Professional Ventilation Duct Supplier in China

Ventilation Duct: The Ultimate Guide

Today’s guide takes a look at all the critical aspects of a ventilation duct system.

It covers both basic and intricate details of ventilation ducts, providing information that is useful to importers, OEM clients, designers and professionals in this industry.

Let’s begin:

Ventilation Duct Definition

Ventilation duct is a piece of equipment consisting of ducts and vents that allows for airflow, which helps in the ventilation of a room(s).

Ventilation duct

Where to Install Ventilation Ducts

Selecting an appropriate location to install your ventilation duct is vital in ensuring its efficiency.

Generally, there are six primary locations for installation of ventilation ducts.

These are:

Ventilation duct systems – Photo courtesy: Fine Home Building

1. Attic Installation

The advantage of this location is that it allows for any ventilation duct system.

Such a ventilation duct system includes the reduction trunk, the radial arrangements, and the extended plenum.

However, you need to insulate the ventilation duct system if you are going to install it in this location.

Also, to avoid exterior duct condensation, you will have to use a proper vapour barrier.

Condensation can lead to rusting and corrosion of your ventilation duct system, which will have an impact on its structure.

You must consider sealing all seams and joints to prevent leaking of the duct.

Ensure you use a sealant that is approved by the local regulations.

The location of the air handler needs to where the shortest ventilation duct runs are possible.

At the shortest run, the air flow resistance will be lower and also the lower the heat losses, and heat gains will be.

Attic installation allows for the use of a wide range of materials.

You need to be careful during the installation of a flexible ventilation duct to avoid sharp bends, kinks, sagging and crimping.

These have the effect of causing friction, which causes malfunctioning of the ventilation duct.

2. Basement Installation

Basement installation requires the use of a moisture barrier to minimize exterior condensation of the ventilation duct. If it is to be unconditioned.

In case of a conditioned basement, you will consider the ventilation duct system as conditioned space.

This means that insulation is not a necessity.

However, for sound attenuation, it is advisable to use a duct liner.

Seal all side seams and joints to prevent leakage of the ventilation duct.

Here, you need to check with your local codes as to which sealant to use.

Install the air handler either within the basement or on the structure’s exterior.

Also, locate the air handler on the shortest ventilation duct run possible.

Basement installation allows for the use of a wide range of materials except for a flexible ventilation duct system.

3. Between Floors of a High-rise Structure

Installation on this location involves the use of fire-down areas using ventilation ducts which run between a combination of floor beams.

Construction of this system includes lines of metal films.

Duct board is necessary for noise and sound control.

Insulation is not relevant between the floors due to its location in a conditioned space.

However, you will have to insulate any duct passing through an unconditioned area, and it should have a vapour barrier.

The vapour barrier prevents the accumulation of condensation on the outer side of the ductwork.

You need to seal all the side seams and joints to prevent the ventilation duct from leaking.

Such sealants include duct tape and waterproof mastic.

Comply with your local codes when selecting which sealant to use.

Like all the above installation locations, the location of the air handler needs to be on the shortest ventilation duct run possible.

The advantage of this installation is that there is no heat loss or gain, which is a problem associated with most ventilation duct systems.

This is because the ventilation duct system is in a conditioned space.

This type of ventilation location allows the return air filter to be on the unit.

4. Crawl space installation

Using this type of installation requires that you insulate the entire system as well as the vapour barrier.

This aids in preventing exterior condensation of the ductwork.

Use an approved sealant to seal the side seams and the joints to minimize duct leakages.

Examples of ventilation duct systems that utilize crawl space installation include reducing trunk, extended plenum and perimeter loop.

Crawl space installation allows for the use of different materials except for flexible duct materials.

This is because they don’t offer ventilation duct support.

Benefits of Ventilation Duct Systems

An effective ventilation duct system offers a wide range of benefits. Such benefits include the following:

Ventilation system – Photo courtesy: HPAC Engineering

· Cleaner air

An effective ventilation system provides cleaner air to the occupants of a room.

Filtering air flowing from the outside into the room using air filters helps in achieving this.

Cleaner air ensures air circulation, which removes stuffiness and drafts in a room.

This goes a long way in reducing airborne diseases.

· Temperature control

A ventilation duct gives you the freedom to control the temperature of a given room.

What happens is the ventilation duct sucks warm air from the room while allowing cold air from outside to flow into the room.

As this happens, you find the temperature of the room is constant at a given level.

The advantage of a ventilation duct system is it allows you to control the air flow, which helps in controlling the temperature of the room.

· Moisture regulation

Ventilation duct helps in maintaining the moisture content of a room at an acceptable level.

Too much moisture within a room encourages the growth of moulds and mildew.

In the other hand, lack of it creates discomfort to the room occupants.

It is therefore practical to install a ventilation duct in your room.

· Energy cost

Having separate heating and cooling equipment in a room increases energy consumption as well as the cost.

It is also tiresome installing these different appliances.

However, a ventilation duct can offer both the heating and the cooling requirements a room may need.

This saves you money, space and installation time.

Types of Ventilation Duct Systems

The market offers different types of ventilation duct systems depending on the various needs.

