New Perspectives on Health-Care Ventilation

May 6, 2016
Although the author learned health-care HVAC the way many do, today he thinks differently. This article summarizes some of what led to the change in his views.

Three years ago, if you would have asked me to describe health-care HVAC, I would have given the everyman answer: “We move ample air to prevent disease transmission. We control temperature and humidity very tightly to control mold and bacteria. We use high-efficiency filters and space pressure. We do all of this to reduce risks of cross-contamination and to keep patients safe.” I may even have noted 20 percent to 30 percent of hospital-acquired infections come from air, even though, at the time, I did not know the source of those numbers (today, I do know, and I do not repeat that statistic anymore).

Although I learned health-care HVAC the way many designers do—I did projects, read handbooks, followed codes, used the air-change table, balanced rooms for pressure, specified controls—today I think a lot differently, and I believe it is time for the health-care HVAC industry to do the same. This article summarizes some of what led to the change in my views.

Why We Should Re-think Health-Care Ventilation

When it comes to energy, hospital buildings are behind the times—to an increasingly embarrassing extent. Hospitals use two to three times the energy of other commercial buildings and are hardly the good examples of environmental responsibility and public-health awareness their owners want them to be.

Energy is an operating cost, falling under “affordability of care.” A new approach to ventilation could be an opportunity for 20-percent to 30-percent energy savings in acute-care spaces, more in some outpatient spaces. For my employer, that is worth about $30 million and 130,000 metric tons of carbon a year.

Red herrings. Three years ago, I might have said most hospital energy goes to plug loads, equipment, and lighting. After all, hospitals are full of equipment and run 24 hours a day seven days a week.

I since have learned ventilation is unquestionably the largest consumer of hospital energy. Two-thirds to three-quarters of a hospital’s energy goes to HVAC systems. Often, the biggest end use is HVAC reheat. In many cases, a hospital could cut its plug or lighting energy in half and realize only 5-percent energy savings.

Three years ago, I might have said a big fraction of a hospital’s energy goes to operating rooms (ORs). ORs are energy-intense and an opportunity for savings, but, when looking at a portfolio of hospitals, I realized ORs are only a fraction of a hospital’s footprint. Their contribution to hospital energy use is oversized, but not the majority. It is safe to say most of the energy hospitals use is consumed outside of ORs.

Equipment, lights, and ORs all represent opportunities for savings, but none of them, alone or in combination, can move the needle more than 10 percent to 15 percent. To significantly reduce the energy footprint of hospitals, we must look at HVAC outside of the OR.

Looking to 2030. State energy codes and national energy standards are moving to net-zero and should be there in 10 to 15 years. As a goal, net-zero makes sense for health-care buildings. You could build a net-zero hospital right now, if you added a massive on-site generation plant. But for a broad movement toward net-zero health care, building consumption needs to be reduced. It will be sad if 2030 comes and new commercial buildings—except health care—are net-zero.

Where We Are

Facts. A lot of what will follow is challenging. So, let’s start by acknowledging some commonly agreed-upon ideas:

  • Mycobacterium tuberculosis and other “truly airborne” diseases can be isolated in a facility with pressurization, dilution, and exhaust.
  • Clean air matters in environments for severely immunocompromised patients (e.g., transplant recipients). Fungal contamination as low as 1 cfu per cubic meter has been linked to infections.1
  • Construction dust can carry spores (e.g., aspergillus) that cause infection. This risk is elevated in areas with immunocompromised patients. Airtight construction barriers and good construction management can reduce this risk.
  • General room air distribution has little effect on transmission of “droplet diseases,” coughed or sneezed particles with diameters greater than 50 µm (e.g., influenza, respiratory syncytial virus).
  • Ultraviolet light and other technologies can kill airborne biological particles. These have been used both in and out of air systems to reduce microbial contamination. In a few cases, a reduction in infection has been shown.
  • Clean air in ORs has been correlated with reduced surgical-site infection rate.

Myths. Now, let’s review some common misperceptions and exaggerations. I need to introduce these by stating I believed nearly all of them just three years ago.

