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How does mechanical filtration work?
Filter out particles
What is the normal maximum air velocity across the face of a low efficiency panel filter?
300 feet per minute
How often should low efficiency panel filter be changed?
How often should renewable media pleated surface be changed?
What factors should be considered when choosing an air filter?
Size of contaminants the filter must remove, its efficiency at removing the contaminants, the airflow, and its resistance.
Describe the MERV filter rating system.
Range from 1 for lowest efficiency filters to 20 for the highest efficiency filters.
Why are the highest rated MERV filters not used in residential applications?
Most residential air conditioning equipment can not operate correctly at pressure drops exceeding .5 in wc across the blower.
Why is panel filter media sometimes coated with a viscous substance?
Helps the particles in the air stick to the filter
What is a HEPA filter?
High efficiency particulate arrestance.
How does increased airflow affect a filters efficiency?
Increased airflow produces increased air-speed, which reduces the effectiveness of the filter.
What is the purpose of extending media area in pleated filters?
Reduce pressure drop across the filter, allowing the use of denser media for increased efficiency.
How does the increased pressure drop across a filter affect a system operation?
Increases the overall pressure that the fan must move air against, reducing system airflow.
List three types of electronic air filter units.
1. Ionizing plate
2. Charges media non- ionized
3. Charged media ionized
What is the common operating voltage range on the cells of electronic air cleaners?
8,000- 12,000 volts DC
Describe the operation of an ionizing plate electronic air cleaner.
Uses high voltage DC current to ionize particles in the air and attract them to oppositely charged plates
What filter characteristics should be considered when selecting an air filter?
MERV rating and pressure drop
Why should a MERV rating always state the air velocity through the filter?
Because the filter efficiency decreases as the velocity increases.
How can a high pressure drop across an air filter adversely affect system performance?
Increased pressure drop across the filter increases the total static that the fan must work against, decreasing the amount of air moved.
What air contaminants are addressed by UV lights?
Mold, fungi, bacteria and any other living organisms
How often do UV lamps need to be replaced?
Every one to 3 years
What is the SI unit measurement for microns?
1/1000 of a millimeter
How many microns are in an inch?
What is the human's hair thickness in microns?
The smallest particles of tobacco smoke are as small as 0.01 microns.
True or False?
What are the most common type of media air filters use to trap contaminants?
What is the purpose of low efficiency panel filters?
To protect the equipment; they do little for cleaning the air.
What do pleated medium efficiency filters create?
Higher pressure drop across the filter, but the pressure drop is still usually within the operating limits.
What were HEPA filters originally developed for?
Remove radioactive contaminants from the air during the development of the atomic bomb.
What are 2 common methods to measure air filter efficiency?
Filter arrestance and dust spot efficiency.
How does the arrestance method work to measure air filter efficiency?
Measures the weight of the material captured by the filter and compares it to the weight of the test material that was released.
How does the dust spot method work to measure the air filter efficiency?
Measures a filters ability to remove very small particles that can easily pass through many filters and cause staining on walls and surfaces.
Arrestance method uses calibrated test dust.
True or False?
Dust spot method uses atmospheric dust.
True or False?
What does MERV stand for?
Minimum Efficiency Reporting Value
What is filter loading?
To describe the amount of material the filter has collected.
What is final pressure drop?
Maximum pressure the filter is designed to withstand.
What are extended area filters made of?
Random fiber mats or blankets of bonded glass fiber, wool felt, or synthetic materials.
Most pleated 4 in and 5 in deep extended media filters will last between 6 months and a year between changes.
True or False?
Where are moving curtain filters are used commonly?
What is the typical voltage for ionizing plate air cleaners?
6,000-10,000 V DC
How often should you clean ionizing plate cleaners?
2 to 4 times a year
What does charger media nonionizing air cleaners consist of?
Dielectric filtering medium, usually arranged in pleats.
What do photocatalytic air cleaners use?
UV lights and titanium dioxide coated metal cells to oxidize gasses and odors in the air stream.
What is photocatalytic oxidation?
Titanium dioxide acts as a catalyst for the oxidation of volatile organic compounds VOCs
What are 2 operating conditions that can cause problems with electronic air filters?
Space charge and ozone.
Recommended textbook explanations
Thermodynamics: An Engineering Approach
Yunus A. Cengel
Engineering Mechanics: Statics
J.L. Meriam, L.G. Kraige
Vector Mechanics for Engineers: Statics and Dynamics
Daniel J Inman
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