Healthy hospital success: HVAC

With hospital projects, it is imperative that engineers get everything exactly right—after all, the lives of patients treated in the health care building may depend on it. HVAC systems are top-of-mind for engineers.

By Consulting-Specifying Engineer November 25, 2015




Richard Heim, PE, LEED AP, Mechanical Project Engineer, RMF Engineering Inc., Baltimore

Tim Koch, PE, LEED AP, Electrical Engineer, HDR Inc., Omaha, Neb.

Nolan Rome, PE, LEED AP, Senior Vice President, ccrd, a WSP | Parsons Brinckerhoff Co., Phoenix

Raymond Schultz, PE, Project Engineer, CannonDesign, Grand Island, N.Y.

Kunal G. Shah, PE, LEED AP, RCDD, President, PBS Engineers, Glendora, Calif.

Tommy Spears, PE, Vice President of Design Solutions, TME, Little Rock, Ark.

CSE: What unique HVAC requirements do hospitals have that you wouldn’t encounter in other buildings?

Shah: The hospital HVAC system’s primary function is to improve indoor air quality (IAQ) and mitigate airborne transmission of diseases. To deal with this, the hospital HVAC system design will have to consider filtration, dry-bulb temperature, wet-bulb temperature/humidity (space dewpoint control), air changes, cross-contamination, pressurization, ventilation (outdoor air) rates, and exhaust. This makes it much different from a typical commercial building HVAC system, where comfort is the main objective and there is a much more lenient set of code requirements to be dealt with.

Rome: Serving a patient-care area requires pressurization, additional filtration levels, and required air changes that other building types don’t have. These requirements minimize infection risks, promote patient healing, and are a significant responsibility to manage alongside minimizing energy use.

Spears: HVAC systems have to meet infection-control standards that include directed airflow paths from more to less clean areas, higher-efficiency air filtration, and tighter humidity and temperature control. Also, a more robust and elaborate BAS is required to both control and monitor performance of HVAC systems and to help hospital owners trend and track energy cost. Automatic fault detection and daily measurement and verification (M&V) of utility costs, often through the HVAC BAS, are becoming much more common tools to help hospital facilities personnel quickly catch anything that is operating improperly to make sure they maintain a high-quality patient-care environment and to minimize any wasted energy.

Heim: Redundancy is a requirement not often found in other buildings. Additionally, hospitals require a "high quality of air" for the building. That varies depending on the space being served, but it frequently means high levels of filtration, humidification for humidity control, and special diffusers for specific environments. Hospitals often have 24/7 requirements, so an "unoccupied mode" does not exist and the equipment must be designed to run through the coldest part of the evening and the hottest day during the summer. Additionally, many hospital systems require emergency power, which has to be factored into the design.

Koch: The biggest difference in HVAC requirements for hospitals versus other buildings is the air-change requirement. Hospital rooms or spaces require a certain amount of ventilation air changes per hour as listed in ASHRAE 170. Certain spaces are also required to maintain certain pressure relationships to surrounding spaces. For example, infectious isolation rooms are required to maintain a negative pressure to surrounding areas to protect staff and other patients from the infectious patient. ORs are required to be positive with respect to surrounding spaces to protect the patient in surgery from contaminants outside the clean environment of the OR.

CSE: What changes in fans, variable frequency drives (VFD), and other related equipment have you experienced?

Schultz: Many health care facilities understand the benefits of fan arrays in air-handling systems. Multiple fans provide a degree of inherent redundancy for system operation beneath peak. If one fan were to shut down, it is likely that its absence would not be realized from an airflow perspective. Additionally, all fans in the array can be controlled with a single VFD. In lieu of providing a bypass on the drive, a second redundant drive can be installed in an adjacent control panel. If the primary drive fails, the secondary redundant drive can be engaged to operate the fan array until the primary drive can be replaced or repaired.

Heim: VFDs are everywhere. Even if the system will not vary flow, due to the relatively low cost and the benefit of balancing the fan, the majority of fans we design have a VFD. In an effort to provide more levels of redundancy, we have seen a move away from one big fan to multiple smaller fans. In many ways, this is like a fan-wall approach. Frequently, we have designed air-handling units with two supply fans, so that in the event of a fan failure one fan could operate and provide partial capacity. When coupled with a VFD, this allows the fan to ramp up to its maximum capacity during this fan-failure mode.

