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In this part of full HVAC Course we are going to learn about Dampers and Different types of dampers used in HVAC.
Dampers
The best way I can think of to explain dampers is that they are basically a switch that is either on or off. When it's on, it allows air (airflow) in and out of the system. When it's off, it prevents airflow in and out of the fan coil unit. Dampers are most commonly seen in ducted systems, and should never be turned off completely, just lowered slightly so that the coils don't overheat.
Dampers in HVAC systems are used in commercial buildings and residences to control airflow and reduce humidity levels. Most residential dampers use a bi-metal mechanism that uses two materials that expand and contract at different rates -- one material expands much faster than the second material. When closed, pressure builds inside the housing to force the door open. When opened, the air pressure drops and causes the door to close.
Dampers are devices that allow air flow in order to remove moisture from the air. A damper is a device that controls the speed at which airflow enters and exits a room. When a door is open, air flows out of the room. When the door is closed, the amount of air flowing out is reduced. In this way, dampers prevent water droplets from entering a room because they slow down the air’s velocity. Airflow rates of 1-10 cubic feet per minute (CFM) are typical for home use.
How Dampers Work?
In order to function properly, dampers require water to flow through them. Dampers operate by opening or closing a vent depending on the size of the opening relative to the pressure difference between the supply side and return side of the damper. A typical damper will have a spring loaded pin that opens or closes the vent. As the pin moves back and forth, it alternately blocks and unblocks the vent. By adjusting the amount of spring tension, the size of the vent may be increased or decreased. In addition, the length of the pin may be adjusted to change how much the vent is blocked.
Dampers in HVAC systems can cause serious damage if not fixed correctly. When these dampers fail they allow air to enter your home and when the system fails to cycle properly, it creates a huge problem for homeowners. There are many reasons a damper might fail to work properly including issues with motor, seal, linkage, and even worn-out springs. If you notice any of these symptoms you should have your heating and cooling system checked right away.
Symptoms:
• Excessive condensation inside the ductwork
• A bad smell in the area where the HVAC system is located
• Dirty filters
• Mold or mildew growing in the ductwork
• Air leaking out of the vents
• Damaged coils
• Hot pipes
• Noisy fans
If you notice any of these problems get them repaired immediately! Your comfort levels could suffer because of a failed damper.
The Vent
A damper's vent should be designed to allow air to pass while preventing contaminants from entering the duct system. To accomplish this, vents are sized according to the desired airflow rate and they are installed at the end of the duct where it connects to a room, if applicable. Vents are sized based upon several factors including the air distribution requirements of the space, the volume of air being moved through the ducting system, the location of the vent (e.g., near the ceiling), and the cost of installation.
Damper Types
Types of dampers in HVAC systems vary widely depending on the application, but they're not always made equal. In fact, some are better than others for specific applications.
There are three basic types of dampers, each with its own advantages and disadvantages.
Air Restriction Damper
An air restriction damper restricts the flow of air through the duct without substantially reducing the total volume of air passing through the duct. Because air restriction dampers do not restrict the total airflow through the duct, they are generally recommended for heating, ventilation and air conditioning (HVAC) systems that receive outside air. Air restriction dampers are commonly used in residential applications because they provide the best balance between efficiency and comfort.
Bi-Metal Damper
A bi-metal damper contains two parts that move together as one unit. One part is generally fixed to the inside wall of the duct and the other part is connected to the spring-loaded door. A bi-metal damper operates as follows: as the door moves toward the closed position, the two parts slide away from each other, increasing the air gap between the two sides of the damper. At the same time, the spring on the door adds a restoring force pushing the door back to its original position. This combination of forces helps prevent the door from slamming shut, since the restoring force holds the door open even after the force of the air pressure decreases.
