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How to Return the HVAC System to Normal Operation FAQ

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  • Q1: Does ASHRAE plan to provide guidance on how to re-occupy a building, especially what measures should be taken to return the HVAC system to normal operation?

    A: The intent of this question is for when the work-remote orders are retracted, and the threat of exposure is greatly reduced. Those are listed below for many systems in the building. If you are restarting a building still at a high-level threat of exposure, please review the Occupancy Guides at www.ashrae.org/Covid19.

    General recommendations:

    1. Prior to starting the building, operators may want to create a strategic plan that includes the following:
      1. Create measures to make occupants feel safer
      2. Ensure supply chain for critical items, such as filters, as confirmed for delivery
      3. Review contractual agreements with tenants with regards to building support
      4. Establish a communication protocol with tenants and include key contacts
      5. Prepare and provide training for tenants on safety measures

    It is important to note, that if you are opening when PPE requirements are still in place, the Occupancy Guides should be referenced as they deal with functioning buildings during the epidemic.

    1. Notify relevant people - include exact dates and times that the building will be reopened.
    2. Follow all local, state and federal executive orders, statutes, regulations, guidelines, restrictions and limitations on use, occupancy and separation until they have been officially relaxed or lifted.
    3. Follow CDC advice regarding PPE
    4. Follow OSHA Guidelines
    5. Ensure that custodial scope includes proper cleaning procedures built from EPA and CDC guidance on approved products and methods:
      1. Disinfect high-touch areas of HVAC and other building service systems (e.g. on/off switches, thermostats)
      2. Disinfect interior of refrigerated devices, e.g. refrigerators, where the virus can potentially survive for long periods of time.
    1. In buildings with operable windows, if the outside air temperature and humidity are moderate, open all windows for two hours minimum before the reoccupation.
    2. Review programming to provide flushing two hours before and post occupancies. This includes operating the exhaust fans as well as opening the outside air dampers.
    3. Run the system on minimum outside air when unoccupied.
    4. Garage exhaust, if any, should run two hours before occupancy.
    5. Install signage to encourage tenants to use a revolving door, if any, rather than opening swing doors in lobby area.
    6. Review all procedures to consider the addition of “touchless” interactions where applicable. As an example, auto-flush valves are considered “touchless”.
    7. Consider future renovations, to be included in the capital budget, to incorporate some of the strategies to mitigate transmission of viruses as indicated in the ASHRAE Position Document “Infectious Aerosols” as well as the Occupancy Guides.

    Heating, Ventilating and Air-Conditioning:

    1. ASHRAE recommends that all building owners and service professionals follow the requirements of ASHRAE Standard 188-2018 which has tables to show the typical maintenance on equipment that has been in operation.
    2. Consider PPE when maintaining ventilation materials, including filters and condensate. Consult additional guidance before duct cleaning.
    3. Check if all the setbacks and setup modes are reversed back to normal.
    4. Open outside air intake dampers to their maximum, 100% preferred, four hours minimum, before the reoccupation. The maximum position the outside air dampers may be opened will depend on the time of year, local climate, the temperature and humidity of the outside air, and the capability of the HVAC equipment to condition the outside air so that the system is able to maintain acceptable indoor temperature and humidity. When operating in this “flush out” mode, monitor the system continuously to make sure that unexpected or unacceptable conditions inside do not develop. Upon completion of the flush, the damper positions should be corrected to provide design levels.
    5. Check to see that space temperature and relative humidity levels are being controlled to the acceptable setpoints.
    6. Check the status of any heat recovery wheels in the systems for leakage and cross-contamination. Consider deactivating these wheels until a service technician checks the operation and condition.

    Airside systems:

    1. Check to see that the fans have turned on, and that air is moving in and out of the building.
    2. Check to make sure the dampers (outside and return) are working properly as this helps control the fresh air to the building. If the building increased its outside air (OA) during the epidemic, rebalancing the dampers may be required to achieve design air flows.
    3. Check overall building pressure to make sure it is positive. Do the same for any critical interior spaces.
    4. Check that the filters are still in acceptable condition. Facility staff should wear PPE, assuming the system may have been contaminated prior to shut down or upon restarting.
    5. Operator should consider increasing the level of filtration in the Air Handling Units (AHUs) for one or two replacement cycles upon opening the building. Make sure the air handling systems and fans can overcome the additional pressure drop of the new filters and still maintain air flow at acceptable levels. Refer to the Filtration Guidance www.ashrae.org/covid19.

    If higher filtration is not available, portable units in the high-traffic areas may be used for a few months.

    Cooling systems:

    1. Check the refrigerant pressures to make sure the system is adequately charged.
    2. Check the water quality in the systems and add chemicals as needed.
    3. Check coil leaving air temperatures to make sure the systems are providing dehumidification.
    4. Check the water levels and make-up water source for cooling towers to ensure they are available.
    5. Check pump operation and that water is flowing.

