Economic and environmental evaluation of micro CHP systems with different operating modes for residential buildings in Japan[edit | edit source]
In this paper, two typical micro CHP alternatives, namely, gas engine and fuel cell for residential buildings, are analyzed. For each facility, two different operating modes including minimum-cost operation and minimum-emission operation are taken into consideration by employing a plan and evaluation model for residential micro CHP systems.
Introduction[edit | edit source]
Besides the grid-connected photovoltaic (PV) system, another timely example of the distributed residential energy supply technology is small-scale combined heat and power (micro CHP) generation, with a maximum electrical output capacity between roughly 1 kW and 10 kW. However, in order to achieve a widespread implementation of micro CHP systems, an interdisciplinary effort including technology, finance and policy etc., is necessary. It is believed that micro CHP offers significant benefits to energy suppliers, to households and to the society as a whole.In this paper, for an optimal efficiency of residential facilities, a study of various alternative micro CHP systems, including gas engine and fuel cell, is undertaken. In order to understand the tradeoff between economical and environmental potentials of the micro CHP systems, two different operating strategies are studied: to minimize annual energy cost and to minimize annual CO2 emissions.
Modelling of Residential CHP unit[edit | edit source]
The system consists of a CHP plant, a storage tank and a back-up burner. The CHP plant which is driven by city gas is used to meet part of the electrical demand (including cooling load with the use of air conditioning), the deficiency is served by the utility grid. As to the thermal load, the recovered heat from micro CHP plant is used for heating and hot water requirements. If the heating does not completely satisfy the application needs, a supplementary burner can be used. The role of storage tank is to store thermal energy during periods of low-thermal energy demand and to supply thermal energy during high demand.
Description of plan and evaluation model[edit | edit source]
1.In order to introduce and operate residential micro CHP system in an effective way, it is necessary to take into full consideration of local conditions, energy requirements, as well as technical and financial information. Based on the investigated electricity and thermal loads, energy (both electricity and city gas) prices, as well as micro CHP performance characteristics, a pre developed plan and evaluation model is employed. 2.Lingo software package has been used for the analysis in this paper.
Economic assessment index[edit | edit source]
1.The economic assessment provides information on how the economic resources (investments, fuels, etc.) are used to meet the customer requirements. 2.Micro CHP system has usually higher initial investment and lower running cost compared with the conventional energy supply system, which serves the electricity load by utility grid and thermal load by gas boiler. 3.Cost saving ratio, important index for the CHP economic assessment. It is given as rate of total energy cost difference between the micro CHP system and the conventional system to the annual energy cost of the conventional system.
Studied Case[edit | edit source]
Energy Demand[edit | edit source]
1.The energy demand in the residence can be divided into electrical demand and thermal demand, which consists of space heating, hot water and cooling load. It should be noted that the cooling load for air conditioning is also an electrical demand. 2.Generally, the above energy consumptions can be obtained through direct no-site measurement or simulation with some building energy simulation software, for example, EnergyPlus, Flexsim, DOE-2, and so on. 3.various hourly load demands of 8760 h, hourly peak load and annual total load for the assumed residential building can be assessed.
Utility Demand[edit | edit source]
1.Utility electricity and gas tariffs are key factors determining the economic benefits of the micro CHP installation.
Micro-CHP alternative[edit | edit source]
1.Commercially available micro CHP technologies include internal combustion engine, Stirling engine, micro-turbine and fuel cell. 2.Micro-gas Engine in MIcro-CHP is the most promising technology which has been introduced in the market and is manufactured by Honda etc. 3.Characteristics of the CHP unit includes capital cost of the unit, Electrical as well as thermal efficinecy and life time. 4. CHP unit with fuell cell Manufacturers (Panasonic, Ebara Ballard, Sanyo and Toshiba) supplying these units are striving to increase the lifetime and reliability and reduce the initial costs.
Simulation Results[edit | edit source]
Micro-CHP with gas engine[edit | edit source]
1. Hourly Electrical and Thermal demand is noted. 2.Compared with the results of gas engine plant, it can be deduced that the fuel cell system supplies more electricity but less thermal energy.
Economic assessment[edit | edit source]
1.In this section, the economic aspects of each scenario illustrated above have been evaluated and the results have been compared with a conventional system 2.It can be found that the introduction of both two micro CHP alternatives with different operation modes leads to considerable cost reductions. 3.The fuel cell system with minimum-cost operation has the least annual energy cost, which is about 26% less than the conventional energy system. 4.Furthermore, Fuel cell CHP system has a relatively higher economic efficiency than the gas engine system, although with a larger investment cost.
Technical and economic feasibility study of using Micro CHP in the different climate zones of Iran[edit | edit source]
In this paper, technical and economic studies for the use of Micro CHP in the different climate zones of Iran are executed. These zones are categorized in to five; Tehran, Rasht, Bandar Abbas, Ardebil and Yazd, based on weather conditions. Later on using an economic model, both annual energy savings and percentage of system profitability in each zone are calculated as well as reduction in annual emissions. It should be mentioned that, for economic calculations, gas and electricity price are determined using a sensitivity analysis. This analysis indicated that profitability of Micro CHP systems are sensitive to energy prices, as well as hours needed for heating room in each climate zones.
Introduction[edit | edit source]
Notes:- 1)Detailed knowledge of energy end use loads is important for selecting an appropriate residential CHP system depending on electrical as well as thermal energy demand. 2)Should have knowledge about the climatic conditions of the area where CHP unit is to be installed.
Model Description[edit | edit source]
1)The system is designed in such a manner that thermal and electrical energy generated by the CHP should satisfy the demand of the families. If excess thermal energy is generated it is stored so that it can be used for future. If excess electric energy is generated it is fed into the grid back.
