The Basics of Air Filtration
The Importance of Air Filtration
Air filtration supplies the means to obtain the level of particulate cleanliness required by any definition of "air conditioning." It extends from the simple task of preventing lint and other debris from plugging heating/cooling coils to removing particles as small as 0.1 micron, which could cause a short circuit on a microchip. In addition to the reasons given above, air filters are used for a wide variety of purposes, some of which include:
• Protecting the general well-being of the occupants of a space
• Protecting the decor of occupied spaces by removing the staining portion of airborne dust
• Reducing maintenance of building interiors by reducing the frequency of washing such items as Venetian blinds and fluorescent bulbs
• Protecting the contents of occupied spaces including paintings, tapestries, and other items of historic or cultural value
• Elimination of fire hazards by removing lint and other materials which might accumulate in ductwork
• Extension of shelf life of perishable dairy products by removing airborne mold during processing operations
• Removing airborne bacteria from operating room air to help prevent postoperative infection.
Performance Ratings of Air Filters
ASHREA (American Society of Heating, Refrigeration and Air Conditioning Engineers) has developed 2 different test methods to rate air filters, 52.1 test and the newer 52.2 test. Both tests are important in determining the proper filter.
THE ASHRAE STANDARD 52.1
ASHRAE Standard 52.1 measures pressure drop, arrestance, dust spot efficiency and dust- holding capacity. This is the test that reports a typical pleated filter as 30% efficient. That means of all the dust particles in the air, all sizes, it will remove an average of 30% of the entire particle range over the life of the filter. It does not let you know how it performs when it is new or what it is really stopping. It also gives an arrestance value, which is usually around 90% for pleated filters. Arrestance is a percentage of weight of particulate the filter will remove. It is always higher than the efficiency because the larger particles are easily captured on the filter and make up most of the weight of the particulate in the air stream.
THE ASHRAE STANDARD 52.2
ASHRAE Standard 52.2 measures the particle size efficiency (PSE) of an HVAC filter. It is not intended to replace the 52.1 standard for measuring a filter's performance. Data measured by Standard 52.1 will remain important performance characteristics (see Table 1 for Application Guidelines for the two standards).
Some of the improvements found in the ASHRAE 52.2 standard include:
• Where 52.1 expressed efficiency as an overall percentage, 52.2 expresses efficiency as a function of specific particle sizes.
• The 52.2 method of test will create results that are reliable and verifiable.
STANDARD 52.2 TEST PROCEDURE: HOW DATA IS OBTAINED
An air filter's performance is determined by measuring the particle counts upstream and downstream of the air-cleaning device being tested.
The lowest values over the six test cycles are then used to determine the Composite Minimum Efficiency Curve. Using the lowest measured efficiency avoids the fiction of averaging and provides ratings based on a "worst case" experience over the loading cycles.
MINIMUM EFFICIENCY REPORTING VALUE (MERV)
An "overall" reporting value of a 52.2-evaluated air filter is the expression of the Minimum Efficiency Reporting Value (MERV). The MERV is a single number that is used, along with the air velocity at which the test was performed; to simplify the extensive data generated by the method of testing. MERV is expressed on a l6 point scale.
What does it really cost for your air filters?
You know the price of your air filters the day you buy them, , but you don’t know the cost until the day you throw them away! The initial cost of the air filter is only part of the true cost. Below are other costs associated with air filtration.
• Price of the Air Filter
• Cost of generating a purchase order
• Cost of receiving and storage
• Labor cost to install
• Cost of disposal of the dirty filter
• Disruption to the tenant
• Cost of the energy to push air through the air filter It most cases, the energy needed to operate an air filter exceeds the cost of the air filter. See the energy model used later in this article.
The Effect of Resistance on Air Flow Filters of any kind present a barrier to air flowing through the ductwork in an air handling system. This barrier creates resistance, which reduces the volume of air delivered by the fan. Resistance is called “Pressure Drop” because the static pressure upstream of the filters is higher than it is on the downstream. Therefore, the reference to pressure drops. There is a loss of cfm with the pressure drop. In a VFD system this created the need for a higher amp draw to keep the proper amount of air needed to cool a space. In a direct drive system the compressor must run longer to deliver the air to cool or heat the space with a higher-pressure drop filter. The results of pressure drop in both types of sytems are a higher energy cost to run the air filters with a higher resistance to airflow. Below is a program that can help calculate the energy cost associated with the pressure drop of an air filter. The comparison uses 2 of our most popular air filters. The higher dust holding capacity is also a factor in this program. It allows us to run 1 extra month with the same filter.
