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The energy and exergy flow for a space heating systems of a typical residential building of natural ventilation system with different heat generation plants have been modeled and compared. The aim of this comparison is to demonstrate which system leads to an efficient conversion and supply of energy/exergy within a building system. The analysis of a fossil plant heating system has been done with a typical building simulation software IDA-ICE. A zone model of a building with natural ventilation is considered and heat is being supplied by condensing boiler. The same zone model is applied for other cases of building heating systems where power generation plants are considered as ground and air source heat pumps at different operating conditions. Since there is no inbuilt simulation model for heat pumps in IDA-ICE, different COP curves of the earlier studies of heat pumps are taken into account for the evaluation of the heat pump input and output energy. The outcome of the energy and exergy flow analysis revealed that the ground source heat pump heating system is better than air source heat pump or conventional heating system. The realistic and efficient system in this study "ground source heat pump with condenser inlet temperature 30 degrees C and varying evaporator inlet temperature" has roughly 25% less demand of absolute primary energy and exergy whereas about 50% high overall primary coefficient of performance and overall primary exergy efficiency than base case (conventional system). The consequence of low absolute energy and exergy demands and high efficiencies lead to a sustainable building heating system

Anaerobic digestion (AD) is a biological decomposition process that occurs in the absence of oxygen. The decomposition of organic matter is a multi-step process of series and parallel reactions that occurs in four stages namely hydrolysis, acidogenesis, acetogenesis and methanogene. Most of the control in anaerobic digestion is undertaken directly by the micro-organisms themselves, however, the operational conditions such as temperature, pH, essential trace nutrients and toxicants can play a major role in modifying reaction rates of individual sub-processes. The energy performance of the anaerobic digestion is depending mainly on the biogas production technology (wet or dry technology, mesophilic or thermophilic), raw materials and geographic location (ambient temperature). Since the feedstocks coming to anaerobic digestion have usually lower heating value as received and the usual energy efficiency calculation used for incineration plant is not useful. Most commonly used method is the input-output method and the estimation is dependent upon the chosen system boundary.

Clean-cooking energy is key to meeting climate-mitigation goals and a range of development objectives, especially for improving the well-being of women and children. Inefficient burning of solid biomass for cooking releases household air pollution that is hazardous to health, while putting pressure on forest resources. This paper provides an overview of the household-cooking-energy transition in Nepal to date. Despite numerous efforts by the government and other actors to speed this transition, energy data spanning the years 2000–18 reveal that ~69% of households nationwide still rely on solid fuels for cooking today. The proportion of solid-fuel users is especially high in rural regions, reaching >80%. Moreover, if the current rate of progress is not accelerated, the use of solid fuels will remain high even in 2030, preventing the achievement of Sustainable Development Goal (SDG) 7. Cooking-fuel choices are heavily constrained by accessibility, demographic and socio-economic factors. Thus, this paper recommends that evidence-based and integrated policies and strategies be urgently deployed to foster a more effective and rapid transition towards clean energy, which is critical to achieving SDG 7.

A radical transformation of the global energy system is underway. Solar photovoltaics and wind now comprise three-quarters of the global net new electricity-generation-capacity additions because they are cheap. The deep renewable electrification of energy services including transport, heating and industry will allow solar and wind to largely eliminate fossil fuels over the next few decades. This paper demonstrates that Nepal will be able to achieve energy self-sufficiency during the twenty-first century. Nepal has good solar and moderate hydroelectric potential but has negligible wind- and fossil-energy resources. The solar potential is about 100 times larger than that required to support a 100% solar-energy system in which all Nepalese citizens enjoy a similar per-person energy consumption to developed countries, without the use of fossil fuels and without the environmental degradation resulting from damming Nepal’s Himalayan rivers. Nepal has vast low-cost off-river pumped hydro-energy-storage potential, thus eliminating the need for on-river hydro storage and moderating the need for large-scale batteries. Solar, with support from hydro and battery storage, is likely to be the primary route for renewable electrification and rapid growth of the Nepalese energy system.