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Air Handling Units Explained - Diagrams, Types of AHU

Air Handling and Distribution: Routine Maintenance


Air Handling Unit - Part 1


In this module, we will look at how to inspect, clean, and replace the air filter in an air handling unit (AHU).


We’ll also provide an overview of blower maintenance. Skip to quiz!


Introduction


Recall that an air handling unit is a large, rectangular, metal box that’s connected to ductwork. We usually call it an AHU for short.


Recall that an AHU contains an air filter, blower, and heating and cooling components. Let’s look at how to maintain each of these AHU components.


Air filters are usually located at the entrance of the return air in an AHU. When inspecting an air filter, we first need to switch off the AHU. Then, we have to open the respective panel by turning the hand keys or removing screws.


Recall that some air filters are reusable and can be cleaned. We can clean air filters with water. We suggest using a garden hose with a medium pressure water jet to clean reusable air filters. Let’s watch a video to understand how to clean air filters.


To clean an air filter, we follow these main steps:

  • Remove the filter and wash it with water,

  • Make sure the filter is dry before replacing it, and

  • Put the filter back.


Recall that we can only clean reusable filters. Other filters must be replaced. Let’s watch a video about how to replace the air filter in an AHU.


When replacing an air filter, we need to switch off the AHU to open the access panel. Recall that access panels are outer covers of AHUs or any other HVAC system. They can be opened by turning the hand keys or removing screws.


After we locate an air filter, we remove it from the AHU. We’ll need to replace this air filter with a new air filter, as shown in the video.



Blowers


Recall that blowers are a type of fan that forces air to move. Commercial AHUs usually have belt-driven blowers.


Blowers are located beside cooling or heating coils to pull or push the air. To locate a blower, we have first to switch off the AHU. Then, we have to open the access panel by turning the hand keys or removing the screws.


We need to inspect V-belts for signs of cracking. If a belt is damaged or looks worn, replace it right away. Let’s watch a video to understand how to replace V-belts.


After replacing a V-belt, we should assess pulley alignment. Good pulley alignment increases the lifespan and efficiency of an AHU by reducing the wear of pulleys, belts, and bearings. Let’s watch a video to understand how to check pulley alignment.


We can check the tightness of a belt by pushing it down in the middle with a finger. If it goes beyond a half-inch, we should make an adjustment. Let’s watch a video about how to tighten a loose belt.


Recall that lubrication is the action of applying oil or grease to a motor to minimize friction and allow smooth movement. Grease guns are a device used to apply grease to an electric motor and bearings. Let’s watch a video to understand how to lubricate blowers with a grease gun.


Recall that bearings support loads and also help them to rotate. Let’s watch a video to understand how to replace a blower bearing.


Air filters are usually located at the entrance of the return air in an AHU. We can clean an air filter with water. We can only clean reusable filters, while other filters must be replaced.


Blowers are located beside cooling or heating coils to pull or push the air. If a belt is frayed or looks worn, replace it right away. We lubricate blower motors to minimize friction and allow smooth movement.



 

Air Handling Unit - Part 2


In this module, we will look at how to inspect and clean the coil and condensate drain of an AHU.


We’ll also look at how to inspect electric heaters. Skip to quiz!


AHU - Coils


Recall that AHUs contain cooling and heating coils. An AHU may contain both heating and cooling coils, or only one of them. Water or refrigerant circulates through these coils.


We need to check for any debris on these coils. We should also check for damaged coil fins, coil leaks, mold growth, and unusual materials on a coil’s surface. Let’s watch a video to learn how to clean coils.


First, we clean coils with a brush. We spray coil cleaner onto the coils and let that sit for ten minutes. We then clean the coils with a water hose in the opposite direction of airflow, as shown in the video.


Recall that we have to straighten coil fins with a fin comb if they’re bent. This process is similar to combing our hair. We should straighten fins slowly, or it could damage the coil.



