People spend roughly one third of their life in a public building and several studies have shown that poor indoor air quality [IAQ] results in increased health problems, more doctor visits, productivity loss1, and reduced learning outcomes2, 3. Poor IAQ costs the US economy over $30B a year in medical expenses alone4. Poor ventilation has been linked to an increase in transmission of aerosolized viruses and pathogens14. Recently, it has also been shown that COVID-19 transmits more easily in poorly ventilated environments5. There is an abundance of literature linking poor IAQ and thermal comfort to academic performance in the form of lower test scores and increased absence rates6, 7, 8; increased health complications among the elderly in the form of COPD related symptoms and upper respiratory effects9, 10; decreased mental health outcomes in the form of depression and anxiety11, 12; and decreased worker productivity in the form of reduced output and distraction13.
Over the past year schools across the US, and the world, have experienced the effects of the novel coronavirus [COVID-19] with school and college closures due to risk of virus transmission between students and faculty. It is imperative to protect the health and well-being of all who return to school, including students, teachers and administrators. The Biden administration has elevated the need to return to in-class learning and has proposed federal assistance to make this a reality. This funding will be provided to assist facilities with the modifications needed to comply with published CDC guidelines to reduce the risks of COVID virus transmission within schools. National Facility Solutions [NFS] has experience with Existing Building Commissioning [EBCx]. Our team possesses the knowledge and expertise to help school districts evaluate and implement a cost-effective, sustainable solution that will help reduce transmission risk within occupied spaces now and in the future.
This paper briefly reviews the potential modifications to air conditioning and control systems typically used in schools that have the highest efficacy to reduce transmission risk without significantly increased operating and maintenance costs. It is essential to understand that the methods discussed here will NOT ELIMINATE the risk, but significantly reduces the potential for transmission safely and cost-effectively.
NFS has completed EBCx [formerly referred to as retro-commissioning] and considered alternate methodologies to upgrade or change these types of existing systems to reduce the potential transmission of the COVID-19 pathogen. The CDC guidelines15 regarding operating schools15 based on ASHRAE guidelines16,17 indicates enhanced filtration, increased outside air dilution, and longer operating hours. Each of these CDC guidelines may add considerable capital, operating, and maintenance costs, with a questionable reduction in transmission rates. These guidelines do not include consideration of alternative methodologies that will attack the viruses with less potential ownership costs.
Alternate methodologies that could be considered include in-room and in-duct germicidal ultraviolet illumination, bi-polar ionization, and photocatalytic oxidation processes that can eliminate or reduce transmission risk. Based on our review, we recommend consideration of the photocatalytic oxidation [PCO] method for the following primary reasons:
- PCO will not require modification to the existing filtration, outside air ventilation, or operating
- PCO continuously disinfects all surfaces in the space, not just those exposed to UV illumination; and does not rely on filtration to trap the virus in the air handling equipment.
- PCO does not require additional janitorial cleaning requirements per CDC guidelines.
- PCO can be installed in-room or in-duct at a reasonable
- PCO requires minimal maintenance, while not increasing energy use, and additional operational
- PCO will significantly reduce COVID-19 transmission risk to students, teachers, and staff members.
However, as part of the EBCx process, NFS will review all options and recommend the best solution for each school while bringing the HVAC systems back to correct operation before changes are implemented
“Ventilation is one of the most important means to control cross infection by removing or diluting virus-laden aerosols exhaled by infected patients,”14. ASHRAE issued an Emerging Issues Brief in 2020 regarding the operation of heating, ventilating, and air-conditioning systems to reduce SARS-CoV-2 transmission. They underscore the critical role properly maintained indoor ventilation brings to society and the need for properly maintained HVAC systems.
ASHRAE guidelines referenced by CDC recommends that professional engineers determine how and if increased ventilation and filtration can be incorporated into existing HVAC systems.
ASHRAE’s position is that “Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning [HVAC] systems, can reduce airborne exposures.”
This guidance has been formulated to help designers retrofit and plan for the improvement of indoor air quality and to slow the transmission of viruses via the HVAC systems. The underlying effort of the designer should be to increase outside air to the spaces and treat return air. The designer should also be concerned with mechanical filtration of the supply air and maintaining indoor comfort as defined by the design temperature and relative humidity.
This guidance should be applied to each unique climate zone, unique school building and HVAC system…The designer needs to work closely with the local school system to work in conjunction with new operational protocols and school operations.
NFS believes that alternative methods for reduced transmission risks have not been included in these guidelines and are addressed in further sections.
Existing schools vary considerably across different educational markets and have a very large variety of system types ranging from simple to more complex. In addition, many facilities have HVAC systems that are aged, at the end of their service life, and/or are suffering from differed maintenance due to budget shortfalls. To incorporate the CDC/ASHRAE guidelines into existing facilities, the existing systems must be brought up to proper operating condition or replaced in their entirety to comply.
EBCx Addresses Operational Concerns
In many existing educational facilities HVAC systems are not operating the way they were designed to operate to comply with the ventilation and filtration needs of the facility. Prior to making modifications to the existing systems, it is very important to ensure that all ventilation systems are operating correctly and providing filtered ventilation air per the design intent. Modifying systems that are not functioning properly will inhibit the ability to achieve the objectives of reduced COVID-19 transmission risk. The remaining discussions assume that the HVAC systems are operating correctly during the time the spaces are occupied.
