GRD Frequently Asked Questions

Why does my OBD fit inside the neck of some diffusers, and outside others?
Almost all diffuser necks are smaller than the duct to which it is attached. (The one notable exception is the 1700.) How much smaller they are sometimes varies from model to model. For example, the actual size of the neck on a 180 is 3/4" smaller than the nominal duct, but on a 6000, it is only 1/4" smaller. What this means is that the OBD may attach INSIDE or OUTSIDE the diffuser neck depending on the model. This can be easily accomplished simply by reversing the direction of the 'S' clip used to attach the OBD.

What does an "earthquake" tab do?
The earthquake tab is used in conjunction with a hanger wire (by others) to prevent the diffuser from falling in the event of an earthquake. The hanger wire is anchored above the ceiling plane to a fixed point on the structure. The free end is then passed through the opening in the tab and back around the wire, much the same way a T-bar is hanged. See your local codes to determine actual and adequate methods.

What is a "mill finish"?
As the name implies, material with a mill finish is fabricated and assembled without any finish. The way the material came from the producing mill is the way it is shipped; we add no additional finishing such as painting or cleaning. As such, these products will show tool marks, weld marks and scratches ordinarily covered by paint. It is also likely that these products will arrived still coated with machine oils. It is assumed that product ordered mill finish will receive post production finishing by the customer, or that it will be installed in an environment where the finish is not important.

If you require an unpainted product that has a higher level of finish, you may request cleaning or polishing. Keep in mind that this requires an SPR, and will typically incur a higher cost than mill finish. See your Pricing and Ordering Procedures for details.

My 1900 throws too far. How can I reduce the throw?
As an architectural diffuser, the 1900 frequently is installed in many demanding environments. These include exterior zones with glass walls, high ceilings and large rooms with a minimal number of diffusers. Such being the case, the 1900 is designed with excellent throw capabilities. But how do you use it in less demanding situations which require shorter throw? The key to this is to take advantage of the 1900's versatile performance. The 1900 offers the ability to adjust both the direction and volume of air using the same pair of control blades. Setting these blades to a more intermediate setting will help shorten the throw in less demanding environments. See our latest catalog for details.

How do I size a 1900 miter?
Actually, there is nothing you need to do to size a 1900 mitered corner. All three versions, the OS, IS and SD are built to specific sizes which are published in our catalog. The real question is, "How long should my straight section be if my total run includes a miter?" The answer is simple. Determine the duct length of the straight run. Use the catalog data to decide how much to subtract for your miters. The resulting length will be the duct length of the straight section. Example: You have a 1950, 1 slot, frame B that is going to be used to form a square with an outside duct length of 20'. The unit is mounted in a ceiling, so you know you want a SD mitered corner. The catalog shows the D, or duct length, dimension on the outside leg to be 12". Since you will have a mitered corner at each end of the straight run, you subtract 24." This leaves you a straight run of 18'. To fill the square you need 4 mitered corners and 4 pieces 18' long.

Why do 1500 linear bar grilles have so many attachment methods?
The 1500 is one of the few diffusers that is installed three different ways: ceiling, sidewall and sill. Additionally, its looks make it valuable to architects who often want to install it adjacent to many different types of material: plaster, terrazzo, carpet, metal and wood. Because of this, we offer a wide variety of methods to mount the diffuser under these wide ranging conditions.

Why doesn't my Varifuser have a remote control?
The Varifuser performs the same function as many expensive electronically controlled diffusers: it offers VAV zone control based on actual room side air temperature. However, the Varifuser does not depend on wires or remote controls to be accurately set. The Varifuser operates on a simple mechanical principle that has been known and used in the HAVC industry for over 50 years. When you install the diffuser, you simply adjust the two screws that limit the high and low temperature range for the unit. For details, contact your Application Engineer.

How should I mount an EX-88, or other extractor?
The purpose of an extractor is to encourage air to flow from a main duct into a stub duct. As such, the device is always mounted with the arm extending into the main duct. The vanes should define the path you wish the air to take. However, where you mount the extractor base is important. Typically, the access to adjust the extractor is from the stub duct. If so, that is the correct location for mounting the base. If instead the access is from the main duct, the extractor base should be mounted there.

How do I mount a 1700?
Unlike most diffusers, the 1700 does not permit access to its neck through the face. To mount the 1700, remove the screws that hold the face to the frame. Install the frame in the duct opening using screws, then reattach the face.

Can I put a blankoff in a 1400?
Unlike many ceiling diffusers, the 1400 utilizes a fixed wing rather than a configurable core. The fixed wing makes it a very attractive diffuser with excellent performance. However, it must sometimes be mounted where a three-way pattern is preferable to its fixed 4-way pattern. For these situations, a blankoff is available from the factory.

