Cost Payback Time Research Articles

Environmental compatibility and economic feasibility of ground source heat pumps in tropical Asia regarding lifecycle aspects: A case study in Bangkok, Thailand

Ground source heat pumps (GSHPs) in tropical regions require a large-scale ground heat exchanger (GHE) owing to the excessive cooling load and high subsurface temperatures, resulting in increased initial costs and greenhouse gas (GHG) emissions in all phases, excluding the operation phase. However, investigations of the compatibility of GSHPs in tropical regions have been limited to evaluations based on energy consumption in the operation phase, leading to a lack of clarity regarding the contribution of increased initial cost and GHG emissions to the environmental compatibility and economic feasibility based on lifecycle aspects. Thus, this study aimed to evaluate the GHG emissions over the entire life cycle and the cost payback time of a 20-kW capacity GSHP in Bangkok, Thailand, designed with a predicted 50-year heat sink temperature. The results confirmed that the required scale of GHEs is twice as large in tropical regions as in mid‒high latitude regions; nevertheless, the energy-saving of the GSHP resulted in an 8.8 % reduction in GHG emissions over the entire life cycle compared to an air source heat pump. However, the capital investment cannot be recovered within the lifetime of the GSHP, requiring incentives and cost reduction due to the growth of the GSHP market.

A holistic sustainability assessment of a zero-emission development in Norway

The decarbonisation of the construction sector is critical to meet national and international climate goals. Literature gives many examples of measures for the reduction of greenhouse gas (GHG) emissions from buildings. However, few studies investigate the trade-offs between potentially conflicting GHG emission reduction measures or the affordability of these measures. Ydalir is a Zero Emission Neighbourhood (ZEN) pilot area in the Norwegian research centre for Zero Emission Neighbourhoods in smart cities. One of the major challenges Ydalir faces is how to reduce GHG emissions from the neighbourhood towards a net zero emission building (nZEB). Additional challenges include retaining social, environmental, and economical sustainability for both the project developer and building owners and avoid suboptimal solutions. This paper investigates the trade-offs between energy efficiency and material use for two scenarios. The scenarios are a Norwegian building code scenario and a passive house scenario. The analysis ascertains total energy demand, whole life cycle GHG emissions, and cost assessment for two housing units within Ydalir Torg. The results show lower total GHG emissions and lower GHG emissions from operational energy use in the passive house scenario, and an increase in GHG emissions from the production phase due to thicker levels of insulation. The cost assessment shows increased investment costs for the project developer in the passive house scenario, despite lower operational costs for the building owner. Total GHG emission payback times for the passive house scenario are at 18 - 19 years. Cost payback time varies between 10 - 37 years. This paper is useful for practitioners that wish to balance GHG emission reduction requirements between operational energy use, material use and affordability.

Evaluating carbon payback time by optimizing insulation materials for different orientations: A cradle-to-gate life cycle assessment

The European Union aims to reduce greenhouse gases emissions by 80–95% compared to 1990 levels by 2050. Therefore the life cycle concept has gained widespread acceptance as a model for evaluating the environmental impact of goods and services. In this study, the optimal thickness of various insulation materials for external walls, roofs, and floors using a Mediterranean climate zone's hot summers and mild winters for a hypothetical residential building for four cardinal orientations was determined. The criteria for determining the optimum thickness represent a turning point in terms of cooling energy consumption (electricity). The optimum thickness of nine different types of insulation materials was defined using the aforementioned approach. These materials included aerogel, polyisocyanurate, polyurethane, extruded polystyrene, expanded polystyrene, phenolic foam, cellulose fiber (cellulose), mineral wool, and glass wool (GW). The purpose of this paper is to calculate the carbon payback time (CPBT) using the cradle-to-gate life cycle assessment method by considering the global warming potential (GWP) of insulation materials at their optimum thickness. The CPBT is calculated as the ratio of the total building's GWP to the GWP of savings from cooling and heating (electricity and natural gas). The results indicated that when evaluating the average CPBT for four cardinal orientations (FCO), aerogel has the longest CPBT of 2.34 years, and GW has the shortest CPBT of just 0.09 years. Aside from cost payback time, the findings of this study provide a new perspective on selecting appropriate thermal insulation.

