Conversion of individual natural gas to district heating: Geographical studies of supply costs and consequences for the Danish energy system

Replacing individual natural gas heating with district heating based to increasing shares of renewable energy sources may further reduce CO₂-emissions in the Danish Building mass, while increasing flexibility of the energy system to accommodate significantly larger amounts of variable renewable energy production. The present paper describes a geographical study of the potential to expand district heating into areas supplied with natural gas. The study uses a highly detailed spatial database of the built environment, its current and potential future energy demand, its supply technologies and its location relative to energy infrastructure. First, using a spatially explicit economic model, the study calculates the potentials and costs of connection to expanded district heating networks by supply technology. Then a comprehensive energy systems analysis is carried out to model how the new district heat can be supplied from an energy system with higher shares of renewable energy. It can be concluded on the basis of these analyses that the methods used proved highly useful to address issues of geographically dependent energy supply; however the spatio-economic model still is rather crude. The analyses suggest to expand district heating from present 46% to somewhere in between 50% and 70%. The most attractive potential is located around towns and cities. The study also suggests that CO₂-emissions, fuel consumption and socio-economic costs can be reduced by expanding district heating, while at the same time investing in energy savings in the building mass as well as increased district heating network efficiency.     

Energy and economic analysis of an integrated solar absorption cooling and heating system in different building types and climates

The use of solar energy in buildings is an important contribution for the reduction of fossil fuel consumption and harmful emissions to the environment. Solar thermal cooling systems are still in their infancy regarding practical applications, although the technology is sufficiently developed for a number of years. In many cases, their application has been conditioned by the lack of integration between cooling and heating systems. This study aims to evaluate the potential of integrated solar absorption cooling and heating systems for building applications. The TRNSYS software tool was used as a basis for assessment. Different building types were considered: residential, office and hotel. The TRNSYS models are able to run for a whole year (365 days), according to control rules (self-deciding whether to operate in heating or cooling modes), and with the possibility of combining cooling, heating and DHW applications. Three different locations and climates were considered: Berlin (Germany), Lisbon (Portugal), and Rome (Italy). Both energy and economic results are presented for all cases. The different local costs for energy (gas, electricity and water) were taken into account. Savings in CO₂ emissions were also assessed. An optimization of solar collector size and other system parameters was also analysed.     

Opportunities for integration of biofuel gasifiers in natural-gas combined heat-and-power plants in district-heating systems

As political pressure to improve efficiency and reduce CO₂-emissions increases, natural gas combined cycle (NGCC) combined heat-and-power (CHP) technology is an increasingly attractive option for district-heating systems. However, as CO₂-emissions reduction targets become more ambitious, it is expected that there will be pressure to reduce CO₂-emissions from such units well before they reach the end of their useful lifetime. One way to achieve this goal is to integrate a biofuel gasification unit at the plant site. After clean-up, the produced syngas can be co-fired in the CHP unit. This paper discusses the economic performance of this type of retrofit, with specific emphasis on the impact of the following parameters: (i) the original NGCC CHP plant’s power-to-heat ratio; (ii) the size of the district-heating system’s annual heat-energy demand; (iii) the fuel mix in the district-heating system; and (iv) the availability of low-cost waste-heat that can be delivered to the district-heating system. The economic performance of the retrofitted CHP unit is measured as the overall cost of electricity production (COE). COE is analysed for four different energy-market parameter sets (referred to as Scenarios), including fuel prices, costs associated with energy and climate change policy instruments, and market electricity prices. The results indicate that even relatively high costs associated with CO₂ emissions are insufficient to motivate retrofitting an NGCC CHP unit with an integrated biofuel-gasification unit. To promote this type of retrofit, an additional premium value for electricity generated from renewable fuel sources is required (such as the Swedish REC renewable energy certificate system). An unexpected result of this study is that the required value of REC is essentially independent of the energy market scenario considered.     

Estimation of the potential for reduced greenhouse gas emission in North-East Russia: A comparison of energy use in mining,mineral processing and residential heating in Kiruna and Kirovsk-Apatity

The energy demand at Murmansk Oblast in North-East Russia is covered at 60% by fossil fuels and at 40% by electricity. This study estimates the potential for reduction of fossil fuel consumption and CO₂-emissions at Murmansk Oblast. The study focus on the municipalities of Apatity and Kirovsk and the apatite ore mining company Apatit JSC . The potential for energy efficiency, reduced fossil fuel consumption and greenhouse gas emissions is estimated by comparison with the of city Kiruna in Northern Sweden, with a climate similar to that of North-East Russia, and with the iron ore mining company LKAB. This study shows that the potential for reduced CO₂-emissions is about 630,700 tons CO₂ annually in the municipalities of Apatity and Kirovsk or 6.3 tons of CO₂ per capita, Apatit JSC not included. These results applied on Murmansk Oblast gives a potential for reduced CO₂-emissions of about 6 Mtons annually in the municipalities together. The specific energy consumption at Apatit JSC is 6–7 times per ton product compared to LKAB. The mining has 4 times higher specific energy consumption per ton raw ore compared to LKAB.     

