Ductwork Design Software Free

[Adele Strecker]

Ductworktypically brings air from the A/C or furnace to its source and sends into your home through a supply duct. The air then naturally flows to different parts of your home where a return duct is located.

If the air pumping into the room is unable to circulate to the return duct, it gets stuck in the area surrounding the supply duct. It stays there while the air pressure continues to rise, and with no other option, the air seeps out of the house. This causes the HVAC system to continually work to generate more cold air.

Leaks or cracks in the ductwork can also impact how much you spend each month on utilities. Up to 20 percent of your conditioned air is lost before it ever reaches its destination. It leaks out of the ducts in places such as the attic or basement where it does no good.

Efficient ductwork design is created to distribute air correctly through the home. Depending on the layout of your home, the general types of ductwork designs for maximum productivity are truck-and-branch style or spider systems. Professional technicians can help with various methods of eliminating energy loss in ductwork for maximum savings.

Incorrectly sized ducts or ductwork which does not allow the air to flow properly will possibly require a redesign to keep the home comfortable. Properly sealed and balanced ductwork will use less energy and reduce costs.

Keep in mind that a leaky ductwork system does not balance air distribution, and the system may be using too much heating or cooling in certain areas of the home, creating unnecessary expense for the homeowner. These leaks may cause you to adjust the thermostat to make the affected rooms comfortable, increasing the cost of running the HVAC system.

If designed correctly, ductwork will include proper methods of supply and return for the air. This insures that the air flows through the system at the proper rate. Proper air flow rates will increase the productivity of the unit, decreasing costs to run the unit.

Accurate air supply and return is critical for maintaining even air pressure throughout your home. Uneven air pressure can force air exchange between indoor and outdoor air, burdens your heating unit, and increases utility costs. Install volume dampers in the ducts to increase your control over air flow.

Ducts that are too small will have a high resistance to airflow which may prevent your air handler from achieving sufficient airflow rates. Even if it does, the high air velocities in the ducts will be noisy. The air velocities in ducts that are too large will not be effective at distributing air throughout the rooms.

Airflow should be closely balanced, with as much air delivered as gets routed back to the HVAC equipment. Otherwise the pressure differential will result in unwanted air loss or gain via air leaks in exterior walls.

You can accomplish this balance by ensuring the return flow has the same airflow capacity as the supply. You will also need to ensure every supply register has a route to a return register. To accomplish this, either include a return register in every room, or install wall and door grilles to supply a suitable route.

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If you have a 2.5 ton air conditioner, the nominal air flow would be 1,000 cfm. (The rule here is 400 cfm per ton.) That means the blower has to push about 81 pounds of air through the system each minute. It takes work to move weight around.

When air comes out of the air handler, several things happen to it. It gets sent to the various rooms in the house. As it travels through a trunk-and-branch duct system, the quantity keeps diminishing because some of it gets diverted down each branch on the way to the end.

Each section of duct, each fitting, each turn of the air adds resistance to that air flow because of friction and turbulence. Grilles and registers, filters, and balancing dampers also add resistance. That resistance results in decreases in the static pressure, or pressure drops.

I am having ac work and new

I am having ac work and new flex duct system run off a main hard board plenum that comes up into the attic out of the ac unit closet. Florida install. The installer wants to run a flex duct directly off the end of the main plenum that comes off the blower/inside unit. I did install for a year in high school and we were taught to have the last run of the main hard board plenum no closer than 12 inches from the end. (to create back pressure) I told the ac guy he can use a prefab sheet metal elbow (12 inch) on a side of the main plenum instead of running it off the top/end. I thought that you never ever want to install anything on the end of the main plenum, even a flex duct system, because it will not allow or will decrease back pressure and therefore decrease airflow in the system?

I am noticing a few

I am noticing a few similarities between how water moves in a plumbing system, how current moves in an electrical system, mechanically pulling electrical cable through ducts (think a duct and manhole system, not hvac ductwork) and how air flow moves through an HVAC system.

Another issue in the electrical sector is the idea of skin effect. Where most of the current flowing through a conductor flows at the edges of the conductor, rather than the the center. Water pipes show the same phenomenon. Turn on your hose and notice that the water sprays from the sides and not the center. What we find in the electrical world, is that a 4/0 stranded conductor can carry a bit more current than a 4/0 solid conductor. So, I wonder if multiple, smaller pipes would lessen the pressure requirements at the blower motor? The idea is less turbulence in the center of the pipe and more consistent air flow across the entire pipe diameter.

Also, in the electrical world, if we have 2 separate, but equally sized conductors, starting and ending in the same spot, but tied together at both ends, the resistance drops by half. I have noticed similar behavior with water. And I wonder, since ducts all have the same starting pressure and ending pressure, if you were to run parallel groupings of smaller pipe (multiple outlets in the same room), if the amount of resistance from blower motor to room would drop? That would also lower the amount of pressure the blower would have to surpass to move the air.

I also wonder if other

I also wonder if other materials can be used for ductwork. In caustic environments, cpvc pipe is used. In the power industry, High Density Poly Ethelene (hdpe) pipe is used. They do make a low smoke version for use in confined spaces like electrical vaults and substation basements.

The reason why I am looking for something besides sheet metal pipe is 1) plastic is a much better insulator and therefore less heat is loss through convection of the duct itself. Sure, you can insulate a sheet metal duct, but why not buy a pipe where that is not necessary?

Another reason is the smoothness of a plastic pipe is better than even galvanized steel, which would then be better to reduce the turbulence mentioned in the article. And because it is a better insulator, there is less sound produced within the pipe than there is in typical sheet metal duct.

A fourth reason is that proper installation requires the pipe to be either fused together or joined by some sort of adhesive. This makes it air and water tight. No additional sealing required (think duct tape that is used with sheet metal duct), which would make for easier and quicker installation.

Fred, yes, it would absolutely be better for air flow to shorten that duct. A lot of poor air flow problems in ducts are on the return side so anything you can do there to fix it should result in noticeable improvement. Two possible reasons your return duct is so much longer than it should be: (1) The installer did it to reduce the transmission of noise from the blower into the living space; or (2) the installer was too lazy to cut the duct.

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You don't have to live with uncomfortable hot and cold spots anymore. With our 30 years of residential HVAC duct design and sizing expertise and your elbow grease, your entire home will be cool in the summer and warm in the winter.

We use the Professional Standards set by the ACCA Manual D HVAC Duct Design Criteria. ACCA is the Air Conditioning Contractors of America. They are responsible for setting and maintaining most of the quality and design standards established for HVAC contractors across the country.

First, your duct layout design expert will work from a drawing of your home that you provide. Then he/she will calculate the individual air requirements of every room in your home using custom industry formulations that ensure comfortable and balanced air delivery throughout your home.

Step One: The process begins with a room-by-room Manual J heat loss/gain calculation. This calculation is the staging point for all aspects of the heating and air conditioning system which will follow. This calculation will determine the air flow requirements for each room, supply register, and return grille.

Step Two: The designer determines from the calculation, the best equipment to meet the system's, or home's, requirements. Here he should follow ACCA's Manual S: Residential Equipment Selection guide. This step determines the the specific blower performance, which then becomes critical in the duct design / sizing process.

Step Three:A rough sketchof the home's preferred air distribution system is drawn showing equipment placement, register and return locations, air flow requirements for each room, each supply register and return grille, and the location and lengths of ductwork to tie it all together. More than 1 sketch may be necessary to determine the best duct layout based on the architectural layout and structural members of the home.

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