  • Health-care ventilation rates are “normal.” Some say the ventilation rates used in health-care spaces are roughly equivalent to those used in office buildings and schools. This is true on the hottest day of summer, but in most office buildings and schools, air is used as needed, with controls to limit reheat. In health care, ventilation rates are used as minimums; air is changed multiple times every hour of the year, and spaces often are over-ventilated. In commercial spaces, 15 to 20 cfm of outdoor air per person is typical. In hospitals, three or four times that is used, and room minimums are even higher.
  • One hundred percent of air should be exhausted. This idea is very popular in England. Some engineers say not returning air is preferable. The idea all hospital air is “dirty” has been fairly well debunked.2
  • All health-care spaces need to be protected against airborne diseases. This may be a carryover from the days of open wards. Today, isolation protocols and rooms are used. Additionally, airborne diseases sometimes are overestimated. I used to think there were hundreds—maybe thousands—of airborne diseases. It turns out there are very few “truly airborne” diseases—primarily, tuberculosis, smallpox, chickenpox, measles, mumps, and rubella.3
  • Air changes and pressures are designed to prevent infection. This idea is fairly popular. In a 2013 survey of HVAC design engineers, about 40 percent said air changes are used to prevent infection.4 For many major categories of infection—catheter, bloodstream, mechanical ventilator—there is no reason to believe HVAC has any bearing, aside from its supporting role in basic hygiene. Most of the air-change rates, pressures, and temperatures we use are based on tradition, rather than science.
  • Patient comfort is a specialty application. This idea is very popular because, well, it’s true! However, there is a second, sadder truth to go with it: There has never been a study on patient comfort. Most human-comfort studies use more generic populations (e.g., offices, schools). So, in health care, we actually know significantly less about predicting comfort than office designers do. Yet our practices sometimes belie we know more.
  • Certain temperature and humidity ranges control bacterial growth. There is some truth to this, but it is fuzzier than one would like. Different organisms have different temperature and humidity responses; there is no perfect state that controls them all. There is a range within which airborne microbial contamination can be minimized, but the range is broader and less rigid than we tend to apply. Most importantly, there is not good evidence tightly controlled spaces lead to better patient outcomes. Some foreign standards use wider control ranges, seemingly without disaster.
  • We need very efficient filters everywhere. During the early 1960s, most U.S. hospitals had operable windows and natural ventilation. In time, that gave way to 100-percent filtered air. Today, many U.S. engineers are skeptical of natural ventilation—they have not seen it done in 30 years. European engineers have a hard time understanding this—they use natural ventilation every day.
  • We are protecting against a pandemic. This interesting idea crops up from time to time (perhaps dependent on the news): “The next airborne pandemic disease could walk into your building tomorrow.” It is well-intentioned, of course, but also very flimsy. A complicated probability and risk assessment would be needed to show high minimum ventilation rates are at all effective in mitigating an outbreak, and such an assessment has not yet been done. I have heard: “We’ve never had an airborne outbreak in the United States, so the ventilation rates must be working.” I’ll leave the reader to judge that logic.

As firmly held as my beliefs on these matters are, I urge you not to take my word for any of this. Investigate your own beliefs; try to validate them. To save you the time of combing through hundreds of journal articles, as I have done, I offer the following. It is a list of good meta-analysis papers on these topics. Several easily can be found on the Web free of charge:

  • “Hospital Ventilation Standards and Energy Conservation: A Summary of the Literature With Conclusions and Recommendations, FY 78 Final Report” (LBL-8316) by Roger L. DeRoos, Robert S. Banks, David Rainer, Jonna L. Anderson, and George S. Michaelsen. This 1978 report includes a review of 359 clinical papers. It found “it is very difficult to draw any precise conclusion” on general ventilation rates and infection.
  • “Ventilation and Exhaust Air Requirements for Hospitals” by Jack B. Chaddock (ASHRAE RP-312). This 1983 study debunked 100-percent exhaust. It is well worth reading for the rest of its contents, too. It says, “Indications now are that this risk has been overestimated, resulting in higher than needed ventilation rates.”
  • “Role of Ventilation in Airborne Transmission of Infectious Agents in the Built Environment – A Multidisciplinary Systematic Review” by Yuguo Li et al. This paper, published in the February 2007 issue of Indoor Air, concluded a “lack of sufficient data on specification and quantification of the minimum ventilation requirements in hospitals, schools, and offices.”
  • “Design Strategy for Low-Energy Ventilation and Cooling of Hospitals” by C. Alan Short and Sura Al-Maiyah. This U.K. energy study, published in Building Research & Information in 2009 (Volume 37, Issue 3), includes a review of literature on infection control. When it comes to infection, the authors conclude, “True airborne infection is rare; what is fairly common is the direct route of infection.”
  • “Natural Ventilation for Infection Control in Health-Care Settings,” edited by James Atkinson, Yves Chartier, Carmen Lúcia Pessoa-Silva, Paul Jensen, Yuguo Li, and Wing-Hong Seto. This 2009 World Health Organization guideline includes a study of 65 scientific papers. It says, “There is moderate evidence available to suggest that insufficient ventilation is associated with an increased risk of infection.” Re-read that sentence a few times. It is my personal favorite, for both what it says and what it does not say.
  • “Literature Review: Room Ventilation and Airborne Disease Transmission” by Farhad Memarzadeh. Jointly published by the American Society for Healthcare Engineering and the Facility Guidelines Institute, this 2013 meta-study features more than 100 citations. It concludes we do not have enough data to set minimum air changes per hour (ACH) on the basis of infection.
  • “The Role of the Hospital Environment in Preventing Healthcare-Associated Infections Caused by Pathogens Transmitted Through the Air” by Jesse T. Jacob, Altug Kasali, James P. Steinberg, Craig Zimring, and Megan E. Denham. Published in the October 2013 issue of Health Environments Research & Design (HERD), this is a very useful read. It was compiled by a team of infectious-disease and architectural researchers. It has a summary table of 37 ventilation research studies and gives concise statements regarding what has been successful.