I know the velocity through the neck of a diffuser. What is the volume?
There is a constant relationship between the area of a diffuser's neck, velocity (FPM) and volume (CFM). Since we are looking for the volume in feet, take the area (A) of the neck in square feet and multiply by the velocity (FPM) in feet per minute. Based on this, the formula is: CFM=A*FPM

I know the volume through the neck of a diffuser. What is the velocity?
There is a constant relationship between the area of a diffuser's neck, velocity (FPM) and volume (CFM). Since we are looking for the velocity in feet, take the area (A) of the neck in square feet and multiply by the volume (CFM) in cubic feet per minute. Based on this, the formula is: FPM=A*CFM.

Can I order security products to ASTM standards?
Krueger can manufacture security grilles that meet ASTM A750. ASTM A750 applies to ventilating grilles for detention areas. ASTM A750 references four material specifications. They are: ASTM A6, A29, A627, and A629. A6 covers structural shapes and plates. A29 is for steel bars. A627 and A269 cover tool-resisting steel. Construction to ASTM standards is expensive due to special testing methods, materials tracing, special material specifications, and heat treating. A most economical way to specify ASTM grilles is to order the Model 1320 with the case-hardened backer plate, or the Model 1310 with the 3/8" X 2-1/2" security bar. These units conform to ASTM A750 when ordered with these options. The other supply units are not for high security areas. It would not be economical at all to order them to ASTM standards. The 1390 is not required to meet ASTM standards if it is not accessible under normal conditions.

Can I order special GRD products with a UL label?
No. Our UL listing on certain products is based on specific configurations tested and approved by the Underwriter's Laboratory. Changes to those products would nullify their UL listing.

Can I use induction diffusers in a lab or cleanroom?
While there have been standards published on desired air change rates in these critical environments, there is no standard on how that air should be controlled within the space. Prior to Krueger developing the TAD, system designers commonly used induction diffusers in these types of applications. However, the known drawback was that these diffusers were designed to MIX air, not dispel it from the space. In the case of a lab accident, this could result in mixing air containing dangerous gases. Typically, system designers would simply specify very high air change rates in an attempt to dilute any potential toxins. One shortcoming of this method is the additional fan required to provide the air change rates. The other shortcoming is that there was no way to determine the exact effectiveness of this method. These high air change rates can also produce airflow velocities that are uncomfortable to personnel and may adversely affect sensitive fume hoods.

The Krueger model TAD is designed to address these specific types of problems. The TAD uses displacement to expel air from a space in a predictable rate and pattern. Its unique radial design ensures that contaminants are flushed from the space in the most direct means possible: one pass, then out. Not only does this contribute to lab safety; but it also potentially reduces the fan power required to run the system. Additionally, the TAD's low velocity diffusion pattern provides a comfortable work environment with no adverse affects on sensitive fume hoods.

These same characteristics make the TAD a good choice for any number of difficult air control situations.

What conditions must be met to have factory personnel on site to certify a Sterilflo® installation?
By test day, the units must be set-up for actual operating room conditions, completely installed and operating at the correct volumes and temperatures. All upstream filters (including HEPA) and dampers must be in place. All returns must be functioning. All doors, windows and other openings in the OR(s) must be in place. If there are vents into other areas of the operating suite, air volumes into those areas must be correct and functioning.

There must be a balancing contractor, or equal, on hand the day of the tests. Krueger cannot adjust the system.

The balancing contractor will need to have a flow hood. A 2'X2', or larger, hood is required for testing the center sections, and a 1'X4', or larger, hood for testing the perimeters.

Krueger will require a stepladder or something similar to reach the units and open them.

Krueger will check for proper installation of the Sterilflo, verify correct air volumes to the center (dilution), perimeter (suppression), and returns. Krueger will also visually check air velocities and flow direction within the curtain for proper extraction of viable particulate. Krueger will also check that the OR(s) has positive air pressure (isolation). You will need to arrange two meetings with the hospital staff. Each takes 10-20 minutes. One will be with the OR staff and any interested surgeons. In it, Krueger will explain how the system functions and how to use it correctly. The second is a meeting with the maintenance staff. During it, Krueger will explain how to maintain the units and verify correct operation.

How do I get a custom Sterilflo® layout?
All Sterilflo® orders are processed to your specific requirements. The units shown in the catalog and their prices are simply a guide to help you get started. Almost all Sterilflo® Systems can be built to meet specific CFM and/or size requirements. The center panels can be sized and located to suit required equipment and lighting layouts. The exact location of connecting ductwork can be specified. Perimeter sections can be designed with gaps for microscope tracks, gas columns, or existing structural members. The Sterilflo® section of your Krueger catalog shows some of the more common variations. Krueger's engineering staff is happy to work with you to develop a unit that meets your specific needs.

