Improved Test Methods for Electronic Air Cleaners; Fall
2002 issue of Air Media
Author(s): JT Hanley; et. al.
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IMPROVED TEST METHODS FOR ELECTRONIC
AIR CLEANERS
Using Furnace Filters as Whole House Room
Air Cleaners
There have been significant improvements on
1" furnace type filters over the last ten years. The
fiberglass furnace filter was originally designed to keep the
house ventilation system clean from large particles and
debris. Since most of the house furnace blowers are not
designed to operate in high static pressure environment, the
fiberglass furnace filter can share only a limited amount of
pressure drop. The 1" fiberglass furnace filter with
low-pressure drop and low cost naturally became the
most common choice.
Two things have changed. First, is the
better design of the filters by adopting pleated structure to
reduce the media velocity. Lower media velocity typically
leads to higher filter efficiency and lower pressure drop.
Secondly, the variety of specialty media (e.g., tribo-charged
media, split fibers, large effective fiber diameter (EFD)
melt-blown electret…), which have significant higher initial
efficiencies with relatively low pressure drops have been
introduced for this application.
The enhanced performance of some of the
pleated type furnace filters has elevated the
traditional role of 1" fiberglass furnace filters from
protecting the residential ventilation system to improving the
indoor air quality (IAQ) in a residential environment1.
Pleated type furnace filters, when selected and used properly,
can potentially reduce the indoor air pollutants significantly
and the advantages are multifold. For example, for allergy
sufferers, houses installed with specialty pleated type media
furnace filters can potentially alleviate the symptoms of
sneezing, watering eyes, itching throat, postnasal drip,
coughing etc. during the pollen season. The reduction of
indoor air particle concentration by pleated type
furnace filters can also slow down the settling of dust and
respirable particles2 inside the house.
Field Tests Setup
Seven different new furnaces were evaluated
in this study. Identification of the seven filters can be seen
in Table 1. Tests were performed in an actual
residential home located in Florida with total square footage
of 2900 ft2. The test house is a high ceiling with
two stories in half of it. A heat pump with a slot for a
20"x20"x1" furnace filter is the ventilation system
used in the house. Air filters used were acquired from local
retail stores.
Two TSI PortaCount Plus used as condensate
nuclei counters (CNC) and one TSI 3755 (two channels: 0.5-5
and >5 micron) optical particle counter (OPC) were used as the
primary monitoring instruments in this study. One CNC (#1) was
placed on a ground floor dining table close to one corner of
the house. One CNC (#2) was placed in a second floor bedroom
whose location was in the exact opposite end of a diagonal of
the house relative to the first CNC. The two-channel optical
particle counter was placed in the first floor master bedroom.
It forms a triangle (with the other two CNCs) that covers
three corners of the house. Each monitoring instrument was
connected to a computer for data acquisition.
CNC recorded the particle concentration
from 0.02-1 mm and
the sampling time was set at 15 seconds for each sampling
period. The optical particle counter recorded the results of
particle concentration in the range of 0.5-5 mm (respirable
particle size range) and the sampling time was set at 20
seconds for each sampling period. Combination of those two
types of instrument covers the particle size range from 0.02
to 5 mm.
Since the main objective of current study is to see how
effective is each furnace filter working as a whole-house room
air cleaner. The decay of particle concentration vs. time
inside the house is the primary focus of each test.
TABLE 1. Furnace Filters Used in Field Tests
|
Description |
Media Type |
Property |
|
MERV11 |
Split Fiber (Fat
Fibers) |
Electret |
|
MERV12 |
Melt-Blown |
Electret |
|
MERV8 |
Cotton and PET Mixed |
Non-Charged |
|
MERV10 |
Tribo-Charged (Fat
Fibers) |
Electret |
|
MERV12 |
Tribo-Charged
Composite |
Electret |
|
Glass Fiber |
Fiberglass
Throwaway-type |
Non-Charged |
|
CFP* MERV8 |
Composite Filter
Pads* |
Non-Charged |
Field Test Procedures
Several sliding doors and windows were open
to let outside ambient particles enter the house through
natural ventilation. Particle concentrations were monitored
throughout the house to make sure the particle concentrations
were stable before each experiment started. All the sliding
doors and windows were then closed once the particle
concentration was stable inside the house. All three counters
were then reset to start to record the data of each test. The
blower of the ventilation system was not turned on for another
10 minutes to establish the initial base line (particle
concentration). Each test lasted 3-8 hours depending on the
performance of each furnace type filter. No activities or
human movements occurred during each test.
A background test was also performed. All
the doors and windows were closed. The blower was off and
there was no activity or any movement in the house. CNC#1 and
OPC recorded the particle concentration over a period of time.
Results and Discussion
The data collected in the first 10 minutes
of each test were averaged and used as the initial
concentration. The numbers collected by each instrument after
the blower was turned on were divided by the initial
concentration and represented as the percentage of the
original concentration.
Fig. 1 illustrates the decay curves of the
CNC #2 placed in the second floor. The CNC #2 was not
available when the test was performed for the WEB furnace
filter. The results are very close to those collected by CNC#1.
The time that requires removing 50%, 75% and 87.5% of the
initial particle concentration for each tested filter is shown
in Table 3.
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