The mechanical engineer begins preliminary ventilation rate calculations during project programming in order to set ventilation quality goals for particular spaces and occupancies. The area of a given multi‐zone system should be broken down by ventilation zones, and all zones within that system must meet the minimum breathing zone ventilation air requirements as per ASHRAE 62.1‐2004. For a typical office space, the mechanical design consists of multiple ventilation zones for which compliance would need to be shown on an individual basis.

Increasing a project’s ventilation rate brings long-term cost benefits. Good indoor air quality can lower operational costs by increasing occupants’ health and productivity as well as the value and marketability of the building.

An integrated design approach among the mechanical engineer, architects, owners and occupants will facilitate design decisions that impact the HVAC design. For example, space planning decisions will impact the architectural programming of the space as well as access to natural ventilation.

Separately evaluate each space to determine air requirements and what type of ventilation will be best.  Metabolic rate of the space activities and the occupant density are factors that determine the amount of fresh air needed in a space.  For example, exercise rooms and conference rooms require more fresh air than offices.

Determine the required ventilation rates for indoor spaces based on occupancy and space types.  ASHRAE 62.1-2007 tables 6-1 and 6-4 list minimum requirements for particular spaces.

Consider the cost implications of natural ventilation. Passive strategies may reduce or eliminate the need for fans and HVAC equipment, but they may also require high quantities of operable windows and a floor plan that is conducive to passive ventilation.  Natural ventilation often requires the cooperation of occupants, to open and close windows when appropriate, for example, be sure that your project is likely to succeed in this respect.

Naturally ventilated core and shell projects must provide the potential for tenant build-out to meet requirements of this credit.  When documenting the credit, you can provide an assumed tenant layout and default occupancy assumptions based on the LEED Reference Guide Appendix 1 to confirm that tenant spaces meet ASHRAE 62.1 requirements.

Airflow modeling early in the design process can help teams by evaluating which space planning and envelope design strategies will create effective natural ventilation. An airflow modeling professional may add some upfront costs, while likely improving system efficiency.

 Airflow modeling can also help to determine compliance for an engineered natural ventilation system outside the prescriptive measures of ASHRAE 62.1-2007.

An integrated design meeting will help determine whether natural ventilation is a high priority and should be a primary driver of the design process.

Review the prescriptive requirements for natural ventilation in ASHRAE 62.1-2007 Paragraph 5.1 (with errata but without addenda).