Change Is Hard

“The oldest and strongest emotion of mankind is fear, and the oldest and strongest kind of fear is fear of the unknown.”

—H. P. Lovecraft

There is a night in Seattle I will never forget. I had just explained to a committee how most outpatient facilities are Group B (business) occupancies: We design them to energy codes, we use variable-air-volume systems, we use return plenums; we do not, typically, use air-change minimums.

From across the room, a member of the audience looked me square in the eyes and said loudly, “Well, how many people are you willing to kill?”

None, of course. To be utterly clear, what I described is common practice across the United States, with decades of precedent. The audience member’s response reminded me how big of a barrier fear can be.

The strong case for “doing nothing.” In health-care HVAC, there are big questions, questions to which we do not—and may never—have complete answers:

  • How relevant are HVAC variables (outside-air ventilation rate, total room ventilation rate, supply-air filtration, room air pattern, room pressure) to disease transmission or infection rates in health-care occupancies?
  • In what rooms or spaces can HVAC variables affect disease transmission or infection rates?
  • What specific disease-transmission or infection rates can HVAC variables affect?

The problem is not that we don’t have answers to these questions; it is that our codes and standards represent that we do. Two generations of architects and engineers—myself among them—learned that air changes, pressures, and filters are bedrocks of health and safety. Such traditions are not easily shaken.

Codes and standards are written by us. They both reflect and transmit our shared beliefs from year to year. Of course, code changes are notoriously slow. Increasing requirements is not easy for a code group. In the case of health-care ventilation, decreasing requirements is even harder. If even one person in the room fears change, the proverbial wheels can grind to a halt.

Often, the “Other Way” Works Just Fine

Compare and contrast. The simplest way to think fresh about health-care ventilation in the United States is to look at countries in which it is different. I have reviewed health-care ventilation guides from the United Kingdom, Germany, and Spain and learned a little about standards in Canada, Australia, Latin America, and Japan. For me, this has been an eye-opening experience. Sometimes, the contrasts are shocking. For instance, Germany has no minimum humidity requirement for ORs. Even worse, the United Kingdom actively discourages humidifiers, saying they create more risk than they avoid. And in Germany and Japan, natural ventilation is allowed—nay, encouraged—in minor-procedure rooms! (The windows have insect screens.) To a U.S. engineer, this is horrifying.

Beyond the shock factor, the clear contrast is the U.S. framework is quite narrow. We use specific, inflexible HVAC solutions. We have long tables of space-by-space prescriptions. Many spaces, such as restrooms, janitor’s closets, corridors, and dining areas, probably could be removed, as, for example, a janitor’s closet in a hospital is not too different from a janitor’s closet in a school—we could use the “normal” design. Several international health-care standards do this, using “special” HVAC in fewer spaces.

I think of management coach Mark Horstman, who says, “The ‘other’ way often works just fine,” explaining: “There’s someone else out there who has succeeded to the same level you have with exactly the opposite intuitions you have. (They wonder how you got where you are, too.) Your idea that your way is the right way is routinely controverted. You just think it’s right because it’s yours.”

Clean spaces. We also can look at domestic trends in HVAC, as some technologies have matured quite a bit over the last 30 years.

