Energy Use in OR Ventilation: Does TcAF Demand More Power?

Series Introduction
This is the fifth article in our series for hospital architects and technical consultants, focused on evaluating common claims about Temperature-controlled Airflow (TcAF) systems. Each post compares TcAF with traditional Unidirectional Airflow (UDAF) systems using scientific reasoning and real-world data. The goal is to support more informed choices when designing ventilation for infection-sensitive operating rooms.

Claim: “TcAF consumes more energy due to higher pressure drops over HEPA filters and diffusers.”

Reality: TcAF is significantly more energy-efficient than UDAF due to its lower airflow requirements.

Context and Analysis
There is a common perception that TcAF, due to its use of HEPA filter boxes separate from the ceiling diffusers, results in higher pressure drops and thus greater energy consumption. This assumption overlooks the much more significant variable: total airflow volume.

UDAF systems typically operate at high air change rates to maintain unidirectional airflow across the surgical field. This generates substantial energy demands not only to move the air but also to cool, filter, and condition it. In contrast, TcAF achieves clean conditions using approximately 30–40% less airflow.

While pressure drop over HEPA filters is a factor, it represents a small portion of the system’s total resistance. TcAF uses fewer, deeper filter frames placed centrally, reducing sealing interfaces and the risk of leakage. With a well-designed air handling unit (AHU) and ducting, pressure loss can be minimized, and energy efficiency optimized.

When total system design is considered: air volume, filter strategy, and airflow distribution, TcAF offers a more efficient solution for maintaining ultra-clean conditions, without the energy overhead associated with high-volume UDAF.

Conclusion
TcAF uses less air and therefore less energy. Concerns about pressure drop miss the broader picture: energy savings are primarily gained through airflow reduction, not marginal differences in filter resistance.

This article is one in our series examining common assumptions about TcAF. The next post will address concerns about filter placement and system reliability in healthcare ventilation.