Delivering sustainability promise to HVAC Air Filtration: part II: life cycle sustainability of air filters.
Delivering sustainability promise to HVAC Air Filtration:
part II: life cycle sustainability of air filters.
What is sustainability? The word sustainability is derived from the Latin sustinere (tenere, to hold;
sus, up). Dictionaries provide more than ten meanings for sustain, the main ones being to
"maintain", "support", or "endure" (Wikipedia, 2009). The concept of sustaining resources for the use
of future generations is not new, but the term "sustainability" did not appear in environmental
dialogue until the 1970s. It became rapidly evident that environmental protections on a global level
could only be accomplished by also addressing the social and economic needs of human populations.
Since the 1980s, sustainability has drawn attentions of people worldwide especially among
politicians, business leaders, policy workers and practitioners of social science disciplines. Today
sustainability or sustainable development is almost related to almost all aspects of our life to address
human, social, economic, and environmental concerns.
There are numerous definitions in the literature but the basic principles and concepts remain
constant: balancing a growing economy, protection for the environment, and social responsibility, so
they together lead to an improved quality of life for ourselves and future generations. The most
widely quoted definition of sustainability and sustainable development is that of the Brundtland
Commission of the United Nations in the report (1987) "Our Common Future": Sustainable
development is 'development that meets the needs of the present without compromising the ability
of future generations to meet their own needs'. It needs the reconciliation of environmental, social
and economic sustainable development.
Science and technology in sustainability Advances in science understanding and technology
development are crucial elements of sustainable development to lead to long-term sustainable
solutions. To identify the critical need for a science and technology approach to sustainability, the
U.S. National Research Council (NRC, 1999), in a follow-up study entitled "Our Common Journey: A
Transition Towards Sustainability," observed:
The political impetus that carried the idea of sustainable development so far and so quickly in public
forums has also increasingly distanced it from its scientific and technological base. As a result, even
when the political will necessary for sustainable development has been present, the knowledge and
know-how to make some headway often has not.
Fortunately, the situation described by NRC is not the case anymore. Scientists and technical
professionals in business, academia and governments have begun to espouse significant and
growing interest in developing a scientific framework for analyzing and applying sustainability
principles systematically. These attempts are aimed at considering the creative human enterprise in
the context of the three domains of sustainability - economic, environmental (or ecological), and
societal. It was recently reported that Harvard Univ. Northwest Science Building, Cambridge, Mass.,
was designed to foster a connection between experts, scientists, and students from different
scientific fields to conduct research. It not only emphasizes cross-disciplinary research through its
design, but it also provides a scientific model that addresses environmental, social, and economic
sustainability (HighBeam, 2009).
What are we doing? According to the U.S. Department of Energy (DOE, 2008), buildings consume
approximately 35% of the total energy and about 65% of the electricity produced in the United
States annually. Implementing energy saving technologies not only reduces the cost to maintain a
building but also reduce the carbon footprint to environment. Air ventilation systems often account
for a significant share of a buildings' energy consumption.
In January 2006, the ASHRAE Board of Directors approved 'ASHRAE's Sustainability Roadmap'
where it defined a strategic plan to lead to the advancement of sustainable building design and
operation. It guides ASHRAE's efforts in helping its members in building sustainability and green
building design, construction and operation. As William Harrison, 2008-2009 ASHRAE President,
said in his speech 'Maintain to Sustain -Delivering ASHRAE's Sustainability Promise' at ASHRAE
annual meeting in Salt Lake City (Harrison, 2008), sustainability for ASHRAE means energy
efficiency and healthy, productive indoor environments. A green building is one that achieves high
performance over the full life cycle in the following areas (ASHRAE, 2006):
* Minimal energy consumption due to reduction of need and more efficient utilization of both
renewable and non-renewable natural resources;
* Minimal atmospheric emissions having negative environmental impacts;
* Minimal discharge of harmful liquid effluents and solid wastes;
* Minimal negative impacts of site ecosystems;
* Maximum quality of the indoor environment.
