Opposed blade dampers in a mixing plenum, complete with mixing baffles. In building services engineering and HVAC, an air-mixing plenum (or mixing box) is used for mixing air from different ductwork systems. The most common application for an air-mixing plenum is the mixing of return air (or extract air) with fresh air to provide a supply air mixture for onward distribution to the building or area which the ventilation system is serving.[1] The air transferred from the return air stream to the supply air stream is termed recirculated air. All air not mixed is rejected to the atmosphere as exhaust air. Air streams are mixed to save energy and improve energy efficiency. The mixing plenum normally combines two air streams, and includes for three sets of dampers: one for the fresh air, one for the exhaust air, and a mixing damper between the two air streams.[2] The mix of fresh air and recirculated air can thus be adjusted to suit the needs of the building's occupants. Most systems will use motorized dampers to control the air mixing, and controlled by the building management system (BMS), or controls system.

Typically as the fresh air and exhaust air dampers are driven from 0% open to 100% open, the mixing damper will in turn be driven from 100% open to 0% open, so as to always ensure a constant volume of supply and extract air. An air handling unit used for the heating and cooling of air Air supply to a building is generally performed by an air handling unit. The process may include for filtering, heating, cooling, humidification, or dehumidification, all of which processes consume energy. Since the fresh air demand for the building occupants may be less than that is required for air conditioning purposes, it would be wasteful if 100% fresh air were used, with wholesome treated air rejected to the atmosphere in its place. Therefore, mixing is used to balance the needs between the occupants requirements for fresh air and the air conditioning process for the building. Enhanced controls systems may monitor the return air quality or carbon dioxide concentration[3] in order to automatically modulate the air mix for optimum energy efficiency whilst maintaining desired fresh air requirements.

Such systems work very well in buildings where the occupancy rate can vary greatly throughout the day, or seasonally. Additionally, when outside air conditions are such, typically mid-season weather conditions, it may be that ambient temperatures are suitable for free cooling purposes. In such conditions the mixing damper will be set to close and the system use full fresh air for optimum energy efficiency. Where fresh air is not required, such as early morning pre-heat or pre-conditioning periods, the mixing damper can be automatically set to full recirculation, again for optimum energy efficiency.The patented KEES Air Mixer is utilized in air handling units and duct work to mix or blend outside and return air streams to a uniform temperature and velocity distribution. The Air Mixer thereby prevents temperature stratification, eliminates coil freeze-ups, and provides a uniform plenum velocity for equalized filter loading and optimal coil performance. The Air Mixer is a static device, which means there are no moving parts, no adjustments to make, and maintenance required.

Plenum Mixers are a complete plenum section with the KEES patented Air Mixer sized for bolting directly to mating duct work or air handling sections. Mixer Boxes are an air inlet plenum with inlet collars and low leakage control dampers integral with an Air Mixer section with outlet to mate directly to air handling unit section or ductwork.Nike Duvet Covers MX & MXP MixersAir Duct Cleaning Blog VIEW / WORD / PDFCat In The Hat Car Seat Covers PMP Mixer in a Plenum Air mixers are available in square sizes from 12" x 12' to 144" x 144" as well as in rectangular sizes within the same range provided one side is not more than two times longer than the other side. Plenum Mixers and Mixer Boxes are available to mate with any size air handler or duct.

PLENUM MIXER AND MIXER BOX OPTIONS Solid double wall construction Perforated double wall construction Contact the factory for blow through fan arrangements, filter or economizer sections, or other custom configurations or applications.The requested URL /HVAC_Ind.php?hi=HVAC was not found on this server.The definition of air handling unit from ANSI/AHRI Standard 430-2009 states that it is "A factory-made encased assembly consisting of a fan or fans and other necessary equipment to perform one or more of the functions of circulating, cleaning, heating, cooling, humidifying, dehumidifying and mixing of air...."The AHU is used to control the following parameters of the space. There are basically two types of air handling unit that are in used and they are the "Draw-Through" or "Blow-Through". In the Draw-Through type, the fan pulls the air through the mixing box, filters and cooling coil before discharging it from the fan outlet to the space to be conditioned or to the ducting network.

The design can be vertical or horizontal. In this case, the section before the fan has negative pressure.In the Blow-Through type, the fan blows the air through the mixing box, filters and cooling coil before discharging them to the space being conditioned or the ducting system. In this case, the section after the fan has positive pressure. An air handling unit where (1) is the supply air,  (2) fan section, (3) vibration isolator, (4) cooling coil, (5) filter and (6) mixed air duct. Components of Air Handling UnitHere are some of the air handling unit components that may be contained in the equipment.The housing that contains all the other components of an AHU is usually make of metal, some are painted to prevent corrosion.In sections where the fans and the coil are located, 1-2 inches of polyurethane foam or PU is used to insulate them to prevent the condensation on the panel. Drain pan is also used as a precaution in the event of condensation of water.Centrifugal fan is used to circulate the air to the various parts of the sections in the building.

The typical types of fan available are Backward Inclined, Backward Curved, Forward Curved and Airfoil.The selection of the fan will depend on the air volume and the static pressure required of the system. Usually, the designer of the system will use a specialized software to do this selection. In order to reduce the effect of vibration on the panel, the motor and the fan are usually installed on the vibration isolator except when the drive assembly is external to the fan casing.In recent years, the use of variable air volume (VAV) system is becoming more popular as the volume of the air being discharged can be varied depending on the load condition. If the load is high, the fan speed will be higher and if the load is lower, the speed of the fan will be lower. The speed of the fan is varied by using frequency inverter instead of conventional motor such as PSC motor. Frequency inverter provides better control of the fan speed as a whole range of fan speed from super low to super high can now be utilized based on the load conditions required.

This technology has enabled better use of energy and is in tandem with the move to go for greener energy.Cooling Coil is used to cool and dehumidify the air. Both DX (direct expansion) cooling and CW (chilled water) cooling coils are available for use depending on the system design. These coils are arranged in rows with different fin spacing. Aluminium fins and copper tubes are used in the design of the coils. The corrosion resistance hydrophilic fins are also used due to its lower cost and lower resistance to the air velocity.Filters are to remove particles and contaminants of various sizes from the air. The type of air filter being used will very much depend on the application of the system.Panel Filter is a flat and rectangular in shape and provides a minimum low efficiency filtration which is acceptable to the air conditioning industry. The high velocity filter is arranged vertically whereas the low velocity filter is arranged in V shape. Typical air velocity that moves through the filters is in the range of 2-3 m/s.HEPA Filter is very efficient and is able to achieve efficiencies up to 99.97%, removing minute particles and airborne bacteria from the air.

It is usually used in clean room applications such as semiconductor production floor, operating theaters and critical processes.Electrostatic Filter is used to remove particles from the air by using highly charged electrodes that ionized the air. Bag Filter is able to remove dust particles and is thrown away after use. Roll Filter is used for high velocity filtration where the used part is rolled up automatically/manually.During winter, the humidity level of the air can be low hence causing discomfort to the occupants. The humidity of the air is increased by using the humidifiers. Here are the commonly used humidifiers:Spray Type has a header and spray nozzles that spray water with a pressure of 15 psi or more.Steam Pan Type has a pan and a heating coil to heat up the water of the pan. The evaporation of water caused by the heating will increase the humidity level of the surrounding air.Steam Grid Type has tiny holes on the pipe to distribute the steam that flows through it. In this case, the water that is heated up to produce the steam to be supplied to the grid is conditioned to prevent odor being discharged to the room.