Each type has unique specifications that make it ideal for use.

Among the common types of ventilation duct system available include:

i. Rigid Metal Ventilation Duct System

Rigid metal ventilation duct system is a kind of ventilation duct system that is hard and reliable.

The different materials used to manufacture this ventilation duct system which comes in either in rectangular or cylindrical shapes.

Rigid metal ventilation duct system

Most rigid metal ventilation duct system is insulated.

The different types of rigid metal ventilation duct system available in the market are:

· Sheet Metal Ventilation Duct System

They are the most common types of rigid metal ventilation duct systems that you will find in the market.

The two common materials that you will find are aluminium or galvanized steel materials.

The advantage of this type of rigid metal ventilation system is that they don’t harbour dangerous growth or moulds.

This is because they are non-porous surfaces.

They are also easy to install and lightweight.

· Fibreglass lined ventilation duct system

These ventilation duct systems have either an external or internal fibreglass lining.

You will find these systems in commercial and office buildings since they absorb sound coming out of the air conditioner system.

However, continuous use of these ventilation ducts causes deterioration of the fibreglass.

This leads to the release of the fibreglass particles which are hazardous into the air.

Another limitation is on the cleaning process.

Cleaning this type of ventilation duct has the effect of damaging the fibreglass lining, thereby releasing the fibres.

Also, these ventilation ducts are prone to bacteria and mould growth.

· Fireboard ventilation ducts

Fireboard constitutes of compressed fibreglass strands which have been bonded using resins and covered foil laminate film.

The purpose of the laminated film is to make the duct moisture proof.

Fireboard ventilation ducts are common in the heating and cooling system due to its self-insulation characteristics.

The imitation of using this ventilation duct is the peeling effect of the fibreglass strands, which are hazardous.

Moulds and bacteria find it a breeding ground which poses a risk to human life.

Also, the roughness of the fibreglass minimizes the airflow, thus affecting the efficiency of the ventilation duct system.

ii. Flexible Ventilation Duct System

A flexible ventilation duct system refers to one which is easy to bend, offering a wide range of applications.

Its use is ideal, especially in areas where it is impossible to use rigid metal ventilation duct system.

Aluminum flexible duct

It is composed of a metal wire coil which is covered using a long-lasting plastic that is easily bendable.

The use of flexible ventilation duct system offers several benefits as compared to a rigid metal ventilation duct system.

For instance, they are quick and easy to install, which you will find it handy if you are installing in a wide area.

And by the way, it is economical, which is a good way of saving money.

Flexible ventilation duct system

Installing this type of ventilation duct requires adherence to special requirements.

Such requirements include firmly securing it on the wall to prevent sagging.

You also need to avoid bending and turning of this type of ventilation duct.

Turns and bends have the effect of reducing airflow, therefore, affecting the efficiency of the ventilation duct.

Parts of Ventilation Duct System

The efficiency of a ventilation duct system depends on the proper functioning of its different parts.

These parts include:

Parts of ventilation duct system – Photo courtesy new Vitruvian

· Filters

Filters refer to that part of a ventilation duct system whose purpose is to remove dust particles from the air.

This ensures clean air flows into the ventilation duct.

Materials such as pleated media, electronic precipitators are used to create filters for various ventilation duct systems.

Due to its function, you have to frequently replace the filters to ensure the proper functioning of the ventilation duct.

An easy way of knowing when to replace these filters is to monitor the air pressure drop.

A pressure gauge will come in handy here.

A drop in the pressure implies it is time to replace the filters.

Failure to replace the filters may result in the collapse of the ventilation duct

· Insulation Material

An insulation material helps to prevent heating up of the ventilation duct through absorption of excess heat.

This aids in ensuring air flowing circulating through the ventilation duct is comfortable to the users.

There are different insulation materials available for use in the ventilation duct.

Fibreglass is the typical material used as an insulation material since it is a non-flammable insulation material.

However, since it is of finely woven silicon, it can hurt you if it gets in touch with your eyes, skin or even lungs.

You, therefore, need to have protective gear when handling it.

The other material is the mineral wool which can either be glass wool, rock wool or even slag wool.

There is a limitation to the use of this material due to the lack of additives.

It is therefore not advisable to use this material in situations of extreme heat.

However, it forms a useful material in conjunction with other materials since it is not easily combustible.

Cellulose is another material available as an insulation material.

The advantage of this material is that it is eco-friendly since it of recycled paper, cardboard or any material that is of loose form.

Cellulose is an alternative insulation material since it is a fire-resistant material due to its compactness which ensures there is no oxygen circulation.

Other materials available include polyurethane foam and polystyrene.

· Exhaust Fan

The function of the exhaust fan is to suck the humid or hot air out of the indoor space.

By doing this, fresh air flows from the ventilation duct into the indoor space.

Once the exhaust fan sucks the hot or humid air, it is expelled outside through the ventilation duct system.

· Fire Dampers

Fire dampers refer to passive resistance substances which are used to avert fire spreading inside the ventilation duct.

What happens is when a fire occurs, there is an increase in temperature, causing the heating element to melt.

Melting of the heating element causes the fire dampers to close.

