Utilizing mechanical filtration, like HEPA filters, has proven effective in producing virtually bacteria-free return air in hospitals, but viruses and many gasses can't be filtered and therefore, pass through unscathed. Introducing 100 percent OSA into the hospital heightens infection control by completely eliminating air transfer from room to room via a return air system. This also means less duct work, reduced construction costs and increased long-term flexibility with reduced ceiling congestion. Within the highly-regulated healthcare industry, most national codes require a minimum of six air changes per hour within the patient room. By employing 100 percent OSA, combined with the use of a radiant system, code permits a reduction to four ACH, thereby cutting energy expenditure.
The system introduces outside air at its current temperature, and when exterior conditions permit, it can be used directly for heating and cooling. However, in some climates, summer temperatures can reach as high as 120? F, while winter weather may drop below freezing. How can the air be conditioned while still maintaining energy-efficiency?
Employing a heat and cooling recovery system will help achieve the desired balance. While exhausting air back outside, the system will recapture some of the heat in the winter and cold during the summer months.
New technologies
In order to reduce the outside air requirements for a patient room, a radiant chilled beam system is being investigated. Employed in European healthcare facilities for years, chilled beam systems are slowly making their way into U.S. hospitals in both active and passive capacities. The ceiling-mounted active chilled beam system releases air into the room, immediately cooling it before it descends, while the passive system allows the room's hot air to rise naturally, and cooling it as it grazes the chilled beam.
Both provide individual temperature control, and are therefore ideal for the larger family-centered hospital room, which demands two different cooling environments to co-exist within the same space. Other benefits include reduced airflow and chiller load, smaller supply and exhausted ducts as well as lower floor-to-floor heights. Many codes require air filtration after a fan and therefore necessitate the use of passive chilled beams. Challenges for chilled beam technology, though, include high humidity levels as well as possible condensation and air dumping.
Specifying ultraviolet germicidal irradiation can heighten infection control (See Figure 4). Here, ultraviolet light is installed in the ceiling to kill viruses and bacteria where air flow is low, with a typical exposure of 30 seconds to a minute.
Distribution of UV radiation from a typical wall-mounted UVGI fixture
However, UVGI lights need to be tucked into the room's ceiling in a way that will avoid patient exposure. When possible, the light should be positioned above a ledge so that it isn't directly visible from anywhere in the room.
Putting it all together
Combining these new technologies with today's best practices and specific project directives can be a tremendous challenge, but computational fluid dynamic modeling can make them a reality for any space. Using room dimensions and internal and external heating and cooling load demands to create a patient room simulation, CFD modeling allows the designer to theorize air flow patterns, air velocity profiles and the mean age of air within the space at key locations, including patient, doctor and nurse positions (See Figure 3).
CFD Model simulates air flow patterns in a patient room, allowing designers to evaluate new and existing technologies
Using CFD modeling can help designers evaluate new and existing technologies as well as architectural design options concurrently to calculate their impact on the infection control, flexibility and energy requirements of each space. HBI
