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HVAC Solutions for Reducing Airborne Pathogens

Posted by Price Industries on August 25, 2020 at 1:22 PM
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Reduce the airborne concentration of pathogens with ventilation and filtration

From improved filtration to alternative supply air methodologies, changes to your HVAC system can reduce the probability of exposure to airborne pathogens within workplaces, schools, and other high occupancy areas.
Woman in face mask works at her desk in an open office, socially distancing from other staff also in masks.

Reducing Airborne Pathogens

Most North Americans spend approximately 90% of their time indoors, whether they are at school, at work, or out shopping. Indoor air quality (IAQ) can have a significant effect on the health of the population.

The quality of the air delivered by an HVAC system is commonly measured by its ventilation effectiveness, which is the ability of the system to remove internally generated airborne pollutants from a space. Generally, the HVAC system removes pollutants through the introduction of fresh, clean air and removal of polluted air. In order to improve the IAQ of an indoor space, the number of pollutants must be reduced. This can be done through:

  1. Removing contaminants with filtration to reduce the overall concentration of contaminants.
  2. Diluting the number of contaminants in the space by increasing air change rates, specifically with filtered or fresh outdoor air.
  3. Increasing ventilation effectiveness, through well designed air movement.

We outline below several solutions that use any or all of the above methods to best suit your application, fit in your budget, and provide improved indoor air quality for your occupants.

HVAC Solutions for Reducing  Airborne Pathogens Brochure

Overhead Mixing System with Integrated Filtration

Easy to implement, this solution replaces or modifies existing diffusers to provide MERV 13 or 15 filtration and remove viral particles with at least 95% effectiveness. Implementing filtration at each diffuser effectively reduces the concentration of airborne contaminants, thereby reducing the probability of exposure to airborne germs and viruses. Upgrading a typical overhead mixing system to include filters at each diffuser requires very few changes to the overall HVAC system, keeping the cost of implementation low.These solutions can be used in almost any space including offices, classrooms, and retail are ideal for retrofit applications and suitable for new construction projects as well.

Typical office with overhead mixing system

Option 1 - Retrofit Existing Diffusers

Retrofit filtration attachments include a 2", MERV 13 or 15 filter and a secondary diffuser face and are suspended directly below existing diffusers so that ductwork changes are not required. Held in place between the t-bar ceiling grid and the original diffuser, this attachment forces air from the original diffuser through a filter before being discharged through the secondary diffuser face. These retrofit filtration attachments protrude 6" from the ceiling providing a visual reminder of the additional precautions taken to provide air cleanliness. Filters are accessible from the room side, by sliding the filter in or out of the side access panel. The secondary diffuser face is available in any of the 24"x 24" Price t-bar ceiling diffuser styles.Square Cone Diffuser with HEPA filter retrofitOption 2 - New Diffusers with Integrated Ceiling-Access Filters

Diffusers with ceiling-access filters have a 6" plenum box and are installed on top of the t-bar ceiling grid, replacing existing diffusers. These diffusers have integrated MERV 13 or 15 filters that require access to the ceiling plenum for periodic replacement. Filters are slid in or out of this diffuser though a hinged access door on the side of the unit. This diffuser style is available in any of the Price t-bar diffuser models. 

Diffuser with integrated ceiling-access filter

Option 3 - Diffusers with Integrated Room-Side Accessible Filter

Diffusers with room-side accessible filters have a 6" plenum box and are installed on top of the t-bar ceiling grid, replacing existing diffusers. As the name implies, room-side replaceable filters provide convenient access to the filter from the room side for periodic filter replacement. These filters make use of a gel seal on the filter frame and a knife edge flange on the diffuser to create a reliable seal that prevents filter bypass. Filters are available in MERV 13 or 15 for at lest 95% viral particle removal or HEPA for 99.99% filter efficiency. Price offers a number of suitable diffusers including the Louvered Face Diffuser with Filter (AMDC) and Radial Vane Diffuser with Filter (RVDC).