Alternatively, activation of an electric signal may also cause the fire dampers to close.

Fire dampers can either be mechanical, intumescent or PFP/AFP hybrid fire dampers.

Duct components – Photo courtesy: CED Engineering

· Condensation Trap

The function of a condensation trap is to prevent the formation of moisture within the duct-work flowing back to the fan unit.

Condensation happens when the warm air extracted from the room hits the cooler parts of the ventilation duct.

Significant cooling the warm air forces the moisture to flow back to the ventilation duct where it is trapped.

· Volume Control Dampers

Volume control dampers are there to regulate the flow of air through the ventilation duct system.

Volume control dampers are either valves or plates which function by either cutting or minimizing or maximizing air flow.

Depending on the type of your ventilation duct system, these dampers can either be automatic or manual.

Manual volume control dampers are controlled using a handle that is on the outside of the ventilation duct system.

On the other hand, operating an automatic volume control damper depend on the pneumatic or electric motors.

· Turning Vanes

The turning vanes ensure the efficiency of the ventilation duct by smoothly directing air flow inside the ventilation duct.

It does this by reducing air turbulence and resistance.

Installation of the Turning Vanes on the ventilation duct is in areas where there are bends and turns, ensuring smooth air flow.

· Air Handler

Also referred to as Air Handling Unit (AHU), it is the part of the ventilation duct whose purpose is to regulate and circulate the air.

It is usually a large metallic box which has heating, cooling or blower elements.

It also has filter chambers, dampers and sound attenuators.

· Outlets (grilles, registers, diffusers)

Outlet refers to the points of the ventilation ducts where warm air from inside the room flows out into the atmosphere.

It is essential in ensuring there is a circulation of clean and fresh air within the ventilation duct system.

· Plenum

Plenum refers to the central collection and distribution points of a ventilation duct system.

There are two types of Plenums, that is, return plenum and supply plenum.

Return plenum function by carrying air from various return vents to the central air handler.

Supply plenum work by directing airflow from a central unit to the different distribution units within the duct system.

· Takeoffs

Take-off is the points that connect to the main trunk.

They serve to facilitate the flow of air from the main duct to the branch ducts.

· Vents

The function of vents in your ventilation duct system is to help in the circulation of air within the ventilation duct system.

Vents can either be return vents or supply vents.

Supply vents help in allowing the flow of air from the supply duct to the indoor spaces.

They are generally smaller when compared to return vents, and they have louvres.

Return vents draw air from the indoor spaces to the return ducts. They are larger than supply vents and lack louvres.

How to Install Ventilation Duct Systems

The installation process of a ventilation duct system is quite simple since it involves following several steps. These steps include:

1) Calculate the Load of in Rooms

The first step when installing your ventilation duct system is the need for calculating the load requirements of your room.

Since there are different sizes of the ventilation duct system, it is essential that you get the requirements of your rooms

Getting the right ventilation duct system helps in ensuring your rooms are well ventilated.

2) Locate a Suitable Place for Placing the Fan Coil

Once you have calculated the ventilation requirements of your rooms, the next step is to locate where to place the fan coil.

As a thumbs rule, placing it in an unconditioned space is ideal.

Such spaces include the garage, the attic or even a crawl space.

You need to protect such spaces need to against the weather.

Alternatively, you can place the fan coil in conditioned areas such as the utility room, basement or the closet.

Remember, you can either have the vertical or horizontal configurations of fan coils.

You also need to consider where to locate the duct and the return air filter, the plenum, air supply tubing and the condensate drain line.

If you are to install the fan coil in an attic space, you need to install a float switch or a secondary drain pan.

You may install the fan coil on a platform which may be fixed or suspended.

However, the platform needs to be as close as possible to the return air box.

This is to aid in connecting the return plenum duct.

3) Cutting of the Return Air Opening

The next step involves cutting off the return air slot.

While doing this, you need to avoid installation of return air box in the living room, kitchen or dining room unless you can install the air duct at a 180-degree bend.

You may pass the fan coil through the opening that you have cut basing it on the dimensions of the return air slot.

The most return air box is designed to fit in spaces that are 14 inches in width and 16 inches at the centre.

If you are using wall applications with the fan coil vertically standing, ensure that your return air duct has a 90-degree bend.

Also, you need to check on the return air box.

Remember to install the return air box only after you have finished the installation.

This gives you space for passing materials during the installation process.

4) Construction of a Platform

Remember the platform we mentioned in step 2?

Now is the time to construct them.

Construction of these platforms depends on the size of your fan coil.

For proper sizing of these platforms ensure that you check on the manufacturer’s installation manual.

Ideally, you can use stud lumber of 2 by 8 inches with a minimum of 0.5-inch plywood for constructing the platforms.

You don’t have to fasten the fan coil on the platform since its weight holds it in its position.

5) Fix the Supply Plenum Ring

You need to consider leaving space between the ground level and the fan coil since the supply plenum ring is a few inches.

You can achieve this by adjusting the fan coil upwards the edge of the platform.

The plenum ring connects to the square slot using the provided screws.

Additionally, before mounting the supply plenum ring, ensure you fasten the plenum ring gasket on the fan coil.

