Ventilation: Is your Building Prepared for Winter?

The rollercoaster that is the pandemic has shown us that fresh air and purging of room air has an enormous influence on the spread of a virus. The chance of contamination increases by viral load (how much of the air has the virus in it) and the length of time a person is exposed to this contaminated air. The purpose of ventilation is to move the air quickly away and out of the building to decrease both of these conditions.

We have enjoyed the ability to congregate outside with friends and feel safe inside buildings with open windows, but, in the north at least, this time is quickly coming to an end. For our economy (and our sanity), we need to ensure our buildings are safe to inhabit. In addition to masking and distancing, ventilation holds the key towards this objective.

Since the summer of 2020, Cx Associates has been assessing schools, nursing homes, daycare centers, small businesses, and non-profits on their existing ventilation systems and recommending what they can do to improve their ventilation rates. Although some customers called us directly, most assessments were conducted through the State of Vermont’s K-12 Indoor Air Quality program and the City of Burlington Ventilation Improvement Program. Both programs paid for our technical assessment of the needs and recommendations. For relatively little money, building owners and managers received a report stating their current conditions, a scope of work for a contractor, and an estimate of the project’s implementation costs. With this document, a contractor could be contacted and, usually, the project could be implemented without further involvement of another party.

How to Assess Your Ventilation Needs and Next Steps

There are basically three possible HVAC systems in your building – an air handling unit with outside air intake, an air handling unit without outside air intake, or no air handling unit (for more detail, please refer to my blog Ventilation During COVID-19: Why & How). A building owner/manager can ascertain their situation and follow the following steps to assess the building needs:

• Step 1

  Is there an air handling unit with a fan and ductwork? If so, trace the ductwork and determine if there is a duct to the outside that brings fresh air into the building.

• Step 2

  Based on the system type, the next step is one of the following:

  • Step 2a | Air Handling Unit with Outside Air Intake

    • Contact a contractor or engineer who can do the following work:
      1. Calculate the amount of ventilation air that is needed for the occupancy rate and space size (calculated according to ASHRAE Standard 62.1).
      2. Install a MERV 13 filter if possible. This filter should be installed before the airflow measurements are taken.
      3. Measure and adjust the air handling unit to provide this calculated amount of ventilation air to the appropriate spaces.
    • Additionally, the owner/manager or the contractor should trace the ductwork and ensure all occupied spaces are being served by the air handling unit. If there are occupied spaces not supported by the air handling unit, please refer to the section of ‘No Ventilation”.

  • Step 2b | Air Handling Unit Without Outside Air Intake

    • This system is an air handling unit without an outside air intake – it conditions only recirculated building air.
    • In this case, ask a contractor or consulting engineer if the unit can be retrofitted to include an outside air intake. If so, pursue a design for this connection and proper duct sizing, ensuring the heating and cooling coils are sized for the extra load, and then go through the same steps as Step 2a above.

  • Step 2c | No Ventilation

    • Buildings without an air handling unit are ones that heat with hydronic baseboard or heat pumps. Hydronic baseboard is very common in small commercial buildings throughout New England.
    • In this case we recommend installing a properly sized heat recovery ventilator. This is typically a small unit that can sit in the ceiling with a small amount of ductwork. It is a heat exchanger which creates heat transfer between outgoing room air and incoming fresh air. This very efficiently tempers the incoming air and the pre-existing baseboard or heat pump can condition it further to maintain the appropriate room temperature. Again, contact a contractor or engineering consultant to calculate the required airflow, the proper recovery unit size, and design of its proper location.

If all else fails and if the space is relatively small, you can also place a portable HEPA filter in the room. This is a good alternative for tenants of small spaces.

How Much is Enough?

Ventilation does cost energy in the form of fan energy needed to bring in the fresh air and exhaust the stale air as well as the additional cooling or heating of this air. So the question of how much is enough is important. ASHRAE, the industry’s guide to all things HVAC, has a publication, Standard 62.1, called Ventilation for Indoor Air Quality. For more detail on this, please refer to my past blog School Airflow Testing & ASHRAE 62.1 about how the industry uses this standard to calculate the recommended minimum ventilation rates dependent on the space type and occupancy level.