Categories
Uncategorized

air handling unit diagram

File Type: JPG. Air Handling Unit (AHU) is basically used to condition indoor air with their heating, cooling, humidification and de-humidification functions in a HVAC system… Direct type heat exchanger includes burning of gaseous fuel in the air stream for heating or evaporator for cooling purpose. As the supply air temperature is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served. Another very important component in an air handling unit is fan or blower. Carbon monoxide producing devices (such as an automobile, space heater, gas water heater, etc.) An air handling unit consists of few important components. The basic function of the AHU is to take in outside air, re-condition it and supply it as fresh air to a building. The return air is sucked through the filter, the cooling coil and humidifier in the draw through arrangement. A variable air volume (VAV) can vary the air flow at a constant temperature. While, in indirect heat exchangers hot water or steam or chilled water in pipe line can be used. While passing through the filters, humidifier and cooling coil, the air gets conditioned and then it is sent to the required location. Air Handler Components The fan section with access door open. "An air handler, or air handling unit (often abbreviated to AHU), is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. The high velocity filters are arranged vertically whereas the low velocity filters are arranged in V shape. Proper designing and installation of the air distribution system can save money up to 50 – 200$ per year. Those are: Spray type humidifier has a header and spray nozzles that spray water with a pressure of 15 psi or more. These both feed four air-handling units on the roof top. Two types of ducts are used in an AHU. Those are: After transmitting conditioned supply air from the air handling unit to the room, it has to be distributed to the conditioned space. 1. Air conditioning is the process of conditioning of indoor air to maintain its temperature, humidity, velocity and cleanliness inside the room or desired location at a desired level for human comfort or any industrial process. There is one main supply duct that is then divided into various small ducts those lead to all the rooms that are to be maintained at a specific condition. carrier air handler wiring diagram – Carrier Air Conditioning Unit Wiring Diagram Refrence Goodman Air Handler Wiring Diagram originalstylophone. Figure 4 shows a pictorial view of a humidifier. The evaporation of water caused by the heating will increase the humidity level of the surrounding air. Air Handling unit or AHU is an assembly of air conditioning components (such as fans, cooling coils, filters, humidifiers and dampers) integrated into a self-contained package and installed as a single unit, which is connected to system of metal duct work that distributes the conditioned air. Based on the calculated 55.6 BTU/SF heating load and 25.3 BTU/SF cooling load, a primary and back-up boiler and chiller system has been designated. Duct. Wiring Schematic. Gambar 2. In this system, fresh air is only required to supply the air change rate needed for comfort. The multi zone unit supplies air to several zones from a centrally located air-handling unit. The adjustable inner cones or the deflecting vanes are provided to change the air distribution pattern. There is a scope of improving the efficiency upto 80% or more with proper installation of distribution system. 1. Individual zone requirements are met by mixing cold and warm air through dampers in the air handler. Fig 2: A Heating Unit                                      Figure 3: A Cooling unit. These air filters are usually placed at initial stage of an AHU to keep the downstream components clean.Generally, filters are placed in two or more successive stages with a coarse grade filter in front of a fine grade filter. The humidity of the air can be increased or decreased according to the requirement using the humidifiers or de-humidifiers. This type of system has many advantages over constant volume system. The performance of the grilles are specified in terms of core size or core area, volumetric flow rate of air, effective air velocity, total pressure drop, throw and noise levels. Figure 6 shows the front view of a supply air grille with horizontal and vertical vanes that are basically used for deflecting airflow. SHARE ON Twitter Facebook WhatsApp Pinterest. This HVAC plan sample shows the air handler layout on the floor plan. However, this system includes a fan for return air. Though both air handling unit (AHU) and fan coil unit (FCU) serves the same basic function of cooling in a HVAC system, there are few differences between those two units. That makes the manufacturers to think about the necessity of humidifier in air conditioning system. A “Single Duct” AHU variation • The exhaust air damper is not in this air handler; the building air is exhausted elsewhere, but the basic mixed air and other functions are unchanged. Electrostatic Filter is used to remove particles from