Air filtration is one of the most important
components of Indoor Air Quality (IAQ), yet may be one of the least
understood areas of the HVAC industry. Every building's air filtration
objective should be to remove as many harmful airborne contaminates at
the lowest possible material and fan energy costs. Most building owners
and facility managers recognize the need for more efficient filtration
to remove sub-micron particles in addition to the dust filters they
typically have in their present systems.
Why Sub-micron Filtration?
Most harmful airborne particles are smaller than one micron in size. Most HVAC
central fan filtration systems do not remove these particles because the
filters used are only capable of removing larger particles such as dust.
Currently, without the application of Uni-Guard technology, in order to
remove sub-micron particles,
special high efficiency sub-micron filters are usually installed in
place of, or in addition to, the existing dust filter(s) at the inlet of
the central fan. Because of their smaller air passages which are
necessary to collect sub-micron particles, these filters have larger air
pressure losses than the conventional dust filters. Therefore more fan
horsepower is required to provide for this increased pressure loss. Also
the sub-micron filters are usually larger in size. Therefore special
framing and/or additional space is required to accommodate them. The
costs to retrofit systems, system down time, and the high operating
costs (increased fan horsepower) as described the above often make this
approach undesirable. Uni-Guard overcomes these problems through its unique
design, and also increases the overall system effectiveness.
Overall System Filtration Effectiveness
The ability of a complete filtration system (which
includes not only the filters, but the air moving fan, duct work, and
air distribution devices) to remove particulates is the principle
critical concern in the design of a central fan filtration system. Due
to the inadequacies of current (without Uni-Guard) system's air circulation to "sweep" the
contaminates to the filter(s), and/or the proper placement of the
filters in the system, the actual overall system filtration
effectiveness is seldom equal to the individual efficiency rating of the
filters used in the system. The individual filter efficiency rating is
only one of many factors which must be considered to determine the
overall system filtration effectiveness. With a given quantity of
re-circulated air flow in a central fan system and all other variables
held equal, the overall system filtration effectiveness is increased
with:
Higher individual filter efficiency
rating of the type of filter(s) used
Greater quantity of filters used
Decreased face
velocity of air entering the filter(s)
The effectiveness of the
re-circulating system to "sweep up" and transport the contaminates to
the filters
Only Uni-Guard filter-diffuser units are designed to take all of
the above into account by making it possible for a system to use a large
number of low cost high efficiency sub-micron filters with low face
velocities, and also provide high performance air diffusion to "sweep"
the contaminants to the filters. With Uni-Guard, the low pressure loss (a result of the low
face velocity through the filters) reduces fan energy cost when compared
to conventional sub-micron filtration systems.
Table 1. FILTRATION SYSTEM COMPARISON TABLE
EXAMPLE for 10,000 CFM CENTRAL FAN RETRO-FIT
FILTER(S) LOCATION
RETURN AIR CENTRAL FAN INLET
UNI-GUARD UNITS
Filter Type
Mini-Pleat
Rigid Cell
Mini-Pleat
Filter Cost
$30
$80
$30
Filter Size -
W x H (in)
24 x 24
24 x 24
24 x 24
Filter Depth
(in)
2
10
2
Quantity of Filters in System
5
5
50
Modifications
to AHU Unit - Required
NO
YES
NO
Larger Fan
Motor H.P.- Required
YES
YES
NO
CFM / Filter
2,000
2,000
200
Filter Face
Velocity (fpm) *
500
500
50
MERV Rating @
Face Velocity
14
16
16
Sub-Micron
Filter Efficiency **
85%
95%
95%
Avg Filter Resistance (in.W.C.)
1.1
1
0.06
Fan Energy
Cost per Year - Increased
$1,425
$1,320
$90
Filter Total
Cost
$150
$400
$1,500
Filter Life
in Months
4
6
30
Filter Cost
per Year
$450
$533
$600
Total
Increased Cost per Year
$2,875
$2,120
$690
*
Denoted KEY FACTOR for
Increased Efficiency at Reduced Operating Costs
**
ASHRAE Standard 52.2
Range No. 1 (0.3 to 1.0 microns)
Notes:
1.
All systems have MERV 2 (dust) pre-filter at fan inlet.
2.
Operating costs are based on 24 hr. / 7 days / 365 days of year
operation, $0.80 per KWH, motor-fan-drive efficiency = 58%
Occupant Thermal Comfort
Thermal comfort provided by room air diffuser devices is
also an important component of IAQ, and is sometimes overlooked in the
design of HVAC systems. In addition to enhancing overall system
filtration effectiveness by high performance air diffusion, Uni-Guard
filter-diffuser units provide draft-free uniform air motion within the
space which allows the occupants to "feel" comfortable at higher
thermostat settings, thus providing energy savings. A one degree F
difference in thermostat setting can result in as much as 10% cooling
energy savings.
How Uni-Guard Works
The unique design of Uni-Guard filter-diffuser units
maximizes the positives and eliminates the negatives as described above.
