Reduction Of Primary Energy Consumption Research Articles

Impact of seasonal thermal energy storage design on the dynamic performance of a solar heating system serving a small-scale Italian district composed of residential and school buildings

Abstract A centralized solar hybrid heating system serving a small-scale district composed of 6 typical Italian residential buildings and 3 schools located in Naples (southern Italy) has been modelled, simulated and analysed by means of the dynamic software TRNSYS over a 5-year period. The plant is based on the operation of solar thermal collectors connected to a seasonal double U-pipe vertical Borehole Thermal Energy Storage (BTES) in order to address the seasonal misalignment between solar energy supply and thermal energy demand for heating purposes. In this paper a parametric analysis has been performed in order to investigate the performance of the district heating network upon varying the characteristics of the BTES in terms of: (i) thermal conductivity of soil, (ii) thermal conductivity of grout, (iii) U-pipe spacing, (iv) heat carrier fluid, (v) number of Borehole Heat Exchangers (BHEs), as well as (vi) type of BHEs connection (series, parallel or mixed). The primary energy consumption, the equivalent carbon dioxide emissions and the operating costs of the proposed district heating plant have been evaluated based on the simulation results upon varying the plant configurations and then compared with those associated to a conventional Italian decentralized heating system assumed as reference with the main aims of (i) assessing the potential reduction of primary energy consumption, global CO2 equivalent emissions and operating costs, (ii) exploring the influence of BTES characteristics on the overall system performance as well as (iii) establishing some simple rules for the initial design of BTES.

Evaluation of the feasibility of distributed energy supply system for existing multi-family housing in Nagoya City

The possibility of introducing distributed energy system consisting of combining heat and power generation (CHP) for existing multi-family housing is discussed in order to make an academic ground for calling for the spread of distributed energy systems in existing multi-family houses. Case study was conducted to evaluate energy conservation effect of the distributed energy supply system and obtain the findings concerning on its feasibility. The case study was focusing on all municipal multi-family housing in Nagoya city, Japan, and it was evaluated based on primary energy consumption reduction, CO2 emission reduction, simple pay-back period, and recurring expenses merit by introducing the system. Annual energy consumption was estimated for nine typical municipal multi-family houses with different average occupied floor area and number of dwelling for each individual building unit. Based on the results of the case study, it was found that the effect of the distributed system varies depending on the average occupied floor area and the number of residences, and the generator capacity of CHP. In addition, when assuming adapting a distributed energy supply system into a type of housing has occupied floor area of 30m2-50m2 per a dwelling that accounts for 83.5% of the total municipal housing in Nagoya, at least the overall reduction of 16.7% CO2 emission reduction rate could be expected.

Artificial intelligence based prediction model for the long-term heat flux losses through ground applied to large non-residential buildings

Abstract One of the most important directions towards global CO2 emissions and primary energy consumption reduction is to increase energy efficiency in the sector of residential and non-residential buildings. The evaluation of building envelope heat losses through ground, as part of the building energy demand and energy consumption, it still has a lack of comprehensive knowledge relative to the large buildings. This article aims to use artificial neural networks (ANNs) to allow long-term prediction of the heat transfer losses through ground during heating season for the large dimensions slabs, which are specific for many non-residential buildings, in order to reduce the significant resources needed for the numerical analysis in time-dependent state. A hybrid approach is proposed by developing an application to study a less investigated area of civil engineering.

Climate control inside a greenhouse by means of a solar cooling system

Microclimate control in the greenhouse is important to improve yield and obtain low environmental impacts. Ventilation, shading, evaporative cooling and refrigeration are methods of controlling air temperature inside the greenhouse; nevertheless, ventilation and shading are often not sufficient to remove the excess heat, refrigeration is generally expensive and evaporative cooling is based on the use of large quantities of water. In order to enhance the sustainability of the greenhouse sector, renewable energy sources can be exploited with the application of solar absorption systems for greenhouse cooling in areas with high outdoor temperatures and solar insolation. This paper describes the application of a solar cooling plant with absorption chiller for thermal control of a greenhouse. The experimental system consisted of a Mediterranean greenhouse, with a surface of 300 m2, and a single-effect LiBr-H2O absorption chiller fed by evacuated-tube solar collectors, located at the University of Bari, Italy. The distribution system provides the cooling power only for the volume surrounding the crop. The research demonstrated that solar cooling systems provide an opportunity for reducing the air temperature around the crop, allowing the reduction of primary energy consumption by exploiting the contemporaneity between the cooling requirements and solar energy availability.