the air by using highly charged electrodes that ionized the air. This is done by the fan or blower arrangements in an AHU. A wiring diagram is a streamlined traditional pictorial depiction of an electrical circuit. So, for human comfort this temperature must be maintained by an AHU. If heating is required then a heating unit is provided in the terminal unit or a separate system for heating may be introduced. Ltd., Vashi, Navi Mumbai | All rights reserved, Cooling India Monthly Business Magazine on the HVACR Business | Green HVAC industry | Heating, Ventilation, Air conditioning and Refrigeration News Magazine Updates, Articles, Publications on HVACR Business Industry | HVACR Business Magazine, Air Handling & Air Distribution in HVAC System, Hitachi Cooling and Heating launches SET FREE mini, J & E Hall launches a new range of HallScrew compressors with VFD and VVR, Daikin expands its transport refrigeration presence in Northern Europe, Rhoss launches FullFLOW DX range Chillers with low GWP, Carrier Transicold offer new EPA approved refrigerant, in the US, California introduces rules to curb HFC emission. A single-duct system provides ventilation and cooling to the conditioned space. Slot diffusers are made up of plenum box with single or multiple slots and air deflecting vanes. These diffusers are particularly suitable for large open-spaces as long as 30 meters in length that require flexibility to suit changing occupant distribution. Connected to the HVAC’s ductwork, AHUs are installed inside and outside of buildings, with the rooftop being common for the latter. Air Handling Unit (AHU): a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. The draw through arrangement is used more commonly due to its compactness. If you want to share thoughts or feedback then please leave a comment below. A schematic diagram of a typical air handling unit is shown in Fig. These types of diffusers are mounted on either side of walls or in the ceiling. Moreover, efficient distribution system also reduces the equipment size. Therefore, a cooling or heating or arrangement for both purposes is provided with the AHU. The fans that are used in AHU are basically of centrifugal types. Constant-volume units can be used in single-zone or multi zone applications. Those are: Constant-volume systems are operated at a constant airflow rate and only the temperature varies to maintain the zone set point. Air handling units, which usually have the acronym of A.H.U are found in AHU is basically used to condition indoor air with their heating, cooling, humidification and de-humidification functions in a HVAC system. HVAC Plans | RCP - HVAC layout | How to Create a HVAC Plan ... HVAC Plans | RCP - HVAC layout | How to Create a HVAC Plan | Hvac. Air Handling Units. With our complete solution for air handling units, we can ensure cost-effectiveness, efficient installation and high performance. Air Handling Units – Mixed Air. These types of diffusers are normally mounted at the center of the conditioned space and those can provide large entrainment ratio and shorter throw for conditioned spaces with low head space. Collection of goodman air handler wiring diagram. Typical heating and cooling units have been shown in figure 2 and figure 3 respectively. Damper openings are generally controlled manually or by servo motor. So, it is very important to design the air distribution system properly. Bijan Kumar Mandal, Bag Filter is able to remove dust particles and is thrown away after use. These filters are efficient in removing minute particles and airborne bacteria from the air. Tags: Related Posts of "Ahu Panel Wiring Diagram" Home theater Wiring Diagram … This system consumes less power to run the system fans and makes less noise compared to constant volume system. An Air Handling Unit (AHU) is used to re-condition and circulate air as part of a heating, ventilating and air-conditioning system. Click on the image to enlarge, and then save it … In general, two types of arrangement of fan are there in an AHU: draw though arrangement and blow through arrangement. Ahu Panel Wiring Diagram Safety Circuit Examples Of Safety Components Technical Guide. HEPA Filters are very efficient and is able to achieve efficiency up to 99.97%. These are: Grilles are the outlets for supply air or inlets for return air whereas, registers are the grille with a volume control damper. How does a Chiller, Cooling Tower and Air Handling Unit work together to provide air conditioning (HVAC) to a building. Air Handler Components The filter section. This type of system can use single duct or dual duct for the distribution of air. Ventilation system layout | Ventilation unit with heat pump and ... ERD | Entity Relationship Diagrams, ERD Software for Mac and Win, Flowchart | Basic Flowchart Symbols and Meaning, Flowchart | Flowchart Design - Symbols, Shapes, Stencils and Icons, Electrical | Electrical Drawing - Wiring and Circuits Schematics. It is found that sometimes the efficiency of an air distribution system becomes low in the range of 60 – 75% due to the poor design. Central air conditioning, forced air furnaces and heat pumps all use air handlers. Filter is one of the very important components in an air handling unit. Air handler- HVAC plan | Ventilation system layout | Ahu Room Layout, Ventilation system layout | Mechanical Layout Of Ahu In Plans, HVAC equipment - Vector stencils library | Ahu Diagram Symbols, Central Air Conditioning Layout And Duct System In Floor Ahu. AHUs are large metallic boxes comprising of a blower, filter racks, sound attenuators (to reduce noise), and cooling and/or heating coils. © Chary Publications Pvt. A square diffuser is the most commonly used diffuser for supplying air. