Airflow In Ducts Pdf

The main cause of turbulence within ducts is turning the air. It would be most effective if you politely asked the outside consultant for the performance curve of the blower he is specifying.

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They cut the amount of air that gets delivered to the rooms. Turbulence The other primary cause of reduced air flow is turbulence. That's true in good duct systems as well as bad. As air moves through a supply duct, the pressure created by the fan behind it keeps it moving. This one is a kind of friction of the air rubbing against itself.

Basics of Airflow

The text is intended as a reference guide to help building owners operate and maintain their home effectively. Or you can skip ahead and go read Manual D. This website requires certain cookies to work and uses other cookies to help you have the best experience. The other primary cause of reduced air flow is turbulence. Friction rates and pressure drops The result of friction and turbulence, as I said above, is that you get a drop in the pressure.

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Friction and turbulence play a big role in whether a duct system does what it's supposed to or not. How to Install Flex Duct Properly. And they can be reduced but not eliminated.

Airflow in Ducts

Frequently Asked Questions (FAQs)

Chilled water system added. These photos show a common ceiling return air plenum over commercial offices. The first cause of reduced air flow is friction.

CFD Flow Modeling

Although I am in no way an airflow expert, I did spend several years trying to troubleshoot a too-cold bedroom. That is what I submit must be added to the list of causes of poor airflow. Return ducts are often under sized for the airflow required, and people often fail to recognize flex ducts need to be sized larger than hard duct for a given air flow. Both of these causes, friction and turbulence, eurodisney plattegrond pdf are included in the friction rates given for various types of ducts and fittings. It makes sense that you need to know how air flows in ducts and what factors affect the flow.

Those things are related, but we need to go back further. If the duct air flow system is out of balance you will find that when heating, some rooms are not warm enough while others are too cool. Or add a new return to increase filter area and air flow capacity.

In the first or left hand photo, notice that rectangular opening in the distance? Conditioned air is usually transported through ductwork. One of our clients who maintained a law office in a strip mall complained of chemical odors which were traced to a beauty parlor located at the extreme other end of the building.


Remember the friction rate is set by the available static pressure after all the non-duct elements pressure drops are subtracted. It's like walking down a busy sidewalk with your shoulder rubbing against the buildings. Do you know what they are? They make the blower push against more pressure, thus reducing air flow or increasing energy use, depending on blower type. Generally we want to keep ductwork as short and direct as possible.

Pick your fittings carefully! The same flex duct pulled tight is shown below. The result of friction and turbulence, as I said above, is that you get a drop in the pressure.

Guidelines for proper installation are treated and illustrated in depth, featuring connections, splices and proper support methods for flexible duct. This increased the air flow, but now the air flow only flows directly down instead of directing the air across the room. By closing this message or continuing to use our site, you agree to the use of cookies. If you're not using Manual D or a ductulator or some other method that quantifies these effects, you may well end up with a system that no amount of commissioning can save. When ductwork runs like a crazy twisting worm all through an attic its unnecessary length and extra sinuous bends and crips can seriously block air flow to some building areas.

Bracciano, Goodheart-Willcox Co. That's where equivalent length comes in, and I'll save that for a future article. Then the available pressure is divided by the total effective length. This is basic physics I'm talking about.

Maybe you're thinking it's flex duct that's not pulled tight or not using rigid elbows or maybe even the dreaded ductopus. You've got to combine it with something else to figure out what the whole pressure drop is.

Good manufacturers will also note the temperature or temperature differences used in their labs during the determination of performance documentation. It includes the fan to move the air and equipment to condition the air before it is delivered to the conditioned space. While in cooling or air conditioning mode you'll find similarly that some rooms are not cool enough while others are too warm. Notice the considerable amount of debris atop the ceiling tiles?

We discuss how to choose the best high-end system for homeowners, tips for selling those systems, and more. Hot water system added to air handling system. David Butler David Butler.

Skin Flakes in Your Air Conditioner. Click on the illustration for an enlarged view. The fan creates pressure that causes air to flow. In this case they are located too close together.

Although I live in the hot-humid Houston area, you might say I'm from Missouri. John Proctor John Proctor. When it makes the turn, however, notice that the air in the elbow with the curved inside edge the throat results in less turbulence. The tech immediately brought a a pair of tin pliers used to bend sheet metal.