May 22, 2020

Engineering Considerations for Your Return to Work

Building upon much of the content on our Returning website, following is a deeper dive into important building engineering considerations to keep in mind as you prepare to reopen your physical environments.


Since the buildingproperty or tenant environment may have been vacated with little warning or preparation, thoroughly inspect for damage or issues caused by the vacancy. The physical condition and operation of equipment and services supporting the building also should be assessed. 

Mechanical Systems  

If the building or tenant area has been unoccupied for more than 48-72 hours it is unlikely that COVID-19 will exist within the system as COVID-19 has been proven to not live on surfaces or in the air for longer than that timeframe (source). The following items are recommendations to implement in your building.

  • Inspect the internal condition of air conveying equipment (Air Handling Units, Fan Coil Units, heat pumps, etc). Systems that have been off for an extended period of time, or not well maintained, may have contaminants that have built up on coils or other surfaces. If contamination is observed (how do you “observe” contamination?) cleaning is recommended in alignment with National Air Duct Cleaning Association Guidelines (NADCA). This cleaning is targeted at not circulating other air contaminants that could have built up while buildings were not used or maintained which could trigger other respiratory issues in occupants upon reactivation.   
  • Replace HVAC Filter(s) prior to reactivation. 
    • Filters with ASHRAE standard 52.2 – MERV 15 ratings or better have been proven through research completed at the University of Minnesota to significantly reduce the amount of droplet nuclei that could harbor airborne transmission of viruses (source).
    • Many commercial building systems will not have the capability to accept filters of MERV 15 class or higher.  In those instances, the highest MERV rated filter that can be accommodated by the system based on size and filter pressure drop should be selected. 
    • If the above measures are not possible, consider the inclusion of space type air cleanerssimilar to this one, that can meet the MERV 15 or better level of filtration.  
  • Ensure that the minimum outdoor air rate meets or exceeds the original system design parameters. 
    • Increase outdoor air ventilation to the greatest extent possible and disable demand-controlled ventilation controls (source). Care must be taken to ensure the system is capable of properly conditioning the added volume of outdoor air. Under this control maintain proper indoor temperature ranges @ 75 deg F and less than 60% RH for cooling season, 70 deg F for the heating season. Building pressurization should also be maintained so that it is not overly positive, not greater than 0.02” water column.  
    • In Variable Air Volume Systems, VAV box minimum airflow setpoints may require adjustment to increase space airflow. 
  • Humidity control in spaces has been shown to have an impact on the ability for viruses to be more readily transported through airborne pathways (source). Additional research has been completed that concludes an optimal humidity range helps the body’s natural defense systems to ward off disease (source). An optimal humidity range of 40-60% Relative Humidity under normal occupied space temperature ranges is recommended. If humification systems are not currently employed in a building, consult with a qualified professional engineer and architect on how a system could be applied. Care must be taken because the humidity in that range, under certain environmental conditions, can cause condensation issues at the building envelope that can lead to other unfavorable results. 
  • Operate any chilled water or condenser water: Ensure related chemical water treatment systems are properly functioning. Be sure to open valves to coils, pumps and other isolated loops in order to circulate chemical treatment to stagnant parts of systems.
  • Operation hours: 
    • If possible allow systems to run 24/7 to enhance flush out of space (source)
    • The CDC has provided the following guidance related to how various air change rates impact the removal efficiency of particulate in the air. CDC recommends the 99% removal efficiency value prior to occupancy (source)
  AC/HR  Time (mins) required for removal 99% efficiency  Time (mins) required for removal 99.9% efficiency 
2  138  207 
4  69  104 
6  46  69 
8  35  52 
10  28  41 
12  23  35 
15  18  28 
20  14  21 
50  6  8 
    •  If the above chart is not applicable, or outdoor airflow rates are not easily established, operate HVAC systems for at least two (2) business days prior to reactivation 

 Electrical Systems  

  • Assess lighting and lighting controls to ensure they are in working order 
  • Consider use of UVGI lights within space (source)
  • If applicable, and space has been unoccupied for long period of time, confirm generator is in working order by performing a “lights out” test

 Plumbing Systems  

  • Drain potable water storage tanks including water heaters and inspect for sediment accumulation 
  • Flush all valves, i.e. faucets, toilets, urinals, bubblers, showers, and test water for bacteria. Do not drink water until acceptable bacteria test are returned which in alignment EPA National Primary Drinking Water Regulations (source)
    • For faucets, showers, bubblers, lines to coffee makers, water filters, refrigerator water dispensers, etc – Run hot water for 15 minutes minimum, allow cold water to run continuously for a minimum of 5 minutes
    • Ice makers – Discard all ice, allow machine to refill, discard all of that ice, clean ice machine, and replace any incoming water filters
    • Run dishwashers through one full cycle with detergent
    • Run clothes washers through one full cycle with bleach
    • Have water filtration machines serviced
    • Flush toilets/urinals 3 times
  • If bacteria levels are present in drinking water sources after flushing, provide chlorination of potable water systems, flush and re-test water for bacteria
  • Test any other water-related features to ensure proper operation 
  • Inspect drains and traps for flow and blockage 
  • Operate and inspect any lift and ejector systems for sanitary or rainwater collection 


  • Confirm that all elevators and escalators are properly functioning. Remedy any deficiencies 
  • If elevators have cab ventilation fans, ensure proper operation and remedy deficiencies 
  • Ensure elevator cab interiors are cleaned often 
  • Consider touchless cab operation using card access 
  • Reduce occupant load according to physical distancing requirements 

Fire Protection & Fire Alarm (FA) Safety Systems  

  • Test FA system or arrange for a FA systems contractor to check system 
  • Visually inspect fire protection systems that incoming water pressure is within original design tolerances and systems have not been compromised by age or freezing situations 
  • Confirm fire protection system tests have been completed required by respective laws or local codes
  • Perform fire extinguisher checks required by respective laws or local codes 

Disclaimer: Public safety codes, building codes, applicable laws and security requirements must not be compromised to reduce the potential for physical contact with items in the workplace.