a b s t r a c tThe energy and IAQ implications of varying prescribed minimum outdoor air ventilation rates (VRs) in California office buildings were estimated using the EnergyPlus building simulation software tool. Weighting factors were used to scale these model predictions to state wide estimates. Energy use predictions were then verified using surveyed California building energy end use data.Models predicted state wide office electricity use that was within 15% of reported electricity consumption from power utilities. The HVAC energy penalty of providing the current Title-24 VRs was approximately 6%, of the total HVAC energy use. Having economizers installed reduced average indoor formaldehyde exposure by 38% and lowered HVAC EUI by 20%. For California offices with economizers, 50% and 100% increases in Title-24 prescribed minimum VRs increased heating, ventilating, and air conditioning (HVAC) modeled energy use by 7.6% and 21.6%, respectively, while decreasing the annual average workplace formaldehyde exposure by 8.6% and 14.4%, respectively. Economizers increased VRs above the minimum 79% of the time lowering annual average concentrations of formaldehyde. Decreasing minimum VRs below the Title-24 rate would have smaller predicted effects on energy use and comparatively larger effects on formaldehyde concentrations. In buildings without economizers in many climate zones, increasing VRs up to 150% of the current Title-24 minimum would save HVAC energy and significantly reduce formaldehyde.A key conclusion is that raising future minimum VRs in California offices is unlikely to significantly improve time-averaged IAQ in buildings with economizers. Lowering future minimum VRs would be unlikely to deliver substantive energy savings.
California's building efficiency standards (Title 24) mandate minimum prescribed ventilation rates (VRs) for commercial buildings. Title 24 standards currently include a prescriptive procedure similar to ASHRAE's prescriptive "ventilation rate procedure", but does not include an alternative procedure, akin to ASHRAE's non-prescriptive "indoor air quality procedure" (IAQP). The IAQP determines minimum VRs based on objectively and subjectively evaluated indoor air quality (IAQ). The first primary goal of this study was to determine, in a set of California retail stores, the adequacy of Title 24 VRs and observed current measured VRs in providing the level of IAQ specified through an IAQP process, The second primary goal was to evaluate whether several VRs implemented experimentally in a big box store would achieve adequate IAQ, assessed objectively and subjectively.For the first goal, a list of contaminants of concern (CoCs) and reference exposure levels (RELs) were selected for evaluating IAQ. Ventilation rates and indoor and outdoor CoC concentrations were measured in 13 stores, including one "big box" store. Mass balance models were employed to calculate indoor contaminant source strengths for CoCs in each store. Using these source strengths and typical outdoor air contaminant concentrations, mass balance models were again used to calculate for each store the "IAQP" VR that would maintain indoor CoC concentrations below selected RELs. These IAQP VRs were compared to the observed VRs and to the Title 24-prescribed VRs.For the second goal, a VR intervention study was performed in the big box store to determine how objectively assessed indoor contaminant levels and subjectively assessed IAQ varied with VR. The three intervention study VRs included an approximation of the store's current VR [0.24 air changes per hour ( Calculations of IAQP-based VRs showed that for the big box store and 11 of the 12 other stores, neither current measured VRs nor the Title 24-prescribed VRs would be sufficient to maintain indoor concentrations of all CoCs below RELs. In the intervention study, with the IAQP-based VR applied in the big box store, all CoCs were controlled below RELs (within margins of error). Also, at all three VRs in this store, the percentage of subjects reporting acceptable air quality exceeded an 80% criterion of acceptability.
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