What if we could eliminate the production and use of steam in hospitals completely? How would we meet the humidification and sterilization needs of facilities without steam? This section will cover technologies that accomplish these essential processes in hospitals without the use of steam including adiabatic humidification and liquid chemical sterilization. While both solutions would require more widespread approval in order to be more implemented for use in facilities, they have been proven to be just as effective (if not more) than current humidification and sterilization strategies.

Technical Description

Background

Chemical sterilization uses a liquid sterilant solution at a lower temperature (around 109°F) to sterilize medical devices. This process is most often used for heat-sensitive items that would be damaged by steam sterilization in an autoclave, but it is safe for sterilization of all types of instruments as long as their material has been validated and deemed safe for chemical exposure. Liquid chemical sterilization (LCS) equipment is safe and adapted for use in hospitals, only requiring a standard power connection, water connection, and drain.

Adiabatic humidification adds small water droplets directly to the air, as opposed to injecting steam, resulting in evaporation in the warm, dry air, which then provides free cooling. This eliminates the need for boiling water, removing combustion from the humidification process, while still maintaining relative humidity requirements set by ASHRAE 170. Adiabatic humidification requires only 10% of the energy when compared to isothermal humidifiers. The water used in the humidification process must be treated to optimize efficiency and provide healthy air to the hospital.

Design considerations

The sterilization cycle time for liquid chemical systems ranges from 18 to 23 minutes. LCS systems use only 8.7 gallons of water per cycle compared to 120 gallons per cycle for a steam autoclave. One of the major concerns of using LCS systems instead of steam or other types of sterilization is the chance of contamination exposure when instruments are removed from the sterilizer because they are not wrapped or in a closed environment. This concern can also be true for equipment sterilized via steam autoclaves, and it is easy to minimize chances for contamination by using proper personal protective equipment (PPE) for workers handling the instruments and maintaining proper air changes and temperature control in the SPD or respective sterilization environment. LCS uses peracetic acid and water to sterilize equipment, which has no detrimental effects on the environment or emissions of any kind. Ethylene Oxide (EO) and vaporized hydrogen peroxide (VHP) are other forms of chemical sterilization that could also be used as an alternative to steam sterilization, but they both have more limitations than that of peracetic acid. Ethylene oxide is a dangerous chemical that can be linked to cancer after long term or occupational exposure. Although EO sterilization is advantageous because it is low temperature and instruments can be wrapped in their final packaging and protected from contamination, the EO sterilization process takes almost thirteen hours to process devices, which is very slow compared to that of LCS. In California there are roughly four facilities that do EO processing because the process is so carefully regulated. VHP is becoming a more common low temperature sterilization process over EO because it is non-toxic and environmentally safe.

In adiabatic humidification, small water droplets introduced into warm air evaporate causing a cooling effect, particularly in warm and dry climates or where there is a high heat load. Energy savings will be limited if the air entering the humidifier is too low since it will then require reheat before being supplied to the space. Adiabatic humidification has a small fraction of the energy use of isothermal even with the pump, water treatment system, and ancillary devices (<10% compared to isothermal system). It can also satisfy large, multiple-zone humidification with one pumping system/controller and has a 90% turn down ratio with steady relative humidity control.

It’s important to select the appropriate type of adiabatic humidifier for the building size, application, and available space. There are several types of adiabatic humidifiers:

1. Wetted media humidifiers: These humidifiers use a wetted surface, such as a wet pad or a wetted wheel, to humidify the air. Air is passed over the wetted surface, and the moisture is evaporated into the air, increasing the humidity.
2. Spray humidifiers: These humidifiers use a spray of water to humidify the air. Air is passed through a spray of water, and the moisture is evaporated into the air, increasing the humidity.
3. Evaporative humidifiers: These humidifiers use a wetted surface and a fan to humidify the air. Air is passed over the wetted surface and then through a fan, which increases the evaporation of moisture into the air.

Best practices

To maximize efficiency and reduce energy waste, it is important to insulate steam pipes and dispersion tubes, recover condensate loss, use electric and high-efficiency gas generators, and use pre-treated water to reduce hard-water scaling. Because water is introduced directly into the air in adiabatic humidification, it is important that the water is pure, clean, and free from biological contaminants.

How does this decarbonize?

Chemical Sterilization

Carbon emissions associated with liquid chemical sterilization are much lower due to the absence of steam and not needing to burn natural gas. The LCS equipment requires electricity which would have a footprint of some sort, but other than that there are no carbon emissions associated with the technology.

Adiabatic Humidification

With the elimination of steam, there is no need to boil water which removes the combustion process from the system. Introducing water vapor into the air reduces the cooling load which then also reduces the load on the chiller.

Implementation

Barriers: Codes

According to the Center for Disease Control and Prevention (CDC) [1], “steam sterilization should be used whenever possible on all critical and semi-critical items that are heat and moisture resistant (e.g., steam sterilizable respiratory therapy and anesthesia equipment), even when not essential to prevent pathogen transmission.” Similarly, the Food and Drug Administration’s (FDA) stance on sterilization [2] is that “sterilization with liquid chemical sterilants does not convey the same sterility assurance as sterilization using thermal or gas/vapor/plasma low temperature sterilization methods.” Currently, these organizations believe that any instrument that can hold up to steam sterilization should only be sterilized with steam and not other processes, essentially forcing facilities to continue using steam autoclaves despite the fact that there are other sterilization methods that are just as effective and have less impact on the environment such as liquid chemical sterilization. In August 2022, the FDA released a statement about its efforts to support innovation in medical device sterilization techniques, specifically around the use of ethylene oxide and reducing its concentration and emissions; however, it did not mention LCS.

Adiabatic Humidification: (a) ASHRAE 170 recently approved adiabatic humidification in healthcare facilities which provides an opportunity to improve energy efficiency and ensure patient comfort through proper humidity. Installation and maintenance costs are reduced since one high-pressure water pump can serve many zones in a facility. Adiabatic humidification does not perform well in regions that are not generally warm or dry. The air will need to be preheated and reheated in cold climates reducing the energy efficiency. Water maintenance is important to limit the presence of bacteria and keep the system efficient by reducing particles in the water that create dust. High pressure atomizers with certain features including reverse-osmosis to treat the water, UV-C sterilization, sub-micrometric filtration, moisture eliminators, and continuously circulated or drained piping, must be used to protect the hygiene level required by the hospital.

Strategy

This guidebook section can serve as a recommendation to Title 24, Part 4 of the California Mechanical Code to allow adiabatic humidification since ASHRAE recently approved it.

Financial analysis and business case

Adiabatic Humidification

High pressure water atomizing humidification is less than 1% of the cost of electric steam because of the lower operating costs. Isothermal humidifiers consume about 800 W of energy per l/h of humidity produced, while high pressure adiabatic atomizers consume 4 W of electricity for operating the pump to deliver the same capacity.

Since ASHRAE 170 recently approved adiabatic humidification in healthcare, there are not many hospital case studies; however, data centers have benefitted from the technology. A reverse osmosis system treated the water which was then pumped from the storage tanks to the dispersion grids where it was atomized at up to 1200 psi. The grids are staged separately and can meet humidification demand in multiple zones with different set points. The system was also up to 100% outside air from the rooftop air handlers, which means potentially large changes in humidification.