Take clean spaces, which have surpassed health care. In 1978, a designer using filters, laminar flow, and over-pressure in an OR was the avant-garde of clean-air-system design. During the 1990s, though, the cleanroom industry took off. Today, the best cleanroom designs are in the semiconductor and pharmaceutical sectors. In comparison, our OR designs look archaic. European hospitals are learning from cleanrooms. In the United Kingdom, Germany, and Spain, OR commissioning includes particle and microbial testing using cleanroom methods.

Over the next 15 years, cost-effective, real-time particle control is realistic. There are examples—both U.S. and European—of real-time particle counting in ORs. We need these clean-system design ideas in hospitals, or, at least, we ought not exclude or prohibit them.

Comfort and indoor-air quality. Today’s design vocabulary for indoor-air quality (IAQ) and comfort also is much advanced. Health-care codes use ACH and explicit temperature ranges. Both are outdated and out of synch with most modern design practice.

For IAQ design, approaches such as those of ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, are used for most spaces. There are several global standards for outdoor-air ventilation, most of which use similar methods.

For comfort, modern designers use an algorithm to predict the percent of people dissatisfied (PPD) and predicted mean vote (PMV). This is known as the PPD/PMV methodology. It comes from U.S. research, but is used globally. In the United States, it is in ANSI/ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy.

Moving to the Future

We need to acknowledge possibilities. Our current practices do not deserve a monopoly. It is possible to think beyond them without compromising the outcomes we all value.

I believe modernization of health-care ventilation can be achieved quickly. All of the expertise needed to develop new approaches exists; we need only to piece together best practices from health-care and commercial engineering, both domestic and international. A new framework might include:

  • A clear and transparent identification of clinical effects. Where HVAC is intended to achieve a clinical end should be articulated. We should be clear about where “normal” HVAC is appropriate. In many spaces, there are no clinical implications; the design drivers are comfort and IAQ.
  • A sound basis in IAQ. We should be using the best available IAQ practices. Some spaces will require a more exhaustive design practice. The practice, however, should be built on the same footing. It should use common methods, common metrics, and common language.
  • A sound basis in human-comfort methods. We always should leverage the best available comfort knowledge. We should use state-of-the-art comfort design and assessment methods. Where comfort is affected by one’s physical state or other factors, we should use the best tools available. We should continue to seek new ones.

What’s happening. Interest in this reform is diverse. Since 2011, my group has published research, corresponded with code groups, and encouraged a larger dialogue. Our research has focused on the history of U.S. standards, benchmarking among HVAC standards, energy, and the relationship between HVAC and patient outcomes. We have requested a few actions from code groups, mostly concerning coordination and benchmarking. We have shared findings with health-care owners, architects, and engineers.

Architects and engineers are taking creative approaches to forge ahead. They often test the limits of standards, sometimes going slightly beyond. Chilled beams, natural ventilation, and displacement ventilators are being deployed on U.S. acute-care projects. Outpatient projects are being designed for very low energy use competitive with the best commercial designs.

Code groups are working on solutions as well. In early 2015, one independent group convened to coordinate across clinical standards and clarify operating protocols. In late 2015, another independent group started to investigate alternative health-care HVAC design methods. Smaller teams are coordinating between domestic standards.

There are a few examples of net-zero or near-net-zero hospitals. More are to come. The examples to date, however, are a bit opportunistic; there has been investment in renewables, but no deep reductions in consumption. A new HVAC toolkit would open the door to lower consumption, more net-zero hospitals, and a greener health-care-building sector.


  1. Vonberg, R.P., & Gastmeier, P. (2006, July). Nosocomial aspergillosis in outbreak settings. Journal of Hospital Infection, 63, 246-254.
  2. Chaddock, J.B. (1983). Ventilation and exhaust air requirements for hospitals. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers.
  3. Siegel, J.D., Rhinehart, E., Jackson, M., Chiarello, L., & HICPAC. (2007). 2007 guideline for isolation precautions: Preventing transmission of infectious agents in healthcare settings. Atlanta, GA: Centers for Disease Control and Prevention.
  4. English, T.R. (2014, May). Engineers’ perspectives on hospital ventilation. HPAC Engineering, pp. 14-19. Available at

Travis R. English, PE, CEM, LEED AP, is engineering manager for health-care provider Kaiser Permanente’s National Facilities Planning group. He has more than 20 years of experience in the design and construction administration of mechanical and power-distribution systems for institutional, commercial, laboratory, and health-care facilities. His experience encompasses renewable-power systems, net-zero-building design, and building control systems.

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