Energy simulation modeling and savings analysis of load sharing between house and office

This paper presents the potential benefits of the thermal load sharing between the two different building types such as residential house and commercial office building through the process of energy simulation modeling. Both the house and office simulation models have the same geometries with the conditioned spaces of 200 m² each for the weather conditions of Seoul, South Korea. This study shows and analyzes the thermal energy demand and consumption results simulated from the four different scenarios using the EnergyPlus V6.0 thermal simulation program; i.e., Case-1) a house with conventional heating and cooling systems, Case-2) an office with conventional heating and cooling systems, and Case-3) a simple sum of the two cases (i.g., Case-2 + Case-3), and Case-4) a load sharing model that provides heating and cooling to both the house and the office using combined HVAC systems. This paper evaluates the thermal energy consumption patterns and potential benefits of the load sharing system compared to the conventional systems. The optimal system configurations of the load sharing systems are proposed. In conclusion, this paper discusses the potential issues and challenges for implementing the load sharing systems as well as the possible solutions for these issues.     

Life cycle assessment of an onshore wind farm located at the northeastern coast of Brazil

This article assesses the life cycle emissions of a fictive onshore wind power station consisting of 141.5-MW wind turbines situated on the northeastern coast of Brazil. The objective is to identify the main sources of CO_2(eq)-emissions during the life cycle of the wind farm. The novelty of this work lies in the focus on Brazil and its emerging national manufacturing industry. With an electricity matrix that is primarily based on renewable energy sources (87% in 2010), this country emits eight times less CO₂ for the production of 1 kWh of electricity than the global average. Although this fact jeopardizes the CO₂ mitigation potential of wind power projects, it also reduces the carbon footprint of parts and components manufactured in Brazil. The analysis showed that reduced CO₂-emissions in the material production stage and the low emissions of the component production stage led to a favorable CO₂-intensity of 7.1 g CO₂/kWh. The bulk of the emissions, a share of over 90%, were unambiguously caused by the production stage, and the transportation stage was responsible for another 6% of the CO₂-emissions. The small contributions from the construction and operation phases could be neglected. Within the manufacturing process, the steel tower was identified as the source responsible for more than half of the emissions. The environmental impacts of the wind farm are small in terms of CO₂-emissions, which can be credited to a green electricity mix. This scenario presents an advantage for the country and for further production sites, particularly in the surroundings of the preferred wind farm sites in Brazil, which should be favored to reduce CO₂ emissions to an even greater extent.     

Energy efficiency measures and conversion of fossil fuel boiler systems in a detached house

There is a large potential to reduce primary energy use and CO₂ emissions from the Swedish building stock. Here detached houses heated by oil, natural gas or electric boilers were assessed. CO₂ emissions, primary energy use and heating costs were evaluated before and after implementing house envelope measures, conversions to more efficient heating systems and changes to biomass fuel use. The study included full energy chains, from natural resources to usable heat in the houses. The aim was to evaluate the societal economic cost effectiveness of reducing CO₂ emission and primary energy use by different combinations of changes. The results demonstrated that for a house using an electric boiler, a conversion to a heat pump combined with house envelope measures could be cost efficient from a societal economic perspective. If the electricity was based on biomass, the primary energy use was at the same time reduced by 70% and the CO₂ emission by 97%. Large emission reductions were also seen for conversions from oil and gas boilers to a biomass-based system. However, for these conversions the heating cost increased, leading to a mitigation cost of around €50/tonne C avoided. The price of oil and natural gas greatly influenced the competitiveness of the alternatives. House envelope measures were more cost-effective for houses with electric boilers as the cost of energy for this system is high. The results are specific to a Swedish context, but also give an indication of the potential in other regions, such as northern European and large parts of North America, which have both a cold climate and a widespread use of domestic boilers.     

