A district cooling system (DCS) is superior to conventional air conditioning as it helps to reduce energy consumption and protect the environment by reducing carbon dioxide emissions. The main disadvantages of a DCS are the high initial investment costs and the long payback period. The distribution network (DN) represents a large share of initial investment costs; therefore, it has a great impact on the decision to construct a DCS. In order to ensure the competitiveness of DCS, the DN has to be optimized. In this paper the exergoeconomic concept is applied to evaluate a DN in a DCS. The objective function in the analysis is defined as the exergy based cost of the final product-cold. The exergy-based cost of cold depends on the total annual cost of a DN, the input exergy to the DN, the exergy losses and the exergy destruction. The aim of this study is to find the exergetic optimal pipe diameter and the insulation thickness, as well as the exergoeconomic optimal pipe diameter and the insulation thickness. The analysis was made for different cooling capacities and for two types of pipes: pre-insulated steel pipes, where the insulation material is polyurethane, and polyethylene pipes, without any insulation.
This paper presents the results of a thermo-economic and primary-energy-factor assessment based on the fieldtest results for a residential air-to-water heat pump (AWHP). The AWHP experimental setup consisted of a supervisory control and data-acquisition system, which was connected to a heat meter, an electricity meter, humidity and temperature sensors, a HP control system and a computer. Based on the experimental data, the 4-year-average seasonal performance factor was determined. This information was then applied in a thermoeconomic and primary-energy-factor (PEF) analysis. The results served for a comparison of the AWHP with eight different heating systems (HSs). The results reveal that the considered AWHP represents the most thermo-economically efficient system in terms of the average final costs for heat production. The results of the PEF analysis reveal that the HS with the AWHP under investigation can be characterized as the most efficient system.
In the past decade, the EU has been taking a more active role in the field of improving energy efficiency, reducing energy consumption and exploiting renewable energy sources. In order to define the actual primary energy efficiency of various energy-related processes, the primary energy factor (PEF) can be used as a tool. The PEF enables a comparison between the input primary energy to the system and the energy delivered to the consumer. Its evaluation involves the energy required for the extracting, processing, storing and transporting to a power plant, energy conversion, transmission, distribution and the losses associated with these processes. The primary energy in this particular case includes the energy contained in the raw fuels as well as other forms of energy received as the input to the energy-supply system. It covers both renewable and non-renewable energy sources and the definition here is in accordance with EN 15316-4-5 [1], which states that '… waste heat, surplus heat and regenerative heat sources are included with the appropriate primary energy factors. ' A set of directives has been approved in order to reduce the energy consumption, increase the efficiency and exploit renewable energy sources. The PEF has been used as a significant metric in order to calculate the actual primary energy efficiency of different processes in several legislations, i.e., in Directive 2012/27/EU on energy efficiency Beretta et al.[7] presented a method that provides a dynamic calculation of the PEF depending on the variation of time and geographical location. Laverge an Janssens [8] attempted to use empirical data to calculate the PEFs for a set of countries in a specific year. However, his study did not follow a complete and replicable methodology and it did not include the losses associated with generation, storage and transportation. Wilby et al. [9] claimed that fixed Primary Energy Factor of a District Cooling System
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