Environomic Optimization of District Heating Network Systems with Both Centralized and Decentralized Heat Pumps.

In Switzerland like in many countries, many of the populated areas are located close to lakes or rivers, offering a large potential for the use of heat pumps. Although district heating is an obvious solution, adapting the delivery temperature to the most exigent users is detrimental to overall system performance. The best system configuration could avoid this pitfall by relying on a centralized plant of heat pumps with cogeneration, supplemented by decentralized heat pumps for the more demanding users. Using expert knowledge to compose a superconfiguration of all possible components for a district heating network system with both centralized and decentralized heat pumps, a novel methodology is proposed for modeling and optimizing, under known sets of economic, user characteristic and environmental constraint data, both the final configuration resulting from the superconfiguration as well as the configuration’s corresponding component designs. The optimization is accomplished with the help of a cutting-edge operations research tool, a genetic algorithm, while the model itself is based on a total cost objective function which unifies in a single model investment, operation, and pollution costs. These latter costs are (for each of the major pollutants) based on the literature as well as on continuous pollution penalty functions adapted to system emissions and to local immissions ratios. These penalties are included to help guide the choice of configuration and component designs away from regions where pollution limits or undesirable levels of actual emissions in combination with local / global conditions are approached too closely. Results are shown for various user distributions and fuel and electricity prices. A comparison between the results found with and without taking into account pollution is also presented.

An Environomic Approach for the Modeling and Optimization of a District Heating Network Based on Centralized and Decentralized Heat Pumps, Cogeneration and/or Gas Furnace (Part II: Application)

Vinicio Curti, Daniel Favrat

Although heat pump based district heating is often an obvious solution from an energy standpoint, adapting the delivery temperature to the most exigent users is detrimental to overall system performance. This pitfall can be avoided with a centralized plant of heat pumps, cogeneration units and an auxiliary furnace, supplemented by decentralized heat pumps. However, the problem of mixed energy production and delivery which this poses is complex and presents for the engineer the daunting if not impossible task of adequately, much less optimally, determining the best system for the job. In the first of a series of two articles (i.e. Part I [1]), an environomic methodology for aiding in this task is described and the details of the environomic model for a district heating network based on centralized and decentralized heat pumps presented. This methodology is used to model the thermodynamic, economic, and environmental characteristics of such a system in order that its final configuration and corresponding component designs can be optimized. In the present article (i.e. Part II), a complete set of results for the optimal synthesis, design and operation of the network is given and discussed. The resulting solution space is highly nonlinear and non-contiguous and is effectively searched using a genetic algorithm. Results are shown for various district heating user distributions, as well as fuel and electricity prices. When properly optimized, solutions with heat pumps are economically very close to traditional district heating solutions, particularly when the main pollution costs are internalized.

2000

An Environomic Approach for the Life Cycle Modeling and Optimization of a District Heating Network Based on Centralized and Decentralized Heat Pumps (Part I: Methodology).

Vinicio Curti, Daniel Favrat

Although heat pump based district heating is often an obvious solution, adapting the delivery temperature to the most exigent users is detrimental to overall system performance. This pitfall can be avoided with a centralized plant of heat pumps, cogeneration and an auxiliary furnace, supplemented by decentralized heat pumps. However, the problem of mixed energy production and delivery which this poses is complex and presents for the daunting if not impossible task of adequately, much less optimally, determining the best system for the job. An environomic methodology for aiding in this task is proposed. It is used to model the thermodynamic, economic, and environmental characteristics of such a system in order that its final configuration and corresponding component designs can be optimized. Our approach is an attempt to respond at the synthesis, design and operational level of an energy system to the concept of sustainablility. The optimization of the model developed results in a highly nonlinear, non- contiguous solution space effectively searched using a genetic algorithm. The system’s environmental characteristics are introduced into the model through pollution damage cost terms and pollution penalty functions adapted to the system’s changing emissions and to local and global pollutant conditions. Results are shown for various district heating user distributions and fuel and electricity prices. In this first of a series of two articles, our methodology is described and the details of the environomic model for a district heating network based on centralized and decentralized heat pumps presented. In the accompanying article [1], a complete set of results for the optimal synthesis, design and operation of the network is given and discussed.

1998

An Environomic Approach for the Life Cycle Modeling and Optimization of a District Heating Network Based on Centralized and Decentralized Heat Pumps (Part II: Application).

Vinicio Curti, Daniel Favrat

Although heat pump based district heating is often an obvious solution, adapting the delivery temperature to the most exigent users is detrimental to overall system performance. This pitfall can be avoided with a centralized plant of heat pumps, cogeneration and an auxiliary furnace, supplemented by decentralized heat pumps. However, the problem of mixed energy production and delivery which this poses is complex and presents for the engineer the dauting if not impossible task of adequately, much less optimally, determining the best system for the job. An environomic methodology for aiding in this task is proposed. It is used for modeling the thermodynamic, economic, and environmental characteristics of such a system in order that its final configuration and corresponding component designs can be optimized. Our approach is an attempt to respond at the synthesis, design and operational level of an evergy system to the concept of sustainability. The optimization of the model developed results in a highly nonlinear, non-contiguous solution space effectively searched using a genetic algorithm. The system’s environmental characteristics are introduced into the model through pollution damage cost terms and pollution penalty functions adapted to the system’s changing emissions and to local and global pollutant conditions. Results are shown for various district heating user distributions and fuel and electricity prices. In this second of a series of two articles, a complete set of results for the optimal synthesis, design and operation of a district heating network based on centralized and decentralized heat pumps is given and discussed. In the accompanying article [1], our methodogy is described and the details of the environomic model for a network presented.

1998