Spanish energy roadmap to 2020: Socioeconomic implications of renewable targets

The European Union has established challenging targets for the share of renewable energies to be achieved by 2020; for Spain, 20% of the final energy consumption must be from renewable sources at such time. The aim of this paper is the analysis of the consequences for the electricity sector (in terms of excess cost of electricity, investment requirements, land occupation, CO₂ emissions and overcapacity of conventional power) of several possibilities to comply with the desired targets. Scenarios are created from different hypotheses for energy demand, biofuel share in final energy in transport, contribution of renewables for heating and cooling, renewable electricity generation (generation mix, deployment rate, learning curves, land availability) and conventional power generation (lifetime of current installations, committed deployment, fossil fuel costs and CO₂ emissions cost). A key input in the estimations presented is the technical potential and the cost of electricity from renewable sources, which have been estimated in previous, detailed studies by the present authors using a methodology based on a GIS (Geographical Information System) and high resolution meteorological data. Depending on the scenario, the attainment of the targets will lead to an increase in the cost of electricity from 19% to 37% with respect to 2007.     

Conventional and advanced CO2 based district energy systems

District energy systems can potentially decrease the CO₂ emissions linked to energy services, thanks to the implementation of large polygeneration energy conversion technologies connected to buildings over a network. To transfer the energy from these large technologies to the users, conventional district energy systems use water with often two independent supply and return piping systems for heat and cold. However, sharing energy or interacting with decentralised heat pump units often results in relatively large heat transfer exergy losses due to the large temperature differences that are economically required from the water network. Besides, the implementation of two independent supply and return piping systems for heat and cold, results in large space requirements in underground technical galleries. Using refrigerants as a district heating or cooling fluid at an intermediate temperature could alleviate some of these drawbacks. A new system has been developed, that requires only two pipes, filled with refrigerant, to meet heating, hot water and cooling requirements. Because of the environmental concerns about conventional refrigerants, CO₂, a natural refrigerant, used under its critical point, is considered an interesting candidate. A comparative analysis shows that both in terms of exergy efficiency and costs the proposed CO₂ network is favourable.     

District heating and energy efficiency in detached houses of differing size and construction

House envelope measures and conversion of heating systems can reduce primary energy use and CO₂ emission in the existing Swedish building stock. We analysed how the size and construction of electrically heated detached houses affect the potential for such measures and the potential for cogenerated district heating. Our starting point was two typical houses built in the 1970s. We altered the floor plans to obtain 6 houses, with heated floor space ranging between 100 and 306 m². One of the houses was also analysed for three energy standards with differing heat loss rates. CO₂ emission, primary energy use and heating cost were estimated after implementing house envelope measures, conversions to other heating systems and changes in the generation of district heat and electricity. The study accounted for primary energy, including energy chains from natural resources to useful heat in the houses. We showed that conversion to district heating based on biomass, together with house envelope measures, reduced the primary energy use by 88% and the CO₂ emission by 96%, while reducing the annual societal cost by 7%. The choice of end-use heating system was decisive for the primary energy use, with district heating being the most efficient. Neither house size nor energy standard did significantly change the ranking of the heating systems, either from a primary energy or an economic viewpoint, but did affect the extent of the annual cost reduction after implementing the measures.     

Operational optimisation of a complex trigeneration system connected to a district heating and cooling network

The combined production of electricity, heat and cold by polygeneration systems ensures maximum utilization of resources by reducing emissions and energy losses during distribution. Polygeneration systems are highly integrated systems characterized by the simultaneously production of different services (electricity, heating, cooling) by means of several technologies using fossil and renewable fuels that operates together to obtain a higher efficiency than that of an equivalent conventional system. The high number of distribution technologies available to produce electricity, heating and cooling and the different levels of integration make it difficult to select of the optimal configuration. Moreover, the high variability in the energy demand renders difficult the selection of the optimal operational strategy. Optimization methodologies are usually applied for the selection of the optimal configuration and operation of energy supply systems. This paper presents a scenario analysis using optimization models to perform an economic, energetic and environmental assessment of a new polygeneration system in Cerdanyola del Vallès (Spain) in the framework of the Polycity project of the European Concerto Program. This polygeneration system comprise high-efficiency natural gas cogeneration engines with thermal cooling facilities and it will provide electricity, heating and cooling for a new area in growth known as Alba park including a Synchrotron Light Facility and a Science and Technological park through a district heating and cooling network of four tubes. The results of the scenario analysis show that the polygeneration plant is an efficient way to reduce the primary energy consumption and CO₂ emissions (up to 24%).     