Koch: The advent of the fan array system in AHUs has changed AHU design as well as VFD technology. The fan array system has brought about a fan system that has replaced the large, single-supply fan system with a smaller array of fans. This has decreased the amount of space required for fan sections, thus minimizing the amount of space required for the AHUs. The use of smaller fans has also virtually eliminated the need for sound attenuators that were previously used to attenuate noise from the large, single-fan system. Multiple manufacturers are utilizing fan array systems in AHUs. These systems have also led to changes in fan horsepower ratings of AHUs. Manufacturers used to list motors at 5, 7.5, and 10 hp. They have begun to list motors at 6, 7, 8, or 9 hp. These are the same motors as before, just relisted with a different horsepower. This allows fan array manufacturers to minimize connected horsepower, thus minimizing electrical requirements. These newer motor ratings have also changed the VFDs that control them. The standard VFD used to operate at 60 Hz for 100% airflow. The newer motors have been listed to operate at 60 to 120 Hz. VFD technology also has evolved with the implementation of fan array systems. In lieu of controlling all fans with a single drive, newer technology allows a micro drive for each fan, thus allowing greater redundancy and individual control of fans in the array.

Rome: Fan arrays and VFDs have revolutionized how we can manage control of the demands of a building while maintaining temperature and humidity performance of specific areas, and it has also been key to energy-reduction strategies for static pressure reset and system performance.

Shah: In recent years (past 10 or so), we noticed a great deal of technological progress in the HVAC and specifically in the air-handling industry. The technological advances are typically reflected in reduction equipment size (modular approach-e.g., FANWALL Technology) and noise-level generation and improvements in energy efficiency. Due to the same recent technological advancements, the VFDs lately became more reliable (increased range of tolerable ambient temperatures) and have a significantly wider range of operability while their cost dramatically dropped. Although apparently more complex due to superior control features with which a modern system comes equipped, combined with the fact that they are typically required to be highly integrated (DDC, BACnet-protocol-governed BMS, etc.), the late generations of air-handling equipment tend to be actually simpler to operate, optimized, serviced, and maintained. All these features combined are ultimately reflected in significantly lower operation cost (energy consumption, maintenance, downtime, emergency calls), allowing the building owner a superior return on investment (given that the considered system is properly designed and implemented).

Spears: An increasing quantity of AHUs for hospitals are equipped with fan array-type fan sections to provide redundancy and flexibility. These usually consist of a matrix of anywhere from two to 16 direct-drive plenum-type fans mounted on a vertical panel inside an AHU’s fan section. VFDs are typically provided with fan arrays and are provided in various configurations depending on the level of redundancy required, including a single drive serving all of the fan motors, redundant drives that include an automatic fail-over sequence to the backup drive, and individual drives for each fan motor. Fan arrays are often provided in shorter-length fan sections, which allows for easier placement and assembly of modular-type AHUs in interior mechanical rooms. Though fan arrays typically have more than standard-type AHU fan sections, their benefits often make it an easy choice based on the project requirements.

CSE: When retrofitting an existing building, what challenges have you faced and how have you overcome them?

Rome: Retrofitting an existing building can be a challenge for space constraint in an existing hospital. A typical situation is changing the modality of an area to improve clinical efficiencies. The new functions have a higher load demand, but the existing structure makes improving horizontal distribution difficult and vertical distribution changes cannot be handled by the architectural space program. Recently, we took an architectural solution to an HVAC issue by creating new architectural elements on the face of the existing building to create a new vertical distribution for the HVAC systems.

Schultz: Central chilled-water plants for large campuses often contend with low delta T syndrome. When the chilled-water temperature returning to the plant is less than 10 F warmer than the supply temperature, loading the chillers can create a challenging situation. During retrofits, coils and valve assemblies can be designed to operate at a 15 F delta T. At a partial load, the delta T can rise above 15 F. By increasing the delta T for new or retrofit units, the delta T seen by the chilled water plant raises proportionally.

Koch: Remodeling or retrofitting projects offer some unique challenges but can be some of the most rewarding work. Typically, remodel work requires the team to design in phases since only a portion of the redesign area can be under construction at any one time. Oftentimes, what might work for architectural phasing might not work for mechanical/electrical phasing. We have found that the following points are key in a successful remodeling project:

  • Develop a phasing plan is challenging. Relaying this plan to the contractor is equally challenging. Simply issuing a "final plan" of the overall design will likely not provide the contractor enough detail to know what your intentions are for phasing. However, the other extreme of developing detailed plans for each phase of work can be time-consuming and oftentimes are heavily modified during construction due to actual conditions and/or contractor input. The best approach we have found is to provide a "proposed phasing sequence" either in the specifications or on the plans that tells the contractor the thought process for the design, but leaves it open for them to modify the phasing based on existing conditions or preference.
  • Where possible, involve a general contractor early in design. Getting a contractor onboard early allows the construction team to have input on phasing of the project. As mentioned above, phasing requirements for architects and engineering can be different. Construction phasing can also have different requirements that might or might not affect a strictly architect/engineering phasing plan.