Environmental and economic management study of phase change material integrated bifacial photovoltaic thermal-greenhouse drying system: A thermal approach

Environmental and economic analysis of any technology is essential for long-term sustainability. The present article explores the environmental and economic aspects of phase change material-integrated bifacial photovoltaic thermal greenhouse drying system (BIPVTGDPCM). The literature discusses that poor operating hours and self-sustainability are key problems with the greenhouse drying system (GD). Along with the performance issue, lack of information available on the environmental and economic impact of GD. The BIPVTGDPCM is designed to minimize all defined problems with the assurance of environmental quality. The designed system is tested at the geographical location of Rohtak, Haryana, India. The study's outcome shows that the integration of PCM (Lauric acid) runs the system even after sunset. The CO2 emission and the carbon credit earned by the system are 49,851 kg and 498,514 US$, respectively. The energy back time was found to be 2.14 years, whereas the cost payback time is 2.6 years. The system recovers energy and money invested quickly and runs with minimal cost after the payback period. The BIPVTGDPCM save almost 90121₹ (1192.94 US$) in a life span of 25 years. The thermal, electrical, environmental, and economic features of the BIPVTGDPCM make it future-ready environment-friendly food preservation technology.

Economic, energy and environmental life cycle assessment of a liquid flow window in different climates

In this study, life cycle assessment was applied to a novel liquid flow window, based on the cases of sports center application in different climates of Hong Kong and Beijing. The economic, environmental and energy impacts of selected window frame material, the expected lifetime and cost of the working fluid and accessory components were assessed. It was found that the use of wooden frame could be advantageous in that the cost payback time is less than 1.4 years in Hong Kong and well below 5.5 years in Beijing. Nevertheless, when stainless steel frame was in use, the cost payback period would increase to 3.0 and 7.0 years for Hong Kong and Beijing respectively. The lengthy payback time of Beijing is mainly caused by the use of expensive anti-freezer in the liquid circulation. Sensitivity test showed that by taking efforts to lower the material costs and to prolong the lifetime of working liquid, the cost payback time in Hong Kong and Beijing could be reduced to 1.5 and 3.6 years or lower.

A practical appraisal of thermoelectric materials for use in an autonomous power supply

We discuss the selection of thermoelectric materials for use in autonomous power supplies for future sensing networks in terms of cost payback time and environmental and material costs, which are critical factors for practical application. Besides cost and the availability of the constituent elements, suitable thermoelectric materials need to have excellent chemical and thermal stability and a good balance between the mechanical properties of hardness and fracture toughness to enable the production of durable power generation modules. We introduce our research on and development of novel thermoelectric materials consisting of the low-cost and non-toxic elements Al, Fe, and Si.

Evaluation of polyethylene and steel heat exchangers of ground source heat pump systems based on seasonal performance comparison and life cycle assessment

Material characteristics of Ground Heat Exchangers (GHE) greatly influence the heat transfer efficiency of Ground Source Heat Pump (GSHP) system, i.e. polyethylene (PE) and steel for the current study. Most of the relevant studies applied numerical simulation or small-scale experiments, which either simplified or neglected the effects of different GHE design on the energy consumption during the operation process of GSHP system. This paper aimed to investigate the seasonal performance (winter and summer) for both PE and steel GSHP systems by using the methods of full-scale experiment monitoring (buried tubes with the depth of 100 m) and life cycle assessment (LCA), which includes energy benefits, economic and environmental impacts. Heat exchange performance was evaluated by heat exchange per tube depth (QL) and real-time monitoring of system power consumption. Energy benefits, economic and environmental impacts were further indicated through four indices including coefficient of performance (COP), energy payback time (EPT), cost payback time (CPT) and CO2 reduction ratio (CRR). In general, we found the seasonal performance of steel system was superior to PE one in the current study. We also noticed that both PE and steel systems showed better performance in summer than winter. For both winter and summer, the annual averaging inlet and outlet temperature difference of steel tubes was 1.4–1.7 °C higher than PE one and the QL of steel tubes increased by 70%. The energy consumption and cost of steel system were decreased by 43.6% and 24.6%, respectively in the whole life cycle compared to PE one. The EPT, CPT and the CRR of steel system (compared to PE system) were calculated as 0.24 year, 1.83 years and 0.45 accordingly. This work further shows future promise of steel GHE application for GSHP systems.

