Center for the Built Environment

Excessively high minimum airflow setpoints for Variable Air Volume (VAV) boxes, caused by outdated energy codes stipulating they should be 30% or higher of the maximum airflow, led to significant energy waste. Lower setpoints meet the ventilation code requirements while minimizing recirculation and reheat energy waste. ASHRAE RP-1515 showcased this by correcting VAV minimums in 1,000,000 ft² (92903 m²) of California office space which yielded 10-30% HVAC energy savings and improved thermal comfort. Consequently, the Title 24 Energy Standards and ASHRAE 90.1 were updated to mandate minimum airflows match ventilation requirements. Beyond increased reheat energy waste caused by elevated VAV minimums, boiler operation issues can also contribute to avoidable energy waste. Despite energy codes mandating low VAV minimums for several years, these issues remain common in new construction and existing buildings. Our goal is to simplify retrofit decision-making for owners and operators by developing a screening method to assess extensive or small-scale building portfolios, using easily accessible data encompassing building type, age, size, and monthly gas consumption. The method entails applying a series of filters to a list of potential buildings to identify those with heating system challenges that should be prioritized for system upgrades. The main filter highlights buildings with elevated summertime gas consumption, as well-functioning systems lacking a major gas end-user should exhibit minimal gas usage during the cooling season. This filter employs a threshold for summer gas consumption we calculated based on standard design parameters, assumptions, and past case studies to serve as a benchmark and pinpoint problematic buildings. We applied this filter, among others, to over a decade of gas consumption data for 22 buildings at California State Polytechnic University, Humboldt. Collaborating with operators enabled us to identify 2 high priority buildings from the data set and validate the filtering process by cross-referencing floor plans and schedules to verify that these issues do in fact exist. Additionally, we applied this methodology to monthly gas data for 3318 buildings in Washington, DC to gauge its applicability on a larger scale. This process prioritized 30 potential buildings that could significantly reduce fossil fuel consumption, elevate thermal comfort, and realize gas bill savings through economical retrofits. While the screening method does not identify all buildings needing heating system upgrades, the results demonstrate how effective they are at highlighting buildings which should be prioritized to see the largest savings from the lowest cost interventions.