It is important to verify as much of the existing systems in the remodel area as possible. Obviously, every duct, pipe, conduit, or piece of equipment cannot possibly be field verified in a remodel area. However, major equipment, piping, and ductwork mains are important to verify in an attempt to coordinate new with existing.

Spears: While all renovation projects in an occupied hospital have typical problems, such as maintaining acceptable infection-control air particle counts in adjacent occupied spaces and keeping noise levels from affecting patient care, the bigger challenges have involved maintaining services to occupied areas during required shutdowns of systems. The impacts of system shutdowns to hospitals can have very significant impacts on patient care and project cost. To reduce or eliminate these impacts, we have incorporated various innovative system hot-tap procedures ranging in complexity from freezing hydronic systems to the use of shape memory couplings for medical-gas systems. Dozens of project team members and facility personnel can be involved in the planning and execution of a single critical system hot-tap procedure.

Heim: One of our biggest challenges has been a limited floor-to-floor height. Buildings that were designed in the 1960s or ’70s and fitted out with terminal-type equipment had a limit required for utilities running above the ceiling. Based on current codes and air-change requirements, more ductwork, piping, etc., is necessary. Close coordination with both the architect and structural engineer have been critical. Designing these projects using Revit has allowed us to see the space in 3-D and optimize our layout. We have found that multiple mechanical shafts (allowing for more vertical ductwork) were key when dealing with limited ceiling space.

Shah: Typically every building retrofit comes with solid budgetary limits and a great deal of expectations. And here is where the engineering versatility and innovative approach comes to play a dramatic role in the outcome of the project. Often, an increase in air conditioned floor area, while expecting improvements in space temperature conditions to be maintained and controlled (sometimes even space humidity control is required for determined areas), while new more abundant code ventilation rates/requirements will have to be applied and complied with. To accomplish the "perfect storm," all those listed above will have to be added to limited spaces. The owner wanted to reuse existing equipment while ideally trying to maintain the new expanded system as consistently or as close as possible to the size of the existing infrastructure to be used (chiller/boiler plant pipes and ductwork). All these had to be accomplished while matching the architect aesthetical and utilitarian vision; access, structural, and existing utilities infrastructure limitations; and at the same time costs.

There are myriad retrofit applications where, to provide adequate engineering solutions for the challenges we had to overcome (like minimized downtime and reduced first-cost and operation expenses, combined with strict and specific OSHPD or Veterans Affairs requirements while complying with available structural and architectural given conditions), our interdisciplinary team, heavily led by mechanical inputs, came up with innovative yet robust and well-thought solutions that took advantage of all available features each particular situation had to offer. As an example, we had to come up with a solution to provide adequate temperature and humidity control for a sterilizer facility (part of a much larger project within a Kaiser Permanente Hospital in Los Angeles). For years, it was the subject of numerous complaints related to the current HVAC system not being capable to maintain the space temperature and humidity within the OSHPD acceptable range. The approach we were required to adopt implied taking advantage of as much of the existing available utility and service infrastructure, maintaining the current HVAC system, and using nearby available chilled water and steam-all while providing complementary sensible and latent capacity. Among the minimal space available to accommodate the additional equipment, minimizing the impact in useful floor area, minimizing the downtime associated with implementing the existing system upgrade, and the fact that we were dealing with a pretty much maxed-out electrical panel, we came up with a creative modular design that was very positively received by the architect and the owner (hospital) since it met all required features and then some. The environmental sustainability (at low cost) aspect of the concept was also greatly appreciated.

Another relevant example would be the VA-San Diego surgery suite retrofit and expansion. We were awarded the task of providing a design based on a study we initially prepared that included a three-way side-by-side economic analysis meant to guide decision making. We had to convert a return-air HVAC system sized to serve the existing hospital surgery suite (unsatisfactorily) into a 100% outdoor-air HVAC system to serve a larger-capacity surgery suite that, unlike in the past, was supposed to offer the capability to maintain significantly colder and drier indoor space conditions. An existing deficient humidification system had to be tackled as well as part of the task. The existing humidification system consisted of one large centralized steam humidifier installed upstream of all OR serving branches. The previous designer’s choice of humidification system was driven by that lack of space (not sufficient sorption duct length available at each OR branch to handle the OR humidification load). The downside of such an approach was the fact that all ORs had to accept the humidity level consistent with the highest humidity level required by any of the ORs at any given time (though each OR had the ability to provide independent temperature control). To provide each OR with independent temperature and humidity control, our approach was consistent with providing an intermediary humidifier (supplying air consistent with to the lowest OR dewpoint to be maintained) while we provided on each OR’s branch a final small-sized humidifier (consistent with very short sorption duct length requirements).

