Hi, we have a DOAS system in the design and our baseline system is Sys#8, VAV with fan power boxes. And the DOAS outdoor air is more than ASHRAE min ventilation requirement (more than 130%). We are trying to decide how to calculate the baseline ventilation rate. According to App G, the baseline shall follow 62.1 (there's other juristiction, etc). When calculating 62.1 min ventilation rate, what zone and system effectiveness we use for the baseline?
Our DOAS supplies cool air, so in the design the zone effectiveness is 1.0 per 62.1. Our DOAS is 100% OSA, so the system effectiveness if 1.0.
But for the Baseline System Type#8, for typical VAV systems, the zone effectivess is 0.8 and the system effectiveness will be whatever calculated based on the IEQp1 spreadsheet.
When we calculate the baseline ventilate rate, should we use the same zone effectiveness and system effectiveness as the design DOAS system (1.0 and 1.0), or use the zone and system effectiveness for a VAV system. For example, do the IEQp1 calculation for the baseline zones and systems (e.g. use 0.8 for overhead diffuser supplying warm air, and whatever system effectiveness the spreadsheet calculates) and use the ventilation rate for that VAV system? Thanks.
Tyler Thumma
7GroupLEEDuser Expert
61 thumbs up
March 4, 2021 - 4:00 pm
My interpretation of this has always been that the minimum ventilation requirement as calculated for the Proposed design should be modeled in the Baseline, rather than running a separate set of ventilation calculations to determine the minimum ventilation requirement for a hypothetical Baseline system. The only exception to this would be for systems with a zone air distribution effectiveness (Ez) greater than 1.0 per G3.1.2.6 exception b.