Hybrid or Hybrid Plus Damper
A hybrid damper combines two features of both air restriction dampers and bi-metal dampers. This gives manufacturers greater flexibility in optimizing the performance characteristics of their damper designs. For example, a hybrid damper might incorporate a bi-metal door with a spring-loaded pin similar to those found in air restriction dampers. Or, the damper could feature a door that slides along a track and is held in place by a torsion spring.
Here are all other damper types.
VAV Dampers
Vav Dampers (Variable Air Volume) regulate airflow through an HVAC system by varying the amount of airflow at any given time. There is no standard set amount of airflow they deliver, but rather they fluctuate based on the level of airflow requested. A typical vav device consists of two components; a motorized damper and an electronic controller. Most vav devices have both components necessary for operation.
The first component, a damper, is simply a way to move air inside the building or space. A damper works as a valve, opening only when the airflow request rises above some threshold. They are normally installed across the return air ductwork, where the air flows from the conditioned space back to the outside. The second component of a vav device is the electronic controller. These controllers work together with the damper to control the amount of airflow delivered to each room. When the controller receives a signal that the airflow demand exceeds the amount being provided, it sends a command to the damper to open slightly. This opens a small gap between the damper blades that allow a portion of the returning air to bypass the damper. As the gap increases, more air will bypass the damper until it reaches its fully open position.
There are five major categories of damping devices used in building heating ventilation and air conditioning (HVAC) systems. These include mechanical dampers, magnetic fluid-filled dampers, thermo-pneumatic dampers, pneumatic dampers, and active dampers. Each category offers different advantages and disadvantages, and each type is appropriate for a certain application.
Mechanical Dampers
Mechanical dampers are passive devices that rely on springs to move valves and allow airflow. Mechanical dampers tend to be inexpensive, reliable, and offer many design options. However, their performance characteristics can be unpredictable. Their movement tends to be slow and stiff, and they have limited flow capacity.
Magnetic Fluid-Filled Dampers
Magnetic fluid-filled dampers use magnetorheological (MR) fluids to reduce unwanted vibrations. MR fluids consist of small particles suspended in a liquid carrier. When exposed to a strong magnetic field, the particles align themselves along the direction of the magnetic force. As a result, the viscosity of the fluid increases dramatically. This increased viscosity reduces the amplitude of vibrations and forces the vibration to dissipate. Magnetic fluid-filled dampers are commonly designed as bypass dampers, variable dampers, or surge dampers.
Thermo-pneumatic Dampers
Thermoplastic polyurethane (TPU) dampers are another type of thermo-based damper. Like magnetic fluid-filled dampeners, TPU dampers use magneto-active materials that change their viscosity to control airflow. Unlike magnetic fluid-filled dampers, however, TPU dampers work based on temperature rather than magnetic fields. To activate the damper, two temperatures are set. If the difference between these two temperatures exceeds a predetermined amount, the damper opens. TPU dampers may be installed for both residential and commercial purposes.
Pneumatic Dampers
Pneumatic dampers operate using compressed gas instead of magnetorheological fluids. Pneumatic dampers are also known as compressible pressure dampers. Similar to TPU dampers, a valve mechanism controls airflow. But unlike TPU dampers, pneumatic dampers do not provide any visual indication of the operation.
Active Damping Devices
Actively controlled dampers incorporate electronics or software to automatically open and close valves. Active dampers require less maintenance and provide more precise control over airflow. Because they are electronically controlled, active dampers can perform in extreme environments, making them ideal for use in industrial settings.
Vent Hood Dampers
Vent hood dampers are commonly added to HVAC system ductwork in order to ensure proper ventilation of a room while preventing over-heating. Vent hood dampers work by allowing warm air to escape out of the ductwork and letting cold air enter the space in order to keep the air flowing efficiently. Vent hood dampers are controlled manually using a handle attached to them, just like regular room fans. By turning the handle, the user can open or close the door. Most vent hood dampers have a thermostat built right onto them, which makes controlling the airflow easier.
