The world we live in is a rapidly changing place. Constantly improving technology, changing trends in healthcare delivery and public health emergencies are driving how we design the inpatient care spaces of the future. With the building lifespans averaging 50+ years the decisions made today will have significant impacts on how a building can adapt to a changing landscape. This article will examine the design of HVAC systems for patient floors and strategies to meet the demanding energy efficiency standards we face as well as be flexible enough for the uncertain future.
A typical inpatient floor consists of a few dozen patient rooms, clinical support spaces, family areas and often a few airborne infection isolation (AII: negative) or protective environment (PE: positive) rooms. Patient floors are commonly combined with one HVAC system serving several floors. While this is desirable from a system efficiency and minimized maintenance perspective, choice of system type can dictate what specific functions those patient rooms can serve. ASHRAE Standard 170 as adopted by the Facility Guidelines Institute permits recirculating room units such as fan coils or chilled beams for a standard patient room. However, in more specialized rooms such as critical / intensive care, AII, or PE, recirculating units are not permitted and the required air change rates can increase by a factor of two or three. While distributed systems such as chilled beams may be desirable for energy and system sizing efficiency, the most adaptable system to all room types, particularly higher acuity, is a traditional variable air volume (VAV) system.
Possible solutions for providing systems that are both energy efficient and flexible focus on designating specific areas to handle extreme events. For example, in a building with several floors or distinct areas of patient rooms one floor or area could be a designated emergency isolation ward and have its own dedicated VAV system while other similar use floors share systems. Best practices dictate that the designated area be separated from other areas with vestibules and gowning areas for use in emergency mode to prevent spread of infection. In normal mode the air handler would provide a mix of fresh (outdoor) and recirculated air to the rooms which would meet the needs of either normal or critical care patient rooms.
In the event of an emergency the entire floor could be easily changed to become a negative pressure isolation ward through automated controls; the exhaust system airflow would be increased to full capacity to create the negatively pressurized area. For emergency conditions, 100% outside air is recommended, meaning all air supplied to the spaces would be fresh (outdoor) air and then completely exhausted with no recirculation. Another adjustment to provide further protection is managing the air change rate during emergency model to reduce the amount of time particulate in the air stays within the space thus reducing potential for contamination.
To accomplish this flexibility, considerations for the air handling system design include:
Heating and cooling coil design in the air handler so that coils have controllability to meet the loads during normal mode and the capacity for emergency mode when loads are the highest. Duct and exhaust fan sizing, particularly exhaust ducts, to accommodate a higher airflow in emergency mode.
UV-C lights to assist in keeping coils as clean as possible (note: effectiveness to actually clean the supply air is dependent on the characteristics of the specific bacteria or virus and is yet to be proven).
Redundancy in coils and fans taking into consideration that servicing failed components during an emergency may not be an option.
In summary, a strategy to prepare for the unknown is to designate a patient floor or floors as a rapidly reconfigurable unit. Using proven, highly adjustable technologies such as VAV systems with automatic configuration controls allows the system to operate efficiently to meet the typical clinical program needs, but can be altered to meet unforeseen, unusual conditions.
Chris Wysoczanski, PE - Associate Jason Butler, PE - Principal
Mechanical Engineering Group Leader Healthcare Market Leader