The potential contribution of geothermal energy to electricity supply in Saudi Arabia

With increase in demand for electricity at 7.5% per year, the major concern of Saudi Arabia is the amount of CO₂ being emitted. The country has the potential of generating 200×10⁶ kWh from hydrothermal sources and 120×10⁶ terawatt hour from Enhanced Geothermal System (EGS) sources. In addition to electricity generation and desalination, the country has substantial source for direct application such as space cooling and heating, a sector that consumes 80% of the electricity generated from fossil fuels. Geothermal energy can offset easily 17 million kWh of electricity that is being used for desalination. At least a part of 181,000 Gg of CO₂ emitted by conventional space cooling units can also be mitigated through ground-source heat pump technology immediately. Future development of EGS sources together with the wet geothermal systems will make the country stronger in terms of oil reserves saved and increase in exports.     

District heating and cooling for business buildings in Madrid

Energy needs for heating and cooling in Spain are of paramount interest in the context of the European roadmap to a decarbonized environment; because of that, it is highly desirable that more examples of district heating and cooling networks are developed. The present work evaluates the implementation of one of them into the climatic environment of Madrid. It consists on a complex of business office buildings with a total useful surface of 50,000 m², linked with heating and cooling rings of 1 km of loop length. Basic energy needs of buildings lead to the following design values: 1.7 MW of electricity, 1.3 MW of heating and 2 MW of cooling. They will be supplied by the trigeneration plant here proposed, which relies on an internal combustion engine.The high demand of cooling for air conditioning makes the dimensioning of the engine critical because of the large differences between the heat demand for summer and the one for winter. If the total amount of the cooling demand is covered with an absorption chiller, the heat demand during the summer reaches about 5 MW. In consequence, a critical decision has to be taken relative to the way the cooling demand is attended: with an absorption chiller (single or double effect) or with a conventional chiller powered by electricity. Applying the criteria developed in the present work, which are focused on maximum primary energy reduction, the fraction of the cooling demand to be met with each technology is determined as a function of the engine nominal power, on the grounds of the instantaneous demand.The high cooling demand during the summer season suggests the inclusion of a thermal solar collector field, to be used for complementing the waste heat rejection from the engine to drive the absorption chiller. During the winter, the heat provided by the solar field could be applied in attending a fraction of the heating demand. Thus a hybrid Trigeneration Plant is introduced. This way, over sizing of the engine can be avoided, as the electric demand is small.The analysis is based on the solution of energy and mass balance equations for a trigeneration plant. Monthly demands and environmental conditions (ambient temperature and solar irradiance) are introduced as input data into the model. Monthly and annual primary energy consumption and CO₂ emission reductions are obtained as outputs. Economical data, such as fuel and operating costs, electricity prices, tariffs and subsidies are considered in order to optimize the size of the plant in terms of its payback period.     

Electricity dependency and CO2 emissions from heating in the Swedish building sector—Current trends in conflict with governmental policy?

Coal-condensing power is marginal production in the deregulated Nordic power market and an increase in electricity consumption will therefore result in increased CO₂ emissions. One goal of the Swedish energy policy is to reduce the amount of electricity used for heating in the building sector. This paper investigates the potential for reduction in electricity dependency and CO₂ emissions from heating, taking the energy infrastructure into account, here defined as the capital stock of the buildings and heating systems together with geographical variations in heat intensity. In order to include the energy infrastructure in the analysis the study is made on a regional level (Southern Sweden) applying a comprehensive database describing the energy infrastructure of the region. The paper compares two scenarios for converting the heating systems of the region: one employing energy savings and with the aim to phase out the oil and most of the electricity used for heating purposes and a second which illustrates the effect if the current trend in the heating market continues. Both scenarios apply commercially available technologies only.From the second scenario it is seen that the current trend—contrary to the aim of the Swedish Governmental policy—shows an increase in electricity dependency for heating, mainly due to a large diffusion of heat pumps, but also due to installations of electrical floor heating and electricity heating systems installed in newly constructed one- and two-dwelling buildings. However, the options proposed in first scenario show that it is possible to reach significant reductions in the electricity dependency due to heating and in corresponding CO₂ emissions. An analysis of the age structure of the heating systems shows that the transformation of the heating system is not completed until the year 2025, if new investments for replacement of heating systems are made only provided they have reached their economical life time, and only applying heating technologies which at present are known to be economically competitive. It can be concluded that future policies on transforming the energy system should be based on an analysis that takes the entire energy infrastructure (in this case of heating system) into account (e.g. not directed towards single technologies). More specifically for the region studied, which is considered representative for Sweden as a whole, policies should aim at installing heat pumps to replace electricity heating only in regions with low heat density where district heating is not competitive, in contrary to the present situation where heat pumps replace all types of heating systems.     