Evaluating Design Strategies for Nearly Zero Energy Buildings in the Middle East and North Africa Regions

There is international pressure for countries to reduce greenhouse gas emissions, which are blamed as the main cause of climate change. The countries in the Middle East and North Africa (MENA) region heavily rely on fossil fuel as the main energy source for buildings. The concept of nearly zero energy buildings (nZEB) has been defined and standardized for some developed countries. While most of the developing countries located in the MENA region with hot and tropical climate lack building energy efficiency standards. With pressure to improve energy and environmental performance of buildings, nZEB buildings are expected to grow over the coming years and employing these buildings in the MENA region can reduce building energy consumption and CO2 emissions. Therefore, the paper focuses on: (a) reviewing the current established nZEB standards and definitions for countries in the hot and warm climate of Europe, (b) investigate the primary energy consumption for current existing buildings in the MENA region, and (c) establishing a standard for nZEB and positive energy buildings in kWh/m2/year for the MENA region using a building simulation platform represented using Autodesk Insight 360. The result of the simulation reveals high energy use intensity for existing buildings in the MENA region. By improving building fabric and applying solar photovoltaics (PV) in the base model, significant reductions in primary energy consumption was achieved. Further design improvements, such as increasing the airtightness and using high efficiency solar PV, also contributed to positive energy buildings that produce more energy than they consume.

Estimation of the energy-saving effect of introducing a heat source water network system with single-loop piping utilizing hot spring heat

The introduction of a heat source water network system using heat from hot spring and drainage water for hot water supply in accommodation facilities in hot spring areas is expected to contribute to increased energy efficiency. In this study, the relationship between the temperature of the heat source water and the energy efficiency of heat pump water heaters introduced in hot spring facilities connected to a single-loop heat source water network was analyzed. The primary energy consumption of the heat source water network system was compared with that of a centralized heat supply system by conducting a dynamic simulation using Modelica in the Dymola environment. The yearly average coefficients of performance of the proposed heat source water network and centralized heat supply systems were estimated to be is 4.56 and 3.24, respectively. The seasonal performance of the proposed system was also investigated based on measurement data. In December, it was estimated that the heat source water network system would achieve a 17.6% reduction in primary energy consumption in comparison with the centralized heat supply system. However, in August, it was estimated that the primary energy consumption of the heat source water network system would be 8.9% higher than that of the centralized system.

Primary energy consumption of heat pumps in high renewable share electricity mixes

The increase of power plants’ conversion efficiencies, together with the high share of renewable energy sources in the electricity production for some countries, pushes for the use of heat pumps for space heating when aiming at reducing the associated primary energy consumption. However, the effective reduction of primary energy consumption should be supported by careful evaluations, as a number of parameters influence the heat pumps performance, including outdoor temperature, supply temperature, heat load and electricity primary energy factor. The variability of such parameters increases the complexity of the analysis, and annual or monthly average calculations might lead to incomplete evaluations and thus to sub-optimal solutions. This paper performs a hourly simulation of the operation of an air-source heat pump for space heating, relying on the available heat demand data of real buildings currently connected to a district heating network. In addition, the paper proposes the calculation of the hourly primary energy factor of the electricity supplied by the power grid, as the variability of the generation sources plays a key role in the global analysis of the energy system’s conversion efficiency. The results show that in all the considered cases the heat pumps provide potential primary energy savings compared to natural gas boilers, thanks to the combined effect of their high coefficient of performance and the low electricity primary energy factor in the analyzed context. The primary energy consumption reduction obtained in each case is in the range 10–40%, with a median value close to 30%. Moreover, the comparison between average and high-resolution calculations of primary energy factors shows the possible underestimation of the potential primary energy savings when yearly or monthly data are adopted.

Policy strategies for achieving large long-term savings from retrofitting existing buildings

In order to achieve long-term targets for energy savings and emission reductions, substantial savings will be needed from existing buildings. For example, a recent analysis for the USA examines aggressive strategies to cut carbon emissions in half by 2040 and finds that in order to achieve this emission reduction target, more than half of existing buildings will need comprehensive energy efficiency retrofits. Germany is targeting an overall primary energy consumption reduction of 50% in 2050 including increasing building renovation rate to 2% per year. In France, ambitious targets have also been set for existing buildings: 50% reduction of primary energy consumption in 2050 compared to the 2012 level. Multiple countries have realized the importance of comprehensive building retrofits and have begun to adopt policies to spur these improvements. For example, Germany is emphasizing grants and loans through the KfW Development Bank, complemented with building and heating system labels, a new “heating check” programme, and possible technical renovation requirements. France has established a goal of bringing all buildings up to “A” performance level (on their A–G scale) by 2050 in order for them to be sold or leased, with lower performance levels required as soon as 2020. In the USA, the focus has been on a combination of rating and disclosure of energy use, financing, and technical assistance. Focused community approaches show promise. This paper summarizes the efforts, successes and challenges, future directions, and savings of building retrofit policies in the three countries. We conclude by contrasting the three countries and discussing areas of opportunity for these and other countries.