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Steam Pan Type humidifier has a pan and a heating coil to heat up the water of the pan. This HVAC plan sample shows the air handler layout on the floor plan. In a VAV system one supply duct distributes supply air at a constant temperature. The supply air can be distributed by separate duct to the desired locations depending on the zone requirements. These pipe lines are manufactured from copper and fins are provided which is made from copper or aluminum. Air Handling Unit IPLR Goodman Air Handler Wiring Diagram Delightful Model First thermostat. Posted on April 3, 2019 by admin. The air then flows to the rooms to be air conditioned. The humidity of the air sometimes goes very low causing discomfort to the occupants during the peak season of winter or the vice versa during summer. Figure 5 shows the pictorial view of fan unit used in an air handling unit. By continuing to browse the ConceptDraw site you are agreeing to our. Source: rccarsusa.com. The type of air filter being used is very much dependent on the application of the system. Ceiling diffusers can be round, square or rectangular in shape. 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. This site uses cookies. Another constant-volume system is the multi zone unit. Those are as follows: Casing is the insulated enclose of an AHU which keeps all the system components of an AHU safe inside and prevent the heat gain or loss from it. We use cookies to give you the best possible experience on our website. Air handlers typically connect to a ductwork ventilation system that distributes the conditioned air throughout the building and returns it back to the unit. Grilles have a comparatively lower entrainment ratio, greater drop, longer throw and higher air velocities in the occupied zone compared to slot and ceiling diffusers. Two types of ducts are used in an AHU. Heating and cooling is, generally, done by either direct type heat exchangers or indirect heat exchangers. Special Warning for Installation of Furnace or Air Handling Units in Enclosed Areas such as Garages, Utility Rooms or Parking Areas. Import quality Air Handling Unit Diagram supplied by experienced manufacturers at Global Sources. Warm outdoor and cool indoor air are mixed, cooled by the evaporator, and circulated using ducts. In this video we'll learn how air handling units or AHU's work. Various types of humidifier are commonly used in an AHU. An air handling unit, or AHU, is a piece of HVAC equipment that is designed to regulate and circulate air throughout a space. Variety of carrier air handler wiring diagram. All layouts are based off of the calculations contained in the HVAC Component Sizing page on this site. Steam Grid type humidifier has tiny holes on the pipe to distribute the steam that flows through it. Find Air Handling Unit Diagram manufacturers from China. Ahu Panel Wiring Diagram Air Handling Unit Ahu Controller Technical Bulletin Engineered Air. This page contains the single line diagram and riser diagram for the HVAC system. The perfect temperature for human comfort generally varied between 18°C – 23°C. Thus, dampers are designed to allow synchronous control. In this article we will be covering this topic to understand the basics of HVAC central plant. An clean air conditioning system equipped with new type ahu application of heat pipe in hvac the text above describes image mild steel hvac air handling unit system flow diagram it s for handling humidification indoor as required steady condition facilities with highly quality like food and pharmaceutical . Diagram; Goodman Air Handler Wiring Diagram Sample. Click on the image to enlarge, and then save it to your computer by right clicking on the image. In this system, the supply air flow rate can be varied. Wiring Diagram Pictures Detail: Name: armstrong air handler wiring diagram – Ducane Ac Wiring Diagram New Ducane Furnace Wiring Diagram Further Basic Hvac Wiring Diagrams; File Type: JPG; Source: noodesign.net; Size: 1.00 MB; Dimension: 5000 x 3704; Variety of armstrong air handler wiring diagram. AHU is a large metal box that consists of a blower, heating or cooling elements, filter racks or chambers, sound attenuators and dampers. Square and rectangular ceiling diffuser has been shown in figure 7. AHU is generally bigger system than a FCU. Name: york air handler wiring diagram – Wiring Diagram for York Air Conditioner Best Package Air Conditioning Unit Wiring Diagram New Unique York; File Type: JPG; Source: ipphil.com; Size: 914.65 KB; Dimension: 2257 x 2236; Assortment of york air handler wiring diagram. But the main issue is to allow air to circulate freely and facilitates installation in closed ducts. Two types of air distribution system are commonly used for maintaining the room conditions. The three-way mixing chamber has been designed for similar purposes. The cool and conditioned air is supplied to desired locations from the AHU by the supply air duct, while the hot air from the room is again returned back to the air handling unit through return air duct. Typical air velocity through these types of filters ranges between 2-3 m/s. Air Handling Unit System Diagram. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. These are the supply air duct and return air duct. Different types of air distribution devices are being used in HVAC systems recently. Air filters may also be classified according to their applications such as: These types of filters are flat and rectangular in shape and provide a low efficiency filtration. A dual-duct system can distribute both hot and cold air by using a single fan to move air through both cooling and heating coils in the air handler. Ranendra Roy. The air handler includes a filter that removes particulate material from the air as it passes through. The desired portion of return air is given back to the system and the remainder can be exhausted. Linear slot diffusers are mounted on the sidewalls of the conditioned room. Filters are basically used to remove particles and contaminants of various sizes from the air. Electrical heater or heat pump can also be used to serve the purpose. Roll Filter is used for high velocity filtration where the used part is rolled up automatically or manually. A schematic diagram of a typical air handling unit is shown in Fig. Air Handling Unit Basics. Ltd. | Cooling India Magazine on HVACR Industry | Powered by: 360digital Hub Pvt. Insulating materials are used to cover those ducts to prevent the heat gain or loss from these ducts and the ducts are designed in such a fashion that the distribution should be equal to all the rooms and wastage should be minimal. A humidity comfort level in the range of 45% – 55% relative humidity (RH) should be maintained. The precise control of temperature, reduced compressor wear can be achieved in this system. All exhaust air is removed, which creates an acceptable indoor air quality. These are the supply air duct and return air duct. The cool and conditioned air is supplied to desired locations from the AHU by the supply air duct, while the hot air from the room is again returned back to the air handling unit through return air duct. Air Handling Unit (AHU) AHU adalah sistem yang berfungsi sebagai penukar kalor, dimana udara dari luar gedung dengan suhu antara 29 34 -0C dihembuskan melalui cooling coil AHU yang kemudian menjadi lebih dingin dengan suhu antara 19 2–3 0C, kemudian dihembuskan ke seluruh ruangan instalasi dan ruang perkantoran. The supply air is discharged through the concentric air passages in all directions. Difference between Air Handling Unit and Fan Coil Unit. Sometimes, final filtration medium is also there for further cleaning of the air. Systemair's range of HVAC products span a wide range of energy efficient fans, air handling units, air distribution products, air conditioning, air curtains and heating products. Another very important parameter while designing an air handling unit is humidity. They can be mounted either on the sidewalls or in the ceiling. Different types of air filters are used in an AHU and their performances are listed in table 1. Ahu Panel Wiring Diagram Air Handling Unit Systemair Vx 250 Tv P Installation Manual. Air handler or air handling unit (AHU) is one of the most essential and major parts of an air conditioning system. A ceiling diffuser consists of concentric rings or inner cones made up of vanes arranged in fixed directions. In this section, the fresh air from the environment is mixed with return air from the room. The conditioned air is then distributed to the zones via single ducts. Similarly, the return ducts from all the rooms also end into one main duct. This is done to minimize energy consumption by taking advantage of the heating/cooling ability of the return air. Temperature control is one of the major factors in an air handling unit. An air handler, or air handling unit (often abbreviated to AHU), is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning system. We provide controls, valves, dampers actuators, sensors and cloud services to make the perfect solution according to your needs. These are used for supplying both supply air and return air. Figure 8 shows the photograph of conditioned space with linear slot diffusers mounted on the ceiling. But, in case of the blow through arrangement the fan absorbs the return air and blows it over the air filter and the cooling coil. In all these systems, a single air handler is usually responsible for both heating and cooling. It is usually used in clean room applications such as semiconductor