CO2 payback–time assessment of a regional-scale heating and cooling system using a ground source heat–pump in a high energy–consumption area in Tokyo

We present an assessment of installing a regional heating and cooling system in the Nishi(West)-Shinjuku area of Tokyo, Japan. In this assessment, we estimate the CO₂ payback–time, when air source heat–pumps (ASHP) are replaced with a ground–source heat–pump (GSHP) system. We calculate CO₂ emissions from transportation of the cooling tower, materials for the underground heat exchanger, and the digging loads and transportation loads incurred when the GSHP system is installed to replace the air source cooling system. The total CO₂ emission from the installation of the GSHP system was estimated to be 67,701t-CO₂, with 87% of the CO₂ emissions resulting from the digging process. CO₂ emissions from the operation of the GSHP system were estimated from the total energy-efficiency of the system and the heating and cooling demand in Nishi-Shinjuku area. Using the GSHP system, 33,935t-CO₂ would be emitted per year. We estimate that using the GSHP system would result in a reduction of 54% of the CO₂ emissions, or 39,519t-CO₂ per year. From these results, the CO₂ payback–time for replacing the conventional ASHP in the 1 km² studied region with the GSHP system is assessed to be 1.7 years.     

Computerized design and economic evaluation of an aqua-ammonia solar operated absorption system

A computerized simulation and design of solar operated NH₃---H₂O absorption refrigeration cycles is presented. The program receives input data and calculates the building, cooling and heating loads initially. Next the absorption cycle is designed along with the solar collectors and auxiliaries. Various economic parameters are also calculated from which the most favorable system may be selected. Two examples were run: one for the Knesset building in Jerusalem (Israeli parliament) and the other for an American office building. Results indicate the existence of various mininal operating parameters, e.g. collectors' outlet temperature, etc. For the Knesset building some 46 per cent of the annual heating and cooling demand may be provided by the solar system. At the 1979 rate of energy cost increase in Israel the system payback period was estimated at 9 yr with a present value total saving of $42.5 m. Yet higher values were obtained for the American office building at about 81 per cent solar fraction for the compound cooling and heating system.     

Potential benefits of cool roofs on commercial buildings: conserving energy, saving money, and reducing emission of greenhouse gases and air pollutants

Cool roofs—roofs that stay cool in the sun by minimizing solar absorption and maximizing thermal emission—lessen the flow of heat from the roof into the building, reducing the need for space cooling energy in conditioned buildings. Cool roofs may also increase the need for heating energy in cold climates. For a commercial building, the decrease in annual cooling load is typically much greater than the increase in annual heating load. This study combines building energy simulations, local energy prices, local electricity emission factors, and local estimates of building density to characterize local, state average, and national average cooling energy savings, heating energy penalties, energy cost savings, and emission reductions per unit conditioned roof area. The annual heating and cooling energy uses of four commercial building prototypes—new office (1980+), old office (pre-1980), new retail (1980+), and old retail (pre-1980)—were simulated in 236 US cities. Substituting a weathered cool white roof (solar reflectance 0.55) for a weathered conventional gray roof (solar reflectance 0.20) yielded annually a cooling energy saving per unit conditioned roof area ranging from 3.30 kWh/m² in Alaska to 7.69 kWh/m² in Arizona (5.02 kWh/m² nationwide); a heating energy penalty ranging from 0.003 therm/m² in Hawaii to 0.14 therm/m² in Wyoming (0.065 therm/m² nationwide); and an energy cost saving ranging from 0.126/m < sup > 2 < /sup > in West Virginia to0.126/m² in West Virginia to 1.14/m² in Arizona ($0.356/m² nationwide). It also offered annually a CO₂ reduction ranging from 1.07 kg/m² in Alaska to 4.97 kg/m² in Hawaii (3.02 kg/m² nationwide); an NO_x reduction ranging from 1.70 g/m² in New York to 11.7 g/m² in Hawaii (4.81 g/m² nationwide); an SO₂ reduction ranging from 1.79 g/m² in California to 26.1 g/m² in Alabama (12.4 g/m² nationwide); and an Hg reduction ranging from 1.08 μg/m² in Alaska to 105 μg/m² in Alabama (61.2 μg/m² nationwide). Retrofitting 80% of the 2.58 billion square meters of commercial building conditioned roof area in the USA would yield an annual cooling energy saving of 10.4 TWh; an annual heating energy penalty of 133 million therms; and an annual energy cost saving of $0.356/m² nationwide). It also offered annually a CO₂ reduction ranging from 1.07 kg/m² in Alaska to 4.97 kg/m² in Hawaii (3.02 kg/m² nationwide); an NO_x reduction ranging from 1.70 g/m² in New York to 11.7 g/m² in Hawaii (4.81 g/m² nationwide); an SO₂ reduction ranging from 1.79 g/m² in California to 26.1 g/m² in Alabama (12.4 g/m² nationwide); and an Hg reduction ranging from 1.08 μg/m² in Alaska to 105 μg/m² in Alabama (61.2 μg/m² nationwide). Retrofitting 80% of the 2.58 billion square meters of commercial building conditioned roof area in the USA would yield an annual cooling energy saving of 10.4 TWh; an annual heating energy penalty of 133 million therms; and an annual energy cost saving of 735 million. It would also offer an annual CO₂ reduction of 6.23 Mt, offsetting the annual CO₂ emissions of 1.20 million typical cars or 25.4 typical peak power plants; an annual NO_x reduction of 9.93 kt, offsetting the annual NO_x emissions of 0.57 million cars or 65.7 peak power plants; an annual SO₂ reduction of 25.6 kt, offsetting the annual SO₂ emissions of 815 peak power plants; and an annual Hg reduction of 126 kg.     

