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Posted on March 15, 2021


In an office or home environment, the HVAC system provides occupants with fresh air, reduces carbon dioxide levels, and sets the temperature and humidity at comfortable levels. Hospital HVAC systems do those same things plus much more.

Health care facilities rely on HVAC systems to promote healthy operating and isolation room environments by keeping clean and contaminated air separate. HVAC design also supports patient recovery. In this article, we’ll talk about what a hospital HVAC system is expected to do and what makes it unique.

Hospital HVAC Requirements

Hospitals can have a huge number of rooms of all different types ranging from isolation and treatment rooms to meditation and laboratory rooms. The ASHRAE Standard 170 sets requirements for different rooms and areas in a hospital to function correctly.

In fact, the ASHRAE Standard 170 lists requirements for over 80 types of rooms and spaces. In some rooms, all the air needs to be exhausted directly to the outside. In other rooms, the HVAC needs to always run whether people are using the space or not. The ASHRAE standard considers nine total variables:

  • Air pressure relationship to adjacent areas
  • Minimum outdoor air changes per hour (ACH)
  • Minimum total ACH
  • Direct exhaust outside
  • Room unit recirculation
  • Unoccupied turndown
  • Minimum filter efficiency
  • Relative humidity
  • Temperature

Below are a few examples of different hospital rooms and some of their requirements from the ASHRAE 170 standard:

Room type Pressure relationship to adjacent areas Minimum total air changes per hour All room air exhausted directly outside? Minimum filter efficiency
Airborne infection isolation room Negative 12 Yes MERV-14
Emergency room waiting area Negative 12 Yes MERV-8
Laser eye room Positive 15 No requirement MERV-14
Operating room Positive 20 No requirement MERV-16
General examination room No requirement 4 No requirement MERV-8
Protective environment room Positive 12 No requirement HEPA

Selected hospital HVAC requirements from ASHRAE Standard 170

You can see that requirements vary drastically between rooms. Minimum filter requirements can range from MERV-8, which is common for homes and offices, to HEPA filters, which remove over 99.97% of 0.3-micron particles. Total air changes per hour can also vary drastically, with the operating rooms seeing the highest minimum rate of 20 ACH.

Hospital Air Pressure Basics

Air pressurization requirements make hospitals unique from a lot of other commercial HVAC applications. Certain hospital rooms need to have a positive or negative pressure compared with the adjacent spaces. This helps keep contaminated and clean air separate.

On a basic level, the atmosphere tends to maintain neutral stasis. Air flows from higher to lower pressure areas to maintain balance. In a room with a neutral setting, the HVAC air supply will introduce air at the same rate as the return air ducts suck it out.

When negative pressure is called for, the HVAC sucks out more air through the return grilles than it adds with the supply duct. This means air from the hallway will get sucked into the room when the door opens. This is ideal for isolation rooms. The contamination is inside the room, so the goal is to keep contaminated air from escaping into the hallway.

When positive air pressure is called for, the HVAC pumps more air into the room with the supply than it removes with the return. That extra air pressure needs a place to escape to. When you open the door, air rushes out from the room and into the neutral hallway. This is ideal for sterile environments like operating rooms. You don’t want air from the outside to get into the clean environment.

Uninterruptible HVAC Design

Healthcare design uses HVAC to balance air pressure across a variety of rooms. Systems need to be well maintained with redundancies in place in case something should fail. Sterile operation rooms and isolation rooms always depend on the right air pressure, and an HVAC failure can jeopardize patient care. A cooling or refrigeration failure can also cause medications, vaccines, and treatments to go bad and become unusable.

If a hospital HVAC fails even for a short time, it can cost millions in damages to sensitive supplies and can increase the spread of disease. HVAC systems in hospitals need uninterruptible power like battery backups for components like drives, chillers, and air-handling units (AHUs). Backups based on site can minimize the risk of costly downtime.

Hospital Isolation Room HVAC System Design

What are the different types of isolation in a hospital? According to MedlinePlus, standard hospital procedure includes using PPE like gloves, gowns, and masks to protect against transmission. Further infection control for contact-based and airborne transmission includes wearing either respirator masks, which protect against small particles, or surgical masks, which protect against larger droplets.

HVAC design uses negative pressure in a room to keep infections from spreading to the hallway and positive pressure to keep a sterile room clean. In health care airborne isolation rooms, ventilation systems send the exhaust directly to the outside. It’s also important to maintain the correct humidity to help patients recover.

VRF in Patient Care Rooms

In addition to managing multiple isolation and sterile rooms, many hospitals use variable refrigerant flow (VRF) systems to allow recovering patients to control their own environments. A VRF system allows refrigerant to flow where it’s needed across a multitude of individual heating and cooling units. This supports wellness and comfort in patient rooms and can contribute to recovery.

Another nice thing about VRF systems is that they reduce energy consumption. The VRF system operates at the right level according to the load required in each zone or room, so the system doesn’t waste energy where it isn’t needed at the moment.

Intelligent HVAC Hospital Design

Intelligent HVAC systems use algorithms to monitor CO2, humidity, indoor air quality, and temperature in real time. That means an HVAC system can adjust airflow to compensate for changing variables where available. Some rooms require HVAC to be on all the time (a protective environment room, for example) while others allow HVAC to return to stasis when occupants are gone.

Intelligent HVAC can monitor and tune air conditioning and ventilation more efficiently than running a schedule. Running HVAC based on sensors can lower HVAC energy consumption, especially when combined with variable speed motors and pumps.

How to Choose the Right HVAC for a Hospital

Hospitals may need multiple types of HVAC systems to maintain standards in all areas of the hospital environment and to comply with building codes. The first thing to do when starting a ventilation system project is to set goals. Do you want to reduce airborne contamination? Reduce hospital-acquired infections? Improve patient comfort? Reduce operating costs?

Next, work with hospital staff to identify specific ventilation requirements for each area (operation, food preparation, laboratory, therapy, patient care, treatment, emergency, etc.). Establish the cost constraints and physical limitations of the building design to set the boundaries of the project.

Work with an HVAC specialist to calculate system loads in all areas of the facility. This will help you identify which type of equipment and systems you need for each hospital department. Once you have a few different optimal systems to choose from, calculate the life cycle cost of each to find out which offers the best combination of energy efficiency and affordability. As an example, our team renovated the HVAC and plumbing systems for the Erie VAMC Ambulatory Surgery Center. Check out the case study here.

Optimize Your Hospital HVAC Project

Our team at Wm. T. Spaeder has extensive experience in health care HVAC planning and installation throughout the mid-Atlantic region. We also provide 24/7 emergency service to make sure your facility is always on. We can use BIM modeling software to tailor an HVAC unit to your specific needs and operating budget. Get in touch with us for hospital HVAC planning, installation, or repair.



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