Global warming’s impact on the performance of GSHP

Since heating and cooling systems of buildings consume 30–50% of the global energy consumption, increased efficiency of such systems means a considerable reduction in energy consumption. Ground source heat pumps (GSHP) are likely to play a central role in achieving this goal due to their high energy efficient performance. The efficiency of GSHP depends on the ground temperature, heating and cooling demands, and the distribution of heating and cooling over the year. However, all of these are affected by the ongoing climatic change. Consequently, global warming has direct effects on the GSHP performance. Within the framework of current study, heating and cooling demands of a reference building were calculated for different global warming scenarios in different climates i.e. cold, mild and hot climate. The prime energy required to drive the GSHP system is compared for each scenario and two configurations of ground heat exchangers. Current study shows that the ongoing climatic change has significant impact on GSHP systems.     

Heat integrated heat pumping for biomass gasification processing

The main part of this paper is an industrial case study. It deals with an application of a heat pump in energy systems for biomass gasification in a wood processing plant. Process integration methodology is applied to deal with complex design interactions as many streams requiring heating and cooling are involved in the energy recovery. A refrigeration cycle maintains low temperature in the scrubber where the production gas (or synthesis gas–syngas) is cooled and undesirable contaminants are removed before the syngas is introduced into the engine. In addition to electricity generation, a large amount of waste heat is available in the biomass gasification system studied in the paper, and its appropriate heat integration with utility systems within a plant allows the available heat to be efficiently utilized for the site. The conceptual understanding gained from the case study provides systematic design guidelines for further process development and industrial implementation in practice.     

Integrated conceptual design of a robust and reliable waste-heat district heating system

The various governmental policies aimed at reducing the dependence on fossil fuels for space heating and the reduction in its associated emission of greenhouse gases such as CO₂ demands innovative measures. District heating systems using residual industrial waste heats could provide such an efficient method for house and space heating. In such systems, heat is produced and/or thermally upgraded in a central plant and then distributed to the final consumers through a pipeline network.This paper studies the technical, economic, institutional and environmental feasibilities of using low-level residual industrial waste heat for the district heating of Delft, The Netherlands.An integrated conceptual design approach that takes into account both the technical and institutional design of the system has been adopted and has resulted in a feasible and robust system design. The technical part of the integrated conceptual design consisted in the estimation of the heat demands, the design of the heat upgrading system, equipment sizing, the network morphology and/or spatial connectivity and the exergy losses in the needed infrastructure as well as the economic viability of the system. An isopropanol–hydrogen–acetone chemical heat pump was selected for the process and has been modelled in ASPEN plus^®. The conventional cost estimation model has been modified to account for uncompensated system downtimes.     

Research and development of the hybrid ground-coupled heat pump technology in China

The hybrid ground-coupled heat pump (HGCHP) systems with supplemental heat rejecter/supplier can effectively solve heat imbalance problems in the subsurface, and consequently improve the operation performance of the geothermal systems. For example, solar energy and/or industrial waste heat may be used as stable heat sources for underground heat storage in northern China with higher heating load, and cooling towers are installed to release heat into the air in southern China, where more cooling demand is needed. This paper reviews and discusses different HGCHP systems, which have been applied in China. And based on the heat transfer model of vertical borehole heat exchangers (BHE) for HGCHP systems, physical and mathematical models of multistage series circuits are developed to illustrate the heat transfer process of the underground thermal storage. A set of parameters, such as borehole spacing, heat recharging rate fractions and thermal properties of soils, which affect the thermal performance of the ground heat exchangers are analyzed, and the optimal solutions are discussed for engineering application.     

Optimisation of structure and operation of district cooling networks in urban regions

Optimisation of the structure and operation of district cooling networks in urban regions was studied. An optimisation model was developed for cooling networks that comprise a number of cooling consumers with different cooling demands in different period of a year, a number of possible cooling generation plant sites as well as cold media storage sites and a number of possible district cooling pipeline routes.The developed Mixed Integer Linear Programming model was applied for the design of a DC network in an urban region. The consumer cooling demands in the region for the year 2006 and a predicted future data with a number of new potential consumers for the year 2020 were used. From the solutions the structure of the district cooling system including the locations where cooling plants should be built, the cooling capacity of the plants, the cold media storage locations, the storage capacities and the routing of the distribution pipelines to individual consumers was obtained for the two cases. Additionally, the solutions comprise also data for the optimal operation, i.e. how the cooling generation plants will be run in different periods of the year, how the storages will be discharged and recharged and what will be the cold medium flow rates in the district cooling pipelines. The developed model is suitable both for optimisation of district cooling in new regions or for expansions of existing networks.     