Damper Controls
In addition to vent hood dampers, there are also damper controls. Damper controls are similar to vent hood dampers except they are used mainly in conjunction with heating and cooling systems. Damper controls allow users to adjust the amount of air being pumped through the HVAC system. These types of dampers are often used in HVAC systems that run continuously, regardless of whether the room is occupied or not. There are also automatic damper controls, which are computerized versions of traditional damper controls. Automatic damper controls allow users to set the minimum and maximum temperatures and automatically adjust the airflow to maintain those settings.
Fan Dampers
Another kind of damper is a fan damper. Fan dampers are simply vents that are covered by a rotating cylinder. Fans are mounted inside the cylinder, and the cylinder rotates around the fans to create a breeze. Fan dampers rotate at a speed that is determined by the desired wind velocity. When the fan damper is turned on, the cylinders cover the vent openings and prevent hot air from escaping into the room. When the fan dampers are turned off, the cylinders turn back and let the air flow freely. Fan dampers are ideal for rooms with high ceilings since they do not block airflow, but require a good deal of power to operate.
Heat/cooling Dampers
A heating damper (or air handler) is designed to move hot air out of a space while keeping cool air flowing in. A cooling damper works just the opposite way. All heat exchangers should have both a heating and cooling damper. The amount of time each side is open determines how much heat or cold the room receives. If only one door is open, you’ll receive more heat than if they are both open at the same time. When opening the doors, make sure to close them completely before turning off the unit.
Air Dampers
Air dampers control the volume of air entering a space. These devices work in conjunction with fans and filters. You may find one in every bathroom, bedroom, or kitchen. When using an air damper, keep the fan running slowly and steadily. The slower the speed of the fan, the less likely the airflow will affect the temperature.
Ventilation Dampers
Ventilation dampers restrict access to vents to prevent excessive airflow and ensure adequate ventilation. They are often installed on the outside wall near vent stacks and on interior ceilings.
Vibration Dampers
Vibration dampers protect windows and furnishings from vibrations caused by high-pitched noises such as refrigerators and dishwashers.
Dampers are a type of air control device used in HVAC systems. They help regulate temperature, humidity and airflow throughout a room or building. Dampers are either active or passive. Active dampers use electricity to directly influence air flow whereas passive ones do not require any power at all. Passive dampers are only activated once they reach set temperatures while active dampers are always running.
There are many different types of dampers including coil, vane, blade, butterfly, and rotary valves. Each type is suited for a specific purpose depending on its size, shape, speed of operation, and cost. The general function of each damper is listed below:
Coil dampers - Coil dampers use a metal bar called a coil. As the temperature rises, the coil expands causing the damper to open wider. When the temperature drops, the coil contracts causing the damper to close tighter. These dampers are cheap and simple but produce less precise results than others.
Blade dampers - Blade dampers are similar to coil dampers except that blades are placed inside coils instead of outside. Blade dampers have a number of advantages over coil dampers. First, they have a higher efficiency rating due to the fact that they operate off the pressure differential rather than the absolute temperature. That means that if the difference between the cold side and hot side is great enough, the blades will open. Second, blade dampers provide a more even distribution of heat across the room. If two rooms have identical settings, a blade damper will create a more uniform temperature in both rooms since the blade dampers work off the same pressure differential. Third, blade dampers are safer because the blades cannot turn loose unless the coils catch fire. Fourth, blade dampers are more durable than coil dampers since the blades are much lighter. Fifth, blade dampers are cheaper to make than coil dampers. Sixth, blade dampers are quieter than coil dampers. Lastly, blade dampers are easier to clean or repair.
Vane dampers - Vane dampers contain no moving parts, making them the least expensive option. A small electric motor causes the vanes to rotate. They are most commonly used to ventilate crawl spaces, basements, garages, attics, sheds, and unheated portions of homes. One major drawback associated with vane dampers is that they often cause drafts. Drafts occur whenever warm air enters a place where cool air is trying to exit. To combat drafts caused by vane dampers, draught excluder mats can be installed beneath them. Draught excluder mats prevent air from entering a crawl space through the floorboards.