6) Connect the Condensate Drain

The next step involves connecting the condensate trap to the fan coil.

For proper connection, follow your manufacturer’s instruction manual.

Try running the condensate trap line from the trap to an ideal drain as per the local codes.

You need to pitch the drain line 0.25 inches per foot.

Avoid connecting the condensate trap to a closed drain system.

For the overhead system, a secondary drain can be an alternative.

7) Connection of the Refrigerant Lines

The refrigerant lines connect to the indoor fan coil from the outdoor condensing unit.

Check your manufacturer installation manual when connecting the refrigerant lines.

8) Connection of the Plenum Duct and the Supply Tubing

It is always advisable to consider the system layout of your air distribution components based on the sizing parameters.

You can run the plenum in any direction as long as it can be accessed when attaching the supply tubing.

You must maintain 18 inches at least for all tees, branches, and elbows from the fan coil.

Ensure you reduce the use of the elbow, branch supply run or tees to minimize pressure drop.

The most plenum is the 6-foot length, but you are at liberty to cut it into different lengths as per the ventilation duct system layout.

As a recommendation, cut the male end of the plenum first when installing it to the unit.

After that, connect the receiving collar that is in the fan coil to the plenum duct.

Remember to push the plenum duct forming a snug joint tightly.

There is a need for the sheet metal tabs to be flattened against the plenum unit then you insert the flat pins.

The next step is covering and sealing the foil faced insulation on top of the taped joint.

Ensure you push the insulation up over the fan coil.

Join the plenum duct, ensuring that the shiplap joints for a snug and tape them securely.

Once you have installed the plenum, you can insert the end cap onto the end of the plenum run.

The end cap has an insulated cushion which you push tightly up against the end of the duct.

Tightly hold the end cap in place and insert the flat pins over the sheet metals at cap end.

Securely tap the end cap using a circumferential cover over the cap.

It is advisable to strap the plenum minimize the movement of the plenum during operations, which can cause loose joints.

https://youtu.be/dsI_3lbwO7E

9) Sound Attenuation Tubing and Terminator Outlet Installation

Once you have connected the plenum duct and the supply tubing, you are now ready to install the room terminators as well as the sound attenuation tubing.

These parts come together with the installation kits.

The first step is to mark the installation location of the room terminators.

While at it, ensure that the terminator centre is at least 5 inches off each wall edge.

Next, drill a 1/8-inch outlet hole.

Give a 2-inch allowance around the 1/8-inch hole.

After that, cut a hole using a 4-inch hole with the 1/8-inch hole as a benchmark.

Join the sound attenuating tubing to the room terminator by binding the connectors together and tightly twisting them.

If you are installing the terminator in a floor location, you need to construct ¼ by ½ inch screen.

Place the screen in between the tubing connector and the terminator faceplate.

Push the sound attenuating free end via the 4-inch hole till the terminator toggles snap into place.

Place the centre of the two spring clips in a line that is parallel to the tubing direction.

You need to ensure the faceplate don’t withdraw from the ceiling.

10) Supply Tubing Installation

The final step involves the installation of a supply tubing.

You need to avoid sharp bends when installing attenuators and supply tubing.

Most supply tubing is 100 ft. in length, but you may cut as into different lengths as per the requirements.

Join the supply tubing to the connector through threading it to the tubing’s cut end.

Slip the Mylar scrim and the insulation under the connector’s collar.

Secure the pieces together by wrapping a tape around the connector.

Lastly, use twisting action to install the connectors securely.

At the location of the plenum, drill a 2-inch hole on the plenum using the hole cutter that is in the kit.

To reduce tension on the plenum, ensure that the hole is at an angle of 20-degrees.

Rotate the cutter forth and back to drill a hole using the hole cutter.

As you do this, apply the required pressure to push the jagged edge into the insulation of the plenum and the foil.

While removing the hole from the plenum, ensure that no flap is left, which could obstruct the gap while you are operating.

Position the takeoff gasket such that it surrounds the hole.

The takeoff gasket comes with the installation kit.

Next, insert the takeoff connector inside the plenum hole.

Align the plenum takeoff to be uniform with the plenum duct curvature.

Place the plenum fasteners one at a time using hands then tighten into place using pliers.

After positioning the plenum takeoff, you can now install the balancing orifices if it is a must.

Follow the same procedure when installing the connector on the space remaining on the supply tubing.

Join the connector to the plenum takeoff from the tubing using twisting action like the way you connected the connectors.

This is the final step when installing the supply run.

The next step is to install the return air box and the return air duct.

To do this, separate the return air filter and the grille from the assembly of the return air box.

Fit the return air box to the return air opening you had earlier on cut.

After that, tighten the frame using four screws via the holes that are on the box’s long side.

Place the return air grille inside the box and tighten using the four screws available on the package.

Open the grille then insert the filter after which join each of the return air tube’s end to the oval edge of the fan coil.

It is important to note that every electrical installation that you make needs to adhere to the local authority’s regulations.

Check on the wiring diagram while you are installing the electrical part of the ventilation duct system.

Remember to connect the fan coil unit to a different circuit using 14-gauge wire and a 15-Amp fuse.

