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What guidance/offerings can we provide to help customers mitigate potential increase in energy use as businesses reopen with emphasis on, or in some cases requirement for, increased air-flow?

Tilak Subrahmanian's picture
Vice President Eversource

As Vice President for Eversource, Tilak Subrahmanian leads a team that is focused on scaling energy efficiency, peak demand management, storage and electric vehicles to develop the clean energy...

  • Member since 2020
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  • Jan 27, 2021

As I outlined in my recent post about 2021 predictions & trends, I'm asking my team at Eversource to look into what energy-saving measures are available and needed for our customers to respond to the specific changes brought about by COVID-19, including for businesses that may be re-opened but with requirements of more open and outdoor spaces. What energy efficiency measures should the utility sector be embracing for this change to business as usual? 

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Hi Tilak: I will leave it to the mechanical engineers to help with the technological solution to the issue but the Covid crisis has accelerated a lot of issues that we all know.  I have been talking with many companies and reading about lots of technology that is now out to deal with air flow and air purification issues in a very direct and very efficient manner.

Many, if not most existing buildings were never designed or built to be particularly healthy.  Clearly, buildings that are now on the drawing board will have an opportunity to do it right from the get go, so that they will not have to repeat our mistakes in the building sector. 

For those buildings that will need a retrofit to meet the new health standards, I would note that there is a very effective source of funding to so so.  Commercial PACE (Property Assessed Clean Energy) programs now exist in nearly 40 states. PACE funds can be used for building retrofit to improve the energy efficiency and by translation the healthiness of the building in a very cost effective manner. There are now numerous commercial PACE funders across the United States, and more and more money is being made available from heavy investors given the investment security associated with commercial PACE activity.  PACE funding requires no out of pocket funding requirement for the building owner, and can be paid back through their property tax assessment over a period that can last as long as 30 years depending on the technology chosen for the retrofit.

Utility companies could offer rebates and incentives that would make PACE funding even more attractive.

When a retrofit is designed to meet a net zero energy standard for the building which is now entirely possible, the use of energy will go down, and operating cost savings will result to the building owner and tenants. With the opportunity to do this with no upfront out of pocket funding requirement, any building owner would be foolish not to take advantage of thus type of opportunity at this time.

Hope this helps.

Best, Larry


This is really an ASHRAE or AHRI question.  There will be more requirements for increased air flow and better filters in buildings.  However, each building tends to be unique.  Generalized answers will not likely fit any particular building.  The best that I can suggest is an energy audit followed by an analysis of energy use to try to determine where there might be savings.

One clarification on HEPA filtration as there is a fair amount of debate on this subject.  The COVID-19 virus particle is stated to be in the 0.125 micron range.  By definition HEPA filters (and there is a strict definition) are designed to remove particle down to 0.3 microns at 99.97% efficiency. (This is the US standard)  Interestingly enough-  HEPA filters become more efficient  as the particles decrease in size (below 0.3 microns) which is where the coronavirus positions itself.  This, apparently due to some interesting physics around particle motion (diffusion filtration).  Also -  these are one-and-done filters, as cleaning will compromise their filtering ability.   I’ll leave the debate of cost, application, etc. to others - but they will remove the virus particle at their stated efficiency.  The DOE standard is here:

I read the great responses to the question so far.  My only addition is that here in hot humid Florida you consume more energy when you increase the ventilation air.  If one increases the ventilation air beyond the design flow the supply air will be humid and then you have a mold problem.

First, a few observations:

  1. There is currently no known and proven filtration system that can filter out or kill viruses.
  2. Most HVAC systems cannot supply more than about 30% fresh air during cold weather, especially in the northern half of the continental US.
  3. Using CO2 sensors and demand control ventilation only reduces the ventilation rate when a building is unoccupied, so it cannot typically be used to increase the ventilation rate.
  4. In the short term, without the development of new technologies the most practical way to introduce more fresh air into the building is to utilize heat exchange systems or energy recovery units (ERUs). These devices, often placed on a roof, are designed to recover heat from air that is being exhausted out of the building in order to preheat the air coming in to ventilate the building. Heat wheels may be another option depending upon the application. Installing these kinds of systems is often structurally difficult, and can be costly. However, it is one of the few strategies that might increase the ventilation rate without breaking the bank on energy cost.
  5. The installation of heat recovery systems is something that could be promoted in some of the governmental programs we have at the state level, such as energy bonds and other governmentally supported energy project finance programs. In some cases, longer paybacks should be allowed in order to help finance these types of systems.
  6. In states that have utility rebate programs, robust financial rebates should be considered to help schools and private businesses to install the heat recovery systems.
  7. Federal programs also exist, such as the Energy Policy Act, which provides tax benefits for energy projects, and could be amended to include such things as increased air ventilation programs.

This is a broad enough issue that a panel, or panels of experts should be brought together to focus on improved ventilation, air filtration, as well as organic contaminant control. Local utilities, as energy providers, should have a seat at the table as air quality strategies are discussed since they will find themselves involved in this process anyway due to the many energy programs that are already managing due to state mandates.

Improved air ventilation is definitely an area that building owners will need to invest in, in order to meet the new requirements and expectations in a post-COVID-19 world. For example, several companies are now offering higher levels of air quality and sterilization as part of maintenance packages for buildings. This may worth adding into existing building commissioning, or retro-commissioning program offerings.

No doubt we will see more of these offerings to building owners and operators as an effort to reduce energy usage and comply with new air quality regulations. 


Hi Tilak,

I reached out to our product team and they provided the following insights:

Demand controlled ventilation is a method that uses CO2 sensors to dynamically adjust the ventilation rate based on the number of people in a space. It's not necessarily new, although advancements in sensors and control equipment have made it more cost-effective and easier to execute. Some regions may not allow for it based on energy code. Upgrades to direct digital controls and air handling equipment may be needed. This would be the best recommendation. Additional measures tied to adjusting ventilation would be heat recovery systems including enthalpy wheel systems that are able to capture more useful heating or cooling from exhausted air to pretreat makeup air. These measures can be addressed through RCx or building tune-up programs.

Hope this helps! If you have more specific questions, I'm happy to put you in direct contact with our engineering team.



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