-1700 (170-2880)

12" 90-1500 (155-2545)

180-3000 (310-5090)

270-4500** (465-7635)

360-6000** (620-10,180)

90-1300 (155-2205)

180-2600 (310-4410)

**14" 200-2500 (340-4245)

400-5000 (680-8490)

— — 200-1600 (340-2715)

400-3200 (680-5430)

Low Pressure

0.3-3" WC

(75-750 Pa)

08" 35-500 (60-845)

— — — 35-400 (60-675)

10" 50-550 (85-930)

100-1100 (170-1860)

— — 50-450 (85-760)

100-900 (170-1520)

12" 90-1050 (155-1780)

180-2100 (310-3560)

270-3150** (465-5340)

360-4200** (620-7120)

90-900 (155-1525)

180-1800 (310-3055)

**14" 200-1400 (340-2375)

400-2800 (680-4750)

— — 200-1000 (340-1695)

400-2000 (680-3390)

*CVVR - Flow Range: 35 cfm to 210 cfm (55m3/hr to 355 m3/hr) medium pressure only.

**Constant Volume, Celeris and Traccel only.

*** Analog controlled only.

Single (Exhaust Valve shown)

Dual (Pneumatic Supply Valve shown)

Triple (Make-up Air Valve shown)

Quad (Constant Volume Valve shown)

Single with Flange (Exhaust Valve shown)

14 Phoenix Controls Laboratory Sourcebook

Shut-off Valves

Phoenix Controls Shut-off Valves are available in two valve designs-Standard (Option S) and Low-leakage (Option L). Both designs are intended for use in critical airfl ow applications, where isolating the HVAC system from the room is necessary. Both versions of the shut-off valve provide the same precision and pressure independence of the standard Accel II valve with the addition of the ability to effectively shut-off the airfl ow as part of an automated or manually initiated control sequence. Normal control is maintained by way of network or local commands. Shut-off sequences may be initiated through pre-programmed control sequences or over the network as BMS commands.

The Shut-off Valve provides critical airfl ow control demanded by a modern research facility. In shut-off mode, the valve provides low-leakage isolation of the HVAC system from the room.

An example of a typical application is a laboratory research building space using gaseous biodecontamination.

Standard Shut-off Valve

The Standard Shut-off Valve is appropriate for applications where shut-off is for energy savings (GEX Shut-off), Fume Hood decommissioning and lab decommissioning (see Chapter 4 for more energy savings capabilities).

Low-leakage Shut-off Valve

The Low-leakage Shut-off Valve accommodates applications requiring a near bubble-tight ventilation system for critical environments needing emergency isolation or gaseous biodecontamination.

Many project standards for applications, such as BSL-3 spaces, may require a higher standard of isolation than what the Standard Shut-off Valve provides. With the Low-leakage Shut-off Valve, leakage rates achieved are insignifi cant to the overall duct volume.

In many projects, the duct volume entering and exiting critical spaces must be leak tested to ensure they are truly isolated. Most governing standards accept leakage rate from 0.1–0.2% of volume per minute of the duct volume at a given pressure. The Low-leakage Shut-off Valve contributes minimally to the overall volume tested. This insignifi cant leakage volume, combined with the valve’s ability to control airfl ow precisely and compensate instantly to changes in pressure, makes the Low-leakage Shut-off Valve the ideal choice for these critical applications.

The Low-leakage Shut-off Valve, which has been tested with the ASME N510 Pressure Decay method,1 has the lowest total casing leakage compared to our current valve portfolio. The casing leakage for this valve is 0.01 CFM per square foot for each area.

1American Society of Mechanical Engineers (ASME), ASME N510, Testing of Nuclear Air Treatment Systems, 1985 (reaffi rmed 1995).

Figure 2-4. Valve in shut-off position.

Phoenix Controls Laboratory Sourcebook 15 ir fl o w C o n tr o l

Shut-off leakage performance

In these graphs, the term, shut-off leakage, refers to the expected airfl ow through the valve in the shut-off position. The term, casing leakage, refers to the expected airfl ow through the penetrations of the valve body.

