The basic differences between air conditioning for hospitals (and related health care facilities) and that for other building types stem from the

(1) need to restrict air movement in and between departments;

 (2) specific requirements for ventilation and filtration to dilute and remove contamination (odor, airborne microorganisms and viruses, hazardous chemicals, and radioactive substances);

 (3) different temperature and humidity requirements for various areas; and

 (4) design sophistication needed for accurate control of environmental conditions.

Air Quality Systems for Sensitive Environments

In designing air quality systems for environments housing patients with sensitive health conditions, it is crucial to ensure the air is virtually free of contaminants. Considerations include:

Air Quality Standards:

• Dust, Dirt, Odor, and Pollutants: The system should effectively remove particulate matter (dust and dirt), odors, and pollutants, including chemical and radioactive contaminants.

Infection Control:

• Bacterial Infections: Bacteria such as Mycobacterium tuberculosis (which causes tuberculosis) and Legionella pneumophila (which causes Legionnaires’ disease) are highly infectious and can spread through the air. Effective air filtration and ventilation are critical, as droplets smaller than 5 micrometers can remain airborne indefinitely.

• Viral Infections: Viruses like Varicella (chickenpox/shingles), Rubella (German measles), and Rubeola (measles) are transmitted through the air. Airborne viruses are often submicron in size but may attach to larger aerosols or conglomerates, which can be more easily filtered from the airstream.

• Molds: Molds such as Aspergillus can be dangerous for patients with weakened immune systems, such as those undergoing advanced leukemia treatment or bone marrow transplants. Effective filtration systems are necessary to capture and remove mold spores.

Design Considerations:

• Air Filtration: Utilize high-efficiency particulate air (HEPA) filters or similar high-efficiency filters to capture fine particulates and microorganisms.

• Ventilation: Ensure ventilation systems are properly designed to manage outdoor air and provide adequate indoor air quality.

• Humidity Control: Maintain optimal humidity levels to prevent mold growth and reduce the risk of airborne infections.

• Regular Maintenance: Implement routine maintenance and monitoring to ensure the air quality systems are operating effectively.

By addressing these factors, air quality systems can reduce the risk of airborne infections and create a safer environment for patients with compromised health.

Air filters are crucial for removing contaminants from the air. While there’s no standard ratio of organic to inorganic particles, a higher concentration of airborne particles generally increases the risk of microorganisms that can lead to infections (Birgand et al. 2015). HVAC engineers should assist owners in selecting the most effective filters based on life cycle cost and performance.

Filters, including prefilters, second-stage filters, and final-stage filters, are typically assessed for their efficiency based on the Minimum Efficiency Reporting Value (MERV) scale, which ranges from 1 to 16. The MERV rating indicates the filter’s ability to remove particles in three size ranges: 0.3 to 1 µm, 1 to 3 µm, and 3 to 10 µm. A higher MERV rating signifies better filtration performance.

For gaseous contaminants, filters are also tested for their efficiency in removing various organic chemicals and ozone. Effective filter management involves proper installation, regular monitoring, timely replacement, and proper disposal. Key factors in selecting air filters include:

1. Contaminant removal efficiency (MERV, MERV-A)
2. Initial and operating costs (Total cost of ownership)
3. Structural integrity

Zoning, which involves using separate air systems for different departments, can help to:

1. Address exposure issues related to building orientation or configuration.
2. Minimize recirculation between departments.
3. Provide operational flexibility.
4. Simplify emergency power operation.
5. Conserve energy.

Ducting air from multiple air-handling units into a central manifold ensures standby capacity. If one unit fails, air can be redirected from non-critical areas to maintain operation in critical areas. This setup is crucial to prevent air supply interruptions during maintenance or component failures.

Separating supply, return, and exhaust systems by department is especially beneficial for areas such as surgical, obstetrical, pathological, and laboratory departments. Maintaining the correct pressure balance in critical areas can be achieved by interlocking supply and exhaust fans, ensuring that exhaust airflow stops if supply airflow ceases, and vice versa.

When a boiler is out of service for maintenance or repair, the remaining boilers should still provide:

• Hot water for clinical, dietary, and patient use
• Steam for sterilization and dietary purposes
• Heating for critical areas such as operating rooms, labor and delivery rooms, intensive care units, nurseries, and general inpatient areas

In climates where temperatures remain at or above 25°F for 99.6% of the heating period, some codes may not require reserve capacity. Boiler feed, heat circulation, condensate return, and fuel oil pumps should be installed to support both normal and standby operations. Supply and return mains for cooling, heating, and process steam should have valves for isolating different sections, with each piece of equipment also valved at both ends.

For critical areas like delivery and operating rooms, supply and exhaust systems should be independent and capable of operating on emergency power. These rooms should be ventilated to maintain functionality even if the main ventilation system fails.

Boiler steam, often treated with chemicals, may affect air-handling systems in critical areas. In such cases, a clean steam system might be preferable for humidification to avoid respiratory irritation.