Low voltage thermostat can connect to a low voltage control on the unit.

Just in case you want to learn more about ventilation duct installation and other related aspects, below are important resources for you:

• Duct Ventilation Installation
• DIY Air Duct Installation
• Installing Flex Duct
• Ductwork Installation Guide

Ventilation Duct Cleaning Process

Once the dirt has accumulated on your ventilation duct, it is time to clean it up, which is very easy.

Follow these steps when cleaning your duct ventilation system.

· Switch Off the Power

The initial step towards cleaning your ventilation duct is to switch off the power.

This will prevent you from damages that may arise due to short circuits.

If possible, disconnect the power cables of the ventilation duct from the primary current.

· Vacuum the Condenser Fins

The condenser fins consist of narrow metal slats which you need to take care not to break them.

For this reason, use a vacuum cleaner to remove debris from the condenser fins.

Run the vacuum cleaner along the condenser fins which will remove the debris.

This will allow the condenser to suck in the air without any obstruction.

It is advisable to use either a wet or dry vacuum cleaner for this function.

Once you have finished this, it is vital to check if the condenser fins are straight.

If there is any bent condenser fin, straighten it.

The purpose of this is to maximize the flow of air into the ventilation duct.

· Cleaning the Fan Coil

On top of the compressor unit is the fan coil which is usually covered using either a grate or a metal wiring.

Use a screwdriver to unscrew the grate or metal wiring to remove the fan coil.

Carefully remove the fan coil to avoid disruption of the electric wires attached to it.

You don’t have to remove the fan col from its position thoroughly.

Once you have completed this, you need carefully wash the fan coil blades together with its inferior fins.

For this function, you can use a garden hose and a rag or a piece of cloth to wipe it clean.

Remember, after cleaning this section, reassemble the compressor unit.

· Clean Inside the Ventilation Duct Unit

There are several things you need to check on when cleaning the inside part of the ventilation duct.

First, you need to replace the air filter at least twice in a year.

To remove the air filter, you need to pull the metal grate covering the air filter.

After this, remove the air filter and replace it.

Typically, air filters are located indoors and measure around 2 ft by 1 ft.

Regular replacement of air filters is necessary since they get clogged over time with dust particles.

If you are to reuse an air filter, you need to clean it properly to remove any particles.

Cleaning of the air filter can be twice a year.

Rectangular flexible duct

While cleaning, ensure you follow the manufacturer’s instructions to avoid destroying it.

Ideally, the cleaning of the air filter is achieved using lukewarm water and dish soap.

Secondly, you need to clean the drainage.

Remember, the function of the evaporator unit is to de-humidify and cool air flowing from the outside.

The product of this is runoff liquid which flows through drainage.

You, therefore, need to clean this drainage frequently to avoid clogging.

You can achieve this by stiffing a wire back and forth into the drainage to remove any particle clogging it.

When to Replace Ventilation Duct

There are certain conditions which when you notice on your ventilation duct, then it is high time you replace it.

Such conditions include the following:

Stainless steel spiral duct

· Damaged or Kinked Ventilation Duct

When you are inspecting your ventilation duct, and you notice that it is either kinked or damaged, then it needs a replacement.

You may replace the ventilation duct if you notice any holes.

Also, flexible ventilation ducts get torn or ripped over time, which affects its efficiency.

If you notice such, you need to replace your ventilation duct.

Another sign that your ventilation duct is damaged if any weight falls on it.

· Strange Noises

You will have to replace your ventilation duct when you notice a strange noise coming out it.

Loose ventilation ducts which are not well secured are the causes of such noises

When the ventilation duct is loose air flows over through holes resulting in noises.

Alternatively, the ventilation ducts being too small causes such noises.

· Uneven Room Temperature

An effective ventilation duct needs to distribute temperature within your room evenly.

Therefore, if you notice a part of your room is cooler than the other parts, then you need to replace your ventilation duct.

The reason for the uneven room temperature can be due to holes within your ventilation duct.

Also, it may be as a result of the unbalanced ventilation duct system.

When replacing, ensure you properly replace the ventilation duct to have an even distribution of temperature.

Consult an expert if you are finding it difficult to replace the ventilation duct properly.

· High Utility Bills

If your utility bills keep rising, then you need to replace your ventilation duct system.

Energy loss due to leakages on the ventilation duct causes high utility bills.

Your energy consumption needs to be at a constant rate.

· Dusty Rooms

Your rooms may be dusty due to leakages within the ventilation duct.

The leakages allow for dust particles to flow into the rooms.

The other cause for your room being dusty is having a torn air filter which allows dust particles to flow into your room.

Calculating Ventilation Duct Size

There are three common methods of calculating the sizes of the ventilation ducts.

These are equal friction method; velocity reduction method and static regain method.

 High temperature flexible duct size

Equal friction method uses the friction rate to size ventilation ducts.

Friction rate defines the mean pressure drop for every 100 ft of the ventilation duct in a system.

You will need either a duct calculator, duct slide rule or a friction rate to determine the relationship between the air flow and the duct size.

Among the benefits of using this method are simplicity and straightforwardness.

