Demand Controlled Ventilation and Classroom Ventilation

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This document summarizes a research effort on demand controlled ventilation and classroom ventilation.

The research on demand controlled ventilation included field studies and building energy modeling. Major findings included:

  • The single-location carbon dioxide sensors widely used for demand controlled ventilation frequently have large errors and will fail to effectively control ventilation rates (VRs).
  • Multi-location carbon dioxide measurement systems with more expensive sensors connected to multi-location sampling systems may measure carbon dioxide more accurately.
  • Currently-available optical people counting systems work well much of the time but have large counting errors in some situations.
  • In meeting rooms, measurements of carbon dioxide at return-air grille appear to be a better choice than wall-mounted sensors.
  • In California, demand controlled ventilation in general office spaces is projected to save significant energy and be cost effective only if typical VRs without demand controlled ventilation are very high relative to VRs in codes. Based on the research, several recommendations were developed for demand controlled ventilation specifications in the California Title 24 Building Energy Efficiency Standards.

The research on classroom ventilation collected data over two years on California elementary school classrooms to investigate associations between VRs and student illness absence (IA).

Major findings included:

  • Median classroom VRs in all studied climate zones were below the California guideline, and 40% lower in portable than permanent buildings.
  • Overall, one additional L/s per person of VR was associated with 1.6% less IA.
  • Increasing average VRs in California K-12classrooms from the current average to the required level is estimated to decrease IA by 3.4%, increasing State attendance-based funding to school districts by $33M, with $6.2 M in increased energy costs. Further VR increases would provide additional benefits.
  • Confirming these findings in intervention studies is recommended.
  • Energy costs of heating/cooling unoccupied classrooms statewide are modest, but a large portion occurs in relatively few classrooms.

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