Butterfly dampers - Butterfly dampers are simply a series of hinges. The dampers hinge around a shaft that runs along the ceiling or wall. They open when the temperature is low and close when the temperature is high. These dampers are most commonly used to control airflow in bathrooms, kitchens, laundry rooms, and offices. Like vane dampers, butterfly dampers can cause draft issues.
Rotary dampers - Rotary dampers consist of a rotor that spins around its central axis and creates friction when it comes into contact with the inner surface of the chamber. The amount of friction created determines the degree of opening or closing the damper. Rotary dampers are the most durable type of damper. They are popularly used for commercial buildings, hospitals, laboratories, retail stores, and residential houses. Because the dampers run using mechanical force, they are extremely reliable and can last long without maintenance. However, they are also quite expensive compared to other dampers.
Dampers are devices that control airflow over heating/cooling coils (heat exchangers). Dampers may consist of mechanical mechanisms or fluid-based systems. Mechanical dampers are often spring-loaded. Fluid-based dampers use air pressure differences between rooms to open and close vents. A damper is either opened or closed to direct airflow over the coil.
Airflow is dependent on the type of coil being installed and its desired capacity. The amount of airflow is determined by the airflow through a single vent and how many times it opens. Airflow rates vary depending on the size of the vent opening; the greater the number of openings, the lower the rate. To maintain similar airflows, the same-sized vents should have similar numbers of openings.
Mechanical dampers: Mechanical dampers are typically controlled via motorized controls. These dampers are designed to provide low airflow in situations where maximum cooling capacity is not needed. Typical applications for these dampers include server cabinets and data centers.
Fluid-Based Dampers: Fluid-based dampers are typically controlled using variable frequency drives. These dampers are ideal for controlling the airflow over larger heating/cooling units.
In all cases, both mechanical and fluid-based dampers are designed to reduce the peak temperature of an area. As peak temperatures are reduced, total annual heat gain in any given room decreases. In all cases, the unit's rated capacity remains unchanged.
Dampers
Dampers are devices that control the amount of airflow passing through ductwork. A damper consists of two parts – a frame and a flap. The frame holds the flap in place, while the flap opens and closes based on air flow. There are three different designs of dampers: disc-style, butterfly-style, and vane-style.
Disc-Style Damper
A disc-style damper is the most commonly used. These types of dampers consist of two discs that open and close based on the direction of airflow. Disc-style dampers work by having two discs connected together that open and close in opposition to each other. When the air flows towards the center of the damper, the larger disc moves away from the smaller disc. Conversely, when the airflow is flowing away from the center of the damper, the smaller disc moves closer to the larger disc. By moving the discs apart and together, the opening and closing of the damper can be controlled.
Butterfly-Style Damper
Butterfly-style dampers have similar specifications to disc-style dampers, except they have one large disc (the butterfly) and one small disc (the bee). Like disc-style dampers, they operate by using opposing discs to control airflow. However, the discs are joined together at their edges. The combination of these two discs creates a chamber that narrows down from the top to the bottom. When the air travels upwards, the upper half of the chamber stays put, while the lower half of the chamber moves downward. As the airflow proceeds downwards, the butterfly disc slides outwards and the bee disc slides inwards, narrowing the chamber further and further until the airflow is stopped entirely. Butterfly-style dampers are ideal for applications where airflow is constant and uniform, like heating and cooling systems.
Vane-Style Damper
Like disc-style dampers and butterfly-style dampers, vane-style dampers have two discs that move apart and together in response to airflow. Unlike disc-style or butterfly-style dampers though, the discs do not have any fixed dimensions. Instead, they change shape depending on the direction of airflow. Vane-style dampers are best suited for applications where airflow varies greatly, such as variable speed fans and supply/return vents.
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