air handling unit working principle (AUTOMATION,PLC,HMI,SCADA,GMAIL)

How Air Handling Units work, AHU working rule , HVAC ventilation

schematic diagram of hvac system

Hey guys, Today we're getting to be discussing air handling units. We'll be watching some typical examples to know how they work and where to seek out them.

what's the difference between an FAHU and an AHU? Let me know your answers within the comment section below. If you do not know, then provides it your best shot. No cheating, just test yourself and I'll offer you the solution at the top .

So where can we find air handling units? Air handling units, which usually have the acronym of AHU, are found in medium to large commercial and industrial buildings. they're usually located within the basement, on the roof or on the floors of the building. and lots of large buildings will likely have a mix of all of those . AHUs will serve a specified area or zone within a building like the E side or office areas from floors one to 10, or perhaps one purpose like just the building's toilets, therefore it's extremely common to seek out multiple AHUs around a building. Some buildings, particularly old high-rise buildings, will have only one large AHU which is typically located on the roof. These will supply the whole building.

they could not have a return duct. Some older designs believe the air just simply leaking out of the building. But this design isn't so common anymore in new buildings because it's extremely inefficient. Now it's commonest to possess multiple smaller AHUs supplying different zones to offer better control and better quality space conditioning. Buildings are now also far more airtight, so we'd like to possess a return duct to manage the pressure inside the building. So what's the aim of an air handling unit?

Air handling unit’s condition and distribute air within a building. They take fresh ambient air from outside then clean this, heat it or calm , maybe humidify or dehumidify it, then they'll force it through some ductwork around to the designated areas within a building. Most units will have a further duct run to then pull this dirty used air out from the rooms, back to the AHU where a lover will discharge it back to the atmosphere. a number of this return air could be re-circulated back to the fresh air supply to save lots of energy. We'll have a glance at that later, otherwise, where that may not possible, thermal energy are often extracted and fed into the fresh air supply in fancy also save energy. Again, we'll check out that in far more detail later.

Let's have a glance at an easy , typical AHU design, then we'll check out some more advanced ones. during this very basic model we've two AHU housings for flow and return air. At the very front on the inlet and therefore the outlet of every housing we've a grill to stop objects and wild life from getting into the mechanical components inside the AHU. Here's a photograph of an AHU in take that would've sucked during a whole bunch of trash if the grill wasn't there, so that's why it is vital to possess this installed. At the inlet of a fresh air housing, and therefore the discharge of the return air housing, we've some dampers.

The dampers are multiple sheets of metal which may rotate. they will on the brink of prevent air from entering or exiting the AHU. they will open fully to completely allow air in or out. and that they also can vary their position somewhere in between to limit the quantity of air which may enter or exit. I'll also show you some examples here of world dampers in AHUs. The one on the left has the motorized controller visible which changes an edge of the dampers. After the dampers, we'll have some filters. These are there to undertake and catch all the dirt and therefore the dust et cetera from entering the AHU, and also the building.

If we do not have these filters, the dust goes to create up inside the ductwork and within the mechanical equipment. it is also getting to enter the building and be breathed in by the occupants, also as make the building dirty. So we would like to get rid of the maximum amount of this as possible. Across each of the filter banks, we'll have a pressure sensor. this may measure how dirty the filters are and warn the engineers when it is time to exchange the filters. because the filters devour dirt, the quantity of air which will flow through them is restricted, and this causes a pressure drop. Typically, we'll have some panel filters, or pre-filters to catch largest dust particles. Then we'll have some bag filters to catch the smaller dust particles.

subsequent thing we'll find are the cooling and heating coils. These are there to chill or heat the air. The air temperature of the availability air is measured because it leaves the AHU. This must be at a designed temperature to stay the people inside the building comfortable. This designed temperature is named the point . If the air temperature is below this value, the heating coil will add heat to extend the air temperature and convey it up to line point. If the air is just too hot, then the cooling coil will remove heat to lower the air temperature and also reach the point . The coils are heat exchangers. Inside the coil may be a hot or cold fluid, usually something sort of a heated or chilled water, refrigerant or perhaps steam.

Next we'll have a lover . this is often getting to pull air in from outside then through the dampers, the filters, the coils, then push this out through the ductwork and round the building. Centrifugal fans are quite common in old and existing AHUs, but EC fans are now being installed and also retrofitted for increased energy efficiency. Across the fan, we'll even have a pressure sensor. this may sense if the fan is running. If it's running, then it'll create a pressure difference, and that we can use this to detect a failure within the equipment and warn the engineers of a drag . We'll also likely have a duct pressure sensor shortly after the fan. this may read the static pressure and in some AHUs, the speed of the fan is controlled as a results of the pressure within the duct.

this may also fairly often find a variable speed drive connected to the fan for variable volume systems. We've covered VAV systems separately. Then we've the duct work which sends the air round the building to the designated areas. We'll even have some duct work returning , which is bringing all the used air from the building back to a separate a part of the AHU. This return AHU is typically located near the availability , but it doesn't need to be. It are often located elsewhere within the building.