Simultaneous optimization of heat-integrated water networks involving process-to-process streams for heat integration

This paper presents an extension of our recent work, in which we addressed the simultaneous synthesis of heat-integrated water networks. The novelty and goal of this work is the development of an extended superstructure and simultaneous optimization model of heat-integrated water networks now involving process-to-process streams, and other streams within the overall network, for heat integration. Those heat-integration opportunities have not yet been fully taken into account in most existing models of heat-integrated water networks. In this study, we presented two strategies for heat integration of process-to-process streams. The first one includes the placement of heat exchangers on each hot and cold process-to-process stream. The second allows for the cooling and splitting of hot streams, and heating and splitting of cold streams. This extended model was formulated as a non-convex mixed-integer non-linear programming (MINLP) problem. The objective was to minimize the total annual network cost. Two examples with single and multiple contaminants are used in order to demonstrate that involving process-to-process streams for heat integration, novel and improved solutions can be obtained compared to those reported in the literature.     

Assessing heating and cooling demands of closed greenhouse systems in a cold climate

Reducing greenhouse gas emissions by providing non‐fossil fuel energy sources is imminently necessary. The area of particular interest in this paper is the agricultural greenhouse industry. In these structures, significant heating demands are present, especially in cold climates, and are typically met by combusting fossil fuels. In an effort towards a sustainable energy supply, the potential of closed greenhouse systems in a cold climate is explored. In these systems, natural ventilation for cooling and dehumidification is replaced with active systems, and the thermal energy removed can be re‐used, reducing the overall heating demand. A transient greenhouse model is created using TRNSYS software and validated with natural gas usage data from a reference greenhouse. The annual heating and cooling demands, effect of varying cover materials and potential for heat recovery ventilation are explored for the most concentrated greenhouse areas in Canada. Copyright © 2017 John Wiley & Sons, Ltd.     

Dynamic model of counter flow air to air heat exchanger for comfort ventilation with condensation and frost formation

In cold climates heat recovery in the ventilation system is essential to reduce heating energy demand. Condensation and freezing occur often in efficient heat exchangers used in cold climates. To develop efficient heat exchangers and defrosting strategies for cold climates, heat and mass transfer must be calculated under conditions with condensation and freezing. This article presents a dynamic model of a counter flow air to air heat exchanger taking into account condensation and freezing and melting of ice. The model is implemented in Simulink and results are compared to measurements on a prototype heat exchanger for cold climates.     

Thermoeconomic assessment of a multi-engine,multi-heat-pump CCHP (combined cooling,heating and power generation) system – A case study

Design and operation of complex systems for combined cooling, heating and power generation (CCHP) are always a matter of matching performance and demand characteristics of a thermal system set to supply electrical, cooling and heating loads, according to specific usage demands. Equipment selection and operation require the characterization of power, heating and cooling load demands, and their time variation during years, seasons, months and even hours or minutes. The paper aims at utilizing a general model for complex CCHP systems. The proposed model is based on the general theory of exergy cost and structural coefficients of internal links. A general model is presented, and a simple hypothetical cogeneration case is studied. The system operates with two heat engines, with waste heat recovery driving a chiller, in order to meet electrical power and refrigeration loads.     

某天然气净化厂供热系统设计

某天然气净化厂需设置一套供热系统,为工艺装置及冬季采暖提供热负荷.根据热用户对用热参数的要求,可采用蒸汽锅炉供热系统或导热油加热炉供热系统.从投资、运行、管理及维护等方面对两种供热系统进行方案比较.导热油加热炉供热系统具有以下优点:运行和维护费用低、不消耗水资源、可露天布置、导热油倾点低,适合当地严寒气象条件.推荐选用...     

Targeting for energy efficiency and improved energy collaboration between different companies using total site analysis (TSA)

