Posted on September 22, 2020 by Buck Nye

Due to the recent COVID-19 crisis, the HVAC industry has pivoted towards improving indoor air quality for occupants in buildings. Indoor air quality incorporates three strategies to manage the indoor environment: source control, filtration, and dilution. 

ASHRAE has recently created an ‘Epidemic Task Force’ to help deploy ASHRAE’s technical resources to address the challenges of the current pandemic. They have produced two guidelines to assist design professionals, servicing contractors, and building owners on how to improve indoor air quality. The documents are ‘Building Readiness’ dated 5-21-20 and ‘Schools and Universities’ dated 7-17-20. These guidelines strive to:

  • Increase the filtration
  • Increase the amount of outside air being delivered to the spaces
  • Still maintain space temperature and humidity conditions.
This article is part 1 of a series of 3 articles that will touch on some of the items discussed in the two task force documents. We will focus on the retrofitting of existing equipment and designing of new or replacement equipment. Part 1 will discuss source control and filtration.  In successive weeks, part 2 will discuss dilution and part 3 will discuss energy recovery and other system implementations. 

Part 1 – Filtration & Source Control:

For upgrading and improving filtration the task forces recommend that the mechanical filter efficiency be increased to as high as possible. One should strive for a MERV 13 rating and preferably MERV 14 or better. Increasing the filtration effect to MERV 13 or higher would help reduce the transmission of infectious aerosols as these types of filters are better at removing particles in the 0.3 to 1.0 micron range, the size of many virus particles. However, be careful!  The increase in filtration will result in:

  • Higher air pressure loss
  • Reduce system airflow
  • Increased energy consumption
  • Increased likelihood of temperature and humidity problems in the space.

Complexities of Increasing Filtration

The  ASHRAE guideline has very detailed instructions on how to evaluate the ability to increase the MERV rating in a HVAC unit. Some of the tasks they recommend performing are:
  • Collect and record data on the existing equipment. 
    • Some of the information would be: 
      • Heating, cooling, and dehumidification capacity
      • Filter sizes and MERV ratings
      • Fan curves/performance
      • Type and size of motors and VFD’s
      • Size of electrical service, etc.
    • Hire a qualified testing, adjusting and balancer (TAB) agent to perform and document a complete temperature and static pressure profile of the existing equipment prior to any filter upgrades.
    • Perform an evaluation of the ability of the existing system to accept an increase in the MERV rating. Some examples of the tasks required would be:
      • Can the existing filter racks accept a thicker filter, if not, can the rack be modified?
      • How does the increase in air pressure drop effect the loss of airflow? 
      • Is enough heating, cooling, and dehumidification still provided at the lower airflows?
      • Does the fan and motor have to increase in size, if they do, is there enough physical space within the unit, is a larger electrical service required? 
    If MERV 13 filters cannot be installed; consider some of the following alternative solutions:
    • Increase the filtration to the maximum available.
    • Provide recirculation fan filtration unit.
    • Provide separate HEPA filtration unit.
    • Consider alternate filter locations, but once again evaluate the implications associated with the higher static pressure loss.

    Air Ionization A Simpler Solution

    Air ionization such as provided by Global Plasma Solutions (GPS) can result in a much simpler, quicker, and more cost-effective solution to the process outlined above on how to increase filtration. Studies have been performed that demonstrate how a MERV 8 filter with the addition of a GPS bi-polar air ionizer is equivalent to the filtration effect of a MERV 13 filter. A copy of this study can be downloaded here

    Adding a GPS device to your existing MERV 8 filtration system versus upgrading to a MERV 13 filter will result in:

    • No reduction of airflow
    • No reduction in your heating, cooling and dehumidification capacity
    • No additional energy usage
    • No loss of temperature and humidity control in the space. 

    GPS products improve indoor air quality by reducing particles, odors, and pathogens. GPS products are made with flexibility in mind and are available for installation in AHU’s, RTU’s, FCU’s, WSHP’s, DFS, VRF, etc., as well as for ductwork. The units are inexpensive, easy to install, and require very little maintenance. Unlike other air ionizing manufacturer’s, GPS’s products are UL-867 and UL-2998 certified that they do not generate harmful ozone or other byproducts. Please contact your local HC Nye salesperson for assistance in selecting a GPS product that best meets the needs of your application.

    • Increase the filtration effect of HVAC equipment
    • Provide additional dilution by increasing the outside air quantities
    • Continue to satisfy indoor comfort conditions
    • Minimize energy costs.

    In each of the documents, to improve indoor air quality and to reduce the chance of the spread of infectious diseases, the task force has recommended the implementation of ultraviolet germicidal irradiation (UVGI) in the form of UV-C lights.  UV-C lights destroy microorganisms (viruses, bacteria, and mold) by destroying and disrupting their nucleic acids; the lights can be selected to destroy pathogens on the surface that it shines on, as well as to reduce and kill the air-borne pathogens that travel past its rays. 

    Another product that could be used to increase the filtration effect in an existing space would be to add a ‘Critical Environment Air Handling Unit’ that is manufactured by Magic Aire. This small, horizontal air handler includes a 2 stage MERV 8 and MERV 13 filtration system as a standard offering; there is also an upgrade available to provide a HEPA or MERV 14 final filter. The unit can provide supplemental heating and cooling for constant volume or VAV application. In addition to the high filtration, it has other indoor air quality features available such as double wall construction with an anti-microbial treatment, UVC lights, a double sloped drain pan, as well as full size access doors.

    In conclusion, ASHRAE’s Epidemic Task Force has done an excellent job in identifying ways to increase indoor air quality in these times of the COVID-19 pandemic. They have developed a thorough and accurate list of recommended items and ways on how to improve the filtration efficiency associated with HVAC equipment. 

    For more than 40 years HC Nye has been a strong advocate for indoor air quality and has many products available to assist the HVAC community. These products can:

  • Increase the filtration effect of HVAC equipment

  • Provide additional dilution by increasing the outside air quantities

  • Continue to satisfy indoor comfort conditions

  • Minimize energy costs.

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