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Japan's long-term strategy submitted to the United Nations Framework Convention on Climate Change emphasizes the importance of improving the electrification rates to reducing GHG emissions. Using the five models participating in Energy Modeling Forum 35 Japan Model Intercomparison project (JMIP), we focused on the demand-side decarbonization and analyzed the final energy composition required to achieve 80% reductions in GHGs by 2050 in Japan. The model results show that the electricity share in final energy use (electrification rate) needs to reach 37–66% in 2050 (26% in 2010) to achieve the emissions reduction of 80%. The electrification rate increases mainly due to switching from fossil fuel end-use technologies (i.e. oil water heater, oil stove and combustion-engine vehicles) to electricity end-use technologies (i.e. heat pump water heater and electric vehicles). The electricity consumption in 2050 other than AIM/Hub ranged between 840 and 1260 TWh (AIM/Hub: 1950TWh), which is comparable to the level seen in the last 10 years (950–1035 TWh). The pace at which electrification rate must be increased is a challenge. The model results suggest to increase the electrification pace to 0.46–1.58%/yr from 2030 to 2050. Neither the past electrification pace (0.30%/year from 1990 to 2010) nor the outlook of the Ministry of Economy, Trade and Industry (0.15%/year from 2010 to 2030) is enough to reach the suggested electrification rates in 2050. Therefore, more concrete measures to accelerate dissemination of electricity end-use technologies across all sectors need to be established. [ABSTRACT FROM AUTHOR]

The present study presents an overview of CO 2 heat pump water heater for residential use in Japan. The contents include the general background, current market, and the technology evolvement of the transcritical CO 2 system, especially on the key components like compressor and gas cooler. Some cutting edge technology associated with the high efficient compressors and its integration with expander, such as swing compressor, sub-compressor, two-stage compressor, scroll expander, and dual-sided scroll-type expander are elaborated in this review. Some ingenious tube designs to promote the performance of gas cooler are also studied. In practice, the dominant thermal resistance may occur in the CO 2 side or water side, thereby implementing twisted tube or dimple tubes may be quite effective. The placement of enhancement on the water side is especially effective when the operational pressure is close to the critical pressure whereas heat transfer enhancement is more helpful if the operational pressure is comparatively high. For augmentation on the CO 2 side, it would be more beneficial to place enhancement a distance away from the pseudo-critical region. [ABSTRACT FROM AUTHOR]

This paper presents a novel review and laboratory test results of four standard test methods for determining the energy consumption of microprocessor controlled gas tankless water heaters. The test standards examined are from Australia, Europe, Japan and North America. The European test standard is found to be technically the most comprehensive in measuring all aspects of energy consumption for these types of appliances. Four water heaters, both conventional and condensing type, ranging in capacity from 28 to 55kW are tested to each of the test standards. The European and North American tests deliver similar results. Those to the Australian standard yield higher energy use while the Japanese method produces the lowest consumption. The relative difference in energy use between water heater models tested to any single standard is consistent, with the exception that the Australian test appears to favour the smaller water heater. Therefore, while consumers cannot use standard test results to calculate their actual running costs, in general, any of the standards will reasonably predict relative running cost differences between models if used as part of the product selection process. While the correlation between the standards varies according to the capacity of the water heater, a simple approximation is developed to convert from the efficiency measured by one standard to another. [ABSTRACT FROM AUTHOR]

Abstract: Simulation models for a variety of new water heater systems were developed and the models were integrated into a city-level residential energy end-use model for Osaka City. Using the model, the potential of energy conservation and CO2 emission-reduction by introducing new residential water heaters was evaluated at the city-level. Optimal water-heating systems for each household category for primary energy reduction, CO2 emission-reduction, or cost reduction were identified by applying the end-use demand model. The effect of subsidies for installing more efficient systems and the influence of diffusion of these systems on electricity load curves were also discussed. [ABSTRACT FROM AUTHOR]

• Multi-level household emission patterns are recognized by machine learning models. • Demographic structure, age and appliances are key factors to vary emission levels. • Customized emission reduction paths are proposed to guide energy-saving behaviours. • Household appliance usage obtains the largest reduction potential to mitigate emissions. Given by the ambitious GHG mitigation targets set by governments worldwide, household is playing an increasingly important role for reaching listed reduction goals. Consequently, a deep understanding of its emission patterns and the corresponding driving factors are of great importance for exploring the untapped potential of household. However, how to accurately capture household emission features still demand further support from both data and method development. To bridge this knowledge gap, we try to use machine learning technology, which is well linked to the micro-level household survey data, to identify key determinants that could explain the household home-energy consumption and associated emissions. Here, we investigate the household CO 2 emissions based on a representative survey which covers 31,133 households in Japan. Six types of machine learning process are employed to find key factors determining to different household emission patterns. Results show that demographic structure, average age and electricity-intensive appliances (electric water heaters, electric heaters, etc.) are most significant driving factors that explain differences in household emissions. Results also further verified that differences in driving factors can be observed in identifying various household emission patterns. The results of study provide vital information for the customized decarbonization pathways for households, as well as discussing further energy-saving behaviours from data-oriented method. [ABSTRACT FROM AUTHOR]

