FAQ

1/What does a textile diffuser look like when the fan is switched off?

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2/ Is it possible to use Fabric Ducting for exhaust or return air?

PŘÍHODA was the first fabric duct manufacturer worldwide to introduce negative pressure ducting into the market. It is made with a square or triangular shape. The principal is based on sufficient stretching of all ducting walls by means of a tensioning system. The construction enables simple disassembly and re-installation. Laser cut perforations are used to draw the air into the duct.

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3/  What is the service-life duration of fabric diffusers?

Prihoda fabric ducts are not a temporary or short term solution. Diffusers made from good quality fabrics will last for 15 years or longer. In fact, some of our first installations from the early 90’s are still in use with the original ducts in place, which is a testament to the longevity of our products. The lighter fabrics (PLI/NLI) or polyethylene ducts have limited durability and are used for short term installations when cost has the highest priority.

Business conditions

4/ What is the pressure loss of a fabric diffuser?

The external static pressure required at the inlet of our round duct systems range from .20inwg - 1inwg, with the average being about .50in wg ESP. Smaller air handlers may have less static pressure available or some projects may require much higher throws or smaller duct diameters (higher inlet velocities) which increases the static pressure needed. Complex systems with elbows, T’s and equalizers present certain pressure losses which needs to be taken into consideration and is easily calculated in our software. Friction loss for fabric ducts is usually lower than traditional metal systems (designed with equal friction) due to the decreasing air speed inside our diffusers (static regain design). Lighter materials or half round ducts require as little as .10 in wg.

5/ What to do with diffusers when they get clogged by contamination?

Diffusers with micro-perforation or larger laser cut holes rarely, if ever, get completely clogged by contamination (if used with minimum pre-filtration EU3/MERV5). Diffusers with laser cut perforations and microperforations are superior to ducts with mesh slots and materials woven to a specific permeability as our diffusers do not act like giant filters. The maintenance (typically washing in a washing machine) is really only necessary for hygienic and aesthetic reasons. Each individual zipped section contains a washing label which provides all washing information. Our experience has proven that our fabrics made of continuous fibers remain practically clean on the inside after many years of operation with proper filtration.

Maintenance Instruction

6/ Can fabric diffusers get moldy?

Generally the answer is no for all of our products when installed and air is running through them. Antimicrobial treatments in our PMI/NMI offer added protection from many forms of bacteria, molds, mildew and fungi however, mold can form on any kind of untreated surface if left moist and unventilated and there is an organic food source such as dirt or cardboard. Therefore, never store moist diffusers and do not keep them out of operation for long periods of time. Mold is extremely difficult and often impossible to remove once established. It is usually best to replace the diffusers if they have gotten wet while stored or have been exposed to mold growth.

7/ Is it possible to use rectangular diffusers?

Prihoda has developed a special construction which enables use of a rectangular cross-section. The principal is based on stretching the fabric in transverse and longitudinal direction by means of a tensioning system. The construction enables simple disassembly and re-installation. Fabric ducting with rectangular cross-section can be assembled directly on the ceiling or suspended from the structure above.

8/ Does the textile diffuser function as a filter at the same time?

If materials woven to a specific permeability are used, the fabric functions as a filter for the part of the transferred air that goes through the fabric. As the fabric contamination gradually increases, the pressure loss grows and the air flow decreases (or energy costs increase). Therefore, it is necessary to frequently wash those types of fabrics. This is why Prihoda utilizes microperforated or laser cut perforated fabric as a better solution because they do not function as filters thus significantly reducing maintenance. Furthermore it is much easier to change a filter before the duct system rather than washing the entire duct system...we are a manufacturer of air distribution ducts and diffusers, we are not in the business of filtering air.

9/ Why doesn’t PRIHODA use plastic nozzles or mesh slots?

Mesh slots were first used as a method to reduce washing maintenance for fabric ducts with no openings that only distributed air through materials woven to a certain permeability. By placing mesh slots in the duct with horizontal discharge maintenance requirements were reduced as the mesh did not clog as quickly as the material. Mesh slots were never intended to solely distribute the air from the ducts and are an outdated flow model which clogs with dirt, creates higher noise, and does not control the air as well as perforations or nozzles do. We offer textile nozzles instead of plastic nozzles because our textile nozzles have the exact same color, texture, flame spread / smoke development as the material itself, will not adversely increase the weight of the duct, and will not crack or degrade which is not the case for plastic nozzles.

10/ Why doesn’t PRIHODA use more permeable fabrics?

We use permeable materials to avoid condensation where supply air temperature is below dew point. However, we only have material of a single permeability value. It is very low and serves just to prevent condensation. Distribution of air is done exclusively using holes (perforation or microperforation or a combination of both) and adjusted holes (nozzles, pockets). Our product portfolio also includes non permeable materials, which are often useful in other situations.

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