These sustainability guidelines call for energy efficient air filters without compromising quality of
the indoor environment as the pressure drop over air filters usually accounts for a large portion of
the total pressure drop in a ventilation system (Eurovent, 2005). In Part I of this study (Sun et. al,
2009), we addressed a strong demand from end-users and manufactures to develop an industrial
standard to classify the air filter energy efficiency and a wattage method was developed based on
airflow dynamics as expressed below:
W = Q * [bar.[DELTA]P]/[eta] = v * A * [bar.[DELTA]P]/[eta] (1)
Where W is the power in Watt; Q is airflow rate in [m.sup.3]/s; [bar.[DELTA]P] is average pressure
drop in Pa; [eta], is system energy efficiency (%), v is face velocity (m/s); and A is the face area
[bar.[DELTA]P]] = [1/M] [[integral].sub.0.sup.M] [DELTA]P(Q, K, T, H, x(t)) (2)
Where Q is the airflow rate; K is a parameter related to dust type and dust loading mechanism; T is
air temperature; H is air humidity; x(t) is a variable of dust mass loaded on a filter; and t is operation
time. It was found that an exponential pressure drop model can be used to simulate real pressure
drop curve vs. dust loading using ASHRAE 52.2 methos, i.e.,
[bar.[DELTA]P] = [1/M][M.[integral] 0]a * [e.sup.bx]dx = [a/Mb]([e.sup.bM] - 1) (3)
Where [DELTA][P.sub.initial] is initial pressure drop in Pa; [DELTA][P.sub.final] is final pressure
drop in Pa. a and b are constants, and M is total dust mass loaded (g).
Purpose of this paper There are more factors that have to be considered in reality beyond filtration
efficiency and energy efficiency in terms of sustainability of the filters in air handling units, such as
material source and disposal, shipping and handling, installation and change-outs, potential by-pass
or contamination, and their impacts on ecosystem, etc. This paper is the second part of a continuous
research project 'Delivering Sustainability Promise to HVAC Air Filtration'. The filter sustainability
will be further investigated through filter service life using life cycle cost analysis. The
demonstration is based on a real case study of an AHU in a commercial building. An in-depth study
on filter design, media structure and dust loading morphology will be also presented for better
understanding a sustainable structural design for the air filters.
MATERIALS AND METHODS
Materials and Measurements Two types of pocket filters (MERV 10) were investigated in this study:
surface loading (SL) and depth loading (DL). They were used in an AHU of a commercial building.
There were 40 filters (24"x24") installed in the AHU of this research. The operation conditions and
cost facts are listed in Table 1. The filter performance was evaluated using ASHRAE 52.2-2007
(Method of Testing General Ventilation air-Cleaning Devices for Removal Efficiency by Particle Size).
The filter energy efficiency was evaluated by the wattage method (Sun, et. al, 2009). In addition,
microscope and SEM (Scanning Electron Microscope) were applied for structural study and
Table 1 AHU operation conditions and cost facts
Air flow (CFM) 80,000
Number of filters 40
Filter face velocity (FPM) 500
Fan/motor/system efficiency ([mu]) 55%
Utility rate (S/kw.hr) 0.08
Operational pattern 14 hr/day, 7day/wk, 50wk/yr
Maintenance labor cost ($/hour) 30
Operating hours per year (hr/yr) 4900
Life cycle period (month) 12
Life Cycle Cost Analysis Life Cycle Cost (LCC) analysis is a method to evaluate the cost along a filter
service life, which generally includes filter cost ([LCC.sub.filter]), energy cost ([LCC.sub.energy]),
freight cost ([LCC.sub.freight]), maintenance cost ([LCC.sub.maint.]), and disposal cost
([LCC.sub.disposal]). It can be expressed as:
LCC = [LCC.sub.filter] + [LCC.sub.energy] + [LCC.sub.freight] + [LCC.sub.maint] +
Life Cycle Cost Analysis
Table 2 lists initial pressure drop, final pressure drop and filter energy efficiency. The energy
efficiency was calculated according to Equations (1-3), a direct indication of energy consumption
used to run air through each filter, i.e. it needs average 296 watts to run each SD filter and 141
watts for each penal prefilter (required for SL filter to ensure its service life). But it uses only 172
watts for each DP filter and there is no need for prefilters when using DP filters.