Fan energy costs of sub-micron filters is reduced by low air
face velocity through the filters. Therefore increased fan horsepower
is, in most cases, not required. Because the space where the
filter-diffuser units are located (ceilings) is virtually unlimited,
more filters may be used than in conventional systems to increase the
overall system filtration effectiveness. This eliminates the requirement
for additional space at the central fan location or special framing.
After the air has been filtered by the Uni-Guard filter-diffuser units,
the air velocity is increased by evenly spaced diffuser outlet jets to
provide high performance air diffusion necessary to enhance overall
system filtration effectiveness, and draft-free energy efficient thermal
comfort. Conventional dust filters at the inlet of the central fan are
retained in the system to ensure extended life of the sub-micron filters
(located downstream) and to protect the equipment (fan, cooling and
heating coils, etc.) in the system.
Individual Filter Ratings
Individual filter efficiency ratings vary depending on
various methods of testing and only indicate a given filter's efficiency
when tested under certain ideal conditions. Because of the many ways a
filter can be applied in systems, often less than ideal, these ratings
cannot indicate overall system filtration effectiveness; however, individual
filter efficiency ratings can be used to compare the relative
effectiveness of filters in any given application. The current and only
standard that concerns sub-micron filtration (other that HEPA) is ASHRAE
Standard 52.2 1999 which comprehensively rates a filter's ability, under
certain conditions, to remove particulates over the entire range of
sizes, including the harmful smaller sub-micron particles. This rating
method is termed the Minimum Efficiency Reporting Value (MERV). MERV
ratings range from 1 to 20 (see Table 2). Uni-Guard
filter-diffusers accommodate any MERV rated filter.
Table 2. Minimum Efficiency Reporting Value (MERV)
Parameters
ASHRAE 52.2
Composite Average Particle Size Efficiency % in Size Range (microns)
Particle Size Range (microns)
Applications
Range #1
Range #2
Range #3
MERV
0.30-1.0
1.0 - 3.0
3.0 - 10.0
1
n/a
n/a
< 20%
> 10
residential, light pollens, dust mites
2
n/a
n/a
< 20%
3
n/a
n/a
< 20%
4
n/a
n/a
< 20%
5
n/a
n/a
20 - 35%
3.0 - 10
industrial, dust, molds, spores
6
n/a
n/a
35 - 50%
7
n/a
n/a
50 - 70%
8
n/a
n/a
> 70%
9
n/a
< 50%
> 85%
1.0 - 3.0
industrial, dust,
Anthrax, Legionella
10
n/a
50 - 65%
> 85%
11
n/a
65 - 80%
> 85%
12
n/a
> 80%
> 90%
13
< 75%
> 90%
> 90%
0.3 - 1.0
hospitals, smoke removal, bacteria
14
75 - 85%
> 90%
> 90%
15
85 - 95%
> 90%
> 90%
16
> 95%
> 95%
> 90%
17
>= 99.97%
< 0.3
HEPA
clean rooms,
chem-bio, viruses
18
>=99.99%
19
>= 99.999%
< 0.3
ULPA
20
> 99.9999%
This table shows the composite
average particle efficiency (%) by size range, of the three size ranges, for ASHRAE Standard 52.2 minimum Efficiency
Reporting Value (MERV).
In addition to using the MERV
number as a general guideline, exact data can be taken from test reports of a filter that has been
tested to ASHRAE Standard 52.2. This table can be used to choose the proper filter
for a specific application.
Applications
Most existing central fan systems may be upgraded with
Uni-Guard. Some examples are as follows:
Constant-volume, low-efficiency filtration systems
are the most common type of systems and can be upgraded with Uni-Guard to sub-micron
filtration efficiency with little or no increase in operating costs. In
some cases where a system may need to be re-balanced, there is only one
diffuser that determines the critical pressure loss path and the
required fan horsepower for the system. In all other, noncritical paths
(run-out ducts to diffusers in the system), the balancing dampers are
partially closed to create pressure drops to those diffusers to achieve
the required air flow. These dampers can be adjusted towards the open
position to offset the small additional pressure loss of each sub-micron
filter in the filter-diffuser unit.
Conventional constant-volume sub-micron filtration
systems, where the filters are located at the central fan inlet, can
be retrofitted to substantially reduce operating costs (fan horsepower)
by eliminating the high- pressure loss, high-efficiency filters (bag
filters, etc.) and replacing them with low-efficiency, low-pressure loss
dust filters. Overall system filtration effectiveness will be
increased by the use of Uni-Guard filter-diffuser units with sub-micron
filters which cost less than conventional filters with equivalent
efficiency. Energy savings are proportional to the pressure loss of the
existing conventional sub-micron filtration system, which is typically
1.0 in. WG (average), compared to a Uni-Guard system where the pressure
loss is typically less than 0.1 in. WG (average).
VAV systems using constant volume fan terminal
units are suitable for Uni-Guard systems because, in most cases,
only the primary air is filtered. Therefore, the amount of filtered air
to the room is reduced in proportion to the volume of primary air
delivered to the room(s) at any given time. This often results in room
filtration levels which are less than 10% of the primary air system
filtration level. For example, if 30% filters are installed in the
primary air system, then only (0.1 X 0.3) = 3% room filtration
efficiency can be expected during light cooling or heating modes. By
using Uni-Guard, both primary and return air passes through the
sub-micron filters regardless of the primary air volume rate.