INPUT DATA |
OPTION A |
OPTION B |
|
Std Cap |
Hi Cap |
Filter Type |
MX40 |
DMK80 |
Filter Type II |
MERV 7 |
MERV 8 |
Model # |
Std Cap |
Hi Cap |
Filter Price ($ per filter) |
$3.86 |
$4.48 |
Number of Filters in Bank |
100 |
100 |
Estimated Filter Life (months) |
3 |
4 |
Initial Resistance ("WG) |
0.32 |
0.26 |
Recommended Final Resistance ("WG) |
0.75 |
0.75 |
System Airflow Rate (cfm) |
200,000 |
200,000 |
Days in Operation (System) |
300 |
300 |
Hours in Operation Per Day |
18 |
18 |
Energy Cost ($/kWh) |
$0.070 |
$0.070 |
Drive Efficiency (%) |
99% |
99% |
Motor Efficiency (%) |
86% |
86% |
Fan Efficiency (%) |
68% |
68% |
|
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OUTPUT DATA |
|
|
Initial Investment Costs |
Std Cap |
Hi Cap |
Number of Filters |
100 |
100 |
Filter Price |
$4.00 |
$5.00 |
Estimated Filter Life (months) |
3 |
4 |
Number of Change outs/Year |
4.00 |
3.00 |
Subtotal Annual Filter Costs |
$1,600.00 |
$1,500.00 |
|
|
|
Energy Costs |
Std Cap |
Hi Cap |
Initial Resistance (Pa) |
80 |
65 |
Recommended Final Resistance (Pa) |
187 |
187 |
Average Resistance (Pa) |
133 |
126 |
System Airflow (m3/sec) |
94.34 |
94.34 |
Filter Airflow (m3/sec) |
0.94 |
0.94 |
Filter Life |
1350 |
1800 |
Fan/Motor/Drive Efficiency (%) |
57.9% |
57.9% |
Energy Consumption (kWh) |
293 |
369 |
Energy Cost Per Filter ($) |
$20.52 |
$25.83 |
Energy Cost Per Change-out ($) |
$2,052.08 |
$2,582.68 |
Subtotal Annual Energy Cost ($) |
$8,208.30 |
$7,748.03 |
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|
|
SUMMARY DATA |
|
|
TOTAL COSTS |
Std Cap |
Hi Cap |
Initial Investment Costs |
$1,600 |
$1,500 |
Energy Costs |
$8,208 |
$7,748 |
Total Operating Cost |
$9,808 |
$9,248 |
|
|
|
|
|
You Save |
OPERATING COST DIFFERENCE |
($560) |
$560 |
|
|
With Option B |
|
|
|
Choose Option B for an Annual Savings of: |
|
$560 |
Percent Saved with Option B: |
|
6% |
Total Operating Cost |
$9,808 |
$9,248 |
|
|
|
|
|
You Save |
OPERATING COST DIFFERENCE |
($560) |
$560 |
|
|
With Option B |
|
|
|
Choose Option B for an Annual Savings of: |
|
$560 |
Percent Saved with Option B: |
|
6% |
Air Filter Comparison of Dave Downing and Associates Products |
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Products listed from lowest price, lowest performance to |
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highest priced, best performing |
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Model Name |
Type |
MERV Rating |
Description |
Facet FG |
Fiberglass Disposable |
1 to 4 @350 fpm |
White Fiberglass |
Pros: |
Low Price, Low Restriction to Air Flow |
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Cons: |
Low efficiency, Off loads captured dust |
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Delta - P |
Fiberglass Disposable |
7 @ 350 fpm |
Red Fiberglass |
Pros: |
Low Price, low restriction to airflow, high dust holding |
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Cons: |
Lower Air flow Rating, off load of dust possible |
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Extreme Pleat |
Pleated |
7 @ 500 fpm |
White media, No Metal |
Pros: |
Lowest price of pleated |
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Cons: |
Low Dust holding Capacity (90 grams) |
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HiE40 |
Pleated |
7 @ 500 fpm |
White, Standard Pleat Count |
Pros: |
Mid Price, higher dust holding (140 grams) |
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Cons: |
Dust holding not the highest |
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MX40 (Max) |
Pleated |
7 @ 500 fpm |
Green, Standard Pleat Count |
Pros: |
Mid Price, higher dust holding (140 grams) |
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Cons: |
Dust Holding not the highest |
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DP40 |
Pleated |
7 @ 500 fpm |
Green, High Pleat Count |
Pros: |
Mid Price, More surface Area than MX40 |
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Cons: |
Only MERV 7 |
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DP-8 |
Pleated |
8 @ 500 fpm |
White, Synthetic Media |
Pros: |
High Pleat Count, MERV 8 rating |
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Cons: |
Lower dust holding than DMK80 |
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DMK80 |
Pleated |
8 @500 fpm |
Blue Synthetic Media |
Pros: |
High Pleat Count, Long Life, Low initial pressure drop |
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Cons: |
Initial price is higher than other pleated filters |
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Powerguard |
Pleated |
11 @500 fpm |
White Synthetic Media |
Pros: |
High Efficiency for a pleated filter |
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Cons: |
High pressure drop, Low Dust Holding |
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PAF11 |
Pleated |
11 @500 fpm |
Yellow Synthetic Media |
Pros: |
High Efficiency for a pleated filter |
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Cons: |
High pressure drop, Low Dust Holding |
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Our most popular 2 medium efficiency products are the Airguard MX40 (MAX) and the Purolator Mark-80-D (DMK80). In most applications the MX40 will last 3 months. It is 4 changes per year. The DMK80 will last 4 months, 3 changes per year. Just like the operating cost model above had indicated.
130 N. 39th Avenue Phoenix, AZ, 85009 |
Phone: (602)-264-5100 Fax: (602)-241-7500 |
info@davedowning.com |