CSE: What indoor air quality (IAQ) or indoor environmental quality (IEQ) challenges have you recently overcome? Describe the project, and how you solved the problem.

Schultz: Protective environment rooms for oncology patients require a high air-change rate as well as nonaspirating laminar flow panels near patient beds. A primary concern is patients’ comfort, as they are sensitive to fluctuations of air temperature and movement. To minimize the discomfort, the laminar flow panels should be located adjacent to the bed’s footprint and the supply air rate-of-change can be strictly controlled to minimize fluctuations in room temperature. Additional perimeter radiant heat can be applied to address skin loss at windows or help minimize condensation on window frames.

Rome: Pharmacies are tested annually to the U.S. Pharmacopeial Convention standards and guidelines. The particle concentrations demand a combination of systems and strategies using high air changes, HEPA filtration, and air-device delivery. We recently have effectively reduced air changes by using strategies employed by our containment laboratory group to improve air distribution in the space. This saved energy, overall system effect, and first cost.

Heim: Recently, we were challenged to design orthopedic operating rooms to maintain a space condition of 58 F at no more than 55% relative humidity. All of this had to be done using standard chilled water of 44 F. Our solution was to provide a dedicated AHU that would produce standard discharge conditions of 55 F. That air was used to serve the support spaces, and the remainder was sent through a desiccant wheel dehumidification unit, which drew additional moisture out of the airstream and conditioned the air back down to 50 F for delivery to the space.

CSE: Have you specified more alternative HVAC systems on hospital projects recently? This may include displacement ventilation, underfloor air distribution, variable refrigerant flow (VRF) systems, chilled beams, etc.

Heim: RMF has more frequently recommended alternative HVAC systems. RMF has used VRF systems in specific situations, but hospitals typically have campus chilled-water and heating-water/steam systems in place, which makes it a hard sell to use alternative utilities. I have begun to see more of an acceptance of chilled beams as well.

Shah: PBS Engineers consistently offers its clients (when required) side-by-side economic analyses. We believe that there is almost always more than one possible solution for each HVAC design task a particular building may require. Therefore, we provide (where required and/or applicable) options and alternatives at the level of single-line/schematic diagram and guide our clients through the decision-making process, clearly and transparently present pros and cons associated with each option/alternative. At Animal Research Center Facility-VA North Hills (Simi Valley), we designed the HVAC system (including the air distribution consisting out of central diffuser screen supplying laminar airflow to the operating table surrounded by air curtain supply linear slot diffusers where applicable). In a typical operating room, where the OSHPD is not required, we tend to apply the American Institute of Architects (AIA) Guidelines that specifies a minimum exchange rate of 15 air changes/hr (ACH). These guidelines only address minimum standards for the air distribution and thermal-control systems. Most hospitals have standards (like OSHPD) that require higher air-exchange rates than the minimum AIA standards. There are other guidelines (again, where the OSHPD is not the governing entity) such as ASHRAE and the Centers for Disease Control and Prevention.

Rome: Outpatient health care facilities/areas have recently been employing alternate strategies such as VRF, chilled beams coupled with energy-recover outside air delivery, and displacement ventilation. A recent inpatient facility we designed is using a 100% outdoor air (OA) system with dual-wheel energy recovery for patient rooms where the VAV terminals at each room have decoupled heating and cooling. It is a similar concept to the systems used in the outpatient facilities, but it keeps the wet systems in the corridor outside the patient room for maintenance and access.

CSE: Describe a challenging building envelope project you recently designed in a hospital.

Schultz: Condensation-resistance qualities of building envelopes need to be more robust in hospitals than in other building types, primarily because these humidified buildings generally operate between 25% and 35% rh. The temperature and relative humidity setpoint criteria should be established early on so the building envelope can be specified to accommodate the indoor air conditions minimizing surface condensation. Once the building envelope begins fabrication, the condensation-resistance performance is fixed and opportunities for adjustments may no longer be available. Wall and glazing manufacturers can run simulations on specific window assemblies to demonstrate that their systems will not result in a surface temperature below the indoor wet bulb during the winter. Establishing the indoor minimum relative humidity along with the dry-bulb temperature during the schematic design is needed so the architect and builder understand the criteria they need to accommodate with the building envelope.