Also, this method minimizes the air velocities directed towards airflow, reducing noise generated by air flow.

If you ate using constant air volume systems (CAVS), then this is the best method to use.

However, there are several limitations to using this method.

First, the duct branches lack an equalization pressure drop except if there is a symmetrical layout.

To solve this, you need to install balancing dampers, which balances the ventilation duct system.

Also, this method is not ideal for use on the VAV system.

In case you use it on VAV, the terminal units need pressure independent controls to minimize high flow rates when pressure is high in the ducts.

Lastly, the inflexibility and inadaptability of this method do not allow for layout changes in the future.

The second method is the velocity reduction method.

This method determines the size of the ducts by observing the variation of air velocity in the main ducts and its branches.

Static regain method is yet another method available for calculating the size f a ventilation duct.

It involves the conversion of static pressure from velocity pressure.

The method relies heavily on Bernoulli’s equation.

The equation states that if there is a reduction in velocity, there is a change in velocity pressure to static pressure.

Bernoulli’s equation

The advantage of using this method is that the ventilation ducts, including branches and ducts, have the same static pressure.

This simplifies the selection of the outlets as well ensuring each outlet has the right air quantity.

Also, it ensures the duct system balances since the gains and losses are equal to the function of the velocities.

As a recommendation, use this method if you are designing variable ventilation duct systems.

There is less use of metal when applying this method as well as it does not produce a lot of noise.

However, there are several limitations to using this method.

For instance, this method does not consider the total mechanical energy flowing produced by the fan.

This results in having large ventilation ducts at the end of the long branch runs.

Again, here is a simple guide on HVAC Size and Design of Ducts.

How to Calculate Air Velocity in Ventilation Ducting System

Knowing the air velocity of your ventilation system helps in the smooth flow of air within the ducts.

One of the ways you can calculate the air velocity is by finding the flow velocity per minute.

Rectangular ducts – Photo courtesy: engineering tool box

Then you get the product of the flow velocity per minute with the cross-sectional area of the duct. That is:

Airflow in Cubic Feet Per Minute (CFM) = Duct cross-sectional area × flow velocity per minute.

Calculating Ventilation Pressure Loss

Ventilation pressure loss refers to the direct proportional growth of air resistance to air flow.

The fan produces static pressure, which forces airflow in the ventilation system to have a certain resistance.

The resistance will be higher when there is higher ventilation causing less air fan from the fan.

To calculate the pressure loss of a ventilation system, you will have to use a combination of tables and diagrams.

Pressure loss calculation in ducts – Photo courtesy: Ventilation Systems

Your manufacturer offers these tables and diagrams together with your ventilation duct.

Ventilation Ductwork Design Considerations

Ventilation ductwork design and considerations are vital aspects if you want your ventilation duct system to work efficiently.

For it to be a success, you need to factor in the following aspects;

Acoustic ducting

·         Methods of Ductwork Design

There are three methods of designing your ductwork.

That is the velocity reduction method, equal friction method and static regain method.

As we have seen from the earlier explanation on duct sizing, each of these methods has its advantages and disadvantages.

· Ductwork Design Considerations

You need to consider the following factors when designing your ductwork.

· Duct Frictional Resistance

There is always a frictional resistance to the flow of air supply in any ventilation duct system.

This frictional resistance differs in proportion to the ratio of the duct velocity at two velocities points.

Your ventilation duct system must have the pressure that is equal to that of frictional resistance.

It should also surpass the friction of the air control dampers, heating and cooling coils, diffusers and filters.

In essence, the total pressure should be equal to the velocity pressure and static pressure.

· Ductwork System Effect

Since ventilation duct system relies on a fan, there can be a serious performance issue if due to system effects.

System effects refer to pressure loss, which acknowledges fan inlet and outlet restriction.

When designing your ventilation duct, you need to consider the effect of the inlet and outlet on your fan’s performance.

· Ductwork System

While designing your duct, certain parts need to have an extra length to compensate for the resistance that these parts offer towards airflow.

Such parts include fittings such as the branches, elbows, and connections.

Other are accessories such as extractors and dampers.

The extra length is known as equivalent length.

· Installation Issues

Consider designing your ventilation duct in such a way that it will be energy- efficient when installing it.

Poorly installed ventilation ducts can be expensive during repairs than the actual installation cost.

Your ventilation duct system needs to be as straight as possible to minimize pressure loss and maximize airflow.

Avoid using building cavities like stud cavities or panning joist as ductworks.

· Duct Noise Consideration

An effective design should consider the level of noise it produces during operation.

The level of noise should be as low as possible.

When designing your ventilation duct system, consider every factor that will minimize noise production.

Ventilation Duct Fitting and Accessories

Apart from the different parts, other parts complement the functioning of a ventilation duct system. These parts include:

· Hose Clamp

The function of a hose clamp is to attach the hose onto a given fitting on the ventilation duct system.

Hose clamp

· Duct Connector

The duct connector helps in joining the duct in a ventilation system to either a blower or a fan.

Duct connector

· Duct Transition

Duct transition can either be rectangular, circular or square in shape.

They serve as a transition point for air flowing from the dryer to the duct.