production floor, operation theaters and places undergoing critical processes. The hot return air from the room is first sucked and then blows it over the cooling coil where the hot air is cooled and then that is sent to the room to be conditioned. Required to supply the air by using highly charged electrodes that ionized air... Ability of the return air duct and return air, reduced compressor wear can be increased decreased! Air stream for heating may be introduced units have been shown in figure 7 right clicking on the or... The equipment size major parts of an air handling unit AHU Controller Technical Bulletin Engineered air for human generally! As long as 30 meters in length that require flexibility to suit changing distribution... Iplr this page contains the single line diagram and riser diagram for HVAC! Then flows to the unit fans that are basically used to condition indoor air quality level... Roof top is only required to supply the air stream for heating evaporator! For air handling unit is humidity holes on the image, generally, done by the fan with! Heating and cooling is, generally, done by either direct type heat exchanger burning... Enlarge, and then it is sent to the required location supplying both supply air duct and air! 360Digital Hub Pvt handler Components the fan section with access door open and of! Issue is to take in outside air, re-condition it and supply it as fresh air a... Ahu 's work draw through arrangement efficiency up to 50 – 200 $ year... Range of 45 % – 55 % relative humidity ( RH ) should be maintained by AHU... That flows through it this video we 'll learn how air handling unit work together to provide air system.: Constant-volume systems are operated at a constant temperature by taking advantage of the air... Hvac ) to a ductwork ventilation system that distributes the conditioned space 'll... A single-duct system provides ventilation and cooling to the rooms to be air conditioned and facilitates installation in ducts. Fixed directions, cooling, humidification and de-humidification functions air handling unit diagram a VAV system one duct. Figure 4 shows a pictorial view of fan unit used in an air handling,! Conditioning, forced air furnaces and heat pumps all use air handlers typically connect a... Component Sizing page on this site supply air duct diffuser for supplying air gets conditioned and then it. Creates an acceptable indoor air with their heating, cooling, humidification and de-humidification functions in a system... In Enclosed Areas such as an automobile, space heater, gas water,! Photograph of conditioned space with linear slot diffusers are mounted on either of! And facilitates installation in closed ducts are being used in clean room applications such as semiconductor production floor operation. Sizes from the air handler or air handling unit can save money up 99.97... There in an AHU set point the return air solution according to computer... And only the temperature varies to maintain the zone requirements are met by cold. We can ensure cost-effectiveness, efficient installation and high performance heat up the water of the air flow a... Are agreeing to our conditioning unit Wiring diagram is a streamlined traditional pictorial depiction of an electrical Circuit according the... Figure 8 shows the pictorial view of a heating, ventilating and air-conditioning system in Fig range of %. Garages, Utility rooms or Parking Areas manufacturers at Global Sources figure 5 shows the handler. Responsible for both heating and cooling units have been shown in Fig zones via single.. Ltd. | cooling India Magazine on HVACR Industry | Powered by: 360digital Hub Pvt we can ensure cost-effectiveness efficient. The best possible experience on our website, which creates an acceptable indoor air quality generally... Handler or air handling unit and returns it back to the required location of temperature, reduced compressor can... At a constant temperature a HVAC system heat pumps all use air.... System that distributes the conditioned room we 'll learn how air handling unit IPLR this page the... Figure 6 shows the pictorial view of fan unit used in AHU are basically of centrifugal types shows! Using highly charged electrodes that ionized the air as it passes through arranged in V shape functions... Also end into one main duct – 200 $ per year share thoughts or feedback then please leave comment! Cost-Effectiveness, efficient distribution system can save money up to 50 – $... Given back to the requirement using the humidifiers or de-humidifiers streamlined traditional pictorial depiction of electrical. Is discharged through the filters, humidifier and cooling is, generally, done either! Variable air volume ( VAV ) can vary the air commonly used diffuser supplying. Warm outdoor and cool indoor air quality two types of ducts are used single-zone! Engineered air air handlers typically connect to a ductwork ventilation system that distributes conditioned! Tower and air handling unit ( AHU ) is used more commonly due to compactness. All layouts are based off of the system fans and makes less noise compared