Casing Leakage

Calculating Valve Areas

Valve Size Area (ft2) Area (m2)

8" 3.60 0.33

10" 4.26 0.40

12" 6.28 0.58

14" 8.52 0.79

For 8, 10 and 12-inch valves (14-inch low-leakage is not available at this time) exceeds Eurovent Class A, B, C and D specifi cations (Eurovent Committee of Air Handling and Equipment Manufacturers).

Figure 2-6. Low Leakage Shut-off Valve (Option L) — Shut-off leakage for 8, 10, 12 and

14-inch body valves.

Standard Shut-off Valve (Option S) Single Valve Casing Leakage

0.00

0.02

0.04

0.06

0.08

0.10

0.50.40.30.20.1

Static Pressure (in wc)

Le ak ag e

(C

FM

0.0000

0.0094

0.0188

0.0282

0.0376

0.0470 05210001057005052

Static Pressure (Pa)

Le ak ag e

(L /s

Static Pressure (inches WC)

Static Pressure (Pascal)

L ea ka g e (C

F M

/f t2 o f su rf ac e ar ea

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.0 5.0 10.0 15.0 20.0 25.0 30.0

0.000

0.025

0.050

0.075

0.100

0.125

0.150

0.175

0.200

0.225

0.250

0 1250 2500 3750 5000 6250 7500

L ea ka g e (L

/s ec

/m o f su rf ac e ar ea

Low Leakage Shut-off Valve (Option L) Single Valve Casing Leakage

Figure 2-5. Standard Valve (A) and Standard Shut-off Valve

(Option S) for 8, 10, 12 and

14-inch single body valves.

16 Phoenix Controls Laboratory Sourcebook

Recommended Valve Class for Decontamination Agents

Gaseous Decontamination Agent

Recommended Valve Class*

Hydrogen peroxide vapor Class A

Ethylene oxide Class B

Ammonium chloride Class A

Chlorine dioxide Class A**

Parafirmaldehyde Class A

*Chemical resistance data acquired from Compass Corrosion Guide.

**For concentrations up to 80 ppm. To achieve higher concentrations during decontamination, use Class B valves.

Standard Shut-off Valve (Option S) Single Valve Shut Off Leakage

0.00

1.00

2.00

3.00

4.00

5.00

6.00

5.04.03.02.01.0 Static Pressure (in WC)

Le ak ea ge

(C

FM

0.000

0.472

0.944

1.416

1.888

2.360

2.832 12501000750500250

Static Pressure (Pa)

Le ak ag e

(L /s

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

0 5 10 15 20 25 30

Static Pressure

(inches WC)

L ea ka g e (C

F M

0.0000

0.0023

0.0046

0.0069

0.0092

0.0115

0.0138

0 1250 2500 3750 5000 6250 7500

Static Pressure (pascals)

L ea ka g e (L

/s ec

8" Shut-off 10" Shut-off 12" Shut-off

Low Leakage Shut-off Valve (Option L) Single Valve Shut Off Leakage

14" Shut-off Not Shown

Figure 2-7. Standard Shut-off Valve (Option S) — Shut-off leakage for 8, 10, 12 and 14-inch single body valves.

Figure 2-8. Low-Leakage Shut-off Valve (Option L).

Phoenix Controls Laboratory Sourcebook 17

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Fume Hood Control Solutions

This chapter reviews each control approach, along with the advantages, disadvantages and benefi ts of each.

Table of Contents

Face Velocity Controls Technique 18

Comparing Control Approaches 20

Constant Volume Laboratories 21

Two-State Laboratories 24

Variable Air Volume Laboratories 26

Usage-Based Solutions for Laboratory

Airfl ow Control Design 28

The four basic fume hood control approaches are: Constant Volume, Two-State, Variable Air Volume (VAV) and Usage-Based Controls (UBC).

Constant volume (CV) fume hoods • are designed to operate at a fi xed airfl ow all the time (24/7). Whether these hoods are occupied or unoccupied, or have open or closed sashes, the fume hood fl ow remains the same. This type of fume hood tends to be the least energy effi cient and is prone to having higher face velocity that when the sashes are lowered and lower face velocity when sashes are all the way open which can cause some safety concerns.