Equation description[edit | edit source]
1)In order to introduce and operate residential Micro CHP system in an effective way, it is necessary to take into full consideration of local conditions, energy requirements, as well as technical and financial information. 2)The economic model is used to calculate annual energy saving and annual CO2 emissions in different zones. 3)Where the average thermal power output of Micro CHP system, is the ratio of annual heat load for space heating and hot water divided by the hours needed for heating and hot water. 4)Total annual hours to supply household’s heating and also hot water demands are determined in each zone, separately. 5)The total amount of electricity generated during the year by CHP system is calculated with electrical rated capacity of CHP plant multiplied by the annual operation hours. 6)Thermal capacity of Micro CHP system is related to electrical capacity, by the electrical and thermal efficiencies of CHP plant. 7)Cost saving ratio is calculated depending on annual energy cost on coventional system and micro-CHP system. 8)Then annual running cost the CHP unit is calculated which depends on fuel as well as maintenance cost. 9)The total cost of electricity purchase has been calculated depending on the demand of electricity by the house as well as the electricity rate purchased from the retailer. 10)If the electrical energy so generated by the CHp system is greater then the required demand then the excess energy is fed into the grid. This also considered while calculating the cost of saving( included in annual energy cost by CHP ) 11)On the other hand if the demand is more then what is being generated by the CHP unit. This is also included in calculations of annual energy cost by CHP. 12)Finally, the payback period can be determined by using initial investment for the CHP unit divided by the amount of cost saving by the CHP unit.
Sensitivity Analysis[edit | edit source]
1)Sensitivity analysis improves understanding the influence of key parameters on the decision to adopt Micro CHP systems. Gas and electricity price are significant factors that show economic benefits of installing Micro CHP systems in buildings. 2)The sensitivity of profitability index to changes in natural gas prices has been analyzed and was reported as the gas price reduces the profitability index increases.Thus, reducing natural gas price is an effective way to stimulate the adoption of Micro CHP system because of the reduced running cost. 3)Another factor that influence the profitability index is electricity price, which also has an important effect on the adoption of residential Micro CHP systems. The intuitive result that Micro CHP economic feasibility is quite sensitive to electricity prices. The sensitivity of profitability index to electricity price in lower prices is much more than higher prices; the analysis shows that if the electricity price there is increase in profitability for CHP system. 4)From the sensitivity analysis for simultaneous changes in electricity price and the gas price it can be observed that, given a fixed capital cost, the profitability index would begin to rise when gas price is reduced and electricity price is increased. It is not surprising that increases in electricity price and decreases in gas price result in corresponding increase in profitability index and decrease in payback period. Furthermore, it can be found that greater profitability result in larger Micro CHP systems installation. 5)Other factors that effect on the profitability index and payback period are building’s area and annual hours needed for space heating.Profitability index and payback period varies with change in the thermal load demand, thus even change in area also changes the profitability index.
Micro-CHP systems for residential applications[edit | edit source]
In this paper, a thorough analysis is made of the operational parameters of 3 types of micro-CHP systems for residential use. For each building type, the energy demands for electricity and heat are dynamically determined. Using these load profiles, several CHP systems are designed for each building type. All CHP systems, if well sized, result in a reduction of primary energy use, though different technologies have very different impacts.
Introduction[edit | edit source]
A large amount of energy in the world is being utilized for heating purpose. Using CHP unit will not only provide heat to the building but will also provide electricity.
Methodology[edit | edit source]
CHP technology[edit | edit source]
Notes: 1.In this paper, five micro-CHP systems (<5 kW) are evaluated for use in residential applications. 2.Most important step is to determine the load demands of the families (Electrical as well as thermal). In the present case DOE 2.5 was used for doing this analysis. The requisite data for the simulation include: building dimensions, building materials, installed equipment and lighting, usage time profiles (schedules), data concerning the heating system and the ventilation rates. 3.CHP technologies being used- a) TWo CHP units using gas engine, running on natural gas.-- b) Two CHP units using sterling engine, running on any fuel. c) CHP unit using Fuel cell, running on hydrogen gas.
Primary Energy[edit | edit source]
Notes: 1.For each configuration, the primary energy savings, CO2 emission reduction and the financial savings are calculated. 2.The cases consider for comparison- a)Electricity coming from gas/steam turbine power plant, whose efficiency is 50% b)Electricity coming from fossil fuel power plant, whose efficiency is 42% c)Electricity coming from nuclear power plant, whose efficiency is 37% 3.The CHP unit running strategy is determined by the heat requirement at the output side. The CHP tries to fulfill all demand but is the requirement is greater then the CHP produces then the excess is taken from grid. Thus, a external boiler is connected along with the CHP to provide excess required demand which cant be fulfilled by the CHP unit.
Electrical equipment and Lightning[edit | edit source]
Notes:- 1.For each room in the houses, the installed equipment and lighting power were listed. 2.The central heating system was present in all houses, temperature demands are highly dependent on the users of the building. The central heating system is controlled by an on/off thermostat with time programming. This data for individual house was noted.
Energy saving[edit | edit source]
Notes:- 1.The simulation results depending on all above taken data gives the total amount of electrical as well as thermal demand. 2.The energy consumption by the CHP each CHP technology is recognized with respect to a base case i.e. gas fired combined cycle power plant. 3.Using the data obtained from above the maximum energy saving by various CHP modules can be determined.
Economics[edit | edit source]
1.Investment and Maintenance cost for each CHP module is considered. 2. Electricity purchasing and selling price. Even gas purchase price is considered. 3.Annual Profit:- The annual profits are the sum of: • The avoided costs for purchasing electricity, equalling the purchasing price. • The money received for the electricity which is sold to the grid. These profits are decreased with • The maintenance costs. • The extra cost due to the extra amount of gas used.