Exploded view of model AMDC diffuser

 

Displacement Supply, Filtered Return, and Room Filtration

These pragmatic solutions use existing ductwork or require minimal retrofitting of ductwork within the zone. Displacement ventilation provides low velocity air at higher temperatures to create a comfortable environment. This type of approach to air delivery relies on natural convection to move the air throughout the space making it energy efficient. The air is supplied at low level and pushes contaminants and particles upwards out of the breathing zone resulting in improved air quality 2,3,4,5,6 instead of recycling contaminants back into the space. Enhanced filtration of the return air is provided by the MERV 13 filters on the series fan powered terminal unit.These solutions are suitable for new construction and retrofit projects, and can be used in almost any space, including offices, classrooms, and retail.

Ttypical office with terminal units and displacement ventilation

Option 1 - Ceiling Displacement

A ceiling model DFC displacement diffuser can be installed into an existing ceiling grid removing the existing supply grille. Existing overhead ductwork and terminal units can be used, minimizing overall renovation costs.

  • Fits into standard T-bar ceiling grid
  • 2’ x 2’ and 2’ x 4’ sizes available
  • Low pressure drop minimizes impact on system
  • Quiet air delivery
  • Comfortable, occupant driven airflow
Model DFC displacement diffuserOption 2 - Ceiling Displacement with Fan Mixing Box
Using existing ductwork, a fan mixing box with a MERV 13 filter replaces the VAV terminal unit. This option requires ceiling mounted displacement diffusers (DFC), and a fan mixing box with a MERV 13 filter for enhanced filtration of the recirculated air. The FDC mixes return air to provide 62°F supply air temperature.
  • Fan mixing box replaces VAV terminal
  • MERV 13 filter option
  • 400 - 1,500 cfm
  • Uses energy efficient ECM motors

Fan mixing box with filter rackOption 3 - Low Level Displacement with Fan Mixing Box

Existing ductwork can be rerouted down from the ceiling and connected to the Displacement Corner Cabinet. This low level supply provides improved ventilation effectiveness, quiet air delivery, and comfortable airflow for occupants.
  • Improved ventilation effectiveness
  • Low level supply
  • Non-intrusive exposed duct
  • Solid and perforated duct cover options
  • Quiet air delivery
  • Comfortable, occupant driven air flow
  • Up to 850 cfm

Corner cabinet displacement diffuser

Overhead Supply with Supplementary Filtration

Retrofit fan powered filtration units can be added above any space to provide MERV 13 rated filtration and removal of airborne contaminants, thereby reducing the probability of exposure to airborne germs and viruses. Overhead filtration units are an easy way to increase air filtration levels in a specific zone. The filtered exhaust booster unit is a great way to filter return without modifying the air handler. Retrofit fan powered filtration units are simple to install and do not require any modifications to the existing air distribution system.

Typical office with overhead supply and supplementary filtration

Option 1 - Filtered Exhaust Booster
 
Filter exhaust air with no additional pressure drop. The booster unit is designed to drop into existing duct work and provide filtration to exhaust air before returning to the air handler. The unit is equipped with a built-in fan which compensates for the filter pressure drop, resulting in zero pressure drop through the unit. This is an excellent option if the central air handler cannot accept a higher rated filter.
  • Quick Installation
  • Simple airflow adjustments with EC motor
  • Easy filter changes
  • 200 – 500 cfm
Filtered Exhaust Booster
Option 2 - Overhead Air Filtration Unit
The goal of the Overhead Air Filtration unit is to filter room air through consistent air changes. The fan powered unit draws air directly from the space, through a MERV rated filter, and discharges the clean air directly back into the space. The Overhead Air Filtration unit is design to be installed directly above any space and does not require modification to existing ductwork or other HVAC equipment.
 