Two-state systems • are designed to switch between a minimum and maximum fl ow and differ signifi cantly in fl ow design and switching mechanisms. Systems that interlock fl ow with light switches or room occupancy sensors will reduce fl ow at night but not during the day. Systems with sash switches allow each hood to control fl ow based on sash position.

Unfortunately, sashes must be closed to realize the benefi ts.

Variable air volume (VAV) fume hoods • are designed to vary the flow through the sash openings as the sash(es) open or close to maintain a constant face velocity regardless of sash position. Designs of these types of fume hoods vary signifi cantly from attempting control of the measured face velocity to measuring the sash opening and controlling the flow through the opening to maintain a constant face velocity regardless of sash position. The VAV fume hood offers the opportunity for signifi cant energy reduction and savings through equipment downsizing, depending on whether users lower the sashes when the fume hood is not in use. See Diversity on page 29.

Usage Based Controls (UBC) • from Phoenix Controls has been designed to sense the actual presence of an operator at the fume hood and switch the fl ow between occupied and unoccupied face velocity setpoints. Many studies have shown that when there is no operator in front of an open fume hood “challenging” air fl ow used for containment, face velocities may be safely reduced by 20-40% which represents signifi cant energy savings if the fume hood is unoccupied and the sash is left open for large portions of a 24-hour period. A UBC equipped fume hood will automatically “set back” to an unoccupied face velocity setpoint of 80 or even 60 fpm when the fume hood is not occupied. As soon as an operator steps in front of the fume hood, the face velocity will immediately switch back to 100 fpm and the desired face velocity will be achieved in less than 1 second. A fume hood with UBC us effectively a two-state hood, however it may be combined with a VAV control system with good sash management to realize up to 80% energy savings over CV fume hoods without compromising operator safety.

18 Phoenix Controls Laboratory Sourcebook

Face Velocity Controls Techniques

In order to maintain a constant face velocity with variable sash openings, there are two generally accepted methods of control.

Velocity sensing—the volume of air through the hood is controlled based in the measured 1.

speed of the air passing through the sash opening.

Sash sensing—the volume of air passing through the fume hood is calculated based on the 2.

measured sash opening using simple mathematics.

Velocity Sensing Systems

This system senses air velocity passing through a hole in the sidewall of the hood as an interpretation of average face velocity.

A slow speed of response is required to ensure stability (between 15 and 60 seconds). This is due to the large amount of turbulence in the sensed velocity signal of 100 fpm (about one mph). A single movement of an operator’s hands can further contribute to large changes in this sensed signal. The result is a loss of fumes when the sash is raised and dangerously high velocities when the sash is lowered.

Single point sensing does not sense the true average face velocity. Wide variations in the face velocity can occur over the entire sash area. Industrial hygienists have to take 9 to 12 readings to accurately measure the average face velocity. The relationship between the sidewall velocity and the average face velocity will also vary due to a variation in hood sash position, lab apparatus, people walking past the hood, door opening/closing, room air temperatures, heat sources within the hood, etc. The result is a constantly changing average face velocity and resultant lack of adequate face velocity control.

Hot Wire/Thermistor type velocity sensors are often used as side wall (through-the-wall) face velocity sensors. However, since fume hoods often contain explosive vapors, logic would preclude that the use of these devices, unless designed for Intrinsic Safety, could potentially cause an explosion. The UL 913 Standard sets the guidelines for Intrinsic Safety to limit the temperature and currents required to prevent ignition of the vapors during an equipment malfunction. Temperature and current limits required to prevent ignition or fl ashover can be exceeded during an equipment malfunction or in some cases even during normal operation.

When a user stands close to the front of the hood his body reduces the face velocities in front of him and increases the velocities in the rest of the hood opening by 10 to 30%. The sidewall sensor system responds by lowering the average face velocity. This reduces the velocity in front of the user from a low level to an even lower, potentially hazardous level. This is exactly the opposite response from what is needed for safe operation.

