Case study: Filter selection in a hospital renovation project

This project profile demonstrates how the different styles of filters can be implemented to achieve the various filtration requirements in a health care facility. The project was a renovation of an existing portion of a hospital to create a new pharmacy department, complete with a clean room suite. The project area was served by a new dedicated rooftop modular air handling unit.

Per ASHRAE Standard 170: Ventilation of Health Care Facilities, the pre-filters were required to be minimum efficiency reporting value 7 and the final filters were required to be MERV 14. Per USP General Chapter <797> Pharmaceutical Compounding – Sterile Preparations and USP General Chapter <800> Hazardous Drugs – Handling in Healthcare Settings, all supply air to rooms in the clean room suite was required to be high-efficiency particulate air filtered.

The overall filter arrangement of the air handling system on the project was as follows: pre-filters and final filters were provided in the AHU while laminar flow diffusers with integral HEPA filters were provided for all rooms in the clean room suite (see Figure 3).

Figure 4: Layout of air handling unit components is shown, including filtration components. Courtesy: IMEG Corp.[/caption]

The laminar flow diffusers were intentionally chosen at very low face velocities to reduce the air pressure drop of the filters. Additionally, the presence of MERV 14 final filters upstream of the HEPA filters should result in a very long HEPA filter life.

In the end, the arrangement and combination of different style filters on the project meet the cleanliness requirements of all project spaces while balancing operating costs, first costs and long-term maintainability.

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