In a hospital, HVAC is part of infection control. It dilutes airborne contaminants, keeps air moving from clean areas toward dirty ones, and filters what it recirculates. If any of those three fail, patients and staff pay for it. This guide covers what a healthcare HVAC system has to do, the numbers it is held to, and what testing and balancing proves.
What HVAC does in a healthcare facility
- Dilutes. A set number of air changes per hour (ACH) brings in outdoor air and removes room air, which lowers the concentration of airborne particles and pathogens.
- Directs. Pressure differences between rooms push air in a chosen direction. Clean rooms are kept positive to their surroundings, and rooms that hold infectious patients are kept negative.
- Filters. Filter banks capture particles. HEPA filters, which are rated to capture 99.97 percent of particles at 0.3 micron, are used where the design calls for them.
Temperature and humidity also matter. Too much humidity encourages mold. Too little dries mucous membranes and raises susceptibility to infection.
The numbers it is held to
ASHRAE/ASHE Standard 170, Ventilation of Health Care Facilities, sets minimum airflow and pressure for each type of space. Three common ones:
| Room type | Pressure relative to surroundings | Minimum total air changes per hour | Minimum outdoor air changes per hour |
|---|---|---|---|
| Operating room | Positive | 20 | 4 |
| Airborne infection isolation room | Negative | 12 | 2 |
| Protective environment room | Positive | 12 | 2 |
These figures are from the standard. Check the edition your jurisdiction has adopted, and the project’s own design documents, before you rely on them. Pressure relationships are normally held at a minimum difference of about 0.01 inch of water column (2.5 pascals). Our guide to air quality rules in healthcare HVAC design goes further into the requirements.
How to calculate air changes per hour
ACH is the airflow into a room, in cubic feet per minute, multiplied by 60 and divided by the room volume in cubic feet. A 12 by 15 foot room with a 9 foot ceiling holds 1,620 cubic feet. At 324 cubic feet per minute, that room gets 324 × 60 ÷ 1,620 = 12 air changes per hour.
What testing and balancing proves
A design on paper does not protect anyone until it is measured in the building. For healthcare spaces, a balance should verify:
- Airflow in every room against the design, and the air changes per hour calculated from it.
- Pressure relationships between each room and its neighbors, measured with a calibrated manometer.
- Direction of airflow at doors and openings.
- Filter pressure drop across each bank, which shows if a filter is loading up.
- Outdoor air quantity at the air handler.
Air balancing in healthcare explains why a system that passes at startup can drift. Read how negative pressure rooms are tested and what TAB involves for critical spaces.
Working in an occupied hospital
Testing in an occupied building needs infection control risk assessment (ICRA). The permit, barriers, pressure control and documentation all have to be in place before the crew starts. Our ICRA checklist for TAB teams covers the steps.
Keeping the system right after turnover
- Change filters on schedule and record the pressure drop. A loaded filter cuts airflow and can upset a room’s pressure.
- Monitor pressure continuously in isolation and critical rooms, and respond to alarms.
- Re-test after changes. A new partition, a door change or a fan adjustment can alter a pressure relationship.
- Plan for outages. A power loss can stop ventilation in the rooms that need it most. See why healthcare HVAC needs emergency power.
- Prepare for the seasons. Summer and winter loads change the system’s demands.
Standards and audits
Accreditors and regulators hold facilities to air quality and pressure requirements, and expect records. A measured air balance report is the document that backs those records up. We certify air changes per hour, room pressure differentials and ventilation performance to ASHRAE 170 standards for operating theaters, clean rooms and critical care environments.
Related reading: The Benefits of Air Filtration Systems for Healthcare Facilities.
For a healthcare facility that needs measured results, call Ghazi Hussain at (908) 323-9780 for a quote.