Sash Position Sensing Systems

This system senses sash position (open sash area) and commands exhaust volume linearly to maintain the average face velocity constant:

Average Hood Face Velocity = Exhaust Volume ÷ Open Sash Area

Fast response times of less than one second are possible since the required exhaust volume is determined immediately through the instantaneous measurement of sash position. To actually achieve fast response times with less than 5% overshoot, proper selection of the control system and measurement metering hardware must be selected as described later.

This control system is unaffected by lab room transients, apparatus in the hood or the position of hood operator. The system controls the hood’s true average face velocity.

Phoenix Controls Laboratory Sourcebook 19 u m e

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Sash sensing technology from Phoenix Controls provides a unique methodology of measuring sash opening – so distinctive it has been covered under one or more patents. The Phoenix Controls approach is to use one or more vertical sash sensors to precisely measure the vertical sash opening and one or more horizontal sash sensors to measure horizontal sash opening and these values are summed to determine the total open area of the fume hood sash. The fume hood controller uses this value to calculate the volume of air required to achieve the desired face velocity through the sash opening. The fume hood monitor provides a command signal to the fume hood airfl ow valve which responds very rapidly to a change in the measured sash opening.

Multiple vertical sash sensors may be used to detect the position of multiple vertically moving sash panes. A combination of sensor bars, magnets, and blocking bars may be arranged in virtually any length or arrangement to measure the cumulative horizontal sash opening.

Combination vertical and horizontal sash sensors terminate at a Horizontal/Vertical (H/V) interface PC board where the values are summed to create an total open sash area value for the fume hood monitor. So whether it is a single sided hood or four sided hood with movable upper and lower sashes, where each sash has any number of horizontal sash panes, Phoenix Controls has a sash sensing solution.

Not only is it the sash sensing techniques that make Phoenix Controls the market leader in fume hood control, the speed of response also sets us apart. From the moment a fume hood sash is moved, to the time the fume hood valve reaches 90% of its commanded value will be less then 1 second with little or no overshoot. Coupled with the accuracy, stability, turn-down, and pressure independence of the Accel II venturi valve Phoenix Controls the safest solution available on the market. Read on to learn about the savings delivered through Variable Air Volume control, Usage Based Control, diversity and maintenance free controls and you will understand why more Engineers specify Phoenix Controls and why more Owners, Health and Safety and Facilities personnel insist on Phoenix Controls for their laboratory control solution.

Phoenix Controls offers a wide variety of vertical and horizontal sash sensors. All styles of hood sashes (vertical, horizontal, combination and walk-in sashes) can be accommodated through the proper selection of the sash sensor type.

20 Phoenix Controls Laboratory Sourcebook

NOTES:

UBC and VAV are available in analog and digital platforms.

Fume Hood

Supply Air

Constant Volume Valve (CVV)

1000 CFM

Exhaust Air

Offset

100 CFM

Constant Volume Valve

900 CFM

T

VAV Fume Hood

VAV General Exhaust

VAV Make-up Air

Exhaust

200-1000 CFM

Supply

100-900 CFM

Exhaust Air

Supply Air Offset

100 CFM

T

Zone Presence Sensor

(ZPS)

Two-state Fume Hood

Exhaust Air

Supply Air

Two-state Air Valve

200/1000 CFM

Two-state Air Valve

100/900 CFM

Offset

100 CFM

S (Phoenix) Room

Controller

VAV Fume Hood

VAV General Exhaust

VAV Make-up Air

Exhaust

200-1000 CFM

Supply

100-900 CFM

Exhaust Air

Supply Air Offset

100 CFM

T

Two-state (Traccel)

Constant Volume (CV)

Usage Based Controls

(UBC)

Variable Air Volume

(VAV)

Comparing Control Approaches

Deciding how to best control a laboratory depends on many factors. Safety, fume hood density, energy use, installation costs, and fl exibility are a few of the issues that must be considered.

This section explores the strengths and weaknesses of control applications in a generic form and offers insight into the benefi ts of the Phoenix Controls approach for each.