Condensate Drains


We check drain lines to see whether the water is flowing freely or not. Recall that when air passes through a cooling coil, moisture in the air converts into water. This condensate water is moved out of an AHU using a drain line.


When cleaning drain lines, we first switch off the air handler. We then pour distilled vinegar in a drain line through the opening and let the solution sit for half an hour.


After that, we have to flush the pipe with water to make sure that it is clean and functioning normally. If a drain line is still dirty after this process, we can use a vacuum cleaner to further clean it. Let’s watch a video to understand how to use a vacuum cleaner to clean a drain line.


We have to locate the end of a drain line outside a building. We then connect a vacuum hose to the end of the drain line and turn on the vacuum pump. Lastly, we pour water into the drain line to clean it, as shown in the video.


Electric Heaters


Recall that we can install electrical heaters in some AHUs in place of heating coils. Electrical heaters serve the same purpose as heating coils, but consume more electricity. Let’s watch a video to understand how to inspect electric heaters.


First, we have to switch off an AHU and remove the electric heaters from it. We then check the resistance and continuity of the electric heaters with a multimeter. If a multimeter shows the specified resistance value, it means that the electric heaters are working properly.


AHUs may contain both heating and cooling coils, or only one of them. We should check for any debris on these coils. First, we need to clean coils with a brush. We then clean coils with a water hose from the inside out.


We check drain lines to see whether water is flowing freely or not. Vacuum cleaners are used to pull out clogs from drain lines. We can install electrical heaters in AHUs in the place of heating coils. Multimeters are used to inspect electric heaters in an AHU.




 

FCU and VAV Box


In this module, we will look at how to inspect and clean FCUs.


We’ll also look at the maintenance work needed for VAV boxes. Skip to quiz!


FCUs


Recall that a fan coil unit is a type of AHU that recirculates indoor air only. FCUs provide cooling or heating to a single room only.


The main components of FCUs are:

  • Coils,

  • Motors,

  • Blower fans,

  • Air filters, and

  • Drain pans.

Let’s watch a video to understand maintenance for floor-mounted FCUs.


When cleaning FCUs, we need to turn off the power in order to open the access panel. Then we have to remove the air filter to check for cleanliness. We should clean drain pans, coils, and other accessible spaces within an FCU with a vacuum cleaner.


We must clean blower housings, FCU casings, and other areas with a slightly moist cloth. Moist cloths draw dust particles in, and remove them from an area rather than moving them around. Then, we pour water into the drain pan and check whether the water is flowing freely or not.


We can re-install an old air filter if it’s clean, or replace it with a new air filter. We’ll need to reassemble the access panel of the FCU. Lastly, we turn on the FCU at the thermostat to check that it’s working properly.



VAV Boxes


Recall that VAV boxes are terminal devices, and are installed at the openings of ducts. These regulate the quantity of air entering a room. Let’s look into how to clean a VAV box.


When cleaning a VAV box, we have to switch it off, as well as the AHU connected to it. We have to remove any dust inside a VAV box using a brush or vacuum cleaner. Then, we have to clean it with a dry cloth.


We check for leaks in a VAV box. Air leaks in a VAV box affect the cooling or heating in a room. We also check the tightness of a VAV box’s screws and hanger bolts.


VAV Boxes - Controls


Recall that the main control systems of a VAV box are:

  • Thermostats, and

  • Damper actuators.

A thermostat connected to a VAV box sends a signal to a damper actuator to change the position of a damper. Let’s look into how we inspect the proper working of these controls.


To inspect a thermostat, we have to check its power connection. Then, we change the batteries of a thermostat if required. Let’s watch a video to understand how to change the batteries in different types of thermostats.


We have to check all of a thermostat’s connections to tighten them. Also, we need to clean inside of it, since dust build up can affect its performance. Dust build up in a thermostat blocks temperature detection, which can cause a thermostat to give inaccurate temperature readings.


