Building energy consumption accounts for 30% of the overall energy end use worldwide. This number is even much higher in urban areas. With rapid urbanization in China, cities are expanding with new constructions. It is essential to create an updated urban-scale building energy consumption database to represent energy use for different types of buildings in China, which could help urban planners, managers and decision makers to understand temporal and spatial building energy consumption distribution and ensure required electricity and/or gas supply. However, such urban-scale database is rarely found in China. This paper creates baseline EnergyPlus models for residential, small office and large office buildings and validates the baseline models using survey data from literature. Parametric simulations are conducted to consider different design factors, such as building enclosure, lighting power density, equipment power density, HVAC schedule, etc. In total 351 EnergyPlus models are generated to cover different energy use intensity scenarios. Data-driven regression analysis is conducted to predict building energy consumption using building price/rent. The prediction results are expected to provide design decision support for urban planning and power distribution for new constructions.

This study is intended to demonstrate the potential for energy savings while providing acceptable Indoor Air Quality (IAQ) for ZNE homes. It uses the concept of Smart Ventilation where ventilation systems are designed and controlled to produce the same, or better, IAQ compared to simple, continuously operated ventilation systems. The key energy saving principle for smart ventilation is that ventilation is shifted in time to when the energy required to condition the air is lower. A variety of smart ventilation controls based on outdoor temperature, occupancy and auxiliary fan sensing were developed and assessed across homes built to the 2016 Title 24 Prescriptive standards in California climate regions. Simulations used a co-simulation strategy that combines EnergyPlus with CONTAM. The IAQ calculations were based on the equivalent ventilation principle outlined in the ASHRAE 62.2-2016 ventilation standard, Appendix C. Two prototype homes were simulated (1-story 2,100 ft2 and 2-story 2,700 ft2). Their envelope airtightness was varied between 1, 3 and 5 ACH50. Climate zones were chosen to reflect the variety of heating and cooling demand throughout California. A weighted average analysis was used to generalize the energy predictions across the projected new housing stock in the state. Temperature-based controls were found to be effective, with the most successful smart controls reducing weighted average site ventilation energy use by about 40%, while TDV weighted average ventilation energy reductions were higher, up to roughly 60%. Results were also normalized to ensure identical IAQ in all cases, and the weighted average site and TDV ventilation savings increased, up to 55% and 72% ventilation savings, respectively, for the top-performing temperature-based controls. Peak demand during the 2-6pm period on the hottest days of the year was reduced by up to 400 watts. More than 90% of site energy savings were for heating end-uses, while TDV energy savings were split fairly evenly between heating and cooling. On average, the smart controls reduced occupant pollutant exposure by 0-10%, and they increased ventilation rates by roughly 20%. Occupancy-based controls that accounted for contaminants released by building materials and furnishings during unoccupied times were generally ineffective, with very low energy savings. Performance was improved somewhat through use of a 1-hour pre-occupancy flush out period, though savings were still marginal compared to temperature-based controls. All temperature and occupancy controls were also tested with auxiliary fan sensing capability (i.e., accounting for the use of other exhaust devices in the home, like bathroom or kitchen fans). Auxiliary fan sensing increased energy savings in all cases, from roughly 5 to 15%.