    Heating System:

    1. Check the fuel source to make sure it is on and available. Old fuel oil may need to be replaced.
    2. Confirm that the flues and make-up air paths are open prior to engaging boilers.
    3. Check that the coil actuators are controlling to temperature, or that heating elements are turned on at the disconnect.
    4. If the boiler system(s) were shut down, follow state boiler codes and the manufacturer's written instructions for starting up, and bring hot water and steam heating systems and plants back online.

    Building Automation System:

    1. Check that the devices and sensors are within an acceptable calibration for controlling space comfort and ventilation.
    2. Check that the alarms are set up and their communication path is correct (it is notifying the right person).
    3. Consider an update to the programming that would incorporate HVAC strategies to reduce virus transmission prior to future events. Automate the control sequences applied as “Epidemic Mode” operation that can be manually selected by the operator with one stroke.
      1. Refer to Occupancy Guides for suggested HVAC strategies to employ when operating the building in an epidemic.

    Plumbing Systems:

    1. Many facilities have a water risk management plan such as an ASHRAE Standard 188-2018, Legionellosis: Risk Management for Building Water Systems, to provide guidance and protocols to minimize the risk of waterborne pathogens, such as legionella pneumophila in their utility water systems.
    2. Turn on the water and run the drinking fountains, lavatories, urinals, water closets, and pantries to ensure water quality before usage.
    3. Make sure all P and U-traps on plumbing drains are wet.
    4. Distributed domestic hot water systems - if possible, keep these systems circulating. Keep water above 140°F to avoid microbial incursion. Do not let it drop below 120°F. If circulation was stopped, try to circulate once every two weeks for two hours at temperature. If the hot water recirculating system goes down for extended duration, do a high temperature flush and pull the strainers before going back online.
    5. Maintenance should wear epidemic-level PPE when maintaining any of the sewage ejectors and lift stations until those systems are sterilized.

    Electrical Systems:

    1. 1. Plug in all appliances that were unplugged to avoid phantom electrical loads, including but not limited to:
      1. Computers
      2. Routers
      3. Modems
      4. Televisions
      5. Printers
      6. Chargers
      7. Microwaves
      8. Things that turn on with a remote control

    Special Systems:

    1. Check on fire alarms and other equipment with battery backup power supplies. Consider having an electrical technician come and check that everything is working properly.
    2. Have fire protection sprinkler systems, fire alarm systems, emergency lighting systems and other life-safety systems inspected by local authorities having jurisdiction (AHJs), if required by state and local statutes and ordinances, and by contract service professionals who routinely maintain these systems.
    3. Check on the battery backup power supplies for Information Technology (IT) and Internet of Things (IOT) devices, especially the ones that are mission critical. That would include servers, building automation systems (BAS), communication systems, lighting control systems and security systems.
    4. If the building is equipped with an emergency or backup generator, arrange to have it tested as required by codes, local jurisdictions and the manufacturer’s recommendations.
  • Glossary

    CIDRAP = U of MN Center for Infectious Disease Research and Policy

    DMHC = ASHRAE Design Manual for Hospitals and Clinics (First Edition)