Cooled solar PV panels for output energy efficiency optimisation

As working temperature plays a critical role in influencing solar PV’s electrical output and efficacy, it is necessary to examine possible way for maintaining the appropriate temperature for solar panels. This research is aiming to investigate practical effects of solar PV surface temperature on output performance, in particular efficiency. Experimental works were carried out under different radiation condition for exploring the variation of the output voltage, current, output power and efficiency. After that, the cooling test was conducted to find how much efficiency improvement can be achieved with the cooling condition. As test results show the efficiency of solar PV can have an increasing rate of 47% with the cooled condition, a cooling system is proposed for possible system setup of residential solar PV application. The system performance and life cycle assessment suggest that the annual PV electric output efficiencies can increase up to 35%, and the annual total system energy efficiency including electric output and hot water energy output can increase up to 107%. The cost payback time can be reduced to 12.1years, compared to 15years of the baseline of a similar system without cooling sub-system.

Lifecycle climate impacts and economic performance of commercial-scale solar PV systems: A study of PV systems at Nevada’s Desert Research Institute (DRI)

The Desert Research Institute (DRI) in Nevada has recently installed eight solar PV systems with a cumulative nameplate capacity of 2.4MW that scale from 3kW to 1145kW. These systems supply approximately 40% of the total electricity used at DRI’s Reno and Las Vegas campuses. This work explored greenhouse gas (GHG) impacts and economic performance of these PV systems by developing and applying comprehensive life cycle analysis (LCA) combined with economic analysis. The LCA model was built using data appropriate for each type of panel used in the DRI systems. Power output was estimated using the National Renewable Energy Laboratory (NREL) model, called PVWatts®. The performance of PVWatts® was verified by comparison with actual measurements from one of DRI’s PV systems over an entire year. Lifecycle metrics quantified for the DRI systems include GHG intensity, energy payback time, cost payback time, and cost of avoided CO2.Manufacturing of PV modules is the major contributor to total lifecycle impacts of a solar PV system. The main benefits are solar electricity’s lower GHG intensity and lifecycle energy use compared with typical grid electricity. Model results showed the 25-year GHG intensity of DRI’s PV systems to be 35–58gCO2e/kWh, and the lifecycle energy use to be 0.586–0.898MJ/kWh. The cost payback times and return on investment (ROI) varied with system size. For the six systems larger than 50kW, the cost payback times ranged from 14.4 to 26.7years, and the 25-year ROI ranged from 0.95 to 2.0. The cost per tonne CO2e avoided by displacing grid electricity was between $100 and $180, which is 2–3 times as high as estimated costs for carbon capture from pulverized coal power plants.The modeled benefits of the PV systems are dependent upon the power mix of the grid electricity that is being displaced. As the grid becomes “cleaner” by elimination of coal and greater use of renewables, the CO2 reduction benefits are diminished. Changing from a “business as usual” scenario to cleaner grid scenarios was shown to reduce the GHG benefits of installed PV systems by up to 40%.

Influence of FIT Rate on the Adoption of Residential PV System in China

The energy consumption in residential sector is increasing rapidly these years in China. The searching for a substitute for fossil energy sources has increased the interest in photovoltaic (PV) system as a friendly and reliable energy technology. In this study, as a promotion policy for PV system, the suitable feed-in tariff (FIT) rates are calculated assuming the cost payback time is within twenty years. Five cities, Harbin, Beijing, Shanghai, Kunming and Guangzhou located in different climate areas in China are selected for study. According to the simulation results, except Shanghai, the optimal FIT rate is close to the grid electricity rate especially in Beijing when there is no subsidy; on the other hand, the optimal FIT rates based on a 1/3 subsidy are less than the situation without a subsidy especially in Shanghai, the optimal FIT rate even reaches to zero when partly access to the grid.

HEATING AND COOLING EXPERIMENTS AND FEASIBILITY STUDY USING HEATING AND COOLING LOAD MODEL FOR GROUND WATER HEAT PUMP SYSTEM

Groundwater heat pump (GWHP) systems can achieve the higher coefficient of performance (COP) and more energy-saving than the conventional air-source heat pump (ASHP) systems. The performance of GWHP system significantly depends on conditions of groundwater and thermal properties of underground. For the optimum design of a GWHP system, it is necessary to comprehensively consider them and building conditions. In this research, heating and cooling experiments with real-scale experimental equipments have been conducted to examine the performance of system. Furthermore, the feasibility study of GWHP system on two different conditions and three local sites has been performed by using heating and cooling load model in building. In the result, cost payback time of this system has been calculated and it has been found that this system is enough efficient in the site where heating and cooling load are balanced.

Energy, cost and LCA results of PV and hybrid PV/T solar systems

Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water-cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water-cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.