Emission of carbon dioxide and other greenhouse gases from human activities are considered the main contributors to the global temperature rise over the past several decades. The global average temperatures have risen by about 1.2 °C since preindustrial times [1]. The building sector is known as a major source of global greenhouse gas (GHG) emissions with nearly 37% contribution of energy-related carbon dioxide emissions worldwide [2]. The substantial carbon footprint of buildings stems from emissions due to buildings' energy and water usage (operational carbon) and the emissions from materials and products used for buildings during manufacturing, transportation, installation, and decommissioning (embodied carbon). As countries strive to better understand and mitigate the impacts of climate change, decarbonizing the building sector is considered a critical priority and an opportunity.
Building decarbonization encompasses reducing carbon emissions throughout the entire lifecycle of buildings, from design and construction to operation and decommissioning for both new and existing buildings. Decarbonizing buildings is a challenging task, considering the large number of stakeholders and types of buildings that are scattered across numerous geographical locations with various needs and constraints. Examples of decarbonization strategies in the building sector include implementing energy efficiency measures to reduce building energy consumption [3–5], using sustainable building materials [6], building electrification [7], using renewable energy sources to address building energy needs [8,9], and specifying using low global warming potential refrigerants for space heating and cooling are among the solutions for decarbonizing buildings. Figure 1 summarizes the sources of carbon in buildings and examples of building decarbonization options.
Several major initiatives have been implemented and/or initiated during the past few years to better understand and advance building decarbonization targets. As an example, the U.S. Department of Energy (DOE) released the first-ever federal blueprint to decarbonize America's building sector [10]. The Blueprint targets reducing greenhouse gas emissions from US buildings by 65% by 2035 and 90% by 2050, compared to 2005 levels, with a focus on equity and providing benefits to communities. Further, a few major cities worldwide have embarked on deep decarbonization policies with buildings as the primary target. This is the case of the most dense city in the United States, New York City (NYC), where buildings represent close to 70% of GHG, which has pledged to reduce 80% of the carbon emissions by 2050 with buildings as the primary target [11]. Meeting these targets would reduce building greenhouse gas emissions extensively and reduce building energy consumption by one-third, resulting in major cost savings while helping with climate resiliency.
This special issue brings together a collection of articles that explore innovative approaches and technologies aimed at reducing carbon emissions across various aspects of building design, construction, and operation. The special issue covers a wide range of topics related to building decarbonization including innovative heating/cooling technologies, utilization of renewable energy sources, energy storage applications, novel materials for building envelopes, and review of technologies suitable for building decarbonization in high-density urban areas.
Abdur Rob et al. [12] studied the performance of air source heat pump (ASHP) systems using R410A refrigerant in the cold winter climate of NY to support the city's decarbonization efforts as noted earlier. ASHP systems are known as a potential alternative to natural gas heating. However, their efficiency declines in extremely low temperatures. Laboratory testing of NYC's winter climate showed that the ASHP's coefficient of performance (COP) increases from 2.56 to 3.52 as outdoor temperatures rise from 16 °F to 50 °F. Exergy analysis showed that the compressor incurs the highest losses and that the overall system performance is a strong function of the outdoor temperature and component optimization, particularly of the condenser and evaporator. The study concludes that ASHP systems could be used as an alternative for natural gas-based heating in NYC, but further research is required to optimize their energy performance, especially for cold climates, including using low-global warming potential (GWP) refrigerants such as CO2. Sharma et al. [13] used EnergyPlus™ simulations and evaluated the energy-saving potential associated with three different high albedo roof coatings including silicone, acrylic, and aluminum with respect to a traditional black roof. For simulations, they considered two DOE prototype commercial buildings in Phoenix, Houston, Los Angeles, and Miami to estimate the decline in rooftop temperatures and how it impacts energy efficiency. They reported significant energy savings in cooling-dominant climates, particularly Phoenix, with minimal heating penalties. They also studied how roof insulation levels affect the performance of the selected coatings for reducing energy consumption for cooling and heating.
Lv et al. [14] presented a review study on the challenges of building decarbonization in high-density urban areas, emphasizing technical difficulties stemming from geographical and resource limitations. Traditional methods for building decarbonization face high incremental costs and therefore they are considered less effective in these settings. The study supports synergistic approaches that integrate surrounding infrastructure, grid-interactive efficient buildings, innovative low-carbon materials, and urban greenery to enhance decarbonization efforts. The study discusses the importance of considering building decarbonization as part of a broader, collaborative strategy with city infrastructure.
Two articles within this collection are focused on the use of renewable energy systems, particularly solar energy. Alasadi et al. [15] studied the thermal and electrical performance of rooftop photovoltaic (PV) panels with reflectors, which enhance PV power output by concentrating solar flux and improving building thermal performance through shading. The addition of reflectors between PV rows reduces rooftop heat flux, leading to cooling energy savings during summer and a minor increase in heating energy during winter. Parametric analyses for three US locations, including Phoenix, Boise, and Dayton, demonstrated that sunny, dry climates benefit the most, with a utility factor increase of up to 22% in Phoenix when reflectors are used. The results show that reflector area and roof absorptivity significantly affect the system's overall performance. Pesantes et al. [16] investigated improving solar irradiance prediction to support rural electrification. They compared various clustering techniques including k-means, Gaussian mixture models (GMM), hierarchical clustering, density-based spatial clustering of applications with noise (DBSCAN), and agglomerative clustering, using historical climate data from Ecuador's coastal region. K-means and GMM demonstrated the most effective, leading to optimal microgrid designs by improving prediction accuracy and reducing energy deficits. The study highlights the critical role of clustering in optimizing renewable energy systems for rural communities, enhancing both economic sustainability and climate adaptation efforts. They discussed that future work will explore improvements in clustering techniques to enhance accuracy in microgrid design and the potential for wind energy for hydraulic water pumping in remote communities to offer sustainable and accessible solutions for water supply.
An approach for evaluating the thermal self-sufficiency of residential buildings with thermal energy storage (TES) is presented by Lüchinger et al. [17]. The ability of a system to satisfy its heating demand from local renewable energy sources is defined by its thermal self-sufficiency which is a critical metric for the design and optimization of energy systems that involves TES. The results demonstrated the important role of TES at different scales to accomplish more thermal self-sufficiency in the residential building sector leading to a more sustainable design.
In conclusion, this special issue presents a selection of high-quality articles that explore diverse approaches to achieve building decarbonization across different climate conditions and building types. We encourage readers to engage with the range of perspectives and innovations featured in this collection, which address both the challenges and opportunities of decarbonization in the building sector. We extend our deep gratitude to the expert reviewers for their dedicated efforts in maintaining the high standards of this issue. Our aim is that this special issue contributes to advancing the body of knowledge on building decarbonization and encourages further research and discussion on this critical topic as we strive toward a more sustainable future.