Dynamic simulation of a microcogeneration system in a Spanish cold climate

Microcogeneration systems guarantee the reduction of primary energy consumption and greenhouse gas emissions in residential sector, by reducing fossil fuels demand and grid losses with respect to conventional energy conversion systems. Energy, environmental and economic benefits can be obtained sharing the cogenerated thermal and electric energy among different end-users to increase the operating hours of the microcogeneration plant with respect to the scenario in which energy demand of each end-user is satisfied by a single cogeneration system. This paper analyses a microcogeneration system used to satisfy electric, space heating and domestic hot water demands of two separate residential buildings located in Spain in a load sharing approach. It consists of a natural gas fuelled internal combustion engine with a thermal and electric power of 12.5 kW and 5.5 kW, respectively. An auxiliary boiler with a nominal thermal power of 24 kW, is also included. The domestic hot water and the heating requirements are managed by means of two different thermal energy storages. The proposed energy conversion systems were experimentally analysed in a test facility in Vitoria Gastéiz (Spain). The models representing the components and the buildings have been implemented in TRNSYS 17. The energy, environmental and economic performance of proposed system are compared with those achieved by a traditional system based on separated energy production. The results highlight that the load sharing between users with different load profiles leads to better environmental and thermo-economic results with respect to the conventional system. The microcogeneration plant works for about 3000 hours per year achieving a primary energy saving of 12.1% and a reduction of equivalent CO2 emissions equal to 27.8%. The payback period of the analysed solution is equal to 11.9 years unless economic support mechanisms are considered. The results of this study show that the introduction of a microcogeneration system in load sharing approach leads to energy, environmental and economic benefits even considering two separate residential buildings, occupied by users with different behaviour.

Energy and cost analysis of an Air Cycle used as prime mover of a Thermal Electricity Storage

The increment of greenhouse gas emissions from human activities have forced the world authorities to ratify stringent environmental protection measurements devoted to the reduction of primary energy consumption and to the spread of Renewable Energy Sources (RES). To reach the fixed targets, governments have established subsidies especially to support the electricity generation from RES like wind and solar. However, the large penetration of variable and intermittent RES is stressing the need of large-scale energy storage able to stabilize the electric grids. But, available large-scale energy storage technologies like Pumped Hydro, Compressed Air Energy Storage or Flow Batteries, suffer of geographical constrains, require fossil fuel streams or are characterized by low cycle life. For this reason, in the present paper, a new Thermal Electricity Storage configuration based on the Air Bottoming Cycle (ABC) concept is proposed and tested. The off-peak power is firstly converted into thermal energy using an electric heater and, then, stored in a high temperature sensible heat storage. When the power demand is high, using a modified ABC the thermal energy is converted back into electricity. Using the plant mathematical model, an energy and a cost analyses are carried out to estimate the performance and the system feasibility.

Indirect Evaporative cooling systems: modelling and performance analysis

Nowadays, there are a lot of ongoing research activities about cooling technologies which can lead to a significant reduction in primary energy consumption of air handling units, in both residential and commercial applications. In this context, one of the most interesting technologies is the indirect evaporative cooling (IEC) system. In this work a phenomenological model of the component, based on a cross flow heat exchanger, has been developed and validated in typical summer operating conditions, at different air streams temperature, humidity ratio and flow rates. Using this tool, performance of the IEC system has been analyzed in different working conditions. Results highlight the advantage of using the IEC unit, which leads to significant energy savings in almost all the investigated conditions.

Energy, environmental and economic assessment of electricity savings from the operation of green roofs in urban office buildings of a warm Mediterranean region

Green roofs are an important technique to efficiently mitigate adverse environmental impacts of buildings. This study focuses both on energy conservation and sustainability related aspects of two alternative green roof solutions applied to a typical urban office building in representative climatic areas of Cyprus in the Eastern Mediterranean. Simulations regarding the buildings’ energy demand were conducted using EnergyPlus software. Based on these results and using an in-house developed algorithm, the primary energy consumption for each alternative solution was computed, assuming variable refrigerant flow air-to-brine heat pump as heating and cooling system, coupled with a calculation of the associated emissions of carbon dioxide, nitrogen oxides and sulphur dioxide. The analysis shows a reduction in primary energy consumption up to 25% in heating and up to 20% in cooling operation, thanks to the use of green roofs, and a corresponding reduction in emissions. The economic viability of the proposed green roof solutions was also examined, taking into consideration both monetary and environmental costs. The results show that the green roof solutions increase the lifetime cost up to 40,000 €, however they can lead to additional environmental and economic benefits which are hard to quantify.

