Your questions answered: HVAC: Hospitals and health care facilities

The March 16 “HVAC: Hospitals and health care facilities” webcast presenters addressed questions not covered during the live event.
By J. Patrick Banse, Smith Seckman Reid & Gregory Quinn, Affiliated Engineers Inc March 21, 2017

Gregory Quinn (left) and J. Patrick Banse respond to questions from the March 16 webcast. Hospital and health care facility projects are especially important due to their sensitive nature. The HVAC system must be based on high design standards—it’s hard to think of an engineering project with higher standards than a hospital or health care facility. Successfully designed and installed systems can be a matter of a patient catching a hospital acquired infection (HAI)—or as severe as life and death situations. Indoor air quality (IAQ) and indoor environmental quality make HVAC systems a high priority, which can create engineering challenges. HVAC engineers must know how to reduce the potential for infection and airborne pathogen dispersion in hospitals and health care facilities as they relate to HVAC systems and design.

Presenters at the March 16, 2017, webcast answered questions not addressed during the live event. Expert panelists were:

Question: When calculating air changes, do you always use supply air cubic feet/minute (cfm)? Or do you use exhaust airflow when room is required to be negative?

Gregory Quinn: In a negatively pressurized space, air changes are measured to include the entire exhaust air flow which equals the sum of supply air plus transfer air (in).

Question: What do you suggest to prevent mold in room air systems?

J. Patrick Banse: Pretreat outside air prior to introduction into either the room or to the room air system or central station air system. Monitor room air temperature and relative humidity (RH) conditions to ensure code-required ranges are met. Monitor cooling coils and equipment for cleanliness and clean if mold growth occurs.

Question: I would like to know the places that need to be under negative pressure in a hospital. I would also like to know the places that require 100% extraction.

Quinn: Table 7.1 in ASHRAE Standard 170-2013: Ventilation of Health Care Facilities shares this information.

Question: Please provide information about air distribution for surgery.

Quinn: ASHRAE Standard 170 shares surgery room air distribution information including minimum filtering requirements (Table 6.4), placement and performance of supply air diffusers and return/exhaust air grilles (Table 6.7.2), and air change data (Table 7.1).

Question: Will you recommend use of chilled water room air recirculation units in areas of high heat dissipation from medical equipment such as nuclear camera, CT scan, MRI, PETSCAN, or a linear accelerator?

Banse: Chilled water cooled recirculation units are fine for the equipment rooms of such diagnostic and imaging rooms. But be aware that proper ventilation and filtration is still required for the exam and patient treatment rooms. Exhaust air, pressure differentials, and radiation protection are also required of ducts penetrating rooms with radioactive treatment or procedures.

Question: What are the air change and exhaust requirements for waiting areas?

Banse: Air changes per hour (ACH) in waiting rooms are subject to the code minimum for the type of waiting rooms and could vary from six to 12 ACH. Consult the requirements enforced by the authority having jurisdiction.

Question: For LINAC bunker, for ventilation, do we need to filter exhaust air (because of radiation)?

Quinn: For the linear accelerator (LINAC) exam room, it’s not required to be exhausted by code and not typically done. Most often, a hot lab is located near the room handling the radiopharmaceuticals or radioactive diagnostic tracers. This hot lab room will be exhausted, but this room exhaust typically is not filtered. If there’s a radioisotope hood within the hot lab, then this exhaust will require HEPA and carbon filtration.

Question: Is a higher (RH) at 50% better than lower RH at 30% to 40%?

Quinn: Not necessarily. Expectations for RH levels depend on the space-type being conditioned and tend to range between 30% and 60%. In general, spaces where patient care is more critical expect RH levels to be controlled in the 40% to 60% range. Dropping the bottom end to 20% often is allowable during winter months and on perimeter zones to limit or eliminate condensation risk on cool surfaces. ASHRAE Standard 170, Table 7.1 offers guidance for acceptable RH levels in health care spaces.

Question: Can you expand on infection control for intensive care units and patient rooms?

Banse: Infection control for ICU and patient rooms involves many functions from hand washing to central station air handlers. From an HVAC perspective, proper filtration to trap bugs (bacteria and such), correct air change rates, and pressurization (clean to less clean air flow). Most codes for ICU rooms do not allow for recirculation of air by in-room units such as fan coil units. The type of ICU room (medical, surgical, cardiac) also makes a difference. Bottom line is that proper filtration, air flow patterns, and air change rates are important considerations.

