HVAC for hospitals and healthcare facilities: technical requirements

HVAC design for a hospital or healthcare facility is one of the most demanding disciplines in building services engineering. It goes well beyond maintaining comfortable temperatures: it is about creating controlled environments that prevent infections, protect immunocompromised patients, guarantee stable conditions for the storage of medicines and equipment, and comply with regulations that leave no room for improvisation.

A design or maintenance error in the HVAC system of an operating theatre, an intensive care unit or a hospital laboratory can have direct consequences for patient health. This article covers the fundamental technical aspects that must be understood when undertaking a healthcare HVAC project.

Reference standards

UNE 100713

The Spanish standard UNE 100713 (“Air conditioning installations in hospitals”) is the primary technical reference for healthcare HVAC design in Spain. It establishes:

• Classification of hospital zones by requirement level.
• Temperature and humidity conditions for each zone type.
• Minimum outdoor air volumes.
• Required filtration levels.
• Differential pressure regimes between zones.

International equivalents include HTM 03-01 in the UK, ASHRAE Standard 170 in the United States, and DIN 1946-4 in Germany. While the specific values vary, the underlying principles of zoning, filtration and pressure control are consistent across all of them.

RITE

Spain’s Regulation on Thermal Installations in Buildings (RITE) applies in general terms, but UNE 100713 takes precedence on aspects specific to the healthcare environment, being more stringent on the majority of parameters.

Infection control guidelines

The guidelines of the ECDC (European Centre for Disease Prevention and Control) and hospital infection control committee protocols supplement the technical standards with specific recommendations on the relationship between HVAC and the control of nosocomial infections.

Hospital zone classification

UNE 100713 classifies hospital zones according to air quality requirements:

Very high risk zone (Class I)

• Operating theatres for specialist surgery (transplants, cardiac, orthopaedic with implants).
• Zones for severely immunocompromised patients.
• Requirements: HEPA filtration (H13), laminar airflow, positive pressure, temperature 20-24 degrees C, relative humidity 45-55%, more than 20 air changes per hour.

High risk zone (Class II)

• Conventional operating theatres, delivery rooms, ICU, neonatal units.
• Requirements: high-efficiency filtration (F9 + H13), positive pressure relative to corridors, 15-20 air changes per hour.

Medium risk zone (Class III)

• Inpatient wards, A&E, outpatient clinics, laboratories.
• Requirements: medium-high filtration (F7-F9), 6-10 air changes per hour, controlled pressure.

Low risk zone (Class IV)

• Administrative areas, waiting rooms, lobbies.
• Requirements: similar to a standard commercial building, with F7 filtration as a minimum.

Negative pressure zones

• Isolation rooms for infectious patients, microbiology laboratories.
• Specific requirements: the room must be maintained at negative pressure relative to the corridor to prevent contaminated air from escaping. Extract air must be treated with HEPA filtration before being discharged.

Air filtration: the barrier against infection

Filtration is the most critical aspect of hospital HVAC. The contaminants the system must capture are not merely dust or particles — they are microorganisms (bacteria, viruses, fungal spores) that can cause serious infections in vulnerable patients.

A typical hospital filtration system has three stages:

1. Pre-filter (G4-M5): at the outdoor air intake, captures coarse particles and protects downstream filters.
2. Intermediate filter (F7-F9): in the Air Handling Unit (AHU), captures the majority of fine particles.
3. Terminal HEPA filter (H13-H14): at the diffuser in the room, immediately before air enters the critical space. H13 HEPA filters capture 99.95% of particles at 0.3 microns.

The integrity of HEPA filters must be verified periodically by aerosol integrity testing (DOP test), which detects leaks in the filter media or in the installation seals. A HEPA filter with a leak of just 0.01% ceases to function as an effective barrier.

Differential pressures: the key concept

Controlling differential pressures between zones is the mechanism that ensures air always moves from cleaner zones to less clean zones, and never in the reverse direction. The principle is straightforward:

• The cleanest zones are maintained at higher pressure (positive pressure).
• Less clean zones are at lower pressure.
• The typical pressure difference between adjacent zones is 5 to 15 Pa.

In an operating theatre, the typical pressure cascade is: operating theatre (highest pressure) > preparation room > clean corridor > general corridor. In this way, if a door opens, air flows from the operating theatre outward, not inward, preventing the entry of contaminants.

In infectious isolation rooms, the logic is reversed: the room is maintained at negative pressure to prevent air from the infectious patient reaching the corridor.

Controlling these pressures requires motorised dampers in ductwork, variable-frequency drives on fans and differential pressure sensors with automatic regulation. A failure in pressure control can invalidate the entire infection prevention strategy of the hospital.

Temperature and humidity conditions

Environmental conditions vary by zone type:

In operating theatres, the temperature must be adjustable by the surgical team according to the type of procedure. Some surgeries require lower temperatures (20 degrees C or even below) to reduce the patient’s metabolic rate.

Relative humidity is critical in operating theatres for two reasons: excessively low humidity encourages electrostatic charge build-up (dangerous in the presence of anaesthetic gases and electrical equipment) and dries out the patient’s mucous membranes; excessively high humidity promotes the proliferation of fungi and bacteria.

Redundancy and reliability

A hospital cannot be left without HVAC. Systems must be designed with sufficient redundancy to guarantee continuous service:

• AHUs with redundant fans: if one fan fails, the other takes over the load automatically.
• Chillers and boilers in N+1 configuration: one standby unit for each group of primary units.
• Emergency power supply: AHUs serving critical zones must be connected to the hospital’s backup generator.
• Centralised Building Management System (BMS): real-time monitoring of all variables with escalating alarms and historical data logging.

Maintenance in healthcare environments

HVAC maintenance in a hospital has specific constraints:

• Interventions in critical zones must be coordinated with clinical activity to minimise contamination risk.
• HEPA filter replacement in operating theatres requires a specific protocol that includes post-replacement decontamination and integrity verification of the new filter.
• Microbiological air quality checks (sampling with an impactor) must be carried out periodically and after any intervention on the system.
• Maintenance documentation must be traceable and available for healthcare audits.

At Acoval Technical Installations we have experience in the installation and maintenance of HVAC systems for the healthcare sector in Valencia. If you manage a healthcare centre, a clinic or a laboratory and need an HVAC system that meets healthcare regulations, or if you want to audit your current installation, get in touch through our contact page.