eQuest Continuous DOAS Ventilation Flow and Intermittent Zone Fans

asked 2016-08-29 11:55:46 -0600

TNZ Energy gravatar image

updated 2016-08-29 13:28:41 -0600

Hello, My understanding of how eQuest handles zone systems such as FCUs and packaged equipment is that the thermal impact of fresh air from a DOAS is only calculated when the zone fan is operating. If so, then putting an FCU fan into intermittent fan mode will only allow DOAS supply temperatures to impact zone loads when the fan is on. This would underestimate zone heating loads since DOAS air is generally cooler than room air and it would overestimate zone cooling loads since credit for the ventilation load is not being claimed. Am I reading this correctly? The issue would potentially apply to any DOAS system working in conjunction with cycling zone fans.

My current DOAS work-round is as follows:

  1. Create the ERV using a packaged VAV system, make ghost space and an associated ghost plenum.
  2. Output hourly return air temperatures for all zones that are served and develop 8,760-hr average return air schedules to feed back into the exhaust side of the DOAS ERV via the ghost plenum.
  3. Apply 100% latent loads into the plenum for occupant and equipment loads.
  4. Specific to correcting the DOAS sensible impact on spaces is to

    a.) Remove the OA for the zone

    b.) Apply a negative process internal energy source to each zone (based on zone ventilation cfm (80-55)1.08), and

    c.) Apply an 8,760-hr average diversity schedule developed from the hourly difference between DOAS supply air (taken from the ghost zone associated with the ERV) and the average return air temperature from all of the spaces that are served.

The downside of this approach is that I am applying an average process load to all spaces based on the average return air temperature. Oh, and it is clunky. Is there something more elegant and accurate out there? Do I need to do this?

Thanks!

Eric

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