Finally, we inspect a thermostat with a multimeter. Let’s watch a video to understand how to inspect a thermostat with a multimeter.


When inspecting a thermostat, we should check the voltage between hot, cold, and fan control wires with COM, respectively. A multimeter should read about 24 volts in energized condition, and 0 volts in de-energized condition.


If a multimeter deviates from the noted conditions, it means that a thermostat is not working properly. We have to replace or repair it.


Recall that damper actuators control the opening and closing of a damper. Damper actuators help adjust the airflow in an HVAC system. Let’s watch a video to understand how to inspect the performance of a Siemens actuator.


We supply line voltage 24V AC and control voltage 0 to 10V DC to actuators. We connect multimeter probes to control voltage terminals and set dials to the ‘V–’ range.


An actuator should be in the closed position at O volts, middle position at 5 volts, and fully open position at 10 volts. If an actuator deviates from the noted conditions, it means that it’s not working properly. We have to replace or repair it.


When cleaning an FCU, we need to turn it off at its thermostat to open the access panel. We should clean drain pans, coils, and other accessible spaces within an FCU with a vacuum cleaner. We can re-install an old air filter if it’s clean, or replace it with a new air filter.


We have to remove any dust inside a VAV box using a brush or vacuum cleaner. We should check the tightness of a VAV box’s screws and hanger bolts. We inspect the performance of thermostats and damper actuators.



 

Air Distribution Components


In this module, we will look at how to inspect and clean ductwork.


We’ll also look at how to clean air terminal devices. Skip to quiz!


Ductwork


Recall that ductwork are closed pathways made of thin metal sheets. The main types of ductwork are:

  • Rigid ductwork - Maintains an exact shape and cannot bend easily.

  • Flexible ductwork - Can bend as needed.


Recall the common problems in ductwork that need to be inspected are:

  • dents,

  • leaks,

  • clogs,

  • mold, and

  • corrosion.

All these problems are inspected visually.


We clean ducts during regular maintenance. Duct cleaning involves cleaning registers, as well as the insides of ducts using a vacuum cleaner. Recall that registers are the grills that we find in the walls at a duct entry.


First, we switch off the HVAC system. Then, we unscrew registers using a screwdriver. We have to clean the insides of ductwork with a brush as far as we can reach. We should collect the loosened dust by inserting a vacuum cleaner hose into the ductwork.


We need to wash all registers with tap water. We have to wash air filters if they are reusable, or replace them. We have to clean any dust that might have come out of the vent and onto the floor. Finally, we screw registers back into place.



Air Terminal Devices


Recall that air terminal devices are where the air is supplied to a room. The main types of air terminal devices used are:

  • Grilles, and

  • Diffusers.

Let’s watch a video to understand how to clean air terminal devices.


First, we switch off the HVAC system connected to an air terminal device. Then, we unscrew it and clean it with a brush or vacuum cleaner. We have to clean an air terminal device with water if it’s dirty. We need to place an air terminal device in its original position and screw it in.


Recall that high humidity in air promotes the growth of mold. Mold on air terminal devices can lead to breathing problems. Mold on air terminal devices can’t be cleaned easily. We use detergents or some other chemicals to clean it. Let’s watch a video to see how we clean mold.


Duct cleaning involves cleaning registers and the insides of ducts using a vacuum cleaner. We have to wash air filters if they are reusable, or replace them. We use detergent or other chemicals to clean mold on air vents.



 

Question #1: Air filters are usually located at the ________ of the return air in an AHU.

  1. entrance

  2. exit

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Answer: entrance

Air filters are usually located at the entrance of the return air in an AHU.


Question #2: Which liquid can be used to clean an air filter?

  1. Brine

  2. Petrol

  3. Refrigerant

  4. Water

Scroll down for the answer...






Answer: Water

Water is used to clean air filters.


Question #3: We have to replace an air filter while the AHU is running.

  1. True

  2. False

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Answer: False

When replacing an air filter, we have to switch off the AHU to open the access panel.


