Stand-alone health care buildings: HVAC
Stand-alone medical buildings and specialized treatment facilities are engineering challenges, and more are being designed and built due to changes in health care requirements. Indoor air quality, indoor environmental quality, and other factors make HVAC systems a high priority.
Neal Boothe, PE, Principal, exp, Maitland, Fla.
Douglas T. Calhoun, PE, Senior Vice President, WSP | Parsons Brinckerhoff (formerly ccrd), Dallas
Caleb Haynes, PE, Principal/Director, TME LLC, Birmingham, Ala.
Brian Kolm, PE, Team Leader, Mechanical, HDR Inc., Omaha, Neb.
Craig Kos, PE, LEED AP, Vice President, Environmental Systems Design Inc., Chicago
Bryan Laginess, PE, LEED AP, Vice President, Peter Basso Associates, Troy, Mich.
CSE: Have you specified distinctive HVAC systems on any stand-alone medical buildings and specialized treatment facilities projects?
Kolm: With the continuous push for more energy-efficient buildings emerging, mechanical technologies are being applied to new health care facilities. One of these technologies is the heat-recovery chiller. Heat-recovery chillers produce chilled water on the evaporator side, but also produce hot water heated to 100° to 140°F on the condenser side. In essence, the heat being rejected from the chilled-water system is being used on the heating hot-water system, which takes loads off the boiler system, saving both gas and electrical energy. This system pairs well for health care facilities, due to the amount of reheat energy required during the summer months to maintain minimum air changes to spaces throughout the building. It works even more efficiently if there is a constant chilled-water load during the winter months as well.
Calhoun: We have used a VRF system for many specialty clinics and FSEDs. This system provides simultaneous heating and cooling and optimizes zoning for temperature control. It also minimizes structural impact and architectural coordination for plan changes from one building to the next, which aligns with the prototype approach.
CSE: In outpatient surgery buildings, what HVAC challenges have you overcome?
Calhoun: Meeting or managing the expectations of surgeons accustomed to working in state-of-the-art, inpatient ORs can be a challenge. We have developed and implemented strategies to achieve low-temperature (below 65°F) ORs while maintaining code-required relative humidity levels using packaged DX equipment.
Boothe: A frequent challenge in outpatient surgery centers is temperature control in the ORs. As these buildings are usually smaller and not part of a larger campus, typical systems, such as packaged DX equipment, may be used for the air conditioning systems (a chilled-water solution is often fiscally impractical for such a small building). We have to work closely with the owner and the staff to understand their temperature needs in the ORs. Some physicians and/or procedures require colder air in these ORs, which can be difficult to obtain with DX-type equipment. This may lead to the need for a small dedicated chiller system just for the ORs when colder air is required in these spaces.
Laginess: Maintaining steady temperatures and humidity levels. In most cases, these buildings are not supported with chilled water, hot-water heating, and steam. Gas-fired/DX-type units are used with steam-generating humidifiers feeding the supply duct. This type of system can be difficult to control, especially during colder seasons. Getting high levels of modulation on both the heating and cooling side of the AHU is important. Fully modulating compressors and the use of modulating reheat can really keep temperatures and humidity levels from spiking either way.
Kolm: Outpatient surgery buildings are designed nearly identical to an inpatient surgical center from an HVAC, medical gas, and plumbing perspective. One distinction between the two is that an outpatient surgery building will typically have periods of time where it is unoccupied either overnight and/or during the weekend. Both the benefit and challenge that can come from this is having the HVAC system turn down to lower air changes while maintaining proper pressurization. The benefit is the energy savings, but the challenge comes with designing the control sequence, commissioning it, and maintaining it by the owner's staff. The key to any control sequence is writing it such that the contractor and building owner understands what is going on. Commissioning it and validating that it works effortlessly to maintain proper minimum air changes, proper pressurization, and a timely response to bring the system back to an occupied mode can be tough, but working the bugs out of the system needs to be done to ensure that the system is correct per the engineers specifications for the owner's and patient's safety. Ultimately, proper owner training on how the system is to operate in such mode is just as important to keep the system running smoothly and efficiently and to maintain the potential energy savings for the life of the building.