VAV systems (single duct) are particularly
suitable for Uni-Guard because the filtration efficiency, in fact,
increases due to lower face velocity of the secondary air through the
terminal unit and filter when the primary air volume is reduced.
Protection Against Bio-terrorism Attacks Create a Safe Room
Individual "safe rooms" can be created in any existing building with the
use of Uni-Guard at minimal cost and inconvenience. Central fan systems
by, their very nature, provide a devastatingly efficient distribution method for
bio-terrorist attacks. Pathogens placed in the return air or outside air
openings can be spread through an entire building in a matter of
seconds. Uni-Guard units with MERV 16 or HEPA filters can provide protection to
the room(s) against bacteriological pathogens such as anthrax. Uni-Guard
units with ULPA filters provide protection against viral pathogens as
well as biological pathogens.
Installation
Installation of Uni-Guard ceiling filter-diffuser units
is simple. Old conventional ceiling diffusers are removed and replaced
by Uni-Guard units in a matter of minutes. No architectural or duct work
modifications are required. The units may be installed one at a time to
suit budget or time constraints without having to shut the system down.
The pressure loss of sub-micron filters when used in Uni-Guard systems
is low, and often is no more than the pressure loss of the existing
conventional diffuser/damper assembly. For this reason, re-balancing is
seldom required when retrofitting a system with Uni-Guard. Most existing
systems have provisions to increase the fan speed with the use of
adjustable pulleys or fan speed controllers. These may be adjusted to
allow for any small increase in static pressure that may be needed for
Uni-Guard sub-micron filters. The AHU fan speed is simply increased in
proportion to the increased static pressure requirement. For example, if
the maximum (critical path) increase in static pressure is 0.06 in. WG,
and the existing external fan static pressure is 1.5 in. WG, the fan
speed will only be increased approximately 2% (fan law).
If selective (partial) Uni-Guard filtration is used, or
in Uni-Guard systems containing filters with various different
efficiencies and pressure losses, then air re-balancing may be required
for optimum results. However, re-balancing can be minimized by simply
measuring the existing velocity pressure at each run-out duct to be
retrofitted with a Uni-Guard unit. After the unit is installed, the
balancing damper can readjusted to duplicate that same value necessary
to produce the original air flow.
Installations are often performed by building
maintenance staffs; however, Warren Technology offers turnkey
installation in most areas nationwide.
Model Selection
Uni-Guard Filter-Diffuser units are comprised of three
elements: 1) plenum casing, 2) filter, and 3) diffuser plate.
1.
Select casing type:
A.
Flush mount (T-bar ceilings)
B.
Surface mount (T-bar, gypsum,
or plastered ceilings)
2.
Select filter type:
A.
Sub-micron filters ( ASHRAE MERV 12-16) are recommended for general applications.
Tests have shown that sub-micron filters in re- circulated air systems
will produce system filtration effectiveness which approaches HEPA
levels. It is generally agreed by experts that the additional expense
for HEPA filters cannot be justified in many commercial applications.
B.
HEPA
filters are recommended for health facilities where immuno-compromised
patients cannot tolerate even small amounts of bacterial or fungal
contamination and non re-circulated air is utilized.
3.
Select diffuser
plate configuration:
A.
Air flow capacity
Low - 180 cfm nominal
Medium - 300 cfm nominal
High - 450 cfm nominal
B.
Air flow patterns
8-way throw (standard)
5, 3, 2, or 1-way throw (options)
Special models are also available.
Consult Factory for details.
Filter Costs and Filter Life Expectancy
The cost of sub-micron filters are typically less than
conventional high-efficiency sub-micron filters, such as bag type, or 10"
deep pleated filters. In a Uni-Guard system, for a given contamination
rate, the overall system filtration effectiveness is greater for all
types of filters and their useful life is longer than conventional
systems because there is up to ten times more filter surface area to
collect particulates. Therefore, for a given environmental application,
the filters in a Uni-Guard system will last longer than filters of equal
performance, used in a conventional system. In a typical Uni-Guard
system, the sub-micron filter life is approximately 24 to 30 months, and
the dust pre-filter life is approximately 2 to 3 months.
System Design
Filtration system analysis and design assistance is
available from Warren Technology. Computer analysis of existing systems
and recommendations for up-grades, including life cycle costing, is
available.
Summary
Uni-Guard is a revolutionary concept that provides
superior sub-micron air filtration and draft free thermal comfort at
lower costs than conventional systems. The concept can be applied to a
single room or zone(s) within a building or to an entire building. Uni-Guard
is simple to install in most central fan systems in existing and new
buildings.
Occupants will SEE and
FEEL the difference.
You may also measure the difference immediately after
installation with a Laser Particle Counter available from Warren
Technology (sale or rent with refundable deposit). Contact factory for
details.
