Commercial building HVAC systems experience many sensing, mechanical, and control-related faults that increase energy consumption and impact occupant comfort. Fault detection & diagnostics (FDD) software has been demonstrated to identify and help diagnose these types of faults. Several studies have demonstrated FDD energy savings potential, but there is limited empirical data characterizing the quantity and type of faults reported by FDD tools. This paper presents results of an FDD fault reporting study, employing multi-year monitoring data for over 60,000 pieces of HVAC equipment, covering over 90 fault types, and using new metrics that we developed to characterize fault prevalence. Study results offer an unprecedented accounting of the quantity of faults reported, the most commonly occurring faults, and fault persistence. We find that 21 air handling unit (AHU) faults were reported on 20% or more AHUs in our dataset, and 18 AHU faults persisted for more than 20% of the time period covered by the data. On any given day, 40% of AHUs and 30% of air terminal units saw a reported fault of some kind. Based on in-depth analysis of these results we provide recommendations for building operators, FDD software developers, and researchers to enable more efficient commercial building operation.

Renewable microgrids are sustainable, resilient solutions to mitigate and adapt to climate change. Making electric loads nearly 100% available (i.e., power remains on) during outages increases cost. Near 100% availability is required when human life or high-cost assets are involved, but availability can be reduced for less consequential loads leading to lower costs. This study analyses costs for photo-voltaic and lithium-ion battery microgrids with availability ranging from 0–99%. We develop a methodology to analyse three Puerto Rican coastal communities. We consider power outage effects for hurricanes, earthquakes, and everyday outages. The results show cost versus availability from 0–99%. There is 27–31% cost reduction at 80% availability in comparison to 99% availability. A regression model of microgrid availability versus three ratios: 1) the annual generation to demand ratio, 2) storage to interruption energy ratio, and 3) peak storage to load ratio produced a coefficient of determination of 0.99949 with 70% of the data used for training and 30% for testing. The results can therefore be extended to other coastal Puerto Rican communities of varying sizes that have ratios within the ranges analysed in this study. This can empower decision makers to rapidly analyse designs that have availabilities well below 100%.

Thermal energy storage (TES) based on phase change materials (PCM) is an effective strategy to reduce energy consumption in buildings. The efficient implementation of TES in building through PCMs, requires modification of their thermal performance, appropriate design and evaluation of their thermal and economic efficiency. One major challenge in the application of PCMs is the selection of high-performance and environmental-friendly supporting materials to overcome the most critical drawback of PCMs (solid-to-liquid transition and resulting leakage). This review focuses on expanded clay (EC) lightweight aggregate (LWA), as one of the promising supporting materials for development of form-stabilized PCM (FSPCM) in the lightweight concrete (LWC) industry. The large specific surface area and porous structure of expanded clay can maintain considerable amount of PCM. In addition, mechanical properties and compatibility with various PCMs make EC a suitable carrier. A detailed review of available researches is presented to elucidate the properties of PCMs embedded in EC for thermally efficient cement-based concrete. Various combinations of EC with the most used PCMs, thermal and mechanical properties of matrices containing PCM-EC, strategies to improve the efficiency of PCM performance, and finally the impact of PCM-EC based concretes on the thermal comfort of buildings are critically summarized.

Active insulation systems (AIS) have been conceptualized to make buildings more responsive to changing environmental conditions, creating energy efficiency and flexibility gains. Building flexibility and efficiency can be further improved if the building is also equipped with optimized HVAC system controls. Optimal control of AIS and HVAC systems can be used to activate thermal mass, and past work has quantified the potential benefits of jointly optimizing both systems. In this work, we more fully elucidate and evaluate the potential tradeoffs between optimal control of these technologies with respect to building energy use and peak demand–including different configurations of heat pump systems and integrated building thermal energy storage. Tradeoffs are revealed by applying a multi-objective optimal control framework and comparing the Pareto optimal sets across various system configurations. Discussion of the results provides insights into how buildings can be best designed and controlled to achieve both energy efficiency and flexibility.

Managers of small commercial building (SCB) portfolios need to understand occupant interactions with heating, ventilation, and air-conditioning (HVAC) systems to reduce energy use and greenhouse gas (GHG) emissions. In Canada, SCBs are currently underserved by energy conservation and thermal analysis tools because of their dispersion and lower payback potential. However, the emergence of smart thermostats (STs) and their central data collection platform provide a cost-effective solution to gather data from portfolios of SCBs and improve our understanding of occupant-HVAC interactions. This article analyzes the relationship between HVAC schedules (temperature set-points), indoor thermal conditions (dry-bulb temperature and relative humidity), and occupant behavior (thermostat overrides) in a portfolio of 30 SCBs in Ontario, Canada. The results reveal that temperature set-points were not properly selected in the portfolio of SCBs, leading to a large range of indoor thermal conditions and increased thermostat overrides. Specifically, the study demonstrates that building- and zone-specific HVAC schedules are necessary to minimize discomfort and reduce energy consumption in the portfolio of SCBs. The findings of this study can provide valuable insights for portfolio managers to improve HVAC schedules in a manner that reduces energy consumption and GHG emissions while accommodating occupants’ thermal comfort and productivity.

