Cost Analysis of Indoor Air Control Techniques
Several studies have been completed addressing the costs and the cost-effectiveness of alternative IAQ control measures.
Methodology for Cost-Effective Selection of IAQ Control Options
A simplified methodology has been defined that can be used by indoor air quality
(IAQ) diagnosticians, architects/engineers, building owners/operators, and
the scientific community, for preliminary comparison of the cost-effectiveness
of alternative IAQ control measures for any given commercial or institutional
building. Such a preliminary analysis could aid the user in initial decision-making
prior to retaining experts (such as HVAC engineers and building modelers)
who could conduct a rigorous evaluation.
This preliminary methodology has been published in an EPA report entitled "A Preliminary Methodology for Evaluating the Cost-Effectiveness of Alternative Indoor Air Quality Control Approaches" (EPA-600/R-99-053; NTIS PB99-156184, June 1999). (Abstract)
This preliminary methodology consists of text, logic diagrams, and detailed worksheets (including reference tables) that are intended to aid the user in:
- assessing which IAQ control option(s) might be applicable in the specific building being addressed;
- designing alternative control measures [involving increased outdoor air (OA) ventilation, air cleaning, or source management steps], and developing rough estimates of the installed costs, operating and maintenance costs, and annualized costs for these measures;
- estimating the approximate effectiveness of the alternative control measures in reducing occupant exposure to contaminants of concern; and
- comparing the cost-effectiveness of the alternative control measures under consideration, to aid in selection of the optimal control approach.
The methodology addresses the following IAQ control options:
- Improved ventilation with OA, including a) installation of enlarged central heating, ventilating, and air-conditioning (HVAC) systems in a new building during construction; b) installation of a dedicated-OA HVAC system in a new building; c) retrofit of an enlarged HVAC system in an existing building; and d) retrofit of a new dedicated-OA system in an existing building
- Air cleaners to remove either particles or gaseous contaminants, including a) air cleaners installed in the ducting of the central HVAC system and b) self-contained air cleaners, independent of the central system
- Source management options, including source removal, replacement, treatment, or rescheduling
The cost data that were used in developing this methodology were obtained from the following sources:
- Cost data books, in particular, Mechanical Cost Data published by R.S. Means Co. (for the installed costs of fans/motors, cooling and heating systems, and ductwork)
- Vendor quotes (for the installed and maintenance costs for air cleaners)
- Published literature, including some in-house publications (for air cleaner performance and maintenance requirements)
- Handbooks published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (for heating/cooling HVAC design data for different climates)
- In-house computer modeling (for heating/cooling energy costs for different climates)
- Cost engineering textbooks (for capital recovery factors)
As used here, the term "cost-effectiveness" refers to the incremental increase in annualized cost per unit reduction in exposure by the building occupants. "Exposure" is the number of person-hours per year during which the occupants are exposed to a unit concentration of the contaminant of concern; in this report, the units of exposure are (mg/m3)-person-hr/yr. The most cost-effective control approach is the one offering the lowest annualized cost per unit reduction in exposure.
Energy Costs of Increased Ventilation in Humid Climates (DOE-2 Modeling)
A series of computer runs has been completed using the DOE-2.1E building energy
model, simulating a small (4,000 ft2) strip mall office cooled
by two packaged single-zone systems, in a hot, humid climate (Miami, FL).
These simulations assessed the energy penalty, and the impact on indoor relative
humidity (RH), when the OA ventilation rate of the office is increased from
5 to 20 cfm/person in this challenging climate to improve indoor air quality.
One objective was to systematically assess how each parameter associated with
the building and with the mechanical system impacts the energy penalty resulting
from increased OA. Another objective was to assess the cost and effectiveness
of off-hour thermostat set-up (vs. system shut-down), and of humidity control
(using overcooling with reheat), as means for reducing the number of hours
that the office space is at an RH above 60% at the 20 cfm/person ventilation
rate.
The results of this analysis have been published in an EPA report entitled "Energy Costs of IAQ Control Through Increased Ventilation in a Small Office in a Warm, Humid Climate: Parametric Analysis Using the DOE-2 Computer Model" (EPA-600/R-97-131; NTIS PB98-113368, November 1997). (Abstract)
Cost Analysis of Air Cleaners for Removing VOCs from Indoor Air
A cost comparison has been conducted of 1 m3/s indoor air cleaners
using granular activated carbon (GAC) vs. photocatalytic oxidation (PCO),
for treating a steady-state inlet volatile organic compound (VOC) concentration
of 0.27 mg/m3. The commercial GAC unit was costed assuming that
the inlet VOCs had a reasonable carbon sorption affinity, representative of
compounds having four or more atoms (exclusive of hydrogen). A representative
model PCO unit for indoor air application was designed and costed, using VOC
oxidation rate data reported in the literature for the low inlet concentration
assumed here, and using a typical illumination intensity. The analysis shows
that, for the assumptions used here, the PCO unit would have an installed
cost more than 10 times greater, and an annual cost almost 7 times greater,
than the GAC unit. It also suggests that PCO costs cannot likely be reduced
by a factor greater than 2 to 4, solely by improvements in the PCO system
configuration and reductions in unit component costs. Rather, an improved
catalyst having a higher quantum efficiency would be needed, increasing reaction
rates and reducing illumination requirements relative to the catalysts reported
in the literature. GAC costs would increase significantly if the VOCs to be
removed were lighter and more poorly sorbed than assumed in this analysis.
This analysis has been published in a journal article entitled "Cost Analysis of Activated Carbon Versus Photocatalytic Oxidation for Removing Organic Compounds from Indoor Air" (Journal of the Air and Waste Management Assoc., October 1998). (Abstract)