Can a linear/laminar device, or simply a laminar device be substituted for a Sterilflo®?
The Sterilflo® System was designed from the ground up as an operating room diffuser. This dictated everything, from the selection of materials, to its simple operation, to its incredible performance characteristics most demanding of environments. Perhaps that is why only Sterilflo® has been proven to meet published standards for air cleanliness under actual operating room conditions.

Krueger has been producing the Sterilflo® for over 30 years and these units are now in use in over 1000 operating suites around the world. No other system comes close to being backed by the experience and engineering expertise that goes into each and every Sterilflo®.

Is neck size on the 5000 model important?
Yes. Like all laminar flow diffusers, the 5000 depends on even pressure over the entire face of the unit. High inlet velocities can create unwanted concentrations of pressure in the center of the face. This can adversely affect performance. On units equipped with HEPA filters, high velocities can erode that filter material media, force it through the filter pack and into the occupied zone. In both cases, these conditions can be alleviated with a sufficiently large neck. Where that is not possible, consider ordering an optional baffle.

What about performance specs for higher CFM in the 5000 models?
Laminar flow devices must typically have some specific geometry to achieve their characteristic columnar flow. For that reason, it is best to stick with size and CFM ranges noted in our catalog. However, under some certain circumstances these rates must be exceeded. Here are some extended data for this product:

CFM / Sq. Ft. of Panel	Static Pressure(Ps)	NC	Velocity @ 6' from Face.-10°F
10	0.008	<20	25
15	0.018	<20	32
20	0.032	<20	40
25	0.051	20	50
30	0.072	25	60
35	0.081	31	70
40	0.128	33	80
45	0.161	35	88
50	0.201	38	95
55	0.261	42	98
60	0.288	46	101
65	0.301	50	105

Can I get "seal welds" on critical environment products such as the TAD or 5000?
Engineers for very critical applications in which leakage from the supplied zone must be completely controlled sometimes request this. For example, we have seen requirements for TADs, which are to be "seal" welded to their backpans. A seal weld is a full, leakproof weld on all seams.

There are some problems that can occur when we attempt this type of weld. The first is warping. Welding creates a great deal of localized heat. In very thin sections, this can cause the weldment to warp. The second problem is discoloration. Welding is accomplished by creating an electrical arc and fusing two pieces of metal by means of the heat from that arc. This not only deposits carbons immediately along the seam, but also discolors the adjoining metal. Much of this can be brushed or sanded off, and it can always be covered with paint. Be aware that welded "mill finish" units will have cosmetic flaws from the welding.

Such products cannot be sold as normal production items. They should be ordered on an SPR.

How do I size HEPA filters?
Krueger makes several products that can sometimes have HEPA filters installed in them. The TAD and the 5000 both have configurations that allow the installation of a HEPA that is removable from room side. The center panels of Sterilflo® can be ordered with a similar construction. (Not recommended.) Krueger does not manufacture or supply HEPA filters for use with these units. You are free to purchase the filters from a supplier of your choice.

The exact dimensions to which HEPA filters are sized vary depending on the manufacturer. Therefore, it is best to follow their recommendation for ordering the filter. In the case of both the TADHF and the 5000HEPA, the design utilizes a 'knife edge.' The knife-edge is designed to penetrate a gel pocket, thus forming a seal. Extending a lip on the backpan forms the 'knife edge' on these models. For both units, the backpan is sized 1.00 inch smaller than the nominal panel size. For example, a 24 X 24 TADHF would have a backpan sized 23.00 X 23.00. This is the dimension of the knife-edge. Using this dimension, you should be able to consult a manufacturer's catalog and determine the correct filter size. The Sterilflo® is a special application. Please contact Application Engineering if you need to use a room side HEPA with these units. For the TADHF, please see our Pricing and Ordering Procedures for suggested specifications.

What are those metal strips that came with my TAD?
The TAD is designed to fit standard ceiling modules much the same as any drop-in ceiling diffuser. In other cases, the application may require that the unit be mounted to a T-bar, but not as a drop-in diffuser. The metal mounting strip that came with your TAD can be used for this second situation. If you do not need it, you may simply discard it. The mounting strip may also be used to attach the TAD to a sheetrock ceiling. However, a better way to do this is to order an appropriately sized HCF23 or HCF23A. If you do use the mounting strip be sure the screws engage a structural component, not just sheetrock.