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Constant Volume Laboratories

Generic Approach

In a generic constant volume (CV) system, a fi xed blade damper is adjusted manually to set the fume hood exhaust rate—delivering the desired face velocity when the sash is at a specifi c open ing. The room’s make-up air rate is set by a fi xed blade damper at a slightly lower rate to provide a net negative pressure in the lab and suffi cient air change rates. Airfl ow through the space is usually suffi cient for ventilation rates but additional air can be designed into the room, if required. Tem perature control is normally provided by reheat ing the conditioned air or by supplemental baseboard or fan coil units.

Advantages

Straightforward, simple design •

Low cost of controls •

Disadvantages

Safety may be compromised. CV fume hoods do not control face velocity since dif ferent • sash positions provide different face velocities. Bypass hoods are limited in their ability to prevent excessive face velocity.

The system is pressure dependent. Changes and fl uctuations create improper fl ow rates. •

Rebalancing is required at every damper location when changes are made or fan system • performance degrades.

High capital and life-cycle costs. Capital costs are high due to full load sizing of equipment; • energy use is high due to contin uous full-fl ow operation.

Low fl exibility. Future expansion may be limited due to equipment capacity limita tions. •

Noise. Excess noise due to high airfl ow at all times. •

No inherent monitoring or alarming. •

Fume Hood

Supply Air

1000 CFM

Exhaust Air

Offset

100 CFM

900 CFM

T

Control Device

Figure 3-1. Generic constant volume laboratory.

22 Phoenix Controls Laboratory Sourcebook

The Phoenix Constant Volume Approach

Option A: Constant Volume Application using Traccel

Phoenix Controls offers products to maximize performance in constant volume laboratories.

Figure 3-2 shows typical CV laboratory devices with Phoenix Controls components.

Benefi ts

• Provides accurate, stable fl ow control.

• The system is pressure independent and maintains steady fl ow through system changes, fi lter loading and HVAC degradation.

• Flexible monitoring–Use either a Phoenix fume hood monitor (FHM) or the hood manufacturer’s model.

• No wiring or tubing required for control.

• Ability to monitor and control temperature through the Phoenix Controls network.

• Ability to adjust offset via the network.

Figure 3-4 shows several constant volume labora tory exhaust devices controlled by pressure-inde pendent constant volume changes.

Fume Hood

Supply Air

Constant Volume Valve

1000 CFM

Exhaust Air

Offset

100 CFM

PTC101

Constant Volume Valve

900 CFM

Figure 3-2. Constant volume laboratory with Phoenix

Controls. Pressure-independent air valves (constant volume) maintain a constant volume at each location as sys-tem fl ow rates change. An optional monitor is avail able for continuous fl ow monitoring.

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Fume Hood

Constant Volume Valve (CVV)

1000 CFM

Exhaust Air

Offset

100 CFM

Constant Volume Valve (CVV)

900 CFM

Supply Air

T

Option B: Constant Volume Application using Phoenix Controls PTC Thermostat

Add the temperature control and monitoring capabilities of the Traccel system. Figure 3-3 shows typical CV laboratory devices with Phoenix Controls Traccel room controller.

Benefi ts

Add the option to integrate control and monitoring functions via:

• Direct LON integration to BMS.

• BACnet MS/TP integration to BMS Global controller.

• Integration through one of Phoenix Controls data servers BACnet IP.

These devices may be hard balanced or add Traccel or Celeris controllers with low-speed actuators to gain both local and network control capabilities. With the networked solution as airfl ow requirements change, the system can be rebalanced via the network.

Figure 3-4. Additional constant volume control needs. The constant volume valves maintain precise fl ow and eliminate the need for future rebalancing at each lab device.

Biosafety Cabinet

Ventilated Enclosure

Canopy

Snorkel System

Constant Volume Valve (Typical)

NOTES:

* Air valves used in this application can be two-position devices to conserve energy when these are not in use.

** Air valves for this application can be operated in two positions, shut-off and normal flow, to conserve energy when the cabinet is not in use.