Increased Ventilation Opportunities
In general, outdoor air ventilation rates can only be increased centrally under outdoor conditions that allow indoor temperature and humidity to remain under control. In individual classroom units, outdoor air [if provided at all] is a fixed quantity directly ducted to the room or fan coil unit [FCU] and cannot be changed. So, this method of improvement has a very limited ability to increase the potential dilution of indoor contaminants.
Central air handling units’ sequence of operation [SoO] can be modified to optimize the amount of ventilation air by increasing outdoor airflow rates. However, increased outdoor airflow can only be introduced until supply air conditions exceed temperature/humidity [or dew point temperature] that will affect conditioned spaces. Typically, the periods where outdoor conditions can increase are limited and the effective results would be minimal. These programming changes assume air handling equipment that is currently being automatically controlled and has the needed economizer dampers installed. If that is not the case, then increasing outdoor air quantities will require capital cost expenditures to upgrade or retrofit the existing system and controls.
Increase Particulate Filtration Opportunities
The purpose of improving filtration is to capture the virus and contaminants from recirculated air systems for both central and classroom systems. Currently, minimum efficiency reporting values [MERV] ratings of MERV 13 for central air handling systems and MERV 8 for classrooms are recommended. [Refer to ASHRAE Standard 52.2 for more information regarding MERV ratings.18] The CDC recommendation to include high-efficiency particulate air [HEPA] or MERV 14 filtration is based on the relative size of virus particles to be captured and the ability of the filtration media to capture and retain the particulate. Capturing virus-laden particles in HEPA filters may also complicate the filter changeout and disposal procedures currently in place.
High-efficiency particulate air [HEPA] filters have an initial pressure drop requirement of 1.5 inches and a final pressure drop requirement of 2.5 – 3.0 inches water column. Therefore, the installation of HEPA filters to the existing central air handling units is not feasible without changes to fans, fan drives, and motor sizes. Additionally, the space required for installation is at a premium in most mechanical equipment rooms and may negate the ability to added HEPA filtration due to physical constraints.
There is considerable discussion in the literature regarding particle size related to the COVID-19 virus and other viruses. However, the ability to modify existing air handling equipment to add HEPA filters will never be easily accomplished and most likely be unnecessary if additional treatment methodologies are used to reduce virus transmission to students and staff.
Why Supplemental Methods Can Reduce Virus Transmission Risk
Since modifications to outdoor air quantities and increased filtration are typically not practical or economically feasible options to remove viruses in recirculated air streams, additional methods were reviewed including:
- Germicidal Ultraviolet [GUV] irradiation, both in-room and in-duct
- Bi-polar ionization [BPI]3, both in-room and in-duct
- Combination in-room or in-duct devices using HEPA, GUV and BPI
- Photocatalytic oxidation [PCO]4, both in-room and in-duct
All these methodologies will reduce transmission risk and can be employed in existing HVAC systems. All in-room options, except upper room GUV, are very easy to employ and can be done immediately. Also not discussed herein, is the use of handheld UV surface disinfection devices that can be used by janitorial or operations staff to disinfect devices.
Reducing the risk of virus transmission needs to be considered in a manner that is sustainable over the long term without significant reduction in student learning ability and staff safety in the workplace. Each of the methods listed above have advantages and disadvantages that can be addressed as they would apply to each facility.
Use of GUV for in-duct disinfection can be applied to both central systems and classroom systems but do require a relatively low flow velocity ≤ 500 FPM, and at least 0.25 seconds of irradiation time; it will require significantly more UV power to make an effective dose rate. It is assumed that some central systems can be modified to have extended duct lengths that would increase the irradiation time and reduce power requirements. Surface contamination can only be addressed by direct irradiation. Complications to the use of in-room GUV is the relatively low amount of air mixing, low ceilings, and low air change rates that are ideal for this type of application.
BPI uses positive and negative ions generated in-room or in-duct and supplied to the space for treatment via either standalone devices or air supply systems. They are a form of oxidation as well as agglomeration of particles that are either captured in the filtration media or a direct reduction of virus and bacteria cells, VOC’s, or other aerosols. These devices can easily be added to central systems and classroom fan coil units without significant duct modifications and only minimal electrical needs. They have been tested to determine that ozone generation is not a concern when properly installed and operated. They do require the air handling systems to operate continuously to maintain the active disinfection.
PCO is a photocatalytic oxidation method that uses UV light to illuminate a proprietary photocatalytic coating, producing hydroxyl radicals [OH-], oxygen ions [O2-], and the disinfection agent hydrogen peroxide [H2O2]. CASPR stands for continuous air and surface pathogen reduction and is a continuous no-touch methodology for enhanced disinfection. The CASPR product was originally developed about 18 years ago for continuous disinfection in the healthcare environment to reduce hospital-acquired infections19 [HAI]; which occurs approximately 2,000,000 times annually in the US and results in nearly 100,000 deaths. CASPR was introduced into the US in 2016 to provide a no-touch technology that does not rely only on janitorial staff for disinfection and to be safely used in occupied spaces. The PCO system can be installed in-duct or standalone in-room units.