Rising fuel prices, increasing costs associated with emissions of green house gases and the threat of global warming make efficient use of energy more and more important. Industrial clusters have the potential to significantly increase energy efficiency by energy collaboration. In this paper Sweden’s largest chemical cluster is analysed using the total site analysis (TSA) method. TSA delivers targets for the amount of utility consumed and generated through excess energy recovery by the different processes. The method enables investigation of opportunities to deliver waste heat from one process to another using a common utility system.The cluster consists of 5 chemical companies producing a variety of products, including polyethylene (PE), polyvinyl chloride (PVC), amines, ethylene, oxygen/nitrogen and plasticisers. The companies already work together by exchanging material streams. In this study the potential for energy collaboration is analysed in order to reach an industrial symbiosis. The overall heating and cooling demands of the site are around 442 MW and 953 MW, respectively. 122 MW of heat is produced in boilers and delivered to the processes.TSA is used to stepwise design a site-wide utility system which improves energy efficiency. It is shown that heat recovery in the cluster can be increased by 129 MW, i.e. the current utility demand could be completely eliminated and further 7 MW excess steam can be made available. The proposed retrofitted utility system involves the introduction of a site-wide hot water circuit, increased recovery of low pressure steam and shifting of heating steam pressure to lower levels in a number heat exchangers when possible. Qualitative evaluation of the suggested measures shows that 60 MW of the savings potential could to be achieved with moderate changes to the process utility system corresponding to 50% of the heat produced from purchased fuel in the boilers of the cluster.Further analysis showed that after implementation of the suggested energy efficiency measures there is still a large excess of heat at temperatures of up to 137 °C.     

Short cut performance method for the design of flexible cooling systems

This paper considers the design of cooling systems in the context of piping costs, exchanger costs, pumping costs and its hydraulic and thermal performance. A methodology for designing coolers in the context of both process needs and cooling water system behaviour is introduced. It is recognised that cooling systems need to be flexible. One way of ensuring this is to design a system for the most demanding load and then use bypasses to control performance under reduced load.The hydraulic modelling is based on new formulations of flow resistance for pipes, pipe fittings and equipment items. By using volumetric flow rate rather than velocity as the prime variable it becomes possible to construct hydraulic models for cooling water systems quickly. These calculations then provide predictions of water flows to the individual heat exchangers in the cooling water network. Knowledge of these flows is fundamental to both the design of new coolers and the prediction of the thermal performance of exchangers of known geometry. Previous studies have ignored this aspect of design.     

Comparison of drying costs in biofuel drying between multi- stage and single-stage drying

The moisture content of wood-based biofuels (bark, forest residues, and waste wood) used by the forest industry typically varies between 50 and 63 w-%. The high moisture content considerably decreases the power production of the power plant. The main target of this paper is to compare the drying costs of two alternative drying systems: multi-stage drying, and single-stage drying with multi-stage heating. Air is used as a drying gas in both systems and is heated in indirect heat exchangers. Secondary heat, back pressure steam, and extraction steam are available for heating the drying air. Both capital and running costs are included in the drying costs. The drying systems are compared in example cases where the availability of heat sources, amortisation time, and price of elecricity are different. According to results, single-stage drying is usually a more economic drying system when the amortisation time is short. However, the competitiveness of multi-stage drying improves as the amortisation time becomes longer.     

Inverse problem and variation method to optimize cascade heat exchange network in central heating system

Urban heating in northern China accounts for 40％ of total building energy usage.In central heating systems,heat is often transfened from heat source to users by the heat network where several heat exchangers arc installed at heat source,substations and terminals respectively.For given overall heating capacity and heat source temperarure,increasing the terminal fluid temperature is an effective way to improve the thermal performance of such cascade heat exchange network for energy saving.In this paper,the mathematical optimization model of the cascade heat exchange network with three-stage heat exchangers in series is established.Aim at maximizing the cold fluid temperature for given hot fluid temperature and overall heating capacity,the optimal heat exchange area distribution and the medium fluids' flow rates are determined through inverse problem and variation method.The preliminary results show that the heat exchange areas should be distributed equally for each heat exchanger.It also indicates that in order to improve the thernmal performance of the whole system,more heat exchange areas should be allocated to the heat exchanger where flow rate difference between two fluids is relatively small.This work is important for guiding the optimization design of practical cascade heating systems.     

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.     

Cooling load density characteristics of an endoreversible variable‐temperature heat reservoir air refrigerator

The performance optimization of an endoreversible air refrigerator with variable‐temperature heat reservoirs is carried out by taking the cooling load density, i.e. the ratio of cooling load density to the maximum specific volume in the cycle, as the optimization objective in this paper. The analytical relations of cooling load, cooling load density and coefficient of performance are derived with the heat resistance losses in the hot‐ and cold‐side heat exchangers. The maximum cooling load density optimization is performed by searching the optimum pressure ratio of the compressor, the optimum distribution of heat conductance of the hot‐ and cold‐side heat exchangers for the fixed total heat exchanger inventory, and the heat capacity rate matching between the working fluid and the heat reservoirs. The influences of some design parameters, including the heat capacitance rate of the working fluid, the inlet temperature ratio of heat reservoirs and the total heat exchanger inventory on the maximum cooling load density, the optimum heat conductance distribution, the optimum pressure ratio and the heat capacity rate matching between the working fluid and the heat reservoirs are provided by numerical examples. The refrigeration plant design with optimization leads to a smaller size including the compressor, expander and the hot‐ and cold‐side heat exchangers. Copyright © 2002 John Wiley & Sons, Ltd.     

