Indoor ventilation follows a set of building codes and standards, which vary depending on the type of building and industry. One of the most stringent requirements is for the clinical and medical field.
In this article, we discuss the standards and requirements for hospital makeup air, HVAC and ventilation systems.
The Importance of Ventilation in Hospitals
Adequate ventilation and filtered makeup air supply are important for hospitals and clinics due to the following:
Disease control and prevention
Bacteria and pathogens that cause infectious diseases need to be controlled. That is why all exhaust needs to be properly treated and sanitized.
Patients with respiratory illnesses require cleaner air supply than regular healthy people. Incoming air must be filtered to more stringent standards compared to other commercial buildings.
Some parts of the hospital such as ER, burn units and recovery wards have specific ventilation requirements. These can range from the temperature level to the amount of humidity to air changes per hour.
The indoor air quality standard for healthcare facilities is governed by the American Institute of Architects (AIA). This includes ventilation rates, temperature levels, humidity levels, pressure relationships, and minimum air changes per hour. The regulations represent a consensus of different government agencies, including Department of Health and Human Services, Department of Labor, OSHA, as well as professional bodies like the ASHRAE, the American Society for Healthcare Engineering (ASHE), and accrediting organizations like the Joint Commission on Accreditation of Healthcare Organizations.
Hospital Ventilation: Major Components
The HVAC system for clinical and medical facilities consist of the following:
- Outside air inlet or intake
- Humidity control mechanisms (i.e., humidity control in summer, humidification in winter)
- Heating and cooling modules
- Air exhaust or out-takes
- Registers or grilles
The outdoor air and recirculated air first pass through filter banks that strain airborne pollutants and contaminants from the outside. The air is then conditioned for proper temperature and humidity level before being circulated as indoor supply air.
Most of the return air is exhausted from the building, but a certain amount may be recirculated mixed with incoming air. One difference is that air from the toilet rooms as well as contaminated areas are exhausted instead of being recirculated, after passing through the appropriate air cleaning measures.
Filtration is the process of physically separating particulate matter from the air. This is the first step in the ventilation system. In a hospital HVAC system, the incoming air passes through two filter beds or banks.
The low-to-medium efficiency filters in the first bank have low resistance to airflow, but allow some small particulates to pass onto heating and air conditioning coils. These should have a filtering efficiency of 20%–40%, able to remove particles 1–5 μm in diameter.
These are stringent with an efficiency of ≥90%, used in most patient-care areas in ambulatory-care facilities and hospitals, including the operating room environment and areas providing central services. Nursing facilities use 90% dust-spot efficient filters as the second bank of filters,while a HEPA filter bank may be indicated for special-care areas of hospitals. These filters are 99.97% efficient in removing particles ≥0.3 μm in diameter.
After the outside air passes through a low- or medium-efficiency filter, the air is conditioned for temperature and humidity control before it passes through the high-efficiency filter.
Temperature standards may be a single temperature or a range, depending on the hospital zone. Cool temperature standards (68°F–73°F) are used for operating rooms, cleanrooms, and endoscopy suites. A warmer temperature of 75°F is observed for areas that require more patient comfort. Most other zones use a temperature range of 70°F–75°F.
HVAC systems in medical facilities are usually single-duct or dual-duct systems. A single-duct system distributes cooled air of around 55°F. The air is warmed using thermostatically controlled reheating boxes installed in the terminal ductwork before reaching individual rooms.
Meanwhile, a dual-duct system consists of two parallel ducts, one with a cold airflow and the other carrying the hot airflow. In this system, a mixing box in the destination room combines the two air streams resulting in the desired temperature.
Healthcare facilities have a relative humidity level of 30% to 60%. Humidity levels higher than 60% are typically uncomfortable, especially for patients with respiratory ailments or advanced age, and can result in fungal growth and mold.
Humidity levels are controlled in two ways.
Water-wash unit: water is sprayed and drops are taken up by the filtered air; additional heating or cooling of this air sets the humidity levels.
Humidifying boxes: uses the water vapor created from steam and added to filtered air.
Reservoir-type humidifiers are not allowed in health-care facilities as per American Institute of Architects guidelines and many state codes. Likewise, cool-mist humidifiers are typically not used in medical settings because they circulate aerosols that contain allergens and microorganisms.
Ventilation rates are voluntary unless mandated by a state standard as part of the healthcare licensing requirement. These standards typically apply to only the design of a facility, rather than its operation. For areas without specific ventilation standards, they should follow the AIA guideline for the year in which the building was constructed. They may also follow the ANSI/ASHRAE Standard 62: Ventilation for Acceptable Indoor Air Quality.
Ventilation is defined in terms of air volume per minute per occupant. For healthcare facilities, ventilation rates may also be expressed as room air changes per hour (ACH). The peak efficiency for particle removal is between 12 ACH to 15 ACH.
Below is the recommended air supply for different zones:
Supply Air flow
(l/s per m2
Supply Air Flow
|15 per person|
10-15 per person
Hospitals without a central HVAC system typically use through-the-wall or fan coil air conditioning units as the sole source of room ventilation. AIA guidelines for newly installed through-the-wall fan-coil units require a permanent or replaceable filter with a minimum efficiency of 68% weight arrestance. However, these units may be used only as recirculating units; all outdoor air requirements must be serviced by a separate central air handling system with proper filtration, with a minimum of two outside air changes in general patient rooms.
For critical zones, the following guidelines are used:
|Zone||Room air changes||Filtration||Recirculation|
|PE room||≥12 ACH||99.97% (Fungal spore filter at point of use (HEPA at 99.97% of 0.3 μm particles))||Allowed|
|Critical care||≥6 ACH||>90%||Allowed|
|Isolation (anteroom)||≥10 ACH||>90%||Not allowed|
|Operating room||≥15 ACH||>90%||Allowed|