The return AHU in its simplest form has just a lover and a damper inside. The fan is pulling air in from round the building, then pushing it all the answer of the building into the atmosphere. The damper is found at the exit of the AHU housing and can close when the AHU turns off. That's a really simple and typical AHU, so what else might we find? If you're during a cold a part of the planet where air temperatures reach melting point or on the brink of it, then we'll find a pre-heater within the inlet of the fresh air intake. this is often usually an electrical heater.

When the surface air gets around six degrees Celsius, or 42.8 degrees Fahrenheit, the heater will activate and warmth up the air to guard the components inside from frost. Otherwise this might freeze the heating and cooling coils inside and burst them.

What about humidity control? Some buildings got to control the humidity of the air they provide into the building. We'll find a humidity sensor at the outlet of the availability AHU to live the moisture within the air supply. this may even have a group point for a way much moisture should be within the air intentionally . If the air's moisture content is below this value, then we'd like to introduce moisture into the air employing a humidifier. this is often usually one among the last things within the AHU. This device will usually either add steam or a sprig of water mist into the air. Many standard office-type buildings in northern Europe and Northern America have turned off their humidity units or uninstall them to save lots of energy.

Although they're still crucial for places like document stores and computer rooms. If the air is just too humid, then this will be reduced through the cooling coil. because the air hits the cooling coil, the cold surface will cause the moisture within the air to condense and flow off . you will find a drain pan under the cooling coil to catch the water and drain this away. The cooling coil are often wont to further reduce the moisture content by removing more heat, but in fact this may decrease the air temperature below the availability point . If this happens , then the heating coil are often turned on to bring the temperature copy .

this may work, although it's very energy intensive. Energy recovery. If the availability and extract AHUs are located in several areas, then a standard thanks to recover a number of the thermal energy is to use a frolic coil. This uses a coil in both AHUs, and a pump circulates water between the 2 . this may devour waste heat from the extract AHU and add this to the availability AHU. this may reduce the heating demand on the heating coil when the surface air temperature is below the availability point temperature and therefore the return air temperature is above the point . the warmth would rather be wasted because it is just rejected to atmosphere. because the pump will consume electricity, it's only cost effective to show on if the energy saved is quite the pump will consume.

Another quite common version we'll encounter is to possess a duct sit between the exhaust and therefore the fresh air intake. this enables a number of the exhaust air to be re-circulated back to the fresh air intake to offset the heating and cooling demand. a further damper sits within the connecting duct to regulate what proportion air are often re-circulated. this is often safe and healthy to try to to so, but you'll got to make sure that the exhaust air features a low CO2 count, so we'd like some CO2 sensors to watch that. If the CO2 level is just too high, then the air cannot be reused. the blending damper will close and every one the return air are going to be rejected from the building.

When in recirculation mode, the most inlet and outlet dampers won't fully draw in this setup because we'll still need a minimum amount of fresh air to enter the building. we will use this within the winter if the return air is warmer than the surface air. and that we also can use this within the summer if the return air is cooler than the surface air, respective to the availability point temperature. We'll also need some temperature sensors at the intake return and just after the blending region. Some buildings require 100% fresh air, so this strategy cannot be used everywhere.

The local laws and regulations will dictate this. Another variation we'd encounter is that the heat wheel. this is often quite common in newer compact AHUs. This uses an outsized rotating wheel. half it sits within the exhaust air stream, and half it sits within the fresh air intake. The wheel will rotate, driven by alittle induction motor. because it rotates, it picks up unwanted heat from the exhaust stream and absorbs this into the wheel's material. The wheel then rotates into the fresh air intake stream. This air is at a lower temperature than the exhaust stream, therefore the heat will transfer from the wheel and into the fresh air stream which obviously heats the incoming air stream up, and thus reduces the demand on the heating coil.

this is often very effective, but some air will leak from the exhaust into the fresh air stream, so this can't be utilized in all buildings.

Another version we'd encounter is that the air plate device . This uses thin sheets of metal to separate the 2 streams of air in order that they are doing not inherit direct contact or mix in the least . The temperature difference between the 2 air streams will cause the warmth to transfer over from the recent exhaust stream, through the metal walls of the warmth exchanger, and into the cold intake stream. the 2 air streams got to crossover for this to occur. So it are often a touch confusing to seem at. Just remember the airstreams aren't mixing.

what's the difference between an AHU and an FAHU is just that FAHU stands for Fresh Air Handling Unit, meaning it's an Air Handling Unit or an AHU, except it can only handle 100% fresh outside air. It doesn't re-circulate any return air back to the availability stream. An AHU on the opposite hand, can re-circulate a number of its return air into the availability stream. The building application and native regulations will dictate when and if this strategy are often utilized in a building.

Okay guys, that's it , many thanks considerably . I hope you've enjoyed this and it's helped you. If so, please do not forget to love , subscribe and share. And also, leave your questions within the comment section below.