Your questions answered: HVAC systems that achieve indoor air quality

Matt Short responded to extra questions from this July 27 webcast

By Matt Short August 9, 2021

During the July 27, 2021, webcast HVAC systems that achieve indoor air quality, several questions were left unanswered. A selection of responses follows.

Depending on the building and its geographic location, there are several techniques for specifying HVAC systems in nonresidential buildings. A new or existing building each has its own requirements and mechanical engineers must understand the client’s needs, the codes and standards, humidification/dehumidification needs, energy efficiency goals and the specific building requirements to successfully design a system.

Based on recent issues brought on by the COVID-19 pandemic, indoor air quality has become more of a focus for mechanical engineers specifying or retrofitting HVAC systems.

Expert responses from: Matt Short, PE, Project Manager/Mechanical Engineer, Smith Seckman Reid

Do you design for the worst particulate manor or the average particulate?

Matt Short: Filtration requirements described in the code are based upon particulate air matter needs of a specific space. For example, an operating room where risk of infection is high will require a filter bank with a higher MERV rating than a typical office space.

Is plenum return still a typical design for office space?

Matt Short: Yes, we often utilize a plenum return type system where code does not require a fully ducted system.

As per ASHRAE 62.1, the way to calculate fresh air requirement is 5 cfm per person + 0.06 area in square foot per person. For offices, the assumption is 200 square feet per person. Would it be appropriate to apply the ASHRAE formula (5 + 0.06) to calculate fresh air requirement in offices where people are packed in much tighter (for example 65 square feet per person of carpet area)?

Matt Short: The ASHRAE 62.1 requirement described does take into account an average space per occupant to establish a minimum ventilation requirement. It is important as designers to understand the use and true occupancy of a space and potentially provide additional ventilation to accommodate the delta.

Are there any guidelines for COVID room design in hospital facilities?

Matt Short: Yes, many codes such as Facility Guidelines Institute Guidelines for the Design and Construction of Health Care Facilities already have spaces described as “airborne isolation patient rooms,” which provide a space that is negative to the adjacent space and are exhausted to the outside of the building. It is also important to look at state and local codes as many authorities provided additional documentation to address the COVID pandemic.

Author Bio: Matt Short is a project manager/mechanical engineer at Smith Seckman Reid. He is a member of the Consulting-Specifying Engineer editorial advisory board.