Koch: On a recently completed project in the upper Midwest, we had to design an addition to an existing hospital. The design incorporated a large soffit system under an elevated second floor. Obviously with patient rooms above this soffit space, and the climate conditions of the upper Midwest, this space had to be heated to avoid freezing pipes or having to heat trace a lot of piping. One of the other challenges on this project was the exterior glass and curtainwall system. Our design called for a thermally broken exterior-glass system. This is especially important in colder Midwest climates as winter design temperatures can be extremely cold, thus increasing the chance of condensation.

Shah: Occasionally we had to work with the architect in implementing all sorts of envelope configuration and consistency (like shading factors, integrating wall "fins," etc.) that are ultimately meant to help optimize the building envelope as an integrant part of accomplishing compliance with T-24 , Cal-Green, or LEED requirements.

Rome: A recent LEED Platinum-certified hospital expansion had a mosaic window system that was featured throughout the building. Calculating the thermal breaks and shading coefficients and then modeling them to the ASHRAE 90.1-2007 requirements for the compliance energy model was a collaborative task among the architect specifying the windows, the window system manufacturer to provide accurate data, and our modeling group adjusting the software inputs to accept 16 different glazing construction types in a single input.

CSE: Explain any special requests you’ve received from clients concerned about Legionellosis (Legionnaires’ disease) after the recent cooling tower episodes in New York City.

Shah: In the case of Westfield Century City Mall, the 3,000-ton nominal heat-rejection cooling tower capacity was designed at the request of the client to provide the ability to integrate the use of water (for the cooling tower’s make-up) from the mall’s rainwater-harvesting system. As a result of that, we had to come up with a chemical-free water-treatment system that provides an increased number of concentration cycles, accomplishes superior piping, and other cooling tower surface descaling while successfully eliminating the biofilm formation, including Legionella. It controls total bacteria counts at a lower and more stable level than conventional cooling tower chemical programs, and better than any other chemical-free system. Destroying and preventing the formation of biofilm is the most critical component in preventing Legionella outbreaks. To minimize the proliferation of Legionella pneumophila and the associated risk of Legionnaires’ disease, our design is set to comply with the following recommendations issued by the Cooling Technology Institute:

  • Minimize water stagnation Minimize process leaks into the cooling system that provide nutrients for bacteria
  • Maintain overall system cleanliness. This will minimize the buildup of sediments that can harbor or provide nutrients for bacteria and other organisms.
  • Apply scale and corrosion inhibitors as appropriate
  • Use high-efficiency mist eliminators on cooling towers
  • Control the overall microbiological population
  • Develop a control strategy and keep records
  • Ensure proper treatment is being applied and monitored frequently
  • Proper treatment includes managing scale, corrosion, and biological growth
  • Monitor bacteria counts and ensure that total heterotrophic plate counts never exceed a 10,000 colony-forming unit mL
  • Confirm that no biofilm is present
  • Avoid stagnant water by circulating it daily during periods of infrequent use and by rotating redundant equipment.

Schultz: In August 2016, the New York State Dept. of Health issued cooling tower regulations with an emergency justification requiring all owners of cooling towers-all general hospitals and residential health care facilities-to register their cooling towers, evaporative condensers, and fluid coolers with recirculating water systems. Initially, the registration consisted of locations and quantities, along with physical data associated with the cooling towers and verification that the chemical-treatment system was appropriate and operating properly. The regulations require that any cooling tower shut down for more than 5 days be clean and disinfected, and that all operating towers have inspections at intervals not exceeding 90 days. The inspections also include bacteriological analysis of tower water. Each year, cooling tower owners are required to obtain a certificate qualifying their cooling towers were inspected, tested, cleaned, and disinfected. By March 2016, owners are now required to construct and implement a maintenance program and plan developed in accordance with ASHRAE Standard 188-2015. Bacteriological sampling and analysis, along with Legionella sampling and culture analysis needs to be performed on a 90-day frequency. If the results come back higher than permitted, the cooling tower needs to undergo a decontamination process that is outlined in the regulations and supported by ASHRAE 188. Any tower that is shut down for more than 5 days or experiences a chemical treatment or power failure of sufficient duration to allow the growth of bacteria is required to be disinfected. Records going back 3 yr need to be stored on-site and shared with the New York State Dept. of Health.

Rome: Our standard procedure is to discuss with our clients their concerns, conditions, and testing procedures. We review the current methodologies that can be implemented and jointly determine the best direction for their specific operation. Many of our clients are opting for a copper/silver ionization system for their incoming-water service.