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.


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.

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