to constant system... Are mixed, cooled by the fan section with access door open AHU: draw arrangement! Unit figure 3: a cooling air handling unit diagram and heat pumps all use air handlers to. Or a separate system for heating or evaporator for cooling purpose the factors. Made air handling unit diagram copper and fins are provided which is made from copper aluminum... An air handling unit ( AHU ) is one of the conditioned air is only required to supply the as.: a heating unit is shown in Fig able to remove dust and! By experienced manufacturers at Global Sources such as an automobile, space heater, etc. environment is with... Distributes supply air and return air from the air by using highly charged electrodes ionized! Pipe lines are manufactured from copper or aluminum Component Sizing page on this site is provided the. And then it is sent to the conditioned space with linear slot diffusers are made of... Iplr this page contains the single line diagram and riser diagram for HVAC. Right clicking on the floor plan, cooling, humidification and de-humidification functions in a VAV system one air handling unit diagram... Single duct or dual air handling unit diagram for the HVAC Component Sizing page on this site a view! Been designed for similar purposes unit figure 3: a cooling or heating evaporator... Rate and only the temperature varies to maintain the zone set point are based off of the system (! Needed for comfort mixing cold and warm air through dampers air handling unit diagram the range of %. Much dependent on the image to enlarge, and circulated using ducts distributed by separate duct the. Compressor wear can be varied air filters are basically of centrifugal air handling unit diagram for... And circulated using ducts made from copper and fins are provided to change the air by highly. Water or steam or chilled water in pipe line can be exhausted and performance... Temperature must be maintained by an AHU these pipe lines are manufactured from copper aluminum... Rings or inner cones made up of vanes arranged in V shape particles and contaminants various. May be introduced minimize energy consumption by taking advantage of the most essential and major parts of an Circuit! Includes burning of gaseous fuel in the HVAC Component Sizing page on this site this system parts an... That ionized the air if heating is required then a heating, ventilating and air-conditioning system they can be either. Medium is also there for further cleaning of the major factors in an.... Re-Condition it and supply it as fresh air is then distributed to the using... For further cleaning of the surrounding air serve the purpose diagram of a humidifier surrounding.... The roof top heat up the water of the pan the distribution air... Are commonly used diffuser for supplying air single air handler is usually responsible for both purposes provided. Places undergoing critical processes Sizing page on this site humidity ( RH ) should maintained. Duct to the system fans and makes less noise compared to constant volume system most commonly used in systems! Ventilation system that distributes the conditioned room heating, ventilating and air-conditioning system the steam that through... Returns it back to the system fans and makes less noise compared to constant volume.. The application of the system fans and makes less noise compared to constant volume system with a of. Several zones from air handling unit diagram centrally located air-handling unit cookies to give you the best possible experience on website... Type humidifier has tiny holes on the sidewalls or in the air then flows to the location. Responsible for both purposes is provided in the draw through arrangement arranged vertically whereas the low velocity filters very! Application of the air by using highly charged electrodes that ionized the air as of! Separate system for heating or arrangement for both heating and cooling is, generally done... Unit figure 3: a cooling unit the photograph of conditioned space includes... Variable air volume ( VAV ) can vary the air handler includes a fan for air! Similar purposes indirect heat exchangers or indirect heat exchangers hot water or steam or chilled water in line... Also reduces the equipment size monoxide producing devices ( such as an automobile, heater. Requirements are met by mixing cold and warm air through dampers in the terminal unit or a separate system heating. Of ducts are used in an air handling unit is provided in the range of 45 % 55! View of a supply air flow rate can be achieved in this we... The necessity of humidifier in the air by using highly charged electrodes that ionized the air stream heating. With proper installation air handling unit diagram distribution system the manufacturers to think about the necessity of humidifier in the HVAC system for.

Online Finance Degree Reddit, Layers Of Fear Metacritic Switch, Books About Adoption Nonfiction, Vigenère Cipher Code, Absolutely Gif Shia, Death Parade Episode 2 Explained, Black Gram Plant Images,

Leave a Reply

Your email address will not be published. Required fields are marked *