Safe Surgical Environments through HVAC Design: Centralized versus Decentralized Systems

Keywords: HVAC system, operating rooms, microbiological safety, hospital building retrofit, room-level control, centralized/decentralized system

Operating room HVAC systems are critical for maintaining air quality, preventing infections, and ensuring safe surgical conditions. The choice of HVAC system structure should consider functional requirements, building limitations, clinical needs, and operational priorities.

Introduction

Modern surgery has turned the operating room into a complex environment where air quality control is crucial for patient safety. Managing the microclimate—by regulating physical, chemical, and biological air properties—is vital to preventing healthcare-associated infections, still a major global concern. Central to this are HVAC systems, which maintain aseptic conditions through air filtration, pressure and flow control, temperature and humidity regulation, and removal of pollutants like surgical smoke and anaesthetic gases. Given the role of airborne transmission in contamination, strict environmental control is essential. This study compares centralized HVAC systems, which serve multiple operating rooms, with decentralized systems dedicated to individual theatres, assessing their respective strengths and limitations in meeting air quality standards.

Technical Standards and Parameters for Operating Room Air Quality

HVAC systems in surgical environments must comply with stringent standards, including ASHRAE 170 (USA), HTM 03-01 (UK), and DIN 1946-4 (Germany), to ensure aseptic conditions and patient safety. These standards define requirements for airflow, filtration, temperature, humidity, and pressure control, despite differences in specific criteria such as air change rates and filtration levels.

Typical operating room conditions include temperatures of 18–24°C, relative humidity of 30–60%, positive pressure relative to adjacent spaces, and ventilation rates of 20–25 ACH, with air quality maintained through HEPA filtration.

Operating rooms are classified by air cleanliness according to surgical infection risk. High-risk procedures, such as orthopaedic, cardiac, neurosurgical, and transplant operations, require ISO 5/ Class I rooms with HEPA-filtered laminar airflow and positive pressure. Moderate- and low-risk procedures may be performed in ISO 7/ Class II rooms with less stringent airflow requirements. In contrast, rooms for infectious patients operate under negative pressure with filtered exhaust air. Overall, air cleanliness classification is directly linked to procedural complexity and contamination control requirements. [1-7]

HVAC System Layouts and Configurations in Surgical Settings

National and international standards define the required microclimate conditions in operating suites and the essential components of HVAC systems, without prescribing specific technical solutions. In practice, two main configurations are used: centralized systems, where a single air-handling unit (AHU) serves multiple operating rooms, and decentralized systems, where each room has an independent AHU.

In centralized systems, outside air is filtered, conditioned, and distributed through a common duct network to several operating rooms, with exhaust air removed through dedicated outlets (Figure 1). Although widely preferred in design practice, centralized systems may be less suitable for spaces with differing cleanliness, temperature, pressure, or humidity requirements [8].

Figure 1. Centralized HVAC system.

Decentralized systems use dedicated AHUs for each operating room or functional area, enabling independent control of microclimate parameters and localized air treatment (Figure 2).

Figure 2. HVAC system designed specifically for a single operating room.

A Comparative Analysis of Centralized versus Decentralized HVAC Systems

A comparative analysis of the two HVAC configurations used in hospitals can be based on criteria related to functional and performance requirements, equipment, operating and maintenance costs, and building constraints.

Microbiological Safety

Microbiological safety in centralized and decentralized HVAC systems differs mainly in terms of airflow control and zone isolation. Centralized systems provide uniform filtration but may increase cross-contamination risk through shared ductwork. Decentralized systems enable room-specific control of airflow, temperature, and pressure, ensuring better isolation and higher microbiological safety.

Technical Performance, Parameter Control, and Functional Characteristics

Technical performance differences between centralized and decentralized HVAC systems are mainly related to control and flexibility. Centralized systems provide uniform air distribution and energy efficiency but offer limited local control. Decentralized systems allow independent regulation of airflow and microclimate parameters, ensuring faster response and better fault isolation, although with higher maintenance requirements.

Costs

Economically, centralized HVAC systems usually have lower initial and maintenance costs, especially in large or new buildings, but extensive ductwork reduces flexibility. Decentralized systems require higher initial investment but provide greater adaptability and easier upgrades, making them more suitable for existing buildings and variable operating conditions.

Energy efficiency

In terms of energy efficiency, centralized HVAC systems benefit from optimized large-unit operations but often waste energy at low demand due to constant airflow. Decentralized systems enable demand-based control of airflow and temperature, reducing energy use and duct losses.

Feasibility of HVAC Systems in a Specific Constructive Environment

System selection is strongly influenced by whether the building is new or existing. Centralized HVAC systems are better suited to new constructions, where space for plant rooms and ductwork is available, but are difficult to retrofit due to structural limitations, long distribution paths, and vibration constraints. Decentralized systems are more adaptable to existing hospitals, as their compact units reduce structural load, require less ductwork, and allow room-specific customization.

Table 1. Comparison of centralized/individual HVAC systems.

In existing buildings, centralized solutions are further constrained by limited space for equipment and services. Heavy units (1–2 tons) may introduce vibration issues, often requiring external installation, which increases duct and piping lengths, may affect system performance, and can raise aesthetic and installation challenges (Figure 3).

Figure 3. Installing a centralized HVAC system in an existing building can be a real challenge. [14]

Discussions

This theoretical analysis compares centralized and decentralized HVAC systems for operating rooms based on design principles rather than experimental data, with the primary objective of ensuring a safe and stable microclimate in surgical environments.

Centralized systems provide integrated environmental control but are vulnerable to system-wide failures due to shared infrastructure. Decentralized systems ensure independent room-level control, improving fault isolation and flexibility, though with higher operational complexity.

Building context is critical: centralized systems suit new constructions with full infrastructure integration, while decentralized systems are better suited to existing buildings due to their compactness and installation flexibility.

Economically, centralized systems tend to have lower initial costs at scale, whereas decentralized systems require higher upfront investment but offer greater adaptability and lifecycle flexibility.

The analysis is conceptual and highlights the need for further validation through experimental or simulation-based studies.

Conclusions

System selection should therefore be guided by functional requirements, building constraints, clinical needs, and overall operational strategy; however, the primary criterion remains ensuring patient and staff health through a safe, stable, and well-controlled indoor microclimate.

References

[1]     ASHRAE. (2021). ANSI/ASHRAE/ASHE Standard 170: Ventilation of Health Care Facilities. Atlanta, GA: American Society of Heating, Refrigerating and Air‑Conditioning Engineers.

[2]     DIN. (2008). DIN 1946‑4: Ventilation and air conditioning – Part 4: Ventilation in buildings and rooms used in health care. Berlin: Deutsches Institut für Normung.

[3]     ISO. (2015). ISO 14644‑1: Cleanrooms and associated controlled environments – Part 1: Classification of air cleanliness by particle concentration. Geneva: International Organization for Standardization.

[4]     ISO. (2019). ISO 14644‑3: Cleanrooms and associated controlled environments – Part 3: Test methods. Geneva: International Organization for Standardization.

[5]     NP 015:2022. (2022). Normative on the design of operating theaters, Bucharest: Ministry of Health, Romania.

[6]     European Committee for Standardization (CEN). (2019). EN 16798‑3: Energy performance of buildings – Ventilation for non‑residential buildings. Brussels.

[7]     World Health Organization. (2016). Global Guidelines for the Prevention of Surgical Site Infection. Geneva: WHO.

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[13]   https://www.weiss-technik.com/klimatechnik/en/ hygienic- climate/hospital

[14]   https://zpl.ro/chiar-asa/