The daytime radiative cooling technology may be effectively used to passively cool the water and hence mitigate the undesirable solar water heating of the roof-top storage tank in the summer. Hence, this work presents the radiative water cooler design, development and experimental and numerical performance characteristics. Radiative water cooler surface coating has been developed using the polymer (PMMA)-particle (barium sulfate) composite structure. The effects of various water inlet temperatures and volume flow rates on the water temperature drop and cooling capacity are experimentally and numerically performed. Sub-ambient water cooling throughout the day is observed for a range of 0.1–0.4 L/min water flow rates at the near-ambient inlet temperature conditions. The maximum sub-ambient water temperature drop of 6.1 °C (that of 3.5 °C at noon) is observed with a developed radiative cooler for the flow rate of 0.1 l/min. The usage of the daytime radiative water cooler for sub-ambient water temperature drop is found to be more suitable for above-ambient water inlet temperature. Apart from the solar irradiance, ambient temperature, ambient humidity, wind velocity and coating surface emissivity characteristics, cooling capacity and surface temperature distribution of radiative water cooler also depend on the water inlet conditions.

Net-zero energy buildings are on the agenda of international community due to reducing energy consumption in the building, thus dropping carbon emissions and negative environmental effects. One of the solutions is to utilize heat pumps to decrease energy consumption in the building. In this study, the idea of ejector utilization in a heat pump system was investigated in an experimental test facility by comparison to a conventional heat pump system (without an ejector). The experimental facility, which utilizes hot and cold water as the heat source, can operate in two modes: The ejector heat pump water heater (EHP-WH) and heat pump water heater (HP-WH). The system was tested in transient conditions and the effect of ejector utilization on the system was determined. Results indicate that EHP-WH mode (COP between 5 and 6) had an average of 5.5% higher COP value than HP-WH mode (COP between 4.5 and 5.5). Furthermore, the heating capacity obtained in EHP-WH mode was 30% higher than in HP-WH. Additionally, the water cooler loop’s water temperature was 64.5% higher in EHP-WH mode than in HP-WH. Finally, it is determined that the ejector positively impacts on the performance of HP-WH system.

People spend about 90% of their time indoors. This extended exposure to indoor conditions affects well-being and performance. Design decisions have a profound impact on IEQ, yet existing IEQ-related assessments normally wait until the post-occupancy evaluation when few opportunities for design improvement exist. This study introduces an efficient simulation-based framework involving parametric modeling to simultaneously quantify the impact of design decisions on all domains of IEQ, namely, thermal comfort, visual comfort, acoustic comfort, and air quality. To achieve this goal, first a set of metrics and corresponding evaluation methods to quantify the four IEQ domains are developed. Then, a number of design parameters that impact multiple IEQ criteria in the design stage including office geometry, facade design, and material properties are investigated. Next, the aggregated score for each domain is presented to measure the room’s IEQ performance. A case study is considered to demonstrate the proposed workflow. The results indicate the importance of considering all comfort domains together, as one design choice might improve one IEQ domain at the cost of others. The proposed workflow is an efficient and effective method for architects and other building stakeholders to compare design scenarios with regards to IEQ performance at preliminary design stages.

The functionality of commercial building thermostats is often not well understood by occupants. This can lead to users feeling discontent and/or frustrated and may contribute to inefficient thermostat operation and related energy outcomes. Thus, the usability of such thermostats is critical to elicit effective operation from users. However, usability principles (e.g., intuitive colors, icon standardization) are rarely prioritized in thermostat interfaces. This study investigates the relationship between usability principles and thermostat interfaces using a comparative study. Two prototype commercial building thermostat interfaces were examined: one that resembles current devices (control thermostat) and one that incorporates usability principles (experimental thermostat). Eighty-five participants participated in an online survey and user test, during which they were asked to perform various tasks on both interfaces. Participants rated various aspects of each interface (e.g., the overall intuitiveness, a specific feature). Human-interface interactions were recorded by Useberry, an interface prototyping software tool. The success rate for usability tasks was largely the same between control and experimental thermostats; however, most participants (78%) preferred the additional features offered by the experimental interface. This paper serves to both explore novel thermostat features that aim to improve usability as well as introducing rapid prototyping as a solution to improve commercial building thermostat usability.

Condensation heat transfer from moist air is critical in dehumidification, fog collection, and cooling tower water reclamation; however, it is less studied than steam condensation. Although there are many visualization studies of dropwise condensation, few dropwise condensation heat transfer coefficients were reported in the literature for moist air. In this work, condensation occurred on a Teflon-coated, aluminum plate which was placed in an environmental chamber with controlled temperatures and relative humidities; air flowed from the plate’s bottom to top at velocities of 3–4 m/s. The plate was cooled on the backside by dry air flowing through five channels in an additively-manufactured, ABS plastic heat exchanger. The apparatus was validated using a heating case at temperatures above the dew point. Dropwise condensation was observed and heat transfer coefficients of approximately 40 W/m2K and 120 W/m2K were measured for the ambient conditions of 40 °C at 40% relative humidity (RH) and 40 °C at 60% RH, respectively. The thermal resistance from diffusion exceeds the thermal resistance of the droplets during condensation from moist air; enhancement mechanisms could focus on improving diffusion.