UNDER THE HOOD

COVID AND FLU

 

COVID-19 and the upcoming flu season keep us on edge: How do we prepare our homes, offices, and indoor space? Encouraged by news that the vaccine development is moving quickly and should be available by then, we must recognize that no vaccine can provide a 100% protection.

 

Since the corona virus and most flu infections are transmitted via air, N5Air focused on creating a healthy air indoor environment, and designed a UVC light air sanitizing system for homes, businesses, and offices.

 

The virus concentration in the air that we inhale determines whether our immune system can overcome the virus invasion. N5Air UVC air sanitizing system reduces virus concentration in the air and lowers the probability of infection.

 

Our system uses the ultraviolet light with a wavelength of about 254 nm. Experiments show that the photons of this wavelength are most effective in killing viruses and other pathogens on impact by scrambling and destroying their genetic material. Note that practically all UVC radiation is filtered out by the earth atmosphere

 

We did some measurements using the SPER SCIENTIFIC's UVC Light Meter 850010. The measured UVC irradiance at the ground level at the time was around  0.5 W/m2. Although this number is small, it is not zero: the sun does provide some very small anti-virus surface and air sanitizing. However, our system produces UVC sanitizing light more than a hundred times more intense than that, delivered continuously!

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BACK-OF-THE-ENVELOPE CALCULATION

 

Photons and Viruses: Size.

According to quantum mechanics, the size of a photon in a light beam cannot be determined "in the flight". The photon reveals itself as an object with size only when it is measured in an experiment or in the course of interacting with a particle: for our purposes, a virus. For the purposes of this calculation, we will assume that the “interaction size” of the photon is equal to its wavelength, 254 nm in the case of UVC light. The average size of a virus is around 150 nm. So, the UVC photons and viruses seem to be in the same same "weight category".

Photon Energy.

A photon energy E=h*c/ λ, where h is Planck’s Constant (6.62607015 10^-34 joule sec), λ is the photon wavelength, and c is the speed of light (299,792,458 m/s). Using this equation, we find the photon’s energy to be approximately 7.8 10^-19 Joules.

 

To get a sense of the number of photons in a light beam, let us assume that the lamps in our UVC sanitizer have an efficiency of 10% in generating ultraviolet light translating to about 300W x 0.1 = 30W of that light. Therefore, the number of photons produced every second in the sanitizer is 30/7.8 10^-19 = 3.8 10^19, about 4 with 19 zeros: an impressive number!

 

Now, all these ultraviolet photons flying through the air duct will be able to hit viruses and do them some serious damage. Depending on the specifics of each photon-virus collision, it may take a few of them to completely obliterate the genetic code of a virus.

Virus and Photon Population.

In a typical indoor environment, there may be around 10^5 viruses in one cubic meter of air. Assuming that the chamber’s volume is one cubic meter, we have, very roughly speaking, 3.8 10^19 photons against 10^5 viruses – seemingly a hands-down win for the photons. However, the probability of photon-virus interaction is extremely low, and so...

 

A PRACTICAL CONCLUSION

The low interaction probability, taken together with a need for multiple interactions for damaging the virus, brings us back to earth – the air will not be instantly sanitized by running it once through our UVC chamber: it takes multiple passes. For this reason, we recommend keeping your AC fan running continuously, 24/7.

 

RELATED NOTE

Many HVAC systems use an "economizer mode" during two yearly seasonal weather transitions when the outside temperature is around the indoor air temperature set on the thermostat. In this mode, to save energy, more of the outside air is brought inside of the building. Since this will lower the effectiveness of UVC sanitizing (less indoor air will be going through the UVC units), we recommend either adjust or turn of the economizer mode.

UVC-ENHANCED AIR CONDITIONING SYSTEM

 

The simplified illustration below shows the key elements of a typical air conditioning system, the air sanitizer consisting of an array of UVC lamps, and the freon and air life cycles, including approximate temperatures.

 

The freon life cycle in the closed-loop AC system has five segments, starting from the point where the freon gas leaves the evaporator carrying away the heat it received from the air of the air-conditioned room.

 

SEGMENT 1. Low pressure/medium temperature (LPMT) freon gas returns to the compressor.

SEGMENT 2. In the compressor, pressure and temperature of the LPMT freon gas is turned into a high pressure, high temperature (HPHT) gas.

SEGMENT 3. The HPHT freon gas enters the condenser coil to condense into high pressure high temperature (HPHT) liquid freon. To facilitate the phase change, the condenser coil is cooled by a flow of the ambient air circulated around the coil by fan.

SEGMENT 4. The HPMT liquid freon enters the expansion device where it sharply cools down and becomes low pressure, low temperature (LPLT) freon gas.

SEGMENT 5. The LPLT freon gas flows inside of the evaporator coil.  The room air is blown over the cold coil by a fan as the gas freon absorbs heat from the air. In the process, the LPLT freon gas converts into a LPMT freon gas that enters the compressor (STEP 1). This completes the freon life cycle in an AC system.

 

Virus-free indoor air space