Table 2 Life cycle analysis of using PL vs. SL filters
Filter Options DL filter SD fillter + Prefilter
No prefilter Prefilter Final (GF1)
Filter Size 24"x24"x26" 24"x24"x2" 24"x24"x30"
Operating Life (month) 24 4 12
Cost($/filter) 100.00 5.00 40.00
Initial filter invest ($) 4000 200 1600
Filter cost ($/yr) 2,000.00 600.00 1,600.00
Initial pressure drop ("WC) 0.21 0.20 0.30
Final pressure drop ("WC) 0.80 0.60 1.50
Average pressure drop ("WC) 0.41 0.33 0.70
Filter energy eff. (watt) 172 141 296
Energy consumption (kw.hr/yr) 33,705 27,627 58,017
Energy cost ($/yr) 2,696.40 2,210.17 4,641.35
Freight (S/filter) 4.00 1.00 2.50
Disposal fee (S/filter) 2.00 0.50 1.25
Labor for filter changeout (hr) 0.20 0.08 0.30
Cost for changeout ($/filter) 6.00 2.40 9.00
Miscellaneous cost ($/yr) 240.00 468.00 510.00
Subtotal cost ($/yr) 4,936.40 3,278.17 6,751.35
Total cost ($/yr) 4,936.40 10,029.52
Saving by using DL filter vs. 5,093.11
SL filter ($/yr)
As you can see from Table 2, although DF filter had a much higher initial filter invest ($4,000) than
did SL filters ($1,800), it saved 60.6% energy in comparison of SD filter plus prefilter, which
indicated a reduction of C02 emission 39.0 tons/yr by using 40 DL filters in the AHU (Carbon dioxide
emissions calculator, 2009). As DL filters have a longer service life, it also reduced the cost of filter
change-out, disposal and freight (see Table 2). It saved $4155.11/yr on the energy cost and
$738.00/yr on miscellaneous cost, including shipping, installation, filter change-out, and disposal
fees. Overall it saved a total of $5,093.11 /yr (50.8%) by using DL filters vs. SL filters.
The pie charts in Figure 1 shows the cost share of each filter in the life cycles. It demonstrated that
energy cost is the major portion of the total filtration system cost, which was 54.6% of life cycle cost
for DL filter, 68.7% for SD filter, 67.4 for prefilter, and 68.3% for SL filter plus prefilter.
Filter cost ($) 40.5%
Energy cost ($) 54.6%
Miscellaneous cost ($) 4.9%
Filter cost ($) 23.7%
Energy cost ($) 68.7%
Miscellaneous cost ($) 7.6%
Filter cost ($) 18.3%
Energy cost ($) 67.4%
Miscellaneous cost ($) 14.3%
Prefilter + SL
Filter cost ($) 21.9%
Energy cost ($) 68.3%
Miscellaneous cost ($) 9.8%
Figure 1 Life cycle cost share of different filters
Note: Table made from pie chart.
A Further Look at Filter Structure for Sustainable Design (1)
Figure 2 shows SL and DL filters after service from the field, where the DL filter showed a rigid self-
supporting structure vs. the soft SD fitter lack of rigidity for self-supporting. The pockets of the DL
filter remain straight regardless of whether the airflow is on or off.
[FIGURE 2 OMITTED]
The DL filter had a gradient fiber density across the depth of the filter media for maximum dust-
loading and particulate retention at minimum resistance to airflow (see Figure 3-a). The fibers are
bonded by self-thermal adhesion without any chemical binders or negative emission to the
environment or harmful to human beings. Every pocket is fabricated by thermal welding and sealing
with high bursting and tear strength. The pockets are built into the frame by molding with no seams
or joints to achieve a structural integrity that ensures no leaking, fiber shedding, or by-pass. In
addition, as you can see from Figure 3-c, there are special designed welded spacers in each pocket
to keep all airflow channels consistently open to minimize the resistance to airflow and provide
uniform dust loading across the filter area during the process of field service.
[FIGURE 3 OMITTED]
Figure 4 showed how the dust captured on the DL filter after 12 months of service. As you can see,
large particles were captured on the relatively open upstream, fine particles were captured in the
middle microlayer. Downstream is a strong substrate with a smooth surface, which was clean with
no dust or particulate migration observed.
[FIGURE 4 OMITTED]
Figure 5 showed how the dust captured on the SD filter after 12 month use. The upstream was
covered with fine particles as large particles were captured by prefilters. Lacking the depth of a
three dimensional gradient structure, the SL filter functioned just like the microlayer of DL filter to
capture small particles which explains why a profiler is necessary to run SL filters to maintain their
normal service life. Figure 4-b showed particle migration from downstream of the SL filter especially
around seaming stitches. The fiber/particles shedding from the SL filter was further confirmed by
downstream membrane test (Figure 4-c).
