Introduction
Country | Professional aociety/government body | Reference |
---|---|---|
Australia | • Queensland Health Facility Guideline (QHFG) | [5] |
Germany | • Verein Deutscher Ingenieure (VDI) | [6] |
India | • Indian Society of Critical Care Medicine (ISCCM) | |
United Arab Emirates | • Dubai Health Authority (DHA) | [9] |
UK | • Department of Health Estates and Facilities Division (DHF), | |
• Health technical memorandum (HTM 2025) | ||
USA | • American Institute of Architects (AIA) | |
• American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) | ||
• Centers for Disease Control and Prevention (CDC) |
Clinical importance of HVAC system
Components of HVAC system
Outdoor air intake and air exhaust ducts and controls
Air handling units (AHU)
Heat exchangers and chillers (humidity modification system)
Compressor
Fans
Filters
Drains and drain pans
Ultraviolet (UV) light emitters or ultraviolet germicidal irradiation (UVGI)
Noise attenuators
Air distribution systems
Supply and return air ducts
Air distribution in special zones—protective isolation rooms
Characteristic | Positive pressure system | Negative pressure system or airborne infection isolation room (AIIR) |
---|---|---|
Purpose | To create a protective environment to the patient to avoid acquiring any airborne infection (does not require an ante-room). | To create a protective environment to the healthcare providers as well as other patients in the ICU (requires an ante-room). |
Type of patients requiring isolation | Burns, post-transplant, febrile neutropenia (also for patients in operating rooms) | Tuberculosis, swine flu, COVID-19 and other airborne viral diseases |
Direction of airflow | Outside the room (away from the patients) | Inside the room (towards the patient) |
Pressure | More than 2.5 Pa preferably + 8 Pa (ideal) | Less than 2.5 Pa |
Supply air | More than the sum of return and exhaust air | Less than the sum of return and exhaust air |
Recirculation | 90–95% | 80–90% (if required) |
Air change per hour | > 20 | ≥ 12 |
Filtration efficiency | Supply: 99.97% at 0.3 μm DOP All supply air must pass through HEPA filters | Supply: 90% (dust spot test) All supply air to be exhausted without recirculation HEPA (99.97% at 0.3 μm DOP) must be used on the supply side if recirculation is used. HEPA is required on the exhaust side too, when exhausting air to the outside is not practical |
Monitoring and maintenance of the HVAC plant
S. N. | HVAC system maintenance |
---|---|
1 | Ensure proper labelling of parts of HVAC plant including the direction of airflow mentioning OA, SA, RA and EA. |
2 | Outside air intakes must be examined for any dust and moisture. |
3 | Drain pans and pipes checked for any accumulation of condensate water. |
4 | Clean condenser and evaporator coils. |
5 | Indoor air quality should be frequently checked usually every 6 months. |
6 | HEPA filter efficiency tests and efficiency rating label every 6 months. |
7 | Lubricate motors bearings, fans and moving parts. |
8 | Continuous monitoring of the humidity and temperature in ICU. |
Air quality standards
Monitoring HEPA filter performance
Maintenance of the HVAC plant
Recommended standards for HVAC system in the ICU from various professional societies and government bodies
Country | Recommendation society/association (reference) | Temperature | Relative humidity | Filtration | Pressurization | Air change (outside air/total) per hour [ACH] | Specific highlights/key differences |
---|---|---|---|---|---|---|---|
Type of ICU—general | |||||||
Australia | QHFG [5] | 21–24 °C | 30–60% | G4–F8 | Positive | 2/6 | Filtration: Standards varied from MERV 7–8 to MERV 15. Few recommend HEPA filters (MERV ≥ 17). Pressurization: Positive pressure inside the ICU zone is recommended by Australian, UAE and UK societies, while neutral pressure is recommended in Germany, India, USA and recent UK HTM 2025. Temperature: Wide range varying from 16 to 25 °C. Relative humidity: Majority suggests 30–60% range whereas Indian and German recommendations remain silent. ACH: HTM 2025 (UK) strongly discourages the use of re-circulation type HVAC, presumably to avoid recirculation of airborne pathogens. Air distribution pattern: There exists no specific recommendation of air distribution pattern |
Germany | VDI [6] | – | – | F9 | Neutral | – | |
India | 16–25 °C | – | 99% efficiency till 5 μm | Neutral | 2/6 | ||
UAE | DHA [9] | 21–24 °C | 30–60% | HEPA | Positive | 2/6 | |
UK | 18–25 °C | – | F7 | Positivea | 10 (total)b | ||
UK | HTM 2025 [12] | 20–22 °C | 40–60% | – | Neutral | 100% FA | |
USA | AIA [13] | 21–24 °C | 30–60% | – | Neutral | 2/6 | |
USA | ASHRAE [14] | 21–24 °C | 30–60% | – | Neutral | 2/6 | |
Type of ICU—burn | |||||||
Australia | QHFG [5] | 21–32 °C | 30–95% | G4–F8 | Positive | 3/6 | Filtration: Australian recommendations suggest filtration similar to general ICUs whereas the USA recommends HEPA filtration of incoming air. Pressurization: Positive pressure isolation is recommended by Australia and the USA, whereas the rest have no mention. Temperature: Higher range (21–32 °C), in comparison to general ICU, is recommended by QHFS. Relative humidity: Higher range (up to 95%), in comparison to general ICU, is recommended by ASHRAE. Air distribution pattern: It should be ‘laminar’, as recommended by ASHRAE. |
USA | ASHRAE [14] | – | 40–60% | HEPA | Positive | 3/6 | |
Type of ICU—neonate | |||||||
Australia | QHFG [5] | 22–26 °C | 30–60% | G4–F8 | Positive | 2/6 | Filtration: There is no mention of air filtration standards by the USA whereas Australia suggests similar filtration standards as general ICUs. Pressurization: Australian recommendations suggest positive pressure whereas the USA recommends neutral pressure Temperature: Slight higher range (22–26 °C) is recommended in comparison to other ICUs. Relative humidity: Neonates having similar RH as in adults is a concern Air distribution pattern: There exists no specific recommendation of air distribution pattern |
USA | ASHRAE [14] | 22–26 °C | 30–60% | – | Neutral | 2/6 |
Temperature
Relative humidity
Filtration
Pressurization
Air change (outside air/total) per hour
Air distribution pattern
Coronavirus disease 2019 (COVID-19) and HVAC system
Name of the organization/society (reference) | ||||
---|---|---|---|---|
CDC [47] | ESICM/SCCM [50] | ECDC [51] | ||
Pressurization | Negative | Negative | Negative | No mention |
Temperature | No mention | No mention | No mention | No mention |
Relative humidity | No mention | No mention | No mention | No mention |
Air change (outside air/total) per hour (ACH) | Minimum of 6, while 12 in new construction or renovation | At least 12 | At least 12 | No mention |
Filtration | HEPA filtration if re-circulated | No mention | HEPA filtration if re-circulated | No mention |
Air distribution pattern | Appropriate directionality | Controlled direction of airflow | No mention | No mention |
Special comments | – | – | – | Increase frequency of cleaning and maintenance of HVAC systems should be considered |