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Air and Climate Change Research

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: US EPA. (1999) "A Preliminary Methodology for Evaluating the Cost-Effectiveness of Alternative Indoor Air Quality Control Approaches." Publication No. EPA/600/R-99/053. NTIS No. PB99-156184.

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: US EPA. (1997). "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." Publication No. EPA-600/R-97-131. NTIS No. PB98-113368.

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).

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