The Role of Air Handling Units in Combating the Spread of Infectious Disease

The Role of Air Handling Units in Combating the Spread of Infectious Disease

Goal To identify those areas within an air handler which poses risk to the healthcare industry and recommended four solutions to mitigate those risks: Ultraviolet Germicidal Irradiation Cooling Coil Drain Pan Design Wash-down Unit Construction Filter Bank Assemblies

Direct Effect on Meeting Industry Guidelines The health or quality of your air distribution system can have a direct effect on the ability to deliver acceptable quality levels of clean air as established by the various guidelines from (AIA, OSHA, ASHE, ASHRAE, DHHS) and other industry regulators.

HVAC Design Heating, ventilation, and air conditioning (HVAC) systems in health-care facilities are designed to maintain indoor air temperature and humidity at comfortable levels for staff, patients and visitors.

HVAC Design The HVAC system is also used as a means to: Remove Contaminated Air Control Odors Protect Staff and Patients from Airborne Pathogens Minimize the Transmitted Pathogens from Patients.

Droplet Nuclei as a Form of Indirect Transmission

The spread of airborne infectious diseases via droplet nuclei is a form of indirect transmission. Protected by a coat of dry secretions Remain suspended indefinitely in the air Can be transported over long distances Indirect Transmission

Greatest Threat Air and water leakage within the air handling systems poses the greatest jeopardy to those within the hospital. Assumption: facility is properly balanced for correct airflow volumes and pressure differentials between rooms.

Base should be fully welded using structural members. All attachments should be welded, no mechanical fasteners. The base should be made of non-corrosive materials. Water Leakage and Containment at the Base Base is designed for wash-down with clean-out drains.

Properly sloped condensate drain pan Condensate drain pan pipe connection Blank-offs and flashing to seal coil to air housing Independent structural support for coils Coil fin-bundle bypass issues Cooling Coil Support Structures

Properly sloped condensate drain pan per ASHRAE 62.1 Active condensate drain pans should be triplesloped The slope of the drain pan should be minimum of 1/8 per foot The length of drain pan should be sized for coil application

Pipe connection is sized for maximum condensate flow Coil drainpipe connection is welded flush to assure condensate completely drains and leaves no standing water behind. Condensate Drain Pan Pipe Connection

Blank-offs and flashing to seal coil to air housing Coil flashing assures all air goes through the finned surface Eliminates condensation on the coil drain pans downstream Upstream flashing is sloped to direct condensate into drain pan Properly flashing will assure condensate is contained and directed to the drain

Each coil includes an independent pan assembly Assures support for each coil and independently removable Coils don t set in the drain pan allows condensate to flow Independent structural support for coils

Gaps between fin-bundle and coil casing reduces performance Bypass air around finbundle causes downstream condensate to form on the drain pans High velocity air gaps causes moisture carryover Coil fin-bundle bypass issues

Since filters collect spores and nutrients the potential for mold growth throughout the HVAC system is present. The surplus moisture within the media compounds this issue. Wetting of final filters can occur when media is located downstream of humidifiers and/or cooling coils. Wetting can also occur when air is accelerated (air cooled) through the system. Keeping your final filters dry

Keeping your final filters dry What to check? Check humidifiers proper operation during season usage. Are set-points correct Confirm uniform leaving air velocities from the cooling coils. Velocities should be +/- 15% of the design overall velocity Are there valves within the airstream leaking moisture? Replace or repair valves as necessary Change the cooling coil from blow-through to draw-through The heat-of-fan provides a couple of degrees of reheat

Cases of wet filters can still persist despite precautions Temperature depression can occur in the filter media as well at any point throughout the system that accelerates flow. It s assumed that total enthalpy remains constant through the air handler; assume 55ºF saturated. A slight acceleration can cause a temperature drop of ~0.03ºF causing moisture to condensate on the surface of the media.

Cases of wet filters can still persist despite precautions To correct this wetting issue the air temperature must be raised slightly above the saturation curve. This can be accomplished adding a reheat coil. (assuming a blow-through configuration) The same can be accomplished using a desaturation coil. This coil functions as a cooling coil and reheat coil in-one. Effectively lowers the RH levels from 100% to ~90%.

Cases of wet filters can still persist despite precautions The desaturation coil effectively adds 2ºF to 4ºF of reheat to the airstream. Reduces the RH level so that any acceleration of airstream through the filters will not induce any condensate.

The use of UVGI is another means to control indirect transmitted pathogens in the HVAC system. Ultraviolet Germicidal Irradiation (UVGI)

Light Spectrum Germicidal UV-C Lamp 253.7 nm

Ultraviolet Light Spectrum 1nm = 1/1000 micron UV-A (315nm - 400nm) - Includes black lights, sun tanning lamps and it is harmful to eyes UV-B (280nm - 315nm) - Causes sunburn and Skin cancer UV-C (200nm - 280nm) - Is naturally germicidal, damages the DNA of microbes and more UV-V (100nm 200nm)- At 185nm Ozone is formed The Sun produces all 3, UV-A & UV-B make it through the Earth s atmosphere. UV-C is mostly filtered out

DNA Response to UV Energy 230 nm 265 nm

DNA Damage

Two distinct applications for UVC: Coils Filters capture and kill Decontaminating moving air-streams ( on-the-fly ) HVAC Applications for UV-C Coil On-The Fly

Filter bank structure integrity Filter holding frame assemblies must be designed for filter loading forces. Deflection of filter bank assembly will break the gasket seal and defeat the media s effectiveness. Filter bank assemblies must be structurally integrated into the air housing to assure long-term effectiveness. Critical HEPA applications can utilize a bypass welded flange configuration to assure zero bypass of particles.

An internal stiffener can be added between the filter frames to increase overall strength of filter bank. Filter Bank Structure Integrity

Filter bank structure integrity Integration of filter bank into air housing should utilize structural members to assure long-term sealing integrity.

Final filter bank design for HEPA applications; HEPA frames are fully welded with extended perimeter flanges. Designed for zero bypass for critical applications.

Final filter bank design for HEPA applications; The fully welded HEPA frame system is installed with extended flanges sandwiched between the air-housing to form an air barrier which will only leak to the ambient exterior under positive pressure and assure zero leakage downstream.

The control of potential infectious diseases within an air handler is directly related to the design and construction techniques used. The core mediums within the air handler; water and air must be controlled to effectively reduce the likelihood of indirect transmission of diseases. Conclusion: Ultraviolet Germicidal Irradiation Wash-down Unit Construction Cooling Coil Drain Pan Design Filter Bank Assemblies

Thank You Questions?