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Designing for Longevity: Creating Affordable Redundancy and Renewability for Hospital MEP Systems - Four Strategies for Equipment Redundancy

© Spiezle Architectural Group
By William R. Procz, PE, LEED AP and Donald S. Procz, PE, LEED
May 13, 2021

The ability to renew or replace aging mechanical equipment in hospitals is a common but complex challenge. All too frequently, facility managers and engineers find that systems have been designed without any provision for their eventual replacement. As healthcare facilities typically require uninterrupted, 24/7 system operations, the process to upgrade or replace equipment can be costly and complicated. For example, if a hospital hasn’t been properly designed for ongoing renewal, these efforts may entail the use of temporary “roll-up” equipment. That is an expensive proposition involving portable units, typically brought in on tractor-trailers, that serve as a temporary backup. 

As we all navigate through the COVID 19 pandemic, many health systems are taking a hard look at their program lines and more specifically space utilization and are concluding that there may be more efficient ways to manage existing space as opposed to developing new space to support their needs.  The understanding is driving more systems to re-invest in existing facilities by using space more efficiently as opposed to building new.  This revised approach puts even more pressure on existing MEP infrastructure and the challenges that engineers face when there is a need to modernize existing equipment.  Innovative thinking is required.

Equipment Redundancy: Four Strategies

As engineers are called upon to design mechanical, electrical, and plumbing systems in new hospitals, it is important to design for renewability as well as sustainability. Equipment redundancy is the key. Today, redundant equipment is often installed for reliability anyway, but when it comes time to replace equipment, the redundant unit can be operated while the base-load unit is replaced, and vice versa.

Although vital for ongoing system renewability, equipment redundancy can be expensive and is frequently deferred due to space and budget constraints—even though the additional costs can often be offset by the significant avoided costs when the system is ultimately replaced. We have identified four potential strategies to consider when seeking redundancy and renewability.

  • Redundancy Strategy #1—Available Space: The most basic and least expensive option to provide for renewability is to designate space for a future redundant unit. The cost of the unit is therefore postponed until it is needed for phasing of the replacement project.  Providing space is not the only consideration.  Much thought and coordination must be put into developing a strategy to place new equipment in the available space in the future, which requires an innovative, holistic approach.
  • Redundancy Strategy #2—The “Utility Infielder”: A step up from simply providing space for a future redundant unit is the “utility infielder” strategy, the most common approach. Like a utility infielder in baseball, a redundant unit is available on site to back up other critical units. For example, a hospital may use a swing unit to facilitate the replacement of older air handling units (AHUs).
  • Redundancy Strategy #3—The Common Header: A further step in planning for renewability is the common header approach, in which engineers “header together” multiple AHUs into common ducts. In other words, the main ductwork is interconnected to enable the units to serve a common zone or zones.
  • Redundancy Strategy #3A focus on Sustainability —The Dedicated Outside Air System: An improvement on the common header concept is the use of one of the AHUs as a dedicated outside air system (DOAS). During normal operation, the DOAS preconditions the minimum outside air, which is then supplied to the other units. This can result in an approximate 25-30% reduction in the peak cooling demand as well as significant energy savings by reducing over-cooling of air, which more than pays for the cost of the DOAS unit. In terms of renewability, when the time comes to replace an AHU, the DOAS can be used as a redundant unit.

Buildings that incorporate renewable systems usually experience improved reliability, performance, and compliance. There is also the added benefit of significant operating and maintenance cost savings over time as compared to buildings with systems that are not renewable.

The life expectancy of redundant systems is often extended because improved maintenance can be accomplished during normal business hours, with the ability to take individual units offline. The most important incentive for renewable systems is the millions of dollars in costs that can be avoided when it comes time to eventually replace the main systems.

Addressing Non-Renewable Systems: A Common Concern

While designing new systems for renewability is an important objective, engineers often find that older hospital MEP systems reflect a lack of planning for future upgrades and replacements. Still, it is important to seek cost-effective renewal strategies that minimize or eliminate downtime.

One example can be found in a system modernization for a major medical center located in the Northeastern part of the United States. Originally built in 1975, the center was experiencing difficulty in maintaining acceptable relative humidity levels in its operating rooms during the summer. On warm and humid days, the relative humidity levels in several of the ORs were exceeding the allowable maximum of 60%, and were therefore out of compliance with the FGI Design Guidelines. To complicate matters, the existing AHUs servicing the ORs were all in need of replacement due to their age and condition, but the hospital could not shut the ORs down for any appreciable amount of time to accommodate replacing the old units.

The situation was similar to that of many older medical facilities in which future renewability had not been well thought out. How can the engineering team improve the performance of the existing AHUs to ensure that the relative humidity levels remain in compliance? How can the units be replaced without shutting down the ORs for an extended period?

The use of a low-temperature chilled water system is the most prevalent solution offered to healthcare institutions to improve temperature and humidity control in ORs. The standard go-to infrastructure replacement tactic is the deployment of “roll-up” equipment: a temporary AHU with interconnecting ductwork. But in the case of the Northeast medical center, our engineering team proposed an alternative: the installation of a permanent AHU on the roof that assumed the burden of cooling and dehumidifying the required minimum outside air that the existing older systems were struggling to process.

This new rooftop air handling unit was designed to function as a DOAS to provide pre-conditioned outside air to the four existing AHUs serving the ORs and other critical spaces. The new rooftop DOAS was equipped with a desiccant wheel for enhanced dehumidification to support the ORs, which are maintained at 62 degrees F to accommodate surgeon preferences. Clever sizing of this unit’s new ductwork allowed for the DOAS to provide full airflow temporarily for one unit at a time, so the outdated equipment could be replaced, and the expense of a temporary unit could be avoided. In addition, the hospital was able to use the rooftop DOAS in the future for temporary full airflow for any floor, should there be an unplanned shutdown of a unit or a planned shutdown for maintenance purposes.

Preconditioning the minimum outside air supply to the four existing AHUs via the new rooftop AHU has eliminated the fluctuations in the relative humidity levels in the ORs during the summer months, ensuring continuous compliance. The success of the project has enabled the hospital to postpone the replacement of the four existing AHUs, resulting in a shift of allocated funds to other pressing budgetary needs.

“Prior to conditioning the outside air, we had to continuously shop-vac the excess condensate that was overflowing the drain pans and spilling out of our air handling units to prevent the water from leaking through the floor onto the Radiology unit below all summer long,” the medical center’s building manager has noted. “The rooftop solution is an innovative engineering approach that will save the hospital millions in costs as well as thousands in energy.”