Duct transition

· Duct Insulation Sleeve

Duct insulation sleeve help in the insulation of semi-rigid or rigid round ducts and the process, minimize loss f heat to the environment.

Duct insulation sleeve

· Duct Boot

A duct boot helps in the transitioning of airflow from a hard or flexible duct to a vent or a rectangular register.

Its long neck lets you connect to the wall and your duct.

 Duct boot

· Duct Splitter

The duct splitter is used to divide the flow of air into different ducts from the main duct.

Duct splitter

· Insulation Protection Shield

The insulation protection shield helps in the protection of the duct insulation from being crushed.

Insulation protection shield

· Flexible Duct Connector

Flexible duct connector eliminates vibrations and noise pollution from other ventilation ducting systems such as blowers, fans, etc.

Flexible duct connector

Cost of Air Duct Ventilation System

The cost of air duct ventilation system differs depending on various factors.

These factors include:

1. Type of Air Duct Ventilation System

There are different types of ventilation systems, each with different functions and price.

The various types include portable air duct ventilation system and air central air duct ventilation system.

Before settling on the cost of a particular air duct ventilation system check on the type that will fit your requirements.

2. Size of Your Air Duct Ventilation System

You will have to purchase an air duct ventilation system that fits your requirements.

However, the bigger the size of your air duct ventilation system, the higher it will cost you.

However, this should not hinder you from purchasing the right air duct ventilation system for your room.

3. SEER (Seasonal Energy Efficiency Ratio) Ratings

SEER ratings refer to the efficiency of a particular air duct ventilation system.

If a given air duct ventilation system has a high SEER ratio, then it will have a higher cost.

The advantage of an air duct ventilation system having a higher SEER ratio is it helps in conserving energy.

You will, therefore, have lower energy bills when selecting such a ventilation system.

4. Ductwork

Another element that will affect the cost of your air duct ventilation system is the ductwork involved.

If you are considering purchasing an air duct ventilation system for the first time, then you will have to pay a higher amount.

5. Installation Contractor

You will have to source the services of an expert to install an air duct ventilation system in your room properly.

This has the effect of increasing the cost of your air ventilation duct system.

However, if the ductwork is already there, then the installation process is minimal, which means you will pay a lower price.

Causes of Airflow Problems in Ventilation Duct Systems

Airflow problems can affect the ventilation of your room.

Symptoms of airflow problems include experiencing cold and hot spots in your room, pressure imbalance or inadequate air circulation.

You, therefore, have to fix the problems causing airflow in your ventilation duct system.

These problems include:

 Air flow in ventilation duct system – Photo courtesy: Joneakes

· Obstructed Condenser Unit

A condenser unit serves as an air exchange point.

If air from the outside does not flow into this unit, your ventilation duct will experience airflow issues.

The effect is that your ventilation duct system will heat up.

You can solve this problem by clearing any item blocking the condenser unit.

· Clogged Filters

If you notice your filters are clogged, then you need to replace them.

The function of filters is to remove dust and other particles from the air as it flows to the ventilation duct.

If they are clogged, air won’t flow in the ventilation duct, causing airflow problems which result in hot and cold spots in your room.

· Sluggish Fan

The function of a fan in your ventilation duct is to force air from the ducts to your room.

As an exception, a fan will always blow blowing at a given rate for efficient circulation of air.

In certain scenarios, the coating of the fan with dust or oil may occur, which slows the movement.

In such cases, you can easily clean the fan for it to circulate air in your room effectively.

If the dirt does not come off the fan, consider replacing the entire fan.

· Dirty Condenser Coils

Condenser coils play a critical role in releasing heat that flowing from your room.

When the condenser coils are dirty, it means there will be no release of heat from the ventilation duct.

This affects the flow of air in your ventilation duct.

For proper airflow, you have to clean the condensation coils.

· Poor Ductwork Design

Improper ductwork design can cause airflow problems.

For instance, if you don’t fasten your ductwork properly or having too many bends in your ductwork.

Design your ductwork as per your manufacturer’s instructions to avoid this problem.

· Leaking Ductwork

Leaking ductwork means your ventilation air duct system will have to work harder to ensure smooth airflow.

By doing this, your ventilation duct quickly wears out.

If you notice any leakages in your ventilation duct, you need to seal it for effective airflow.

Signs of Poorly Installed Ventilation Ducts

Noticing any of the following signs indicate that there is the poor installation of your ventilation ducts.

Non insulated flexible duct

1) Leakages in Air Ducts

If you observe any leaks in your ventilation duct system, then it is an indication that there was poor installation.

Leaks cause your air duct ventilation system to work extra hard consuming a lot of energy in the process.

The following signs indicate there is a leakage in your ventilation air duct.

Signs such as high energy bills, stuff, and uncomfortable room, difficulty to cool or heat your room indicate there are leaks in your duct.

2) Ducts Lacking Support

For proper installation, you need to fix a ventilation duct on the wall firmly.

Sagging ducts indicates poor fixation of the ventilation duct system.

Lack of support on the ducts affects airflow as well as wearing out faster.

As a recommendation, effective installation should have support at an interval of four feet.

3) Non-insulated Ducts

A properly installed ventilation duct needs to be insulated.

