The outbreak of the novel coronavirus (COVID-19) has pushed medical facilities around the world to rapidly develop strategies for treatment and containment. UNC REX Hospital in Raleigh, North Carolina is one of the many healthcare centers in the United States working to mitigate the spread of the virus and prepare for an increased number of COVID-19 patients.
Protecting healthcare workers and hospital staff as well as limiting the spread of the virus to other areas of the hospital is critical in providing care for those affected by COVID-19. Working with the UNC REX facilities department, mechanical designers at RMF Engineering, Inc. were able to retrofit a typical patient suite to be able to handle an influx of COVID-19 patients. This process involved several modifications to the existing HVAC and building management systems, as well as to the hospital workflow.
The existing air handling unit is dedicated to this patient suite, providing ideal conditions for the retrofit application. In other words, the associated HVAC system does not communicate with any other spaces of the hospital and is contained to only the areas being converted into the isolation suite. The existing AHU consists of a supply fan and a return/relief fan with a mixed air damper. This type of configuration is typical for most applications of large central station air handling systems. Supply air is delivered to the spaces, providing conditioning, before it is cycled back to the unit by the return fan. Within the unit, control dampers vary the amount of return air that is allowed back into the supply system. The rest of the air is then “relieved” to the outdoors. The remaining volume of air is made up via a separate outside air intake louver. Outside air is pulled in by the supply fan, where it mixes with the returned air from the building. This mixing pre-treats the air, by bringing the temperature of the outside air closer to the temperature of the space, which helps in energy savings. However, the recycling of air through the unit is not acceptable when considering the containment of COVID-19. Several modifications to the existing system were made in order to address this.
The first step was to eliminate the possible recirculation of air to the supply system. This was accomplished by sealing the mixed air control damper, which forces the system to exhaust all of the air out to the atmosphere. Because there is no longer mixing, all air supplied to the suite is 100% outside air. With the change in season, this presents its own problem. Because the unit was converted to process 100% outside air, it no longer had the cooling or heating capacity to properly condition the air supplied to the suite. Split system heat pumps were chosen to pretreat the outside air to the suite. They provide cooling and heating, and are easily installed on the roof, causing no interruption to the suites preparation for occupancy. Having this space operational as soon as possible for the admission of patients was a critical path driver in equipment selections. Equipment with the shortest lead time and best controllability were considered here.
Next, we addressed how changes in air pressure within the suite and adjacent corridors could lead to the possibility of transmission outside of the patient area (e.g., in the admission of new patients). When new patients enter the suite, there is a period of time when the suite doors will be open, exposing the corridor and those passing to potential infection. To address this, the air handling unit on the roof was retrofit with a variable frequency drive, which allows controllability of the supply air into the suite. This is controlled via a duct mounted pressure sensor, which will sense when the space pressure requirements are no longer met. When this happens, the variable frequency drive slows the operation of the supply fan, while the exhaust remains at full flow, making the suite negatively pressurized for this period of time. After the suite is sealed, the system returns to its normal operation.
Modifications within the suite were just as critical in ensuring proper care and protection of the staff. Anterooms were created in the suite, partitioning off the designated entrance and exits for improved workflow management. The entrance opens into a staff area and locker room where employees garb up and prepare for their shift. The HVAC system serving this space was modified to ensure positive pressurization and protection of this “clean” area. After passing through the anteroom door into the suite, the workers are unable to reenter the clean area. To exit, all workers are directed to the opposite end of the suite, where they enter another anteroom that is 100% exhausted. Here, the staff removes their soiled clothing and equipment and are eventually cleared to leave. It is critical that there is a defined airflow direction from cleanest to least clean. Because of this, there are several areas where the airflow relationship of two adjacent spaces is necessary to maintain and additional measures were needed to ensure protection. Door sweeps were added to increase the pressure differential between the spaces, thus reducing the chance for air transferring in the wrong direction. Digital differential pressure monitors display the relationship between spaces and will alarm if the relationship is not met within a period of time. Given the nature of patient care in these areas, it is not uncommon that a door is accidentally left slightly open. In this event, the staff will be alerted quickly with a visual indicator and can make the proper corrections.
As a result of these measures, the COVID-19 patient suite at UNC REX Hospital is currently occupied with affected patients and healthcare workers are able to safely provide care. Because of the accelerated schedule and coordination between UNC and RMF, design and construction happened concurrently over a period of 2 weeks. This type of fit out would typically be done in phases over the course of several months. Although the management of COVID-19 patients would best be carried out at a facility ready to accommodate such a large influx of cases, this may not always be possible. In the interim, similar building conversions and pop-up facilities are what many are relying on for treatment. Modifications to an existing building for patient overflow can offer the ability to provide appropriate treatment and help slow the spread of the virus to levels that are manageable for the worldwide healthcare system.
About the Author: Brandon Nevin, Mechanical Designer
Nevin is a mechanical designer at RMF Engineering in their Raleigh, NC office. He is experienced with mechanical, plumbing, medical gas, and fire protection system design. His project experience includes design of mechanical systems for healthcare facilities, commercial buildings, higher education / universities, as well as central heating and cooling plants. His experience also includes assessment of existing conditions, BIM coordination and management, contract drawing production, and construction administration phase review and management.