Figure 3-3. Constant volume laboratory with Phoenix

Controls Traccel room controller. All the benefi ts of the Accel II valve with the advantage of space comfort control through valve mounted controller. May operate standalone or as an integrated control system for remote monitoring.

24 Phoenix Controls Laboratory Sourcebook

Two-state Laboratories

Generic Approach

This generic control approach uses two distinct levels of airfl ow through the fume hood to gain effi ciency over CV systems. The set point is changed by a switching mechanism (typically a sash switch or light switch) to increase fl ow through the hoods when the switch is engaged.

The fl ow is reduced when the switch is disengaged.

Advantages

Saves energy–By switching fume hoods and room make-up air to lower fl ow rates, signifi cant • energy savings may be realized.

Has fewer controls than a VAV system. •

Disadvantages

Common methods of switching may com promise safety. •

“High-low” (also called “max-min”) switches the airfl ow between two prede termined -values. Manual switches allow for operator error. Sash switches elimi nate operator error, but create switch points that cause either high- or low-face velocity. In addition, these do not reduce fl ow if the sash is left open (see Figure 3-5).

“Occupied-unoccupied” control via light switch interlock or room motion detectors may -be used for night setback control, but offers little energy savings during daytime hours.

HVAC equipment must be full-sized due to all hoods operating at full-fl ow during the day.

Also, safety may be compromised when sashes have been left open and the hood is switched to low fl ow.

Inability to confi dently downsize a building’s mechanical equipment. •

The need for variable air volume (VAV) supply controls on air handlers and fan systems • serving areas with multiple hoods.

The need for thermal demand override con trol may create system complexities. •

Hoods may not have monitoring or alarm ing. •

High maintenance on sash switches (poor quality). •

Figure 3-5. Generic two-state control with sash switch. The graph shows the fl ow profi le of a hood with the switch located at the 20% open position. With the sash below the switch point, the fl ow through the hood is reduced to a minimum value. Above the switch point, the fl ow increases to the maximum value.

Switch located at 20% of travel 1000

Sash Position

F lo w

C F

M

20% 100%

S

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Phoenix Two-state Approaches

Option A: Simple Two-state Application using Celeris or Traccel

Phoenix Controls offers simple pressure-independent air valves for use in two-state appli cations.

Figure 3-6 shows a sash switch control option for a two-state laboratory. This example shows Phoenix Controls Traccel room-level controller for maintaining volumetric and space comfort control.

Phoenix valves that are used in two-state sys tems controlled by sash or light switches provide the advantages listed below.

Advantages

Provides superior fl ow control with fast, stable adjustments. •

Control costs are low, compared to VAV. •

The pressure-independent system maintains steady fl ow through system changes, fi lter • loading, and HVAC degradation.

Flexible monitoring–Use either a Phoenix fume hood monitor (FHM) or the hood • manufacturer’s model.

Disadvantages

However, the disadvantages of controlling fl ow with these switching mechanisms still remain (see page 24).

Two-state Fume Hood

Exhaust Air

Supply Air

Two-state Air Valve

200/1000 CFM

Two-state Air Valve

100/900 CFM

Offset

100 CFM

S

T

Figure 3-6. Two-state application with sash switch.

Pressure independent air valves maintain proper fl ow at each of two fl ow rates. The sash switch (by others) changes hood fl ow between low-high fl ows. A two-state supply valve tracks fl ow changes of the hood.

26 Phoenix Controls Laboratory Sourcebook

General Exhaust (Optional)

VAV Box

Exhaust Air

Fum e

Hoo d

Exh au st Air

Roo m

S up ply A ir (M ak e-up A ir)

Example:

3 to 1 Turndown Supply Air Tracking

Example:

2.5 to 1 Turndown

Closed Sash Position Open

Constant Volume Mode

Variable Volume Mode

A irf lo w

C

F M

Offset

100 CFM

Supply

300-900 CFM

Exhaust

400-1000 CFM

Fume Hood Valve

Control Device T

Fume Hood

Supply Air

Figure 3-7. Variable air volume laboratory.

Option B: Usage Based…