The total costs of different air filtration options per unit of filtered air flow are estimated considering the costs of periodically replacing the filters (materials plus labor) and the incremental costs of energy used by fans. Since products with a similar particle removal performance can vary in price and airflow resistance (which affects energy costs), our estimates are examples that serve only to illustrate approximate costs and their variability among the filtration options.

1^st Cost
Filters vary a great deal in the degree of pleating (i.e., folding of the filtration media) and in the depth in direction of airflow. Depth may vary from approximately 2 cm to 30 cm. With an increase in depth and pleating, the area of filtration media increases, price usually increases, and the ratio of pressure drop to efficiency usually decreases. To limit pressure drops, more efficient filters tend to have increased pleating and depth. Because of their increased surface area, these larger filters will often have an increased lifetime between replacements.

Replacement Cost
Limited information is available for estimating the costs of labor for periodic filter replacement (removing old filters and installing new ones). The standard handbook for estimating labor time required for facilities management and repair (RS Means) does not provide different time estimates for filters with different efficiency ratings and allocates only 0.078 labor-hours for filter replacement in air handling systems that would typically have 3 to 8 filters, corresponding to 0.6 to 1.6 minutes of labor per filter. With the total labor cost of $46 per hour (RS Means), including overhead and profit, the cost per filter installation is only $0.5 to $1.2. We have used $1.2 per filter in one set of calculations. However, based on our experience, filter installation labor and costs will often be higher than these estimates. For example, documentation from the U.S. Department of Defense estimates 0.07 labor-hours (4.2 minutes) per filter for removal and replacement of cartridge filters, the most common type of filter. In addition, we believe that installation labor and costs will increase with filter efficiency because more efficient air filters are larger and heavier, and sometimes have more complex installation hardware. Consequently, calculations were also performed using the following installation labor cost schedule: $3 (4 min.) per filter for filters with a depth in the direction of airflow 10.2 cm; $5 (6.5 min.) per filter for filters with a depth of 15.2 cm, and $10 (13 min.) per filter for filters with a depth 30.5 cm.

Replacement Frequency
The lifetime of filters can be roughly estimated. As filters collect particles their resistance to airflow (i.e., pressure drop) increases. Filter manufacturers usually provide a recommended maximum pressure drop, e.g., 250 Pa, at which replacement of the filter is recommended. The increase in pressure drop across a filter as it loads with deposited particles is determined in a standard test involving a special test dust (ASHRAE). The resulting data yield a "dust holding capacity" at maximum recommended pressure drop and a particle removal efficiency (arrestance) for this test dust.

Energy costs
There is a general tendency toward higher energy and total costs with higher efficiency filters; however, the costs of using different filter models of the same efficiency vary widely. Consequently, use of more efficient air filters does not always increase cost.

Figure 4. Estimated cost of particle air filtration technologies. (LBNL-47833)
 

Figure 5. Modeling the Benefits and Costs of Enhanced Filtration Efficiency (LBNL-47833)