Lifecycle Cost Analysis for Single-Use Systems - Less complicated single-use systems have more favorable lifecycle economics. - BioPharm International


Lifecycle Cost Analysis for Single-Use Systems
Less complicated single-use systems have more favorable lifecycle economics.

BioPharm International Supplements

Disposables Versus Stainless-Steel Systems

Decisions to use single-use systems should be made early in a project, typically during conceptual engineering. Single-use systems have a large impact on the layout of a facility and also may affect automation strategies, clean utility requirements, floor-to-floor heights, project timelines, procurement schedules, and even area classifications like heating, ventilation, and air-conditioning (HVAC) design. Facilities that use only single-use processing sometimes realize substantial advantages over conventional designs, but tend to be limited in scale.1 Most biopharmaceutical facilities use a mixture of stainless-steel and single-use systems and for these facilities, an analysis of lifecycle economics can help determine the optimum mix.

Estimating Capital Costs

Table 1. Capital savings for single-use buffer bags
Capital costs for single-use systems are always lower than for conventional stainless-steel systems, so evaluating lifecycle economics comes down to comparing differences in operating cost versus the cost of capital. In conceptual design, capital costs are estimated from equipment cost using the Lange factor, which is an empirical multiplier that accounts for the cost of installing the equipment. Lange factors vary depending on the type of equipment and whether it arrives as a preassembled skid or as individual equipment items that are assembled in the field. The factor accounts for all direct costs associated with equipment installation including setting up the equipment, utility and process piping hookups, and automation.

Table 2a. Estimated facility and HVAC costs (USD)
Table 1 shows how the Lange factor is used to estimate capital-cost savings for a simple scenario involving replacing multiple stainless-steel buffer hold vessels with single-use bags. By doing so, not only are we able to delete the stainless-steel buffer hold vessels, but also we are able to delete two CIP skids and their corresponding infrastructure. The single-use case still has some capital cost (for bag holders) but its Lange factor is much lower than for stainless-steel vessels, reflecting the bags' simpler installation. The total direct capital cost savings for this alternative are just over eight million dollars.

Table 2b. Difference in facility space costs as a result of implementation of single-use systems. Only ISO 9 (Grade D) and controlled not classified space are affected, along with space needed in mechanical areas as a result of decreased HVAC needs by reducing cleanroom space.
Often, the use of single-use systems affects either the area required in a facility or the cleanliness classification of that area. For the above alternative, using single-use bags eliminated 1,100 square feet of grade D space, which originally contained the stainless-steel buffer hold vessels but added back 1,075 square feet of controlled not classified space for storing single-use bags. These changes affect both capital and operating costs that are quickly estimated from rough order of magnitude benchmarks in Tables 2a and 2b. Experience suggests each added square foot of cleanroom space also contributes additional mechanical space, which is included in Table 2b. Capital and HVAC costs are calculated for a base location and discounted 25% to adjust for the local market. For this alternative, savings in facility costs are a relatively small ($58,000) with an annual savings in HVAC costs of $791.

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