• Decarbonization scenarios for residential sector using bottom-up end-use simulation. • Net zero energy is achievable by energy efficiency tech. and building integrated PV. • More than half of current energy demand can be reduced with existing technologies. • Dissemination of PV will create an imbalance between electricity supply and demand. • Residential energy demand will rely on long term energy storage such as hydrogen. Decarbonization scenarios for achieving net zero greenhouse gas emissions in the Japanese residential sector by 2050 were examined using a bottom-up simulation model of energy end-use demand. The examined scenarios involve the dissemination of currently available technology, including highly insulated houses, high-efficiency equipment, high-efficiency appliances, electrification, and building-integrated photovoltaics (PV) in detached houses. The results show that decarbonization can be mostly achieved by the studied scenarios, especially through the dissemination of highly insulated buildings and high-efficiency water heaters as well as the installation of PV for all detached houses. This scenario reduced the total primary energy demand by 61% in 2013. A land-use strategy for increased detached houses is preferable for increasing PV capacity. For the scenario that achieves net zero energy, the predicted heat load intensity and electricity consumption per capita are almost the same as those of the Low Energy Demand (LED) scenario. Increased dependence on PV will create an imbalance in the relationship between electricity supply and demand, and 26% of the residential energy demand would rely on non-battery energy storage, such as pumped hydropower and hydrogen, owing to the seasonal time gap between residual and deficit electricity. [ABSTRACT FROM AUTHOR]

• Water heater uses the most energy in residential houses in Japan. • Households with higher income or occupancy consume more electricity. • Household characteristics affect energy use under various facets. • Detailed hourly electricity load data shows noticeable energy loss. • To save household energy need an in-depth approach to behavioral patterns. This study aims to characterize the Japanese household properties, meanwhile investigates the electricity consumption by end-use of 12 households in electric-only apartments in Kitakyushu, Japan. Achieved electricity data from the measurement and household surveys, the author perceived significant relationships between the household characteristics and Electricity End-Use. Since the investigation conducted in the winter, heating systems become the primary consuming appliances with 38 % in total usage. Energy-related behavior closely linked to the room's function and house appliance ownership than floor areas, while the distribution of energy varied according to each lifestyle circumstance. Living rooms seemed to get more usage priority at these residential apartments, while private spaces indicated less often used. By classifying pair groups of participants in common and different traits, comparison analysis carries out numerous relationships among energy consumption, housing characteristics, and household characteristics. Finally, the study lays a platform for applying energy monitors and household surveys, which defines the contribution of detailed data in analyzing household energy-related lifestyle. Thus, the energy performance reports can help to elevate awareness of saving energy in residential apartments. This paper suggested a combination of experiments, surveys, and questionnaire methodology to give an example for future studies regarding energy-related lifestyle and energy-saving strategies. [ABSTRACT FROM AUTHOR]

• GHG reduction target should be planned by aggregating effects of concrete measures. • A bottom-up energy use simulation can be used as a reliable policymaking tool. • An operation-based approach should be adopted for policymaking. • Technology distribution is important since the effects differ by household type. • Distribution of water heaters and heating systems must be considered together. The national policy in Japan for reducing greenhouse gas (GHG) emissions in the residential sector by 2030 is evaluated using a bottom-up-type simulation model called the Total Residential End-use Energy Simulation (TREES) model. According to the Japanese Plan for Global Warming Countermeasures (PGWC), the target GHG reduction in the residential sector is expected to be realized through the aggregated effect of various mitigation measures. In evaluating the impact of these measures, the following three factors must be considered: occupant behavior, differences in the effect among households, and secondary impacts. In this paper, to discuss the required specifications for supporting the policies related to GHG reduction, these factors are examined via the TREES model, considering the differences in the energy use among households due to occupant behavior, appliance/equipment ownership, and building energy efficiency. The simulation results of the end-use energy in the Japanese residential sector in 2013 show good agreement with available statistical values. The results of the TREES model applied to evaluate the proposed countermeasures suggest that 1) The Japanese government may be overestimating the effect of high-efficiency lighting installations, 2) The reduction in the total energy use varies by a factor of two depending on the combination of high-efficiency water heaters and household characteristics, 3) The relationship between the types of water heater and space heating system influences the effect of high-efficiency water heater installations, and 4) Energy demand reduction affects the electricity load curve and CO 2 emission intensity of the electricity grid. [ABSTRACT FROM AUTHOR]

Large-capacity photovoltaic ( PV) systems will be installed in future power systems. According to Japan's energy outlook, the target capacity of PV systems for 2030 is about 50 GW. When large-volume PV systems are installed in a power system, the reverse power flow from PV systems may cause a surplus of electric power. To utilize the surplus electric power without reduction of PV power generation, the operation of customer equipment such as heat pump water heaters ( HPWH) according to PV power generation is expected to be one of the solutions. In this paper, a method of cooperative control of customer equipment with PV power generation is proposed, and the effectiveness of the proposed control is evaluated by simulation analyses. [ABSTRACT FROM AUTHOR]

The article features the experiments conducted on the significance of noise reduction in vacuumed electric water heater in Osaka, Japan. It is revealed that eventhough heat storage of electric water heater is vital it is necessary to add the function of rapid heat storage. Results of the experiment show that the duration time for rapid heat storage can be reduced to 1/4 and the noise can be reduced by 17 decibels.