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Healthy Building Strategies – Pros and Cons

Healthy Building Strategies – Pros and Cons

By:CTS Group - Jim Thurman, PE, CEM

Healthy building strategies that improve air quality and clean surfaces should be incorporated as part of a layered defense against COVID-19. For improving indoor air quality, we recommend prioritizing control CTS Group strategies – ventilation, filtration, supplemental air cleaning – and verifying system performance regularly.  The following steps and products can be recommended from an HVAC perspective that will help school facilities be better able to combat and control indoor air contaminants including allergens, bacteria and virus carriers.  But there is no one size fits all solution.  Schools should work with facilities managers and outside professionals to tailor these recommendations for their unique building systems. 

Filtration/Ventilation Recommendations

Increase MERV rating of media filters to a minimum of 13

  1. Ensure that there is sufficient fan capacity and static pressure to handle the added efficiency of the higher MERV filters in order to avoid undue stress on an existing HVAC system
  2. The higher the MERV rating, the better a facility’s occupants are protected
  3. HEPA filters can achieve even higher MERV ratings (15-20) but at a higher pressure drop

Pros:

  • Meets CDC guidelines for the filtration of bacteria and virus carriers from the air being introduced to building spaces
  • Removal of airborne contaminants

Cons:

  • High MERV filter cost
  • Increased static pressure of filters adds energy costs
  • Increased filtration may cause an increase in loading of the filter, which will require added replacements throughout the year
  • Increased filter loading can reduce the air flow to a space, which will affect occupant comfort and increase system runtime equating to higher energy costs and stress on the equipment

Increase Ventilation Air

  1. Disable Demand Controlled Ventilation control in order to provide constant volumes of outside air to a facility
  2. Increase minimum settings on Outdoor Air Dampers during occupied hours without jeopardizing the ability of a unit to reach its design supply air temperature
  3. Flush the spaces with Outdoor Air during the unoccupied hours

Pros:

  • Dilution of airborne contaminants

Cons:

  • Increased ventilation air adds heating and cooling load to the HVAC system, which may cause a system to operate outside of its design parameters especially during periods of extreme hot and cold outdoor air temperatures
  • Increased Energy Cost

 

Air Cleaning/Purification System Options

Hybrid Polarized Media Air Filters – Small/Unitary Equipment

  1. Able to be utilized on smaller, unitary equipment such as heat pump units and residential style split systems
  2. Tested and certified to MERV 13 and higher to remove up to 95% of unwanted airborne particles
  3. Oxidizes and absorbs VOC gases, plus kills mold, viruses, bacteria and other airborne microbials
  4. Polarized media that is non-ozonating
  5. Typically, 1/3 of the static pressure drop of the more popularly utilized pleated filters, therefore achieves an additional benefit of fan energy savings
  6. Replacement of the internal media pads during a typical quarterly service
  7. Available in multiple sizes
  8. Low voltage power requirement

 Image 1

Pros:

  • Will not adversely affect the operation of a typical unitary fan coil unit
  • Meets CDC guidelines for the filtration of bacteria and virus carriers from the air being introduced to building spaces
  • Removal of airborne contaminants

Cons:

  • Media is recommended to be procured from the unit manufacturer (cost implications?)

Air Cleaning Systems

  1. Utilized on larger, centralized systems
  2. MERV 15 performance and higher to remove up to 95% of unwanted airborne particles
  3. Oxidizes and absorbs VOC gases, plus kills mold, viruses, bacteria and other airborne microbials
  4. Polarized media that is non-ozonating
  5. Typically, 1/3 of the static pressure drop of a MERV 14 cartridge filter array
  6. Long maintenance cycle. Case studies indicate that the media at the ASHRAE facility in Atlanta was not replaced until 7+ years of being in operation.
  7. Customized to the existing air-handling equipment
  8. Low voltage power requirement

 Image 2

Pros:

  • Low Life Cycle Costs with energy, maintenance and disposal savings allowing the typical payback to be less than 3 years on average.
  • Originally designed to meet the requirements of Green buildings, Data Centers, hospitals, pharmaceutical companies and clean rooms.
  • Most effective air cleaning system with energy and operational savings as an added benefit. Potential Energy Conservation Measure for most every application requiring a high level of Indoor Air Quality

Cons-

  • Initial Cost

Needlepoint Bipolar Plasma Ionization

  1. The unit produces both positive and negative ions that bind to VOC, Bacteria, Mold, Viruses and Dust in the spaces served by the air-handling equipment
  2. Needlepoint units are easily mounted in the air-handling equipment prior to the cooling coil. Cathode units can be mounted in the unit or ductwork.
  3. Can be retrofitted to existing air-handling equipment of all sizes, i.e., unitary or centralized systems
  4. Low voltage power requirement that is typically fed from the air-handling equipment’s control panel.
  5. Allows for the reduction in outdoor air requirement with the utilization of the IAQP OA calculation method.

 Image 3

 

 Pros:

  • Low initial cost, low ongoing power and maintenance requirements.
  • Will provide a cleaner indoor environment that can reduce the ventilation air requirement for a facility and eliminate the need for additional overnight flushing of a facility with outdoor air.
  • Potential Energy Conservation Measure due to the reduced OA requirement that can allow for smaller sized units to serve large spaces.
  • Allows the Demand Controlled Ventilation to remain useful in a retrofit application.

Cons-

  • The units are ozone emitting but will generally not be an issue when using a quality manufacture’s products. Ozone was an issue with the earlier cathode tube ionization units.
  • CO2 levels have the potential to rise in a space, but the IAQP calculation method utilized CO2 as an indicator of occupancy, not indoor air quality. With the other contaminants (VOCs) being controlled to a minimum state in the spaces, the effects of CO2 are minimized.

Ultraviolet Germicidal Irradiation (UVGI)

  1. Short wavelength ultraviolet light (UVC) has been found to be an effective way to inactivate or kill microorganisms and pathogens (germs).
  2. UV lights can be retrofitted to an existing piece of air-handling equipment or installed in the ductwork, open air plenums and directly in the occupied space. In the case where they are mounted in the occupied spaces, the UV light should be installed with a shield to ensure that the radiation is directed upward as to not harm the occupants and at a height far enough from the ground that the people are not hurt by the distant radiation and cannot touch the bulbs.
  3. The effectiveness of UV light depends on the length of time the microorganism is exposed to the UV and the intensity and wavelength of the UV radiation.

 

 Image 4

 

Pros:

  • Easily applied to new and existing equipment, ductwork and spaces.

Cons-

  • UVGI is an effective means of disinfection, but the intensity and exposure time to eliminate the COVID-19 germ is unknown.
  • High initial cost.
  • High energy cost.
  • A UV light source loses 15% of its effectiveness annually, thus requiring replacement in approximately 3 years.