Greenhouse gas (GHG) emissions from the building sector in 2021 contributed 36% of overall US carbon dioxide (CO₂)­ emissions according to Energy Information Administration (EIA 2021). The space heating of buildings, a large part of the overall emissions, relies heavily on natural gas. Electrification with a heat pump eliminates onsite emissions from space heating but results in indirect emissions from the electric grid. The generation mix of the electric grid evolves over time and varies widely by geographic location. This study presents a temporal and spatial distribution of the impacts of electrification of space heating in residential and office buildings. A comprehensive analysis was conducted to compare modeled GHG emissions over the operational life of a heat pump and a gas furnace installed between years 2022-2036 in six regions across the US. A residential home and a three-story medium office building were considered in this study and Energy Plus prototype models were used to simulate the energy use for space heating in 99 locations across the continental US. GHG impact calculations accounted for long-run marginal emissions from electricity generation from 2022 to 2050, emissions from natural gas combustion, and emissions from leakage of methane and refrigerant. The population weighted average results in the US for the residential home show a 30 - 68% reduction in 100-Year global warming potential (GWP) emissions for a heat pump over a gas furnace, with savings increasing as the year of the installation is deferred (2022-2036). Similarly, for the medium office building, the emissions change ranged from a 1% increase to 51% reduction. Office buildings show lower GHG emission savings in the initial years because of increase in refrigerant charge from the installation of a heat pump and reliance on electric-reheat in the variable air-volume boxes.

Evaporative pre-cooling of condenser air improves the efficiency of compressor-based cooling, particularly in the hot, dry climate that exists in most of California. When implementing evaporative pre‐cooling technologies, one of the main concerns for end‐users is deposition of minerals contained in the water onto the surfaces of the heat exchanger, condenser coils, or cellulose based media. This project consisted of a laboratory investigation of the performance of two commercially-available non-chemical water treatment systems, as applied to evaporative pre-cooling of condenser air. The major claim of most non‐chemical water treatment technologies regarding the mechanism by which they work is that they precipitate minerals in bulk water and reduce the amount of calcium carbonate scale that forms on heat exchanger surfaces. An experimental method and apparatus was developed to evaluate non‐chemical water treatment products applied to a spray‐evaporative cooling application and to provide results on two specific products. A physical treatment device manufactured by Watts OneFlow extended the life of the heat exchanger under test by 14% over the baseline when installed with a sufficient flow rate through the device. A permanent magnet device manufactured by GMX extended the life of the heat exchanger under test by 28% over the baseline. Execution of the tests and analysis of the results generated additional insight into how future testing can be improved to reduce uncertainty. However, the results obtained to date provide confidence that physical water treatment systems have the potential to reduce scale formation in evaporative cooling systems and should be further investigated.

Air cleaning technologies are needed to reduce indoor concentrations and exposure to volatile organic compounds (VOCs). Currently, air cleaning technologies lack an accepted test standard to evaluate their VOC removal performance. A protocol to evaluate the VOC removal performance of air cleaning devices was developed and piloted with two devices. This method injects a VOC mixture and carbon dioxide into a test chamber, supplies outdoor air at a standard building ventilation rate, periodically measures the VOC concentrations in the chamber using solid phase microextraction-gas chromatography-mass spectrometry over a 3-h decay period, and compares the decay rate of VOCs to carbon dioxide to measure the VOC removal air cleaning performance. The method was demonstrated with both a hydroxyl radical generator and an activated carbon air cleaner. It was shown that the activated carbon air cleaner device tested had a clean air delivery rate an order of magnitude greater than the hydroxyl radical generator device (72.10 vs 6.32 m³/h).

Air filtration serves to reduce concentrations of particles in indoor environments. Most standalone, also referred to as portable or in-room, air filtration systems use HEPA filters, and cost generally scales with the clean air delivery rate. A “do-it-yourself” lower-cost alternative, known as the Corsi-Rosenthal Box, that uses MERV-13 filters coupled with a box fan has been recently proposed, but lacks systematic performance characterization. We have characterized the performance of a five-panel Corsi-Rosenthal air cleaner using both research-grade instrumentation (an aerodynamic particle sizer, APS) and a low-cost particle sensor. Measurements of size-resolved and overall decay rates of aerosol particles larger than 0.5 microns emitted into rooms of varying size with and without the air cleaner allowed for determination of the apparent clean air delivery rate—both as a function of size and integrated across particle sizes for a number-weighted median particle diameter of 1.2 ± 0.12 microns. The measurements made in the different rooms produced similar results, demonstrating the robustness of the method used. The size-integrated effective clean air delivery rate increases with fan speed, from about 600 to 850 ft3 min−1 (1019 to 1444 m3 h−1) as determined with the APS. The low-cost sensor yields similar clean air delivery rates as the APS, demonstrating a method by which others who lack access to research-grade instruments can determine the effectiveness of Corsi-Rosenthal Boxes that use components that differ from those used here. Overall, our results demonstrate that our Corsi-Rosenthal air cleaner efficiently reduces suspended particle concentrations in indoor environments.

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.