We are working to certify a 30 year old office tower. While we have copies of original mechanical design drawings and schedules, the building systems have experienced a number of retrofits over the years, and the as-built documentation is sparse. The ASHRAE 62.1-2007 ventilation rate procedure calculations for multiple zone systems rely on precision understanding of the ventilation zones (areas served by each terminal unit), zone airflow rates and VAV terminal unit minimum flow settings, and the system airflow rates. The extent to which the building must be surveyed and the systems tested to provide a high level of confidence in the VRP calculation inputs would be onerous and cost prohibitive. Without this survey information, the inputs to the calculator rely heavily on engineering judgement.
Can we instead use this simpler ventilation rate procedure calculation, to determine how much outdoor air should be supplied to the building?
Ventilation required in IP units = (0.06 cfm/sf x gross building area (in sf) ) + ( 5 cfm per person x building occupancy )
and ventilation required in SI units: = (0.3 L/s*m2 x gross building area (in m2)) + (2.5 L/s per person x building occupancy)
Yes, for office building projects, the proposed simplified calculation may be used. Other project types should use the appropriate Rp value from 62.1-2007, Table 6-1. Projects with multi-zone systems utilizing this simplified calculation approach should provide a supplemental narrative and may document the ventilation calculations as single zone systems within the EQ Minimum IAQ Performance Calculator.
The measured outdoor airflow rate for the building should be equal to or greater than the value calculated.
**Update for 1.11.19
A separate calculation must be performed for each air handling unit serving the project.