On demand humidity control used alongside conventional heating/cooling systems (psychrometrics) is a method widely employed to increase the perceived human comfort levels indoors. On demand humidity control is also important as it can be used to reduce dust and electrostatic charges in clean rooms. Strict regulations covering the risk of system wise bacterial contamination might evolve in such humidification devices.
There are many parameters to consider when selecting a suitable HVAC/clean room humidifier type, such as energy consumption, installation complexity, capacity of humidification and maintenance costs.
Evaporative and ultrasonic humidifiers are more commonly available for in-duct systems. Evaporative humidifiers, though, most commonly suffer from large operation and maintenance costs whilst ultrasonic humidifiers suffer from saturated vapour condensation effects. Both types of devices have high installation fees and provide a favourable bacteria growth environment, as in most cases, they require pools of stagnant water to operate. This imparts a significant maintenance cost to satisfy local regulations.
Furthermore, of particular importance given the current pandemic outbreak, several studies1 have indicated factors pertaining to the use of humidity to control the spread of virus infections in aerosolised droplets.
Virus-containing aerosolised droplets are created either naturally e.g. when an infected person coughs or sneezes or mechanically when an infected person undergoes a medical procedure (e.g. intubation, dental etc.). The studies indicated that maintaining a relative humidity between 40-60% is key to significantly reducing the viability in droplets of membrane bound viruses (such as the influenza virus and SARS-CoV-2 virus). This is achieved by a mechanism relating to the limitation of virial droplet evaporation that, in combination, reduces the droplet suspension time in air and allows physiochemical processes within a virus-carrying droplet to deactivate it.
A novel high capacity humidifying device which limits significantly in-duct saturated vapour condensation, is fast acting, employs a running filtered water supply for humidification, is easy to install and has low operating, installation and maintenance costs has been developed by researchers at Imperial College London. The deep knowledge of fluid dynamics was employed to create a prototype humidifying device that can suspend up to 12kg/hr of micron sized water droplets in large airflow volumes (up to 4500 L/min has been tested). The device can rapidly humidify large spaces in seconds as this has been practically demonstrated. The humidification prototype requires no electricity at the installation point as the device can be operated via the actuation of valves. There is low energy consumption operating the device, as this does not employ a forced evaporation cycle (no need for a heat source).
The device could be adapted to run as a standalone air-purifier and humidifier device combo with an on-board water tank for domestic use. The benefit of the current design for such small-scale applications is the rapid suspension of humidifying droplets without a need of a humidification pool-and-wig filter, ultrasonic/evaporation pool or/and UVC water sterilisation designs. This limits the complexity of manufacturing and improves the user experience especially when it comes to regular user maintenance requirements and everyday use as well as limitation of bacterial contamination and spread. The flexibility offered by standalone compact devices could offer greater deployment of humidity control devices as retrofitted solutions in domestic settings.
Humidifier systems using a rapid humidification process offer:
- Can be adapted to different applications
- Potential membrane bound virus suppression such as influenza and SARS-CoV-19 via control of humidity
- Low energy consumption in operation, no requirement of electricity at point of installation
- An effective solution to in-duct condensation issues
- Fast response
- Limits bacterial growth
- Large humidifying capacity
- Can be adapted for domestic applications (air-purifier and humidifier combo devices)
Intellectual property information
Ultrafast humidifier: International application number PCT/GB2020/051957
Prof Yannis Hardalupas, Professor of Multiphase Flows at the Faculty of Engineering, Imperial College London
Dr Antonis Sergis, Research Fellow at the Faculty of Engineering, Imperial College London
1 Coil and Fretz, 2020; http://msystems.asm.org/ on May 18 , 2020 at Imperial College London, Noti et al., 2013; High Humidity Leads to Loss of Infectious Influenza Virus from Simulated Coughs. PLoS One 8, 2–9. doi:10.1371/journal.pone.0057485, Yang et al., 2012; Relationship between Humidity and Influenza A Viability in Droplets and Implications for Influenza’s Seasonality. PLoS One 7, 1–8. doi:10.1371/journal.pone.0046789, Yang and Marr, 2011) Dynamics of Airborne influenza A viruses indoors and dependence on humidity. PLoS One 6. doi:10.1371/journal.pone.0021481
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