Thermo-fluid dynamic model of large district heating networks for the analysis of primary energy savings

Among the various heating technologies that can be applied to urban areas district heating is recognized to allow significant reduction in primary energy consumption, provided that the system is properly designed and operated. Thermo-fluid dynamic simulation tools can be of extreme importance in order to achieve this objective. This paper aims at presenting a thermo fluid dynamic model for the detailed simulation of large district heating network and showing how it can be usefully applied to examine options for the reduction of primary energy consumption. The model is tested using experimental data and then applied for analyzing transient operations of the Turin district heating network, which is the largest network in Italy and one of the largest in Europe. A comparison between simulations and experimental results shows that the model is able to predict the temperature in the nodes of the network with good accuracy. The thermal power required to each plant is also calculated with a good level of accuracy. The model can be used for the simulation of operational strategies, thus representing a versatile and important tool for the implementation of advanced management such as the installation of local storage units or the variation of user request schedules.

Decision-making strategy for cogeneration power systems integration in the Lebanese electricity grid

Cogeneration and trigeneration systems can contribute to the reduction of primary energy consumption and greenhouse gas emissions in residential and tertiary sectors, by reducing fossil fuels demand and grid losses with respect to conventional systems. The cogeneration systems are characterized by a very high energy efficiency (80 to 90%) as well as a less polluting aspect compared to the conventional energy production. The integration of these systems into the energy network must simultaneously take into account their economic and environmental challenges. Moreover, the electricity distribution service can motivate the users of these systems by buying their residual electrical and thermal products. In this case, the "smart-grid" is the interface that manages the client-network interaction.In this paper, we will find the best cogeneration power that had to be integrated in the Lebanese electricity grid using a new decision-making technique.

Development of an energy management system for optimal operation of fuel cell based residential energy systems

Residential fuel cell based combined heat and power (FC-CHP) systems have been commercialized and are penetrating the marketed in Japan. In order to utilize FC-CHP systems efficiently, operational strategies are required. Energy interchange among consumers improves efficiency by allowing flexible operation of equipment. An energy management system (EMS), which is installed at the consumer dwelling, can integrate the control and management of energy equipment by using an optimized planning approach that incorporates the energy interchange and can operates equipment whilst adjusting to real conditions. An EMS has been developed, which achieves optimal operation of FC-CHP systems with energy interchange between dwellings in a residential area. Case studies were performed to evaluate the EMS model by using evaluation indices including energy costs, CO2 emissions, and primary energy consumption. The results showed that 1) energy management and energy interchange were effective and contributed to cost reductions, CO2 mitigation, and reduction of primary energy consumption and 2) the developed EMS model achieved optimal operations.

Comparative analysis on operation strategies of CCHP system with cool thermal storage for a data center

Combined Cooling, Heating, and Power (CCHP) systems with cool thermal storage can provide an appropriate energy supply for data centers. In this work, we evaluate the CCHP system performance under two different operation strategies, i.e., following thermal load (FTL) and following electric load (FEL). The evaluation is performed through a case study by using TRNSYS software. In the FEL system, the amount of cool thermal energy generated by the absorption chillers is larger than the cooling load and it can be therefore stored and reused at the off-peak times. Results indicate that systems under both operation strategies have advantages in the fields of energy saving and environmental protection. The largest percentage of reduction of primary energy consumption, CO2 emissions, and operation cost for the FEL system, are 18.5%, 37.4% and 46.5%, respectively. Besides, the system performance is closely dependent on the equipment selection. The relation between the amount of energy recovered through cool thermal storage and the primary energy consumption has also been taken into account. Moreover, the introduction of cool thermal storage can adjust the heat to power ratio on the energy supply side close to that on the consumer side and consequently promote system flexibility and energy efficiency.

