Mines Facilities is following ASHRAE guidelines to make sure our buildings are as safe as possible during the COVID-19 pandemic. For Fall 2021, Mines is moving to more normal operations, including a full return of students to campus. However, Mines will still be implementing some heating, ventilation and air conditioning (HVAC) protocols and controls to make buildings safer and more resilient to viruses of all kinds.

Specific action recommended by the COVID HVAC Team and Facilities are explained below:

Increase outside air

  • HVAC systems in labs are already supplying 100 percent outdoor air.
  • All newer buildings supply adequate amounts of outdoor air that meets or exceeds ASHRAE Standard 62.1 and have MERV 13 filters.
  • Most buildings on campus have smart controls that supply 100 percent outdoor air when conditions are ideal (outdoor air is cooler than indoor). This is also known as “free cooling.” For the rest of the time, we supply an amount of outdoor air that meets or exceeds ASHRAE Standard 62.1.

Improve air filter efficiencies to MERV 13 or higher, as possible

  • All newer buildings supply adequate amount of outdoor air and have MERV 13 (or better) filters.
  • For not-so-new buildings, we have increased outdoor air and/or installed MERV 13 filters, and if not already in place, provided the equipment that can handle the thicker filters.
  • We are checking the operation of outside air dampers at the air handling units during preventive maintenance activities every quarter. This also includes cleaning and disinfecting critical areas of air handling units.
  • For rooms with local HVAC systems (like fan coil units), we have installed MERV 13 filters or the highest the system can accommodate.
  • For rooms with lower outdoor air but with MERV 13 filters in place, we have increased the number of times air will go over these filters (recirculation airflow), to ensure they filter out as many contaminants as possible.
  • For the few rooms with inadequate ventilation, we have installed portable HEPA filters. We continue to identify possible areas of poor ventilation to see if additional HEPA filters are warranted. We will continue using HEPA filters for these offices/spaces.
  • All filters are replaced regularly depending on the location and filter type. HEPA filters will be replaced this summer in the units we have provided.

“Optimal start” strategy

  • HVAC units in campus buildings are brought on before the building is occupied. This is usually at least an hour or two before the scheduled occupancy time.

Frequently Asked Questions

Q: Can I bring a portable HEPA filter to my office?

A: Yes, but please be aware that filters will produce background noise.  If you are considering buying one, please follow our suggestions below:

  • Please remember to replace filter as suggested by the manufacturer (every 4-8 months) and carefully dispose of the old filter.
  • We recommend that you buy a HEPA filter certified by the State of California and by AHAM. Make sure the filter you buy does not produce ozone or they might do more harm than good.
  • See some filter recommendations by CU Professor Shelly Miller.
  • Buy a portable HEPA filter with an appropriate flow rate for the space it will be in. Most have a space square foot rating.
  • Avoid electronic filters, ionizers or plasma. Many of these can produce ozone or have not been widely analyzed.

Q: How do I know if the device I want to buy is a quality unit or something counterfeit?

A: Make sure to buy a HEPA filter certified by the state of California and by AHAM. Specifically, see some filter recommendations from CU Professor Shelly Miller. Avoid plasmas and ionizers. Feel free to email Paulo Tabares if you have any questions: tabares@mines.edu.

Q: How big of a space can I put one unit in? How to determine what size unit to get for a space?

A: It is important that you buy a portable HEPA filter that is rated for a similar space to where it will be located. For example, don’t buy a portable HEPA filter rated for a 100-square-foot room if you are going to install it in a 300-square-foot room. Why? It is important that all the air in your office/room goes to the filter at least twice an hour (or 2 ACH).

Q: The information on the unit I am considering buying says it has a charcoal filter as well as a HEPA filter. What is the charcoal filter doing? Do I need that for COVID-19 protection?

A: Charcoal filters are typically installed as a prefilter to capture larger particles and gases in the space. It extends the lifetime of your HEPA filter, but the HEPA filter is the system that is filtering small particles. While they are not required, they extend the lifetime of the HEPA filter.

Q: Is noise from the unit going to be an issue?

A: A portable HEPA filter will add some background noise, but most portable HEPA filters have 1-3 speeds that you can vary. The added noise should not be loud enough to impact your work.

Q: What is CADR?