An acute care general hospital is divided into seven principal areas:

1. Surgery and Critical Care

   • Surgical Suites: Require strict control of aseptic conditions to minimize airborne contamination. Effective air movement is achieved by delivering air from the ceiling and using exhaust/return openings located low on opposite walls. Laminar flow systems are preferred for maintaining a sterile environment.
   • Operating Rooms: Air should be supplied at 25 to 35 fpm through a ceiling array with a mix of low and high exhaust openings. The goal is to maintain cleanliness in the central surgical field.
   • Patient Rooms: Each room should have individual temperature control, and air pressure can be neutral. Toilets must be exhausted directly outdoors to control odors and aerosols. Efficient HVAC design is essential due to high occupancy rates and energy demands.

2. Ancillary

   • Radiology Department: Requires ventilation systems that handle odors and prevent radiation leakage. Temperature and humidity must be controlled within specific ranges, and lead lining may be necessary in ducts.
   • Bacteriology Laboratories: Should have minimal air movement to maintain sterility, with HEPA filters installed in supply ducts. Proper ventilation is required to manage odors and steam.
   • Infectious Disease Laboratories: Must have a minimum ventilation rate of 6 air changes per hour and negative pressure to prevent contamination spread.
   • Nuclear Medicine Laboratories: Focus on minimizing airborne contamination, particularly with iodine-131 and xenon-133 used in diagnostics.

3. Administration

   • Lobby and Offices: Should have separate air-handling systems from the hospital to enable energy savings and to handle potential airborne infections from undiagnosed patients. Avoid open-water features to prevent infectious aerosols.

4. Diagnostic and Treatment

   • Procedures Rooms: Bronchoscopy and similar procedures should have local capture exhaust and isolation similar to airborne infection isolation (AII) rooms. MRI rooms should manage heat from equipment and use nonferrous materials as per manufacturer requirements.
   • Heat Gains: Account for varying heat outputs from medical equipment and adjust HVAC design accordingly.
   • Treatment Rooms: Should have independent temperature and humidity control, matching the requirements of patient rooms.

5. Sterilization and Supply

   • Central Sterile Processing Unit: Includes separate areas for decontamination, preparation, and sterilization. Air should flow from clean to contaminated areas, and strict temperature and humidity controls are necessary. For ethylene oxide (ETO) gas sterilizers, dedicated exhaust systems with alarms and high negative pressure are required. Similar measures apply to hydrogen peroxide sterilizers.

6. Service

   • Service Areas: Includes dietary, housekeeping, and mechanical facilities. Adequate ventilation must include both supply and exhaust air, with filtered and temperature-controlled air. Open windows are ineffective, and air-to-air heat exchangers can improve energy efficiency.

Key areas requiring special attention in laundry and linen facilities include:

• Soiled Linen Storage Room: Must be well-ventilated, exhausted, and maintained at negative air pressure to manage odors and contamination.
• Soiled Utility Room: Should be mechanically exhausted directly outdoors to handle noxious odors.
• Laundry Processing Area: Equipment such as washers, flatwork ironers, and tumblers need direct overhead exhaust to control humidity and manage radiant heat. Use canopies and localized exhausts, and ensure independent exhaust systems with lint filters for heat-producing equipment. Position air inlets to direct airflow towards heat sources and consider heat recovery from exhaust air.

Outpatient health care facilities connected to a hospital and using its HVAC systems should follow the design standards for hospital facilities. Detached outpatient facilities with their own HVAC systems can be categorized into types such as diagnostic clinics, treatment clinics, or others like primary care or urgent care centers. Facilities performing treatments similar to hospital-based ones should adhere to hospital environmental design guidelines.

A diagnostic clinic provides diagnostic services or minor treatments but does not perform major procedures requiring general anesthesia or surgery. It may use specialized medical imaging equipment, which requires specific humidity levels and can generate significant heat. Design criteria for these clinics should address:

• Infection Sources
• Control Measures
• Air Quality
• Air Movement
• Temperature and Humidity
• Smoke Control

Departments in outpatient treatment clinics with design criteria similar to hospitals include:

• Surgical: operating, recovery, and anesthesia storage rooms
• Ancillary
• Diagnostic and treatment
• Decontamination and sterilization
• Service: soiled workrooms, mechanical facilities, and locker rooms

FGI’s 2014 Guidelines cover design and construction requirements for various residential health, care, and support facilities, including nursing homes, hospice, assisted living, independent living, adult day care, wellness centers, and outpatient rehabilitation centers. HVAC design needs can vary significantly depending on the facility type.

Nursing Facilities include:

• Extended Care Facilities: For patients needing continued therapy post-hospitalization; typically short-term stays.
• Skilled Nursing Homes: For individuals needing daily assistance, often elderly with multiple health issues; longer-term stays.
• Residential Care Homes: For elderly individuals who need minimal assistance and lead relatively normal lives; generally long-term stays.

HVAC design considerations for these facilities include:

1. Administrative and support areas
2. Patient service areas
3. Treatment areas
4. Clean workrooms
5. Soiled workrooms