Multiple energy complementation based on distributed energy systems – Case study of Chongming county, China

Chongming’s current energy system is highly import-dependent and the distributed energy system with high renewable energy penetration should be taken into consideration. In this paper, a simulation model based on EnergyPLAN software with 2014 as the reference year is developed to represent Chongming’s present energy structure. Four future scenarios which propose different further energy constructions have been observed. Results show that reductions in primary energy consumption, electricity import, annual operating costs as well as CO2 emissions are realizable when switching to an energy system with a high share of renewable sources combining natural gas CHP (Combined Heating and Power). After preliminary discussions, the feasibility of different renewable sources penetration are analyzed through calculating the excess electricity production (CEEP). The estimated optimal combination is generated when the PV fraction is 20% while wind energy fraction is 80%. Moreover, the analyses have taken into account that several flexible techniques are needed in order to balance supply and demand and to ensure the grid voltage and frequency stabilities. As a result, through the recommended three techniques, the excess production can be avoided as far as a renewable energy input of up to nearly 60%.

Effects of load following operational strategy on CCHP system with an auxiliary ground source heat pump considering carbon tax and electricity feed in tariff

Combined cooling, heating and power (CCHP) system plays a significant role in efficient usage of energy in field of small scale power system for application ranging from residence to utilities. In the paper, a new CCHP system is proposed which consists of a power generation unit (PGU), an absorption chiller, a storage tank and a ground source heat pump (GSHP) to substitute conventional electric chiller and auxiliary boiler to supply the deficient cooling or heating load. In the study, three basic load following strategies: following electric load (FEL), following thermal load (FTL) and following hybrid load (FHL) are employed to analyze the annual total cost (ATC), operational cost (COST), carbon dioxide emissions (CDE) and primary energy consumption (PEC) based on a case study of a regional energy system in Sino-Singapore eco-city. For the evaluated case, carbon tax and electricity feed in tariff are both considered to compare with the performances of following maximum electric efficiency of the PGU (Max-eff) strategy. The results show that the proposed system performed well on COST, CDE and PEC reduction and the ATC are all increased except that of Max-eff strategy with carbon tax and electricity feed in tariff. When carbon tax and electricity feed in tariff are considered, performances of the Max-eff strategy is the best. Otherwise, the application of FEL is better. Finally, for the Max-eff and FEL strategy, sensitivity analysis is performed and results are presented with varying of electricity and gas price.

Technical and economic assessment of a SOFC-based energy system for combined cooling, heating and power

Here we present the technical and economical performances of a small scale trigeneration power plant based on solid oxide fuel cells and designed for a small residential cluster (i.e. 10 apartments). The energy system features a natural gas solid oxide fuel cell, a boiler, a refrigerator, and a thermal storage system. We compare different power plant configurations varying the size of the fuel cell and the refrigeration technology to satisfy the chilling demand (i.e. absorption or mechanical chiller). Given that the ability to meet the power demand is crucial in this kind of applications, the plant performances are assessed following an optimal control strategy, as a function of different energy demand profiles and electricity prices, and of rated and part load efficiencies of each energy converter. The optimization of the energy system operating strategy is performed through a graph theory-based methodology. Results are provided in terms of electrical and thermal efficiency, operating strategy, as well as economic saving, primary energy consumption reduction, and pay back period, considering different capital costs of the fuel cell.

Multi-stage and multi-objective optimization for energy retrofitting a developed hospital reference building: A new approach to assess cost-optimality

The ‘Energy Performance of Buildings Directive’ Recast (i.e., 2010/31/EU) establishes that building energy retrofit should pursue “cost-optimal levels”. However, a reliable and rigorous cost-optimal analysis is an arduous and computationally-expensive issue, especially for complex buildings such as hospitals. The paper tackles this issue by providing a novel methodology to identify robust cost-optimal energy retrofit solutions. Multi-stage and multi-objective (Pareto) optimization is performed with the aim of minimizing the computational burden required to achieve reliable outcomes. The methodology combines EnergyPlus and MATLAB® and includes two optimization stages, preceded by a preliminary energy investigation that performs Latin hypercube sampling and sensitivity analysis. The preliminary investigation and the first optimization stage, which runs a genetic algorithm, aim at detecting efficient energy retrofit measures (ERMs) to reduce thermal energy demand for space heating and cooling. In the second optimization stage, these ERMs are combined with further ERMs, addressed to improve the efficiency of energy systems and to exploit renewable energy sources. Investment cost, primary energy consumption and global cost related to the resulting retrofit packages are investigated by means of smart exhaustive sampling. Finally, the cost-optimal solution is identified both in presence of a limitless economic availability and of limited budgets. The methodology is applied to a hospital reference building (RB), which represents hospitals built in South Italy between 1991 and 2005. The RB is defined by using an original approach, as required by the complexity of the examined building category. The achieved cost-optimal retrofit packages imply a reduction of primary energy consumption up to 67.9kWh/m2a (12.2%) and of global cost up to 2932k€ (24.5%) with a maximum investment of 1236k€.