Energy conservation measures in buildings heated by district heating – A local energy system perspective

The extensive energy use in the European building sector creates opportunities for implementing energy conservation measures (ECMs) in residential buildings. If ECM are implemented in buildings that are connected to a district heating (DH) system, the operation of DH plants may be affected, which in turn may change both revenue and electricity production in cogeneration plants. In this study a local energy system, containing a DH supplier and its customer, has been analysed when implementing three ECMs: heat load control, attic insulation and electricity savings. This study is unique since it analyses economic and CO₂ impacts of the ECMs in both a user and a supplier perspective in combination with a deregulated European electricity market. Results show that for the local energy system electricity savings should be prioritised over a reduction in DH use, both from an economic and a global CO₂ perspective. For the DH supplier attic insulation demonstrates unprofitable results, even though this measure affects the expensive peak load boilers most. Heat load control is however financially beneficial for both the DH supplier and the residences. Furthermore, the relation between the fixed and variable DH costs is highlighted as a key factor for the profitability of the ECMs.     

On the potential trade-offs between energy supply and end-use technologies for residential heating

In Sweden, where district heating accounts for a significant share of residential heating, it has been argued that improvements in end-use energy efficiency may be counter-productive since such measures reduce the potential of energy efficient combined heat and power production. In this paper we model how the potential trade-offs between energy supply and end-use technologies depend on climate policy and energy prices. The model optimizes a combination of energy efficiency measures, technologies and fuels for heat supply and district heating extensions over a 50 year period. We ask under what circumstances improved end-use efficiency may be cost-effective in buildings connected to district heating? The answer hinges on the available technologies for electricity production. In a scenario with no alternatives to basic condensing electricity production, high CO₂ prices result in very high electricity prices, high profitability of combined heat and power production, and little incentive to reduce heat demand in buildings with district heating. In contrast, in a scenario where electricity production alternatives with low CO₂ emissions are available, the electricity price will level out at high CO₂ prices. This gives heat prices that increase with the CO₂ price and make end-use efficiency cost-effective also in buildings with district heating.     

Performance comparison of combined cooling heating and power system in different operation modes

Operation mode of combined cooling heating and power (CCHP) system determines its energetic and environmental performances. This paper analyzes the energy flows of CCHP system and separated production (SP) system. The fuel energy consumptions of CCHP system following electrical demand management (EDM) and thermal demand management (TDM) are deduced respectively. Three indicators: primary energy saving, exergy efficiency and CO₂ emission reduction, are employed to evaluate the performances of CCHP system for a commercial building in Beijing, China. The feasibility analysis shows that the performance of CCHP system is strictly dependent upon building energy demands. The selection of CCHP operation modes is systemically based on building loads, CCHP system and local SP system. The calculation results conclude that CCHP system in winter under EDM achieves more benefits than in summer. The sensitivity discussion indicates that the coefficient of performance for cooling and the efficiency of electricity generation are the most sensitive variables to the energetic and environmental performances of CCHP system.