A Healthy Buildings Guide to re-open small commercial buildings:
Restarting HVAC systems post COVID-19 shutdowns.

A comprehensive checklist by EcoEnergy Insights.


In recent months, most small commercial buildings, such as convenience stores, bank branches and salons, have been closed in line with efforts to combat the pandemic. This has made it imperative for the building operators to ensure that their HVAC equipment are maintained properly during the closure and are ready for occupancy when they reopen. The buildings or stores need to be cleaned effectively during the closure period to reduce risk upon reopening.

Based on industry best practices for maintaining and operating HVAC equipment, including recommendations and guidelines from American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) for HVAC systems in the time of the COVID-19 pandemic and beyond, the following ‘to do’ list was created for businesses as they prepare to reopen their buildings or stores or branches for business.

Step 1: Purge

"Purging" involves removing contaminants inside the confined space by displacement with outside air to achieve acceptable contaminant levels relative to atmospheric levels. One of the best ways to achieve this is through “ventilation”, which is the intentional introduction of outdoor air into a confined space by mechanical means to control indoor air quality.

Altered occupancy patterns during lockdown affect building heat load and indoor relative humidity levels, which can lead to conditions favoring mold growth. To prevent such situations, the building should be purged of stale air. At least one purge cycle is recommended after a complete shutdown.

Here is the list of actions we recommend:

  1. Ventilate the building floors utilizing maximum outdoor air, preferably during night hours or in the early morning hours.
  2. This purge operation is to be done once during the shutdown condition for approximately 6 hours in aggregate. Ventilation should be carried out after checking outdoor air humidity condition from weather forecasting website, to ensure that the operation is not carried out during outdoor conditions with high humidity, i.e. greater than 70% RH.
  3. The following steps can be followed:
    1. Create a purge schedule for the purge period (preferably starting from 12am) in the controller for the direct expansion air conditioning (DX) system.
    2. If any fresh air damper is provided at the return air path of the DX system (Ducted Split Air Conditioner), ensure there is no restriction to air flow.
    3. Ensure the fresh air intake operation by ‘Firing UP’ all the fresh air fans and exhaust fans in the store. Compressor operation of DX units will cool down the outdoor air.

Step 2: Conduct cyclic equipment health checks

In order to ensure that HVAC equipment are in a proper working condition, their performance should be periodically reviewed till the time of reopening of the branches or stores. Equipment health can be periodically checked by operating them in conditions similar to a full-load environment.

Here is the list of actions we recommend:

  1. Each DX unit should be operated for approximately 45 minutes every 2 weeks during the period of the branch or store shutdown.
  2. Turn ON all Hi-wall split air conditioner units - Ducted split units for a smaller size site - if it caters to a single area within the building. We break up a building into Service Consumption Areas (SCA).
  3. We recommend splitting a space into SCAs and focusing on each SCA individually if possible.
  4. An example Health Check of DX units based on SCAs involves the following steps:
    1. Set the DX unit to ‘ON’ Mode. Run the DX units on ‘ON’ Mode for 45 minutes.
    2. Let the Group of DX units run based on SCAs in the above condition for 45 minutes.
    3. After 45 minutes, check whether the zone temperature has met the desired site temperature policy. If zone air temperature meets the desired level, conclude the exercise for the SCA by releasing all overrides and reverting the DX units back to normal condition.
  5. Once the health check condition reaches a steady state for a particular SCA, start the process on the remaining DX units (Hi-wall split units, Ducted units), one SCA at a time.

Step 3: Prepare for start up

A day before the scheduled opening of the site or before pre-opening activities such as cleaning, the HVAC equipment should be operated in “Occupied Mode” for 12 hours. This will help the equipment purge any accumulated contamination so that the indoor environment is prepared for returning occupants.

Here is the list of actions we recommend:

  1. Set the DX unit (Hi-wall unit, Ducted unit) to ‘ON’ Mode.
  2. Create a 12 hour ‘ON’ schedule for the DX unit in the energy management system.
  3. Check the performance of DX unit for any deviations.
  4. Ensure the fresh air and exhaust fans are ‘ON’ for outdoor air ventilation if conditions permit.
  5. Identify any issues such as zone sensor faults, communication issues or unhealthy equipment for further checks. If needed, schedule a technician’s visit.

Step 4: Run ‘Normal’ operations

Following the startup preparation, the modes/schedules of HVAC equipment are to be returned to normal occupancy schedules. Sites operators should prioritize providing maximum outdoor air ventilation and maintaining the sensors and fresh air systems accordingly.

Here is the list of actions we recommend:

  1. Update schedules to the normal/adjusted site occupied hours.
  2. If supported by the energy management system, update batch programs for planned schedules.

Write to us at info.ecoenergy@carrier.com for more on restarting your buildings