Hvac Duct Design

 Errors in Duct Design Causing Low Airflow

If you have a central AC in your house then the ducts are like arteries that enable you to make your life indoors bearable with optimal temperature and humidity. Therefore if your ducts are poorly designed or badly installed, then it can have lots of consequences. The foremost is poor airflow. Let’s see what problems in duct design or installation can cause poor airflow.

 The first is friction

The first cause of poor airflow is friction in your duct system. When the air moves through your duct it rubs against the inner surface which decreases its velocity. Its pressure also drops. You can compare the situation with writing on a very un smooth and rough backboard with a chalk. The chalk will hardly move. The cause of friction could be many- dirty ducts, un smooth surface which generally happens in case of flex ducts. If your ducts are too full of gunk and debris, the air will often collide with it while passing through the conduit. By the time its reaches your room, its pressure and velocity will drop to minimum. Again flex ducts often get kinked or constricted due to their flexible construction. They have to be pulled very tight to allow proper movement of air. Otherwise the air will often bump against the protruding surfaces.

 The second is turbulence

The air pausing though an air duct often has to go through bends and turns to reach the rooms. This depends on the design of the house. Hairpin bends in the duct work decrease the amount of air that actually reaches the space to be cooled. However in such a case the ducts have to be designed appropriately to enable an optimal airflow to rooms. The best way to do so is fitting turning vanes. These vanes allow airflow to remain smooth and let the change in direction happen gradually rather than sharply. Thus the flow the air is less impacted.

Many HVAC duct designers are a bit skeptical about using these vanes as they add friction. Here you have to make comparison. The amount of energy lost to friction is almost negligible compared to what you lose in the impact resulting from an abrupt or significant change in direction.

 The third is under-sizing

Some times contractors are in haste and they make erroneous calculations of load requirement of individual rooms in your house. They also fail to consider the type of system you have,the type of duct material, and also their location to be. As result they design undersized ducts. Undersized ducts restrict airflow. You will often hear whistling noises coming out of your ducts.

The fourth is Long ducts

The location of your HVAC is also plays an important role in allowing a good air flow. If your central unit is located in a corner from where serpentine ducts run to deliver air to your rooms then you should forget about good airflow. The unit should be centrally located to ensure minimal duct run to all rooms. Long ducts decrease the system’s ability to move conditioned air to remote sections of the house. Its velocity and pressure drops on the way.

 The fifth is leakages

Leakages in the duct can cause havoc. They lead to loss of heated or cold air into the surrounding.Your system's efficiency can go down by 30 percent or more. So when designing and installing the ducts, care should be taken so that joints are secured well in mastic and foil tapes. There should not be leaks in unconditioned zones such as attic, basement etc.

The last is lack of returns

This is very common flaw in HVAC duct design. You can relate the situation to breathing through a straw when jogging. If your return ducts are too small it will not be able to return enough of room air to the cooling init. According to National Comfort Institute on an average a duct system returns 25% less air than required. The poor airflow will make your system work longer to produce the desired cooling. This will increase your power bills.

 Things to take into account when designing ducts:

• Consider the size of each room and calculate the load
• Device the easiest way to carry air from your air conditioner or furnace to each room
• First make a layout of the main duct; it will run to various zones of the house
• If the size of the main duct is a bit upscale then it goes to your advantage
• Next the smaller ducting have to be designed that will branch out of the ma induct
• Decide an appropriate location and size for fan that will blow the air
• Also decide on strategic locations for the filers
• Insulation of the duct should be foolproof
• The location of the cooling unit should be central

 Consequences of Poor Duct Design

• High power bills
• Rapid wear and tear of air conditioner and furnace
• Bad air filtration
• Blocked ducts
• Unsightly marks around outlets
• Growth of insects and mold in the ducts

Get Service Calls

Duct Cleaning Cost - AC, Heat Pumps & Furnaces

Get Service Calls