R-Zero & HVAC
HVAC systems serve the critical roles of keeping our indoor spaces at a comfortable temperature and achieving basic IAQ. But, when it comes to removing microorganisms from the air, HVAC systems cannot compare to the efficacy and sustainability of UV-C.
R-Zero sets a new standard by creating
hospital-grade disinfection in any space
Faster turnover of air for hospital-grade air disinfection
Most non-healthcare spaces are required to provide 2-3 air changes per hour. Beam adds 10 equivalent ACH, in line with hospital ventilation requirements of 6-20 ACH.
More cost effective than ventilation and portable air filters
Considering the Total Cost of Ownership (TCO) from installation and operation of different approaches, upper-room UV-C is the clear winner.
Addressing transmission risk at the source
Infection transmission occurs in-room
Leading experts from CDC1, ASHRAE2, and academia3 agree that, because transmission primarily occurs in-room, in-duct approaches, like MERV filtration and in-duct UV, which disinfect air moving from one room to another, are ineffective and unnecessary.
"To a person sharing air in a room with someone with infectious COVID-19, there is little comfort in knowing that the air will be decontaminated only after it leaves the room. A more effective air disinfection strategy is to rapidly decontaminate the air within the room where person-to-person transmission occurs." Dr. Edward Nardell
Harvard Medical School
What are the options for providing cleaner in-room air?
There are three main methods for air cleaning: increased HVAC ventilation, in-room UV-C, and portable air filters. The most important consideration is how fast each approach can deliver clean air. This is commonly discussed in terms of air changes per hour (ACH), or equivalent ACH (eACH) for UV-C approaches.
According to ASHRAE, the minimum required ventilation rates4 are:
- 0.5-3 ACH for office buildings
- 2.8-3.5 ACH for K-12 classrooms
- 6-20 ACH for healthcare facilities, where absence of pathogens is a design consideration
Accordingly, several organizations5 including the Lancet Covid-19 Commission and the Harvard T.H. Chan School of Public Health, have recommended higher ventilation rates for all buildings to be more in line with healthcare standards to reduce the spread of COVID-19 and other airborne pathogens.
R-Zero Beam
10 eACH added
Upper-room UVGI disinfects large volumes of air at once enabling Beam to achieve an additional 10 eACH in a 500 sq. ft. space.
Limitations:
- For safety reasons, commissioning is required for upper-room UV-C disinfection
- Unfamiliar technology
Increased Ventilation
1-2 eACH added
As most HVAC systems operate at 70-80% of capacity to achieve the 2-3 ACH target, forcing them to operate at 100%, only achieves 3-4 ACH.
Limitations:
- Significant energy costs (and GHG emissions)
- Can affect occupant comfort
- Increases wear and tear, requiring add'l maintenance
- Not targeted to spaces with highest risk
Portable Air Filters
1-3 eACH added
Most portable air filters are inadequately-sized for the volume of air they clean. Typical filters only add 1-3 ACH.6
Limitations:
- Noisy
- Obstructive
- High maintenance filter replacements
- Not considered a permanent solution as it's not installed
Cost Comparison
More cost effective than portable air filters and ventilation
Studies cited by ASHRAE and leading academics find upper-air UVGI to be 3-13x more cost effective than portable air filters and HVAC.
ASHRAE cites a 2001 study that finds upper-room UV-C disinfection to be less expensive than HEPA and ventilation by a factor of 3 and 13, respectively, per avoided TB infection.
Dr. Nardell's paper explains that CDC scientists, Volchenkov and Jensen, found upper-room UV-C to be 9 times more cost effective, per eACH, than mechanical ventilation via HVAC and three different portable air cleaners.
Payback period compared to existing HVAC systems
Even without the cost of HVAC upgrades, installing and operating Beam has a 1-yr payback period compared to HVAC due to the increased energy costs of higher ventilation rates, plus faster depreciation of equipment, and MERV 14 filters and replacements.
Additional Considerations
Practicality of Implementation
To achieve 6+ ACH, most HVAC systems (outside of healthcare facilities) require significant capital investment. This tends to include replacing the existing air handler and ductwork to allow greater airflow. This work often takes months or even years to complete and costs upwards of $30-40 per square foot. Alternatively, Beam can add 10+ eACH and be installed in days or weeks for less than $1 per square foot.
Sustainability
HVAC systems already account for 35-40% of most buildings' energy consumption. Increasing airflow by 30% and beyond will incur a significant increase in energy costs as well as greenhouse gas emissions at a time of enhanced scrutiny. Independent energy consultants have concluded that R-Zero can achieve incremental eACH at 90%+ less energy and GHG emissions.
Consistency and Targeting
For a variety of reasons ranging from inadequate system maintenance to prioritizing thermal comfort above IAQ, air changes per hour can vary from space to space within the same building and over time within the same space, including to levels below ASHRAE's recommended minimums. A 2015 paper found that the air changes in a building ranged from 0.25 to >2.5 ACH (that's a 10x range!) due to the effects of temperature, exhaust fans, window openings, and more. Thus, while a building may have a compliant average ACH, occupants may be spending most of their time in a room well below the minimum ACH.
Occupant Comfort
An increased fan speed to achieve greater ACH may surpass the heating, cooling, and dehumidification capacity of the system, resulting in uncomfortable temperatures and/or humidity. HVAC is a long enough acronym, let's not give it another competing priority of disinfection and force us to rename it HVACD - it just doesn't have the same ring to it.
Endnotes
- "...there is no definitive evidence to date that viable virus has been transmitted through an HVAC system to result in disease transmission to people in other spaces served by the same system." - CDC, Covid-19, Ventilation FAQs
- "The growing science around far-field aerosol transmission essentially negates the need for in-duct or air system control technologies such as UV lights." - ASHRAE Journal, "Preparing HVAC Systems Before Reoccupying A Building"
- "...the value of high-efficiency filters or germicidal UV in recirculating ventilation ducts for preventing spread is speculative and limited at best" - Dr. Edward Nardell, Harvard T.H. Chan School of Public Health
- Note despite these minimum standards, experts have found typical ACH values to be 0.65 ACH in office buildings and 1.5 ACH in schools
- Harvard T.H. Chan School of Public Health, Lancet Covid-19 Commission
- Most units sized for greater than 500 sq. ft. add less than 4 ACH