A: AHAM seal/certification provides a clean air delivery rate (CADR) that characterizes the volume of filtered air that a specific air cleaner can deliver. CADR is calculated and reported by three different particles sizes: smoke (smallest), dust (smaller) and pollen (small). The CADR most relevant for COVID-19 are smoke and dust. This also helps you size your filter, by using the AHAM 2/3 rule: Size your unit using a CADR at least 2/3 your room’s area. So, if your room is 10 feet by 10 feet (and 8 feet tall), find a filter with a CADR of 67 or higher. The AHAM seal also includes recommended room size.

Q: Can buildings help reduce the risk of infection?

A: Yes, however, it is important to mention that vaccination is the first action we all must take. Building heating, ventilation and air conditioning (HVAC) have a role in aerosol transmission by disturbing their transmission pathways inside buildings. HVAC systems can help dilute and filter these aerosols to some extent.

Q: What can buildings do to help reduce exposure?

A: What building HVAC systems can do is to reduce the aerosol load (amount of virus in the air), which in turns reduces exposure, thus reducing the overall risk of getting sick. This can be done by the following methods:

  1. Ventilation: Supply cleaner, outdoor air with the main goal to dilute indoor air contaminants and aerosol load. This could be done by simply opening a window or by the mechanical system, using fans to bring more outdoor air to the indoors.
  2. Filtration: Use filters that can be either in rooms or inside HVAC systems (air handling units) to filter out particulates. ASHRAE recommends using filters rated MERV (Minimum Efficiency Reporting Value) 13 or higher or using HEPA filters (best in class). HEPA filters can block particulates as small as 0.01 microns. MERV 13 is not as efficient as HEPA but combined with other measures, can be very effective.  Most existing HVAC systems cannot be retrofitted with HEPA filters due to size and the resulting restriction of airflow.
  3. Filtration with high flow rates to ensure air passes to MERV13 filters at least 4 times an hour.

Q: What is HVAC?

A: HVAC stands for heating, ventilation and air conditioning. These systems process outdoor air so we can be comfortable inside. It consists of fans, pumps, heat exchangers, dampers, filters, smart controls and many other subcomponents that add heat (warm up) or moisture (humidify), remove heat (cool down) and/or moisture (dehumidify), and remove contaminants from the air before the air enters our buildings. In many buildings around campus, most of these subcomponents are inside huge boxes called air handing units (AHU) that you might see on top of our buildings.

Q: Given that SARS-CoV-2 is new and there are many unknowns, how is Mines keeping up to date with respect to building operation?

A: Facilities and the COVID HVAC Committee have been following guidelines from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). ASHRAE has developed a taskforce consisting of building, HVAC, and indoor air experts that are keeping track of (and also publishing) the latest research on SARS-CoV-2. Some of these members have been in major news outlets and authored scientific articles about HVAC, indoor air, and SARS-CoV-2.

At Mines, Professors Paulo Tabares, Alina Handorean and Mahadevan Ganesh have developed a data collection and probability evaluation framework that facilitates obtaining and processing data from Mines’ HVAC building automation system. This, combined with a room database, provides an environment for modeling probability of potential aerosol infection. We will continue monitoring HVAC system utilizing this framework.

Q: If my office has a window, should I open it?

A: Yes, opening your window will allow outdoor air to get into your office, thus improving ventilation. Some offices and dorms around campus can do that, and you can certainly do this. However, we just ask that you close your window when you leave your office/dorm. Leaving an open window unattended can let rain/snow inside and in winter produce cold drafts or even freeze some pipes which can cause major problems.

Q: Can I leave my classroom door open?

A: For most buildings, leaving a classroom door open is not recommended and in some cases may be against fire code. Also, more fresh ventilation air is provided to classrooms than to transient spaces like hallways, so the effect of leaving the door open might be to actually get less ventilation air in the classroom.

Q: If HEPA filters are best in class, why Mines is not installing these everywhere?

A: While HEPA filters are best in class, it takes a lot of energy (and huge fans) for air to pass through them, as there is a significant pressure drop across them, which fans must overcome. Most building HVAC fans were not designed to handle this pressure drop, so using HEPA filters will substantially reduce airflow in buildings, reduce the capacity of HVAC to dilute contaminants and overall increase risk. Also, in a lot of cases HEPA filters simply won’t fit inside the air handling unit.

Q: Will HEPA filters and ventilation allow me to come to work when I am sick?

A: No. If you are sick, you should notify your supervisor and stay at home.