Question: Is the average diameter/filter efficiency graphic available commercially?

Quinn: The graphic shared in the presentation was developed proprietarily. However, data was obtained via various online resources, notably the Centers for Disease Control and Prevention (CDC). The graphic represents filter effectiveness against particle sizes of various fungal pathogens, bacteria, and virus.

Question: Do chilled beams help avoid hospital acquired infection (HAI) transmission? Or do they introduce a different set of challenges?

Quinn: Chilled beams are an effective means for creating high-quality occupant comfort in both thermal and acoustic qualities. Further, chilled beams are an effective means for measurably lowering energy use when reviewed against comparable all-air systems. They should not be misrepresented as an improved means for avoiding HAI transmission, however. Current standards for elevated minimum filtered air changes (six or above) in critical care spaces limit the lifecycle effectiveness of chilled beams.

Question: Can an architectural engineering firm get in trouble for not designing to ASHRAE Standard 62.1-2013: Ventilation for Acceptable Indoor Air Quality? Or is this just a guideline that cannot be enforced?

Banse: A design firm is required to protect the public health, safety, and welfare through its work, which means designing to building codes and other codes in force at the time of the design. ASHRAE 62.1 is a standard, not a guideline, and if adopted either alone or by reference, must be followed unless specifically superseded by another adopted document.

Question: How was the slide that shows different filter MERVs developed for HVAC filtration requirements for hospitals?

Quinn: The graphic shared in the presentation was developed proprietarily. However, data was obtained via various online resources, notably the CDC. The graphic represents filter effectiveness against particle sizes of various fungal pathogens, bacteria, and virus.

Question: You meant the patient room is negative to the anti-room with the anti-room being negative to the corridor?

Quinn: For an airborne infectious isolation suite, this is correct.

Question: In one health care facility I designed, the exhaust air grilles in bathrooms and restrooms were designed to be located on the wall, low (about 8 in. above floor level) and set as near as possible to the toilet. Any comments?

Quinn: My experience is similar and this was a specific client request. Applicable guidelines for position of exhaust grilles in patient bathrooms do not state this as a requirement. However, for specialty patient rooms, e.g., airborne infectious isolation patient rooms, this would be considered good engineering practice.

Question: Can you discuss how to calculate the design supply and exhaust differential to achieve a specific pressure differential between spaces?

Banse: First, code-minimum air changes or the room heating and cooling loads must be met on the supply side. Exhaust air of the room (if required) must then be greater to create a negative pressure difference. In addition, 50 cfm is the smallest measurable air quantity for a ¾-in door undercut. The door type, size, edge cracks, and room construction integrity must be reviewed and calculated for leakage. An ICU-type sliding glass door may require as much as 200 cfm difference. It depends on the crack size and air velocity needed. Also keep in mind the air test and balance tolerances. Ten percent one way or the other may interfere with the required pressure difference.

Question: Facility Guidelines Institute (FGI) guidelines makes anterooms optional. For a regular patient room retrofit to an airborne infection isolation rooms, do you recommend an anteroom be added?

Quinn: Yes. To achieve the most confidence on obtaining and controlling suite air pressurization and to provide space for donning/doffing and hand-washing, an anteroom is recommended.

Question: One of the slides at the beginning of the presentation showed that duct lining was listed as being important for indoor air quality (IAQ). Would you recommend a closed cell, fiber-free, non-particulating, formaldehyde-free insulation with Microban to prohibit mold growth for lining the ducts verses fiber glass/mineral fiber insulation products to improve IAQ especially in operating room type areas?

Quinn: In the context we presented duct-lining material, it was listed as a potential contributor to hospital acquired infections, not necessarily as an IAQ inhibitor. While it’s a decent sound attenuating means, duct lining of any kind in hospitals is generally discouraged.

Question: What’s the optimum RH level to maintain?

Banse: The answer in many cases is “It depends.” In health care settings, it depends on patient acuity and treatment. In a central sterile processing area, it will depend on the packaging and sterilization process and the recommendations of Association for the Advancement of Medical Instrumentation (AAMI). Specialized patient treatment areas such as burn units will have higher relative humidity requirements. Most generally, a relative humidity in the 40% to 60% range will be sufficient.

Question: What IAQ is needed in an operating room?