Question #4: We replace the V-belt in an AHU with the _____ size V-belt.

  1. bigger

  2. same

  3. smaller

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Answer: same

We replace the V-belt in an AHU with the same size V-belt.


Question #5: Grease guns are used for _________.

  1. lubricating parts

  2. cutting wires

  3. filling refrigerant

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Answer: lubricating parts

Grease guns are used for lubricating parts.


Question #6: Which of the following is used to support a blower shaft and help it to rotate?

  1. Metering device

  2. Bearing

  3. Grill

  4. Vibration isolator

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Answer: Bearing

Bearings are used to support blower shafts and help them to rotate.


Question #7: Which of the following will happen if we spray a coil with high-pressure water?

  1. Coil fins will bend

  2. The condensate drain will be clogged

  3. The air filter will tear off

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Answer: Coil fins will bend

AHU coil fins will bend if we spray a coil with high-pressure water.


Question #8: How can we stop a rotating blower even after turning off an HVAC system?

  1. Air purifier

  2. Vacuum cleaner

  3. Screwdriver

  4. Bearing

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Answer: Vacuum cleaner

A vacuum cleaner is used to pull out clogs from a drain line.


Question #9: Which of the following instruments is used to inspect electric heaters in an AHU?

  1. Screwdriver

  2. Multimeter

  3. Manifold gauge

  4. Hygrometer

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Answer: Multimeter

Multimeters are used to inspect electric heaters in an AHU.


Question #10: Which of the following is poured into a drain pan to check whether the drain line is clogged or not?

  1. Refrigerant

  2. Petrol

  3. Water

  4. Vinegar

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Answer: Water

Water is poured into a drain pan to check whether a drain line is clogged or not.

Vinegar can be poured into a drain line to clean a clog.


Question #11: How can we stop a rotating blower after turning off an HVAC system during routine maintenance?

  1. We can stop a blower with our hands

  2. We have to wait till it stops rotating

  3. We can a use mechanical tool to stop a blower

  4. We can insert a screwdriver to stop a blower

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Answer: We have to wait till it stops rotating

We shouldn’t try to stop a rotating blower with our hands or any other mechanical tool. We have to wait until a blower stops rotating.


Question #12: When cleaning a VAV box, we have to switch off the ________, as well as the ______ connected to it.

  1. VAV box; AHU

  2. VAV box; FCU

  3. VAV box; Window AC

  4. AHU; FCU

Scroll down for the answer...








Answer: VAV box; AHU

When cleaning a VAV box, we have to switch it off, as well as the AHU connected to it.


Question #13: Dust build up in a thermostat blocks ________ detection.

  1. refrigerant

  2. smell

  3. pressure

  4. temperature

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Answer: temperature

Dust build up in a thermostat blocks temperature detection.


Question #14: Which of the following affects the performance of a thermostat?

  1. Loose wire connections

  2. Dead batteries

  3. Dust buildup inside the thermostat

  4. All the above

Scroll down for the answer...







Answer: All the above

Loose wire connections, dead batteries, and dust buildup inside a thermostat can affect its performance.


Question #15: A damper actuator is in the fully open position at ____ of the control voltage.

  1. 0 volts

  2. 5 volts

  3. 10 volts

Scroll down for the answer...








Answer: 10 volts

A damper actuator is in the fully open position at 10 volts of the control voltage.


Question #16: We usually clean the insides of ductwork with a water hose.

  1. True

  2. False

Scroll down for the answer...






Answer: False

We do not clean the insides of ductwork with a water hose. We use a vacuum cleaner or brush to clean ductwork.


Question #17: Mold on air terminal devices can be easily cleaned with _____.

  1. dry cloth

  2. detergent

  3. water

  4. brush

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Answer: detergent

Mold on air vents can not be easily cleaned with a dry cloth, water or brush.

We use detergents or some other chemicals to clean air terminal devices.

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