Drawing on over 35 years’ experience and a continued commitment to our mission statement, we here at Lenity Architecture are dedicated to the health and safety of our clients, staff and residents alike.
As Senior Housing industry leaders, Lenity’s MEP Department specialists would like to offer a few HVAC options to utilize in your buildings to help keep you, your staff, and residents healthy and safe during this time of uncertainty. As with all suggestions, only you know what’s right for your business operations.
Each building is unique; and there is no blanket solution that would completely stop the transmission of COVID-19 or any other virus at all buildings, baring a full HVAC redesign and upgrade. However, with moderate investments, more attentive cleaning schedules, and changes in AC operational setpoints, a building owner can make vast improvements in the building’s capacity to stop the transmission of airborne particulates. However, the following recommendations are a large step in the right direction – all are within reasonable budgets.
Ultraviolet Germicidal Irradiation (UVGI) is a tested form of disinfection control in conditioned spaces. The wavelength of 280 to 200nm (also classified as UVC) is ideal for disrupting the DNA of many airborne viruses, bacteria, mycobacteria, bacterial spores, and fungal spores. According to ASHRAE, UVC has been used since the 1900’s and can make a significant effect on the spread of infections. By exposing microbes to UVC, thier DNA is altered to stop their reproductive capabilities. Once microbes lose the ability to reproduce, they become practically harmless, even if they land on a person. There are two types of UVC devices on the market that are common, Upper-Air UVC Devices and In-Duct UVC Systems.
Upper-Air UVC Devices
- Easy to install and integrate into existing structures.
- Flexible – can be installed either as permanent or temporary fixtures
- Can be a more economical solution.
- These types of units are typically not visually appealing.
In-Duct UVC Devices
In-Duct UVC Devices
- They can disinfect more area than Upper-Air and are hidden from public view.
- When compared to other options, UVC systems are some of the lower priced solutions in initial capital investments.
- In-Duct devices are more expensive than the Upper-Air devices
High Efficiency Particulate Air (HEPA) Filters are deep space folded, sub-micrometer glass fiber paper filters. Most are designed to be installed in ducts with a velocity between 250 and 500 feet per minute (FPM) and have a static resistance between 0.5” and 2” of water column (in W.C.). In a standard senior living facility, ducts are typically sized for a 900 FPM rate, and total static loss of 1.5 to 2” W.C.
- MERV 13-16, can be installed without any HVAC design consulting
- Filters can be expensive overtime
- Need to maintain a cleaning/replacement schedule to ensure optimum filter performance
What this means is that most high-grade HEPA filters could not simply be installed in a typical commercial HVAC system without causing reduced performance in the filter, and/or cause harm to the mechanical systems. That being said, HEPA is not the only option for filters.
MERV is a rating system for air filters; the higher the MERV rating, the smaller the particulates that the filter can capture. HEPA filters are rated at MERV 17 and higher, and can capture particles less than 0.3 microns, (virus and carbon dust size). One range step down in MERV ratings, to 13 to 16, still provides superior air filtration, and can be ordered in sizes that would work with most current building HVAC systems.
Per ASHARE’s recommendations on filter use, MERV 13-16 filters can help stop viruses and droplet nuclei, and are recommended for hospital general ventilation. Regardless of what type of filter is used, any filter MERV 13-rated or higher should be installed with a pre-filter in front of it. A pre-filter should be MERV 3-6 rated. The purpose of the pre-filter is to capture all the large particles before they hit the higher MERV filter. Without the pre-filter, the higher MERV filter would become clogged with debris so fast that it would become ineffective months before it should. Additionally, the more clogged the higher MERV rated filter is, the more strain is put on the blower in the AC unit. If left unchecked, it could lead to damaging the AC unit’s motors.
New studies have shown that keeping buildings between 40-60% humidity fosters the best indoor environment to curb the spread of aerosol contagions. Furthermore, studies show that air that is recirculated within a building, over time has a drop in particulate diversity in the air, and that the particulates that remain tend to be more harmful to humans. This is a driving factor on why ASHARE’s recommendations for medical facilities is to increase the amount of outside air that is brought into the building as much as possible. Almost all your building’s HVAC systems have outside air connections, and any adjustments to the outside air intake rate should be done with caution, for a few reasons.
First, conditioning outside air is one of the highest operational costs; the more outside air you want to condition, the more it will cost to operate. Second, unless you purchased an HVAC unit with all the bells and whistles to take raw outside air and condition it to ideal room temperatures and humidities, most HVAC units are not able to handle large percentages in outside air, especially in peak summer and winter times.
- Does not require purchases of new materials
- As a side effect, more ventilation will reduce odors within the building envelope
- Can be cost-prohibitive to retrofit/add to the rooftop HVAC systems to handle more outside air
- In humid climates, too much humid air brought into a building can result in unwanted mold growth.
Keeping that in mind, with climate design evaluations, building owners, can adjust the outside air intakes on their current HVAC units to bring in more outside air without getting the building’s humidity out of the 40-60% range or the temperature to an uncomfortable point.
The resource for this is a cool 45-minute video released by ASHRAE as an EDH in December 2019.
No one solution can completely stop the transmission of COVID-19 or any other virus — just as there is no one-size-fits-all solution that works for all building types. However, with moderate investments, more attentive cleaning schedules, and changes in AC operational set-points, a building owner can make improvements in the building’s capacity to stop the transmission of airborne particulates. Combining any or all of these strategies will compound the effectiveness of any solution.
We recommend consulting with your local HVAC manufacturer’s representative about adjusting your outdoor air intake rate. Most HVAC representatives can quickly run computer simulations to see how much outside air could be increased without hurting the performance of the equipment.
Please feel free to discuss these options with your maintenance staff, your HVAC local manufacturer’s representative, or Lenity Architecture.