Quinn: ASHRAE Standard 170 shares surgery room air distribution information including minimum filtering requirements (Table 6.4), placement and performance of supply air diffusers and return/exhaust air grilles (Table 6.7.2), and air change data (Table 7.1).

Question: We can design the systems to meet the best requirements, what documentation do we supply to ensure that the equipment is maintained correctly?

Quinn: (Answer provided assumes this question is from an owner’s perspective.) When embarking on new projects, designers seek information on three levels:

  • Operations and maintenance records for major existing equipment, to assure continuity of specifications for new equipment, where applicable
  • Institutional preferences for controls technology, to assure new controls systems are consistent with the facilities staff’s ability to maintain.
  • Expectations for access, so new work zones may be judiciously applied.

Question: Where is the humidifier introduced in the HVAC system?

Banse: A humidifier can be located in several different locations within an HVAC system. It can be within an air handling unit, but care must be taken for adequate absorption prior to any filtration downstream so wetting of the filter media does not occur. Humidifiers are most often found in supply ducts where an adequate straight length of duct is available for adequate absorption of the moisture into the airstream. This humidifier can be in the main supply duct or in each supply duct to patient treatment rooms, depending on the need.

Question: How often should the HVAC system be cleaned and filters be replaced?

Quinn: The following recommendations apply to standard health care ventilation systems and may vary depending on site-specific seasonal impacts (e.g., pollen, insects), weather conditions (e.g., snow), and/or other site matters (e.g., urban pollutants):

  • Pre-filters: quarterly
  • Mid- or final-filters: semi-annually
  • HEPA filters: annually.

Seek specific filter replacement recommendations for specialty systems, such as airborne infectious isolation exhaust filters, from clinical guidelines available from regulating authorities like the CDC. Similarly, frequency of HVAC system cleaning can vary greatly depending on application of service, filter maintenance protocols, etc. Typical recommendations are to thoroughly inspect healthcare facility HVAC systems no less than annually.

Question: Is it not true that a heat wheel type of heat recovery poses the greatest risk of contamination? Why not use other types of air-to-air heat recovery?

Quinn: Heat wheel technology offers substantial total energy recovery opportunity, on the order of 70% to 80% for a 100% outdoor air system. Cross contamination risk does occur, however. Thus, application of this technology must be done judiciously in spaces where exhaust hazard levels are concerning. Other air-to-air heat recovery systems are available but are typically less effective.

Question: Is the cost of ultraviolet germicidal irradiation (UVGI) systems substantially more to install and maintain than that of alternative ventilation systems?

Quinn: Initial cost for UVGI in air handling systems is typically in the 10 cents to 25 cents per cfm range, ongoing operations and maintenance regarding cleaning and bulb replacement. We recommend performing a lifecycle cost analysis to measure the qualitative and quantities benefits of UVGI over other available technologies.

Question: If an AHU must be off at night for repairs, how long is needed to get the operating room temperature and humidity back to preferred levels?

Quinn: Typically, no longer than 15 minutes.

Question: How often should the balance of the system be checked or reviewed to ensure the proper operation of the system?

Banse: Air balances are needed to verify that proper air change rates and pressure relationships are maintained. Hospital accrediting organizations generally require documentation showing code minimum or hospital requirements are being met. With properly operating control systems and not renovations, a full rebalance may not be needed for several years after initial setup if design conditions were originally met. A preventive maintenance program with regular airflow and pressure differential checks of critical spaces (operating rooms, infectious isolation rooms, and similar) also may be adequate. It is best to check with the accrediting agency as to its requirements.

Question: Do you know if California HVAC standards for hospitals are more or less stringent?

Quinn: In general, HVAC standards in California tend to be more stringent regarding attention to life safety matters; i.e., seismic bracing and/or isolation, dampering, etc. Fundamental performance parameters regarding air change rates, filtering, and relative humidity requirements are similar to other states.

Question: Mechanical filters and ultraviolet systems were discussed. Is there any chemical cleaning process or treatment that can be effectively used to sterilize and maintain the full length of HVAC ducts?

Quinn: Good question. Institutional grade, permanently-installed cleaning systems are discouraged (or not allowed) in general hospital HVAC systems where patient exposure to chemicals and/or life safety risks are a potential. You may seek advice from a cleaning contractor for more effective means of full-length ductwork cleaning strategies and/or application of permanent access to more conveniently allow for life-of-system cleaning to occur.