CSE: What unique HVAC requirements do such projects have that you wouldn't encounter in other buildings?
Kos: One unique HVAC requirement in outpatient sites can be humidity control, particularly in imaging suites. For example, MRI spaces require a minimum relative humidity of 40%. In business occupancies in the northern parts of the United States, maintaining a minimum humidity level of 40% in the winter months can be a challenge. Typically, these buildings are not humidified, so supplemental systems are required to control the environment. We also review the room construction and the surrounding areas with the architect for opportunities to barrier the areas requiring special control, to increase the effectiveness of the supplemental systems.
Kolm: There are many unique HVAC requirements for a health care facility versus other buildings, such as filtration requirements, minimum air-change requirements, humidity requirements, and different exhaust systems. However, one major distinction is the temperature requirements for spaces such as pharmacies and ORs. For these space types, it is not unusual to see room temperatures as low as 62°F to keep the staff conditioned. To provide room temperatures as low as this, one cannot design an HVAC system similar to an office building. Instead of delivering supply air at 55°F, one would have to deliver air as low as 48°F to keep the space comfortable and not humid.
Boothe: Health care facilities, including outpatient facilities, must meet guidelines that mandate pressure relationships be maintained in many spaces. For example, ORs must always be positively pressurized to reduce the risk of infection to patients. This usually means constant-volume (always running) systems are used for the HVAC design to ensure proper pressures are maintained as needed. In non-health care buildings (such as offices), typically a variable air system is used (so that air conditioning/heating systems only run to meet temperature and then turn off until needed again).
CSE: When retrofitting existing buildings for stand-alone medical buildings and specialized treatment facilities projects, what challenges have you faced and how have you overcome them?
Laginess: Working with the existing infrastructure is the biggest challenge. Renovating a space from an office to a medical office is not a big change, but if that office use is converting to an ambulatory procedure suite, then air systems, plumbing infrastructure, lighting, and power all need to be closely evaluated to make this change.
Calhoun: Putting medical facilities in a building designed for office use presents challenges in making existing air units provide the zone temperature control required by code. In many cases, the existing equipment has to be replaced or retrofitted to provide the more specific temperature control required for medical usage. In addition, plenum clearances tend to be less than what is typically provided in traditional medical facilities, because return-air systems are typically not ducted in nonmedical applications. This has required extensive coordination with architects and contractors to make sure everything fits within the plenum while still maintaining the code-required ceiling heights.
Kolm: One of the main retrofit problems that arise is the existing floor-to-floor heights. When retrofitting older buildings, more times than not the floor-to-floor heights are 12 ft or lower with beams as deep as 2 ft. When dealing with minimum air-change requirements and meeting energy codes, ductwork sizes can be large and routing them through these types of buildings can be difficult. Thus, to route ductwork through the building, engineers need to be creative in their designs. Some strategies include building soffits at locations of duct mains, creating several chases through the building to eliminate duct crossovers and main sizes, and attempting different mechanical technologies that can still maintain proper air changes but would require smaller equipment and duct sizes.
Kos: One of the biggest challenges when repurposing a building is adapting the HVAC system for the new usage. At one site, the existing systems were designed for the open retail spaces of a bookstore. The existing configuration used multiple systems that were dedicated to each large, open zone. The new medical office spaces required the ability to control temperature in offices, exam rooms, work areas, and staff and procedure areas. The existing systems were converted to variable volume and temperature systems to provide additional zones of temperature control for the new space usage. At another site, the existing HVAC systems designed for a 4-story speculative office building were not adequately sized for the new clinical functions. A new rooftop unit and supply and return risers were installed in the occupied building to support the new cooling and ventilation loads. Additionally, a new dry-cooler system was added for 24/7 cooling-only building loads.