This project developed and demonstrated approaches to synergistically improve ventilation and indoor environmental quality during replacements of packaged heating, ventilation, and air conditioning (HVAC) systems in California schools. The research team 1) characterized HVAC systems, carbon dioxide concentration, and indoor thermal conditions in 104 classrooms that had replaced packaged HVAC systems serving a single classroom (single-zone) between 2013 and 2016; 2) evaluated HVAC system retrofits with regard to energy efficiency and indoor environmental quality performance at two field sites; and 3) completed building energy and indoor environmental quality modeling of HVAC equipment and filter selection for four climate and outdoor air conditions representative of California’s regional variation and two different classroom vintages. Inspections of 104 classrooms with HVAC equipment installed between 2013-2016 showed that only 15 percent of classrooms’ estimated median daily ventilation rates met the 7.1 liters per second per person Title 24 code requirement, and 9 percent had carbon dioxide levels above 2,000 parts per million for significant portions of the school day, which implies a ventilation rate of less than half of that required. Where under-ventilation occurred, it tended to affect several observed classrooms within a given school and not occur as an isolated case. Periodic testing of ventilation systems and continuous real-time carbon dioxide monitoring could help to detect ventilation problems. Field testing and modeling of HVAC technologies determined that variable speed motors for indoor blowers, two-speed compressors, economizers, demand control ventilation technology, and air filters with a minimum efficiency reporting value of 13 constitute an HVAC package suitable for all of California’s climates. The combination of technologies can save between 28 and 57 percent of HVAC electricity use, depending on climate. Filters with a minimum efficiency reporting value of 13 can reduce indoor particulate matter exposures by 40 percent or more compared to filters with a value of 8.

Previous research has shown that under-ventilation of classrooms is common and negatively impacts student health and learning. To advance understanding of contributing factors, this study visited 104 classrooms from 11 schools that had recently been retrofitted with new heating, ventilation, and air-conditioning (HVAC) units. CO2 concentration, room and supply air temperature and relative humidity, and door opening were measured for four weeks in each classroom. Field inspections identified HVAC equipment, fan control, and/or filter maintenance problems in 51% of the studied classrooms. Across 94 classrooms with valid data, average CO2 concentrations measured during school hours had a mean of 895 ppm and a standard deviation (SD) of 263 ppm. Ventilation rates (VRs), estimated using the daily maximum 15-min CO2 in each classroom, had a mean of 5.2 L/s-person and a SD of 2.0 L/s-person across 94 classrooms. Classrooms with economizers, with or without demand control ventilation (DCV), tended to have lower mean CO2. Improperly selected equipment, lack of commissioning, incorrect fan control settings and maintenance issues (heavily loaded filters) were all associated with under-ventilation in classrooms. Many classrooms in this sample were frequently too warm to support learning. There were 23 out of 103 classrooms that had indoor air temperature above 25.6 °C for more than 20% of the school hours. Better oversight on HVAC system installation and commissioning are needed to ensure adequate classroom ventilation. Periodic testing of ventilation systems and/or continuous real-time CO2 monitoring (either as stand-alone monitors or incorporated into thermostats) is recommended to detect and correct ventilation problems.

This project investigated smart ventilation approaches to minimize energy use for providing indoor air quality (IAQ) in high performance new California homes. Evaluation criteria included annual ventilation-related energy, peak energy and time-of-use savings, and the indoor air quality relative to a minimally code-compliant ventilation system. The simulations used CONTAM’s air flow and contaminant transport model, combined with the EnergyPlus building loads model. House types representing the default California Energy Code compliance homes were investigated for four California climate zones, covering a wide range of climate types. Both single and multi-zone smart ventilation controls were investigated. Contaminant sources included contaminants emitted continuously and varying with time, temperature and relative humidity, episodic emissions from occupant activities and outdoor particles. Single-zone ventilation controls that varied ventilation depending on outdoor temperatures were able to consistently save half of ventilation-related energy without compromising long-term IAQ. Ventilation strategies that tracked occupancy were less successful, because this work included generic contaminants with constant background emission rates. Energy performance for occupancy controls improved with a one-hour pre-occupancy flush out strategy. The addition of zoning ventilation controls did not offer significant IAQ to energy improvements compared to non-zonal versions of the same ventilation system type. The best controls had HVAC energy savings of 10-20%, with individual cases reaching up to 40% savings. However, these savings cannot be achieved without worsening personal exposures for at least one contaminant. A metric is needed to assess the competing changes in exposure to different contaminants in order to determine the net-health impacts of a control strategy. Controls that directly sensed contaminants and controlled them to acceptable levels showed that the California OEHHA limit for formaldehyde completely dominates system performance, with homes not able to meet the limit even with continuous operation of a fan sized to twice the current code minimum.