Energy and indoor air quality implications of alternative minimum ventilation rates in California offices

Abstract

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.

Energy and IAQ Implications of Alternative Minimum Ventilation Rates in California Retail and School Buildings

“…Eliminating mechanical ventilation modestly increased the energy use for air conditioning in schools. This same trend was shown for offices without economizer controls [1]. In the hottest climate, CZ15, total HVAC energy use increases with each incremental step up in the minimum VR.…”

“…In the retail store, average VR's were higher for all VR scenarios compared to the schools, in part due to the higher design VR , and in part due to the use of economizers in the core retail zone of the store. The economizers did not increase VR by as much as was observed in the earlier study in offices [1] . In the retail building model, located in CZ03, using the Title-24 VR scenario, the economizer was in use 95% of the time.…”

“…The 6 methods employed in this analysis are very similar to those employed for our prior analysis of the effects of minimum VRs on energy use and contaminant concentrations in offices [1].…”

“…Envelope and heating, ventilating, and air conditioning (HVAC) systems were modeled as per the published reference building models. Prior modeling efforts for offices [1] found that transitioning the envelope to a Title 24-compliant envelope was time intensive, and had a limited impact on the energy use of ventilation. Data from the California End Use Survey (CEUS) [14] indicate that the majority of both secondary and primary schools in California did not make use of economizers, to reflect this fact, the economizers were deactivated on these two models.…”

“…This report adds to our prior analysis of the energy and IAQ implication of minimum ventilation rates (VRs) in offices [1] , by presenting an analysis for a stand-alone retail building, primary school, and secondary school.…”