Insulation helps in minimizing external heating and cooling of air.

Failure to insulate the ducts cause the inconsistent temperature in your room.

Confirm insulation of all ducts for the proper functioning of your ventilation duct.

4) Nonexistent or Tiny Air Returns

Air returns are important for air to flow properly in your room.

Having tiny air returns or lack of it means air does not flow effectively in the room.

The result is your ventilation air ducts will work hard to circulate air in your room, which means they wear out quickly.

5) Inconsistent Room Temperature

If your room is experiencing inconsistent temperatures, it is a sign of poor installation of your ventilation duct.

Inconsistency may be due to having incorrect airflow ducts, which affect the inflow and outflow of air.

Ventilation Duct Testing Process

Ventilation duct testing process refers to a system of checking and verifying the working of a ventilation duct system for its proper functioning.

The testing determines if the air flow in a given room is correct, the total air supply and the static pressure.

It also determines the tightness of the air handler, the plenum and the ducts.

Through testing, we can determine if the ventilation duct works properly and measuring the leakages.

The results of the tests need to identify the following: Adjust system of the fans and other parts to offer design quantities.

The controls for setting and operating of automatic controls.

Also, there is a need for reporting on noise and vibration, which will look at how to minimize the noise for efficient airflow.

Lastly, electrical measurement determines the accurate voltage and watts to use on the ventilation duct system.

Light proof ducting

Depending on the type of ventilation duct system, it should conform to the UL, RHoS, CE, ASTM and ISO standards.

Here are more resources to learn from:

• Duct Leakage Testing
• HVAC Indoor Air Quality Design
• Ventilation Investigation

Working Principle of Ventilation Duct System

The basic working principle of a ventilation duct system involves pumping fresh air inside the room while removing stuff air from the room.

However, it involves a bit more than this.

Air from the outside is drawn into the ventilation duct system using a fan located on the outside part of the system.

As it flows through the system, it passes through the air filters where removal of dust and unwanted particles takes place.

Due to its air filtration function, air filters get clogged after a while, which affects the quality of air in the room.

It is vital to clean them often to facilitate the filtration process.

From there, air flows into the main duct and in the vents.

Two factors are of considerations when ensuring a smooth flow of air.

Semi rigid aluminum duct

Fist, there is a need to check that there are no leaks in your ventilation duct system.

Leakages cause uneven distribution of air in the room as well as the production of noise in the system.

The second factor is the need to have sufficient turning vanes in your ventilation duct system.

Turning Vanes help in directing the flow of air, especially where there are bends.

To minimize chances of external heating of air, make sure your entire ventilation duct system is insulated.

It is from the branch ducts that air flows into your rooms using the supply vents, at the same time, warm and stuffy air from the room flows into the ducts via the return vents.

This air from the room passes through the condenser unit where it is cooled.

The condenser coils are the ones responsible for cooling the air.

The heat derived from the air extrudes outside of the environment.

There are certain types of ventilation duct system that lets you control the temperature of the air flowing into your room.

Such ventilation duct systems have a thermostat for that function.

Ventilation Duct Specification (Considerations when Buying Ventilation Duct Systems)

Among the several specifications you have to consider before purchasing a given ventilation duct include the following:

PVC flexible ducting

I. Ventilation Duct Design

The design of your ventilation duct needs to fit the design of your room(s).

That is, the electrical components and the outlet and inlet parts should be compatible with your space.

II. Dimensions of the Ventilation Duct System

The dimensions of your ventilation duct will determine the space that you will leave on your room for its installation.

Check with a particular ventilation duct system to ensure it has the correct dimension before selecting it.

III. Ventilation Duct Function

Different types of ventilation ducts function in different locations.

If you are to select a given ventilation duct, it needs to offer you the ventilation needs that you require for your location.

IV. Ventilation Duct Noise Reduction Capability

A high-quality ventilation duct needs to be noise free while operating.

Turning vanes help in reducing the noise produced by air flow.

Therefore, you need to be sure the ventilation duct you are purchasing has enough turning vanes, which will give you a noise free airflow.

V. Ventilation Fire Protection

A proper ventilation duct needs to have mechanisms that will protect itself from the incident of a fire breakout.

An insulated ventilation duct with fire dampers makes the best selection since they will reduce the risk of fire spread.

VI. Quality Standards for Ventilation Duct Systems

You need to be certain that a given ventilation duct has passed the set certifications.

Your duct ventilation systems must come with necessary certifications.

This ensures that a particular ventilation duct won’t cause harm to those who are utilizing it.

VII. Material for Ventilation Duct

Quality materials are vital in the proper working of your ventilation duct.

Your manufacturer needs to ascertain that the materials of a given ventilation duct adhere to the set standards.

VIII. Ventilation Duct Efficiency

You need to consider how efficient a particular ventilation duct will be at ventilating your room before selecting it.

An efficient ventilation duct is one that can conveniently ventilate your room, giving you the comfort, you desire.

Conclusion

That is all you need to know.

You are now in a better position to purchase a ventilation duct system that fits your requirements.

If you still have any question, get in touch with us today and we will be glad to assist you.