    WHO = World Health Organization


    ASHRAE PD = ASHRAE Position Document on Infectious Aerosols

    FGI = Facility Guidelines Institute


    Term Definition Source
    Aerosol generating procedure (AGP) Procedures that are likely to induce coughing. Procedures that are believed to generate aerosols and droplets as a source of respiratory pathogens include positive pressure ventilation (bi-level positive airway pressure [BiPAP] and continuous positive airway pressure [CPAP]), endotracheal intubation, airway suction, high-frequency oscillatory ventilation, tracheostomy, chest physiotherapy, nebulizer treatment, sputum induction, and bronchoscopy. AGPs should ideally take place in an airborne infection isolation room (AIIR). CDC
    Aerosol, infectious An infectious aerosol is a system of liquid or solid particles uniformly distributed in a finely divided state through a gas, usually air. (They are small and buoyant enough to behave much like a gas yet they can be filtered out of the gas.) ASHRAE PD
    Aerosol, Short-range transmission Transmitting disease by inhalation of aerosols near the source. The distance for this transmission has not been studied beyond two meters. CIDRAP
    Age of Air The time that has elapsed after the air enters a space (at any given point.) DMHC
    Air change rate Airflow in volume units per hour divided by the building space volume in identical volume units (normally expressed in air changes per hour [ACH or ACPH]) DMHC
    Air irritant A particle or volatile chemical in air that causes physiological response when in contact with mucosa in the eye, nose, or throat. DMHC
    Air volume migration The volume of air that is exchanged during room entry/exit (through a door-way between a room and the area beyond its door) DMHC
    Air, exhaust Air removed from a space and discharged outside the building by mechanical or natural ventilation systems. DMHC
    Air, makeup Any combination of outdoor and transfer air intended to replace exhaust air and exfiltration. DMHC
    Air, outdoor (1) Air outside a building or taken from the outdoors and not previously circulated through the system;
    (2) Ambient air that enters a building through a ventilation system, through intentional openings for natural ventilation, or by infiltration.
    Air, recirculated Air removed from a space and reused as supply air. DMHC
    Air, supply Air delivered by mechanical or natural ventilation to a space that is composed of any combination of outdoor air, recirculated air, or transfer air. DMHC
    Air, transfer Air moved from one indoor space to another. DMHC
    Airborne droplet nuclei Small-particle residue (5 µm or smaller) of evaporated droplets containing microorganisms that remain suspended in air and can be dispersed widely by air currents with a room or over a long distance. DMHC
    Airborne infection isolation room (AIIR) A room designed with negative pressurization to protect patients and people outside the room from the spread of microorganisms (transmitted airborne droplet nuclei) that infect the patient inside the room. DMHC
    Airborne infectious agent An airborne particle that can cause an infection. DMHC
    Airborne pathogen An airborne particle that can cause disease. DMHC
    Airborne transmission Airborne transmission is defined as "dissemination of either airborne droplet nuclei or small particles in the respirable size range containing infectious agents that remain infective over time and distance." An important requirement of airborne transmission is that it can occur only at a long distance from the source, according to the CDC. CIDRAP
    Air-cleaning system A device or combination of devices used to reduce the concentration of airborne contaminants, such as microorganisms, dust, fumes, respirable particles, other particulate matter, gases and/or vapors in air. Related term: HEPA Filter. DMHC
    Anteroom A room separating an isolation room from a corridor. DMHC
    Bay (patient) A space for human occupancy with one hard wall at the headwall and three soft walls. FGI
    Bioaerosol Particles or droplets suspended in air that consist of or contain biological matter such as bacteria, pollens, fungi, skin flakes, and viruses. DMHC
    Building air infiltration Uncontrolled inward leakage of air (that may contain entrained water vapor) through cracks and interstices in any building element and around windows and doors of a building, caused by the pressure effects of wind or the effect of differences in the indoor and outdoor air density. DMHC
    CADR Clean Air Delivery Rate which is the combined effect of actually how much air is moved through the filter and the filter efficiency. AHAM AC-1
    Community acquired infection An infection present or incubating in a patient upon admission to a hospital (or who subsequently shelters in place outside the hospital). DMHC
    Contaminant or Pollutant Any impurity, any material of an extraneous nature, associated with a chemical, a pharmaceutical preparation, a phuysiologic principle, or an infectious agent. DMHC
    Contaminant, airborne An unwanted airborne constituent that may reduce the acceptability of air. DMHC
    Contamination The act of contaminating, especially the introduction of disease germs or infectious material into or on normally sterile objects. DMHC
    COVID-19 COVID-19 is the short name for “coronavirus disease 2019" WHO
    Cubicle A space intended for human occupancy that has at least one opening and no door and is enclosed on three sides with full height or partial height partitions. FGI
    Droplet transmission Droplet transmission is defined as "respiratory droplets carrying infectious pathogens that transmit infection when they travel directly from the respiratory tract of the infectious individual to susceptible mucosal surfaces of the recipient, generally over short distances, necessitating facial protection." Close contact involves hand transfer of surface contamination to mouth, nose or eyes, hand washing and gloves being common controls. CIDRAP
    Epidemiology Study of the distribution and determinants of disease. DMHC
    HEPA filter (or absolute filter)  High efficiency particle air filter with an efficiency of 99.97% removal of particulates larger than 0.30 microns. DMHC
    Hospital Acquired Infection (HAI) See Nosocomial infection.
    Intensive care rooms (ICU)(also critical care rooms CCU) Rooms in which the level of patient care and electronic monitoring of patients are greatly increased over conventional patient rooms. FGI
    MERV Minimum Efficiency Reporting Value: The fraction of particles removed from air passing through a filter is termed “filter efficiency” ASHRAE 52.2-2017
    Nosocomial infection (or Hospital Acquired Infection [HAI]) An infection that is acquired in a hospital and that was not present or incubating upon admission. DMHC
    Occupationally acquired infection An infection acquired while working in a medical care setting. DMHC
    Opportunistic organism An ordinarily non-infectious agent that becomes infectious in an immunocompromised host. (any novel organism, especially aerosolized respiratory viruses for which there is no vaccine or herd immunity becomes an opportunistic organism.) DMHC
    Pneumonia Inflammation of lung tissue. DMHC
    PPE Personal Preotective Equipment is equipment worn to minimize exposure to hazards that cause serious workplace injuries and illnesses. Occupational Safety and Health Administration, PPE
    Pressurization A difference in pressure between a space and a reference pressure. DMHC
    Room A space enclosed by hard walls and having a door. FGI
    SARS-CoV-2 Severe Acute Respiratory Syndrome CoronaVirus 2 International Committee on Taxonomy of Viruses (ICTV)
    UV Ultraviolet irradiation. DMHC
    UVGI Ultraviolet germicidal irradiation. DMHC
    Ventilation A process of supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity, or temperature within the space. Such air may or may not have been conditioned. DMHC
    Ventilation effectiveness The ability of a system to remove contaminants generated by a source in a room. DMHC