Total planning of combined district heating,cooling and power generation systems for a new town—Part II

The objective of this study is to introduce one of the main results of the project for studying energy conservation technologies in a new airport town, which is organized by the Osaka Science and Technology Center, Japan. First, based on the estimated energy demands in the new town, technological aspects are investigated for the district heating, cooling and hot water supply system. Then, the economic and energy saving characteristics are compared for several alternative systems according to the differences of the type of absorption refrigerating machine and so forth. Assuming that a combined heat and power plant is used as the heat source plant of the district thermal distribution system, the optimal combined district heating, cooling and power generation system has been selected from a comprehensive economic viewpoint. Lastly, it is ascertained that if fuel costs continue to rise at the rate of 8 per cent per year, the best energy conservation system becomes superior economically to the conventional district thermal distribution system.     

New methodology to design ground coupled heat pump systems based on total cost minimization

This paper introduces a method for designing vertical ground heat exchangers and heat pump systems, by minimizing the total cost of the project. The total cost includes an initial cost composed of drilling, excavation, heat pump and piping network. An operational cost is also included to account for the energy consumed for heating/cooling a building. The procedure allows determining the optimal number of boreholes, their depth and spacing, and the optimal size of the heat pump. The method is tested for different ground conductivity and heat demands. The method can also be used to determine the economical viability of a TRT. For tested cases, results show that the excess cost due to uncertainty on ground thermal conductivity increases with the number of boreholes. Also, a cost sensibility analysis shows that the most influential parameters are the number of boreholes and their depth.     

System analysis in a European perspective of new industrial cooling supply in a CHP system

In the municipality of Södertälje two large industries use much of the electricity, district heating (DH) and chilled water in the area. The Södertälje energy system is not isolated, however, but is connected to the DH systems of southern and central Stockholm, and a change in the Södertälje energy system will also influence the connected energy systems in Stockholm. The cooling demand in Södertälje is currently covered by lake water cooling and compression chillers, but in order to reduce the use of electricity, conversion to absorption cooling or increased lake water cooling can be considered. The large combined heat and power (CHP) plant in Södertälje is not used to its full potential today, but investment in absorption cooling and/or a cold condenser unit integrated with the CHP plant could increase the plant’s operation hours. In this paper the system effects of introducing new industrial cooling supply in Södertälje has been investigated through optimizations of a model including both the industries and the district heating supply in Södertälje and Stockholm. The results show that, independently of whether condensing power production is feasible in the CHP plant or not, investments in both increased lake water cooling and absorption cooling are profitable. A sensitivity analysis of how energy market prices affect the results shows that even though the system cost will change depending on energy market prices, the optimum cooling technology mix will remain the same. However, a sensitivity analysis of the transfer DH capacity between the Södertälje and Stockholm energy systems shows that if the transfer DH capacity is increased, absorption cooling will be less profitable since more heat can be sold from Södertälje to Stockholm while at the same time reducing the use of fuel resources.     

On cost‐effective technical measures to avoid environmental damages of regional energy systems

The production of heat and electricity can cause large environmental impacts and, hence, large costs for society. Those are costs that are seldom taken into consideration. An important question is how the future technical energy systems should be formed if environmental costs were considered as any other good or service, such as raw material, capital and labour. This study comprises cost‐effective technical measures when monetary values of external effects are included in an energy system analysis. It is an analysis of how the present energy system can for society be cost‐effectively reconstructed to be more sustainable. A regional energy system model has been developed to perform the study and it concentrates upon production of heat in single‐family houses, multi‐dwelling buildings, non‐residential premises and district heating systems. The analysis adopts a business economic perspective, using present prices of energy carriers, and a more socio‐economic perspective, in which external costs are included. The result of the analysis is the optimal mix of energy carriers as well as new and existing heating plants that minimizes the costs of satisfying a demand for heat. The results show that it is profitable to invest in new heating plants fuelled with woody biomass. Furthermore, the external costs arising with satisfying the demand for heat can decrease substantially, 60%, by carrying through with the investments that are cost‐effective according to the institutional rules valid today. When monetary values of external costs are taken into consideration, this number is additional 5‐percentage points lower. It is shown that if environmental costs are included it is more expensive to continue with business as usual than it is to reconstruct and run a more sustainable energy system. Copyright © 2002 John Wiley & Sons, Ltd.