#ductsock

If you're starting a new career in the HVAC industry, chances are you'll feel somewhat overwhelmed with an exorbitant amount of information needed to better serve your customers.

In this blog I will provide in layman's words, with a smattering of technical data this is in an effort to provide beginners some insight while reinforcing the terms in my own brain as I am learning them. 

First off, what does HVAC mean?

HVAC is the acronym for "Heating, Ventilation & Air Conditioning". In essence an HVAC contractor will fabricate or custom order and install air systems that heat, ventilate or cool a building.

Essentially, HVAC plays an imperative role in the design of medium to large scale industrial office buildings such as skyscrapers, residential buildings, and even marine environments such as aquariums, where safe and healthy air flow is required for ecological sustainability.

As a new entry level employee in the fabric duct industry myself, I've learned some key words that will enable you to better communicate with contractors and others who work in this field. Knowing these basic definitions play a vital role in your day to day job responsibilities.

CFM: Cubic feet per minute, the volume of air that an air system can deliver, or one cubic foot of air every sixty seconds.

Ton: A ton of refrigeration is approximately equal to the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. For duct sizing 1 ton in generally = 400cfm 

Velocity: The rate of speed in which the air is traveling either inside a duct, out of or into an air device or at the point it reaches a person.

VFD: Variable frequency drive.  A power source that ramps the fan/airflow up or down.

VAV: Variable air volume. The ability to change the volume of air that a system can supply.

Duct: A duct system is often called ductwork. Planning ('laying out'), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design.

Dew point: The temperature where the duct system starts accumulating condensation.

Air diffuser: A device in a duct system from which air is delivered.

Static pressure: The static pressure, which is measured in relation to the atmospheric pressure, works identical in all directions. This is what keeps a fabric duct inflated. The static pressure of a duct system can be both positive or negative.

Throw: The distance in which the air distribution device throws the air.

Pressure loss: The external static pressure lost over a fitting, elbow, T, or air device.

Dynamic pressure: the dynamic pressure or velocity pressure, is working in the same direction as the air flows in a duct. See Bernoulli's principle for a complete understanding of how Static pressure and dynamic pressure are related in a closed system such as an air duct.

Delta T : Temperature difference. The difference in the supply air temperature and room temperature.

Ducts can be made out of the following materials:

Galvanized steel is the standard and most common material used in fabricating ductwork. For insulation purposes, metal ducts are typically lined with faced fiber glass blanket (duct liner) or wrapped externally with fiber glass blankets (duct wrap), or a double wall duct which is internally lined.  Double wall duct are also called “spiral ducts” due to the way they are manufactured as a ( lock seam) which give the appearance of a spiral design.

Aluminum and stainless steel is usually used for corrosive environments such as community swimming pools and industrial chemical plants.

Flex ducts : Flexible ducts, known as flex, have a variety of configurations, but for HVAC applications, they are typically flexible plastic over a metal wire coil to make round, flexible duct. In the United States, the insulation is usually glass wool, but other markets such as Australia, use both polyester fiber and glass wool for thermal insulation. Flexible duct is very convenient for attaching supply air outlets to the rigid ductwork. However, the pressure loss through flex is higher than for most other types of ducts. As such, designers and installers attempt to keep their installed lengths (runs) short, e.g., less than 15 feet or so, and to minimize turns. Kinks in flex must be avoided. Some flexible duct markets prefer to avoid using flexible duct on the return air portions of HVAC systems, however flexible duct can tolerate moderate negative pressures.

Fabrics ducts are a little bit different considering they’re normally made of special UL classified fire retardant polyester material. These ducts can provide air to a space more effectively than a conventional exposed metal duct system, considering they typically distribute air continuously from the inlet to the end cap, so they are really more of an air distribution device than a duct. Many times fabric ducts are deemed more applicable in controlled environments due to lack of condensation at higher dew points because permeable fabric ducts will not sweat.

Depending on the material and manufacturer, materials that eliminate moisture may also be considered healthier and provide an active anti-microbial agent to inhibit bacteria growth. Porous material also tends to require less maintenance as it repels dust and other airborne contaminants from settling on top of the ducts.

Again this may all seem overwhelming at first, but with hard work, practice and actual work experience, you will become more proficient as time passes, as well as becoming an asset to your employers.

I hope this brief synopsis has helped you grasp the basic fundamentals of a very rewarding field of work.

  Larry Bolton

Internal Sales Consultant