[FIGURE 5 OMITTED]
Sustainability has reached almost every aspect of our life today. Though there are numerous
definitions of it, the basic principles and concepts remain constant: balancing a growing economy,
protection for the environment, and social responsibility, so they together lead to an improved
quality of life for ourselves and future generations. Scientific understanding and technology
development are crucial elements of sustainable development, which will play a more and more
important role to lead to long-term sustainable solutions.
Buildings consume approximately 35% of the total energy in the US. Air ventilation systems account
for a significant share of a building's energy consumption, where the pressure drop of air filters
accounts for a large portion of the total pressure drop. To deliver sustainability promise to air
filtration in HVAC systems, there are more issues which need to be considered in reality besides
filtration efficiency and energy efficiency, such as material source and production, filter installation
and change-out, shipping and handling, disposal and waste management, potential by-pass or
contamination, etc. This paper was not intended to provide a complete method to assess
sustainability of the air filters but rather a starting point to look at filter life cycle cost from an end-
user's side, including filter cost, energy cost, and miscellaneous cost. The real case study revealed
that energy cost is the largest portion of filter life cycle operation, followed by filter cost and
miscellaneous cost including maintenance, freight, and disposal cost.
Finally, the depth-loading (DL) filter in this research showed significant advantage in sustainable
filter design. Though the investment cost was much higher, it saved 60.6% energy cost in operation,
generating a saving of $5093.11/year (50.8%) and a reduction of C02 emission of 39.0 tons/year,
which demonstrated an example of a sustainable solution for quality indoor environment.
The author would like to thank Mr. Dan Woodman, Dr. Thomas Caesar and Mr. Barry Kellar for their
valuable comments and support to this research project.
ASHRAE, ASHRAE's Sustainability Roadmap, January 22, 2006.
ANSI/ASHRAE Standard 52.2-2007, Method of Testing General Ventilation Air-Cleaning Devices for
Removal Efficiency by Particle Size, ASHRAE 2007, ISBN: 1041-2336.
Carbon dioxide emissions calculator, http://www.carbonify.com/carbon-calculator.htm, September,
2009.Department of Energy (DOE), Energy Efficiency Trends in Residential and Commercial
Buildings, October 2008.
EN779:2002, Particulate air filters for general ventilation. Determination of the filtration
performance, ISBN 058040903 1, 05/12/02.
Environmental Protection Agency (EPA), Sustainability, http://www.epa.gov/Sustainability/, 17
Eurovent, Recommendation concerning calculation of life cycle cost for calculating of life cycle cost
for air filters, September 2005.
Harrison, W. A., "Maintain to Sustain - Delivering ASHRAE's Sustainability Promise", ASHRAE
Meeting, Salt Lake City, June 21-25, 2008.
HighBeamResearch, http://www.highbeam.com/doc/1G1205989345.html, RD.Advantage Business
Media, 17 Dec. 2009.
National Research Council, 'Our Common Journey: A Transition Toward Sustainability', November
1999, ISBN-10: 0-309-08638-8.
Robert Goodland, 'Sustainability: Human, Social, Economic and Environmental, Encyclopedia of
Global Environmental Change. Copyright[C]2002 John Wiley Sons, Ltd.
Sikdar, Subhas Achieving Technical Sustainability', Chemical Engineering Progress, January 1, 2009.
Sun, C and D. Woodman, 2009, Delivering Sustainability Promise to HVAC Air Filtration, Part I:
Classification of Energy Efficiency for Air Filters, ASHRAE Transactions, Vol. 115, Part 2.
Sun, O., D. Woodman, L. J. Clark, Novel HVAC Filtration Solution for Healthy and Sustainable
Environment, HB2009, Syracuse, NY, September 13-17, 2009
UN Brundtland Commission, Report of the World Commission on Environment and Development,
'Our Common Future', March 1987, ISBN 0-19-282080-X.
Wikipedia Sustainability, http://en.wikipedia.org/wiki/Sustainability, 17 December 2009.
(1) Contents in this section were partially presented earlier at HB2009, Syracuse, NY, September
Christine Sun is RD Manager, Freudenberg Filtration Technologies, L.P., Hopkinsville, Kentucky.
Christine Sun, PhD
COPYRIGHT 2010 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the
Copyright 2010 Gale, Cengage Learning. All rights reserved.
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