The Overhead Air Filtration unit can be installed in a T-Bar ceiling or an exposed ductwork layout. The unit pair perfectly with any Price grilles or diffusers. The Overhead Air Filtration unit is suitable for offices, classrooms, or any space requiring increased air filtration.
  • Quick installation
  • Simple air flow adjustments with EC motor
  • Easy filter changes
  • Quiet, low energy operation
  • 200-500 CFM
  • Larger sizes available
  • Compatible with MERV filters
In the cutaway view below, air flows from the space through the return grille (left) and then through a MERV 13 filter (center). This provides increased filtration while also using the fan to overcome the additional pressure drop. The filtered air exits the Air Filtration unit and is sent into the occupied space through the ceiling diffuser (right).Cutaway view of installed overhead filtration unit to visualize airflow through the unit
Stratified Air Systems That Promote Occupant Wellness

For larger scale remodels, renovations, additions, or new construction consider Underfloor Air Distribution or Displacement Ventilation.

Stratified Air Systems deliver air directly into the breathing zone pushing contaminants up and out of the space. The results are improved indoor air quality, and less contaminants and airborne pathogens in the occupied zone. 2,7,8 

Research studies have found that stratified air system ventilation effectiveness can be twice as high as mixing systems. [Price Engineer’s HVAC Handbook, Ch4 Table 4.1]

Underfloor service and air delivery can cut reconfiguration costs and time significantly through easily accessed power and data cabling and non-ducted air devices. This will reduce long term costs as businesses adjust to meet continually evolving office requirements for occupant density and furniture layouts. 2,9

Underfloor Air Distribution (UFAD) is an alternative to traditional overhead air distribution that delivers air from a pressurized air plenum beneath a raised access floor, relying on the natural buoyancy of air to remove heat and contaminants.
 
Office with Moduflex Underfloor air distribution system
 
 
Displacement Ventilation operates on the same principles as UFAD supplying air directly into the occupied zone and creating stratification. Typically diffusers are ducted from the ceiling to a low level supply diffuser. In some cases ceiling diffusers can be used to free up wall or floor space.
 
Classroom environment showing displacement ventilation system options
To learn more about these solutions, download the HVAC Solutions for Reducing Airborne Pathogens brochure.
Visit our COVID-19 Resources Page
 
References:
2. Bauman, Fred, P.E., Center for the Built Environment (CBE). (October 2007). TechNote Topic: Air Change Effective of UFAD and DV Systems Compared to Overhead Mixing Systems.
3. United States Environmental Protection Agency. (2019, March 11). Creating Healthy Indoor Air Quality in Schools. Retrieved from United States Environmental Protection Agency: https://www.epa.gov/iaq-schools
4. ASHRAE. (2013). ANSI/ASHRAE Standard 62.1-2013: Ventilation for Acceptable Indoor Air Quality. 5. Arent, J., Eley, C., & Meister, B. (2006). Displacement Ventilation in Action: Performance Monitoring of Demonstration Classrooms. ACEE Summer Study on Energy Efficiency in Buildings.
6. Smedje, G., & . (2000). New Ventilation Systems at Select Schools in Sweden - Effects on Asthma and Exposure.
7. Hines. (2018, December 11). Underfloor Specs. Retrieved from 609 Main at Texas: http://www.609mainattexas.com/#techspecs
8. Alspach, Peter, P.E., & Moellenberndt, Anne Marie, P.E., Copyright ASHRAE. (2014). Impatient Optimism. Posted at: https://www.hpbmagazine.org/
9. NSF/IUCRC Center for Building Performance and Diagnostics at Carnegie Mellon University (2004). Advanced Building Systems Integration Consortium: Guidelines for High Performance Buildings 2004.

Topics: GRD, Diffusers, Grilles, Terminals, Displacement, Underfloor, HVAC Fundamentals, hvac, engineering, Design Engineering, Tech Tip, Filtration, Airborne pathogens

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