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Integrating a heat pump into a 4th generation district heating (4GDH) system – Two-mode configuration inputting operational data
Energy and Buildings ( IF 6.6 ) Pub Date : 2022-09-15 , DOI: 10.1016/j.enbuild.2022.112445
Stanislav Chicherin , Andrey Zhuikov , Lyazzat Junussova

The aim is to examine integrating a heat pump (HP) into a district heating (DH) system versus potential savings in the separate scenario. It takes into account all the properties of both DH system and a HP operation, and gives the understanding of temperature, pressure and enthalpy of refrigerant at each cycle point. Contribution to the pool of knowledge is considering a novel configuration, which allows to get rid of a heat exchanger between the water-source HP and the network. Scenarios of (i) separate operation of a HP, and (ii) integrating it into a DH system and inputting design data only, or (iii) utilizing operational data have been analyzed. Multiple thermal simulations have been performed. We also allow traditional coverage of heat demand with the help of a supply line of high-temperature DH (HTDH), thus elaborated what happens when the outdoor air temperature drops below lower threshold. Hence, the model identifies two stages of operating a HP integrated into a DH system. Starting from it, the temperature of the supply water should be 50 °C and above, so it is more effective to use supply water directly until the outdoor temperature rises again. This outdoor temperature implies change of operational mode, which leads to the following results. On cold winter days, the available amount of heat is lower than the energy consumption, therefore, energy from a supply line of HTDH is utilized, which gives overall energy saving effect of about 14 %. Mass flow rates through the configuration suggested are identical during moderate-cold fall and spring days, since the control logic is established with the help of variation of supply temperature only. Single HP has the lowest efficiency because of high temperatures needed: with a nominal temperature difference of 25 °C, the coefficient of performance (COP) rises to 5.0 only. At the break-even point, HP in each configuration has COP ranging between 3.51 and 4.43, while the rest of the time COP is just above 2. In different cases, the lowest threshold of HP's performance is 2.4, 2.6, and 2.89, respectively. The DH-assisted scenario, where peak energy demand was covered by DH system directly, clearly outperformed separate installation, where a HP was the only thing responsible to provide the necessary supply temperatures. For this case, lower COP stipulates less energy is supplied from the DH system, and therefore a lower share of consumption is supplied directly from supply line, which decreases the overall seasonal COP. Scenario (iii) of inputting DH operational data has the highest seasonal COPs, reasoned to higher than design return temperatures. Given the low performance of a HP raising water temperature to 55 °C (the lowest threshold acceptable in winter) a single HP with no backup capacity accounts for 23 % more energy use. Supported by a coal-fired combined heat-and-power plant, distribution of primary energy consumption is more favorable, i.e. coal-fired generation covers the peak. The positive effect is expanded by converting a part of heat demand from HP operation to cheaper HTDH operation.



中文翻译:

将热泵集成到第四代区域供热 (4GDH) 系统中——输入运行数据的两种模式配置

目的是检查将热泵 (HP) 集成到区域供热 (DH) 系统中与单独方案中的潜在节省。它考虑了 DH 系统和 HP 运行的所有特性,并提供了对每个循环点制冷剂温度、压力和焓的理解。对知识库的贡献正在考虑一种新颖的配置,该配置允许摆脱水源 HP 和网络之间的热交换器。(i) 单独运行 HP,和 (ii) 将其集成到 DH 系统并仅输入设计数据,或 (iii) 使用运行数据的情况已经过分析。已经进行了多次热模拟。我们还允许在高温 DH (HTDH) 供应线的帮助下满足传统的供热需求,因此详细说明了当室外空气温度低于下限时会发生什么。因此,该模型确定了运行集成到 DH 系统中的 HP 的两个阶段。从它开始,供水温度应在50°C及以上,因此直接使用供水,直到室外温度再次升高时更有效。这个室外温度意味着操作模式的改变,这导致了以下结果。在寒冷的冬季,可用热量低于能耗,因此,利用HTDH供应线的能量,整体节能效果约为14%。在中等寒冷的秋季和春季期间,通过建议配置的质量流量是相同的,因为控制逻辑仅在供应温度变化的帮助下建立。由于需要高温,单个 HP 的效率最低:标称温差为 25 °C,性能系数 (COP) 仅上升到 5.0。在盈亏平衡点,HP 每种配置的 COP 介于 3.51 和 4.43 之间,而其余时间 COP 仅高于 2。在不同情况下,HP 性能的最低阈值分别为 2.4、2.6 和 2.89 . DH 辅助方案(其中峰值能源需求由 DH 系统直接满足)明显优于单独安装,其中 HP 是唯一负责提供必要供应温度的设备。在这种情况下,较低的 COP 规定从 DH 系统提供的能量较少,因此直接从供应线提供的消耗份额较低,这会降低整体季节性 COP。输入 DH 运行数据的场景 (iii) 具有最高的季节性 COP,原因是高于设计返回温度。鉴于 HP 将水温提高到 55 °C(冬季可接受的最低阈值)的低性能,没有备用容量的单个 HP 会多消耗 23% 的能源。在燃煤热电联产的支持下,一次能源消费分布更加有利,即燃煤发电覆盖高峰。通过将部分热量需求从 HP 操作转换为更便宜的 HTDH 操作,可以扩大积极影响。鉴于 HP 将水温提高到 55 °C(冬季可接受的最低阈值)的低性能,没有备用容量的单个 HP 会多消耗 23% 的能源。在燃煤热电联产的支持下,一次能源消费分布更加有利,即燃煤发电覆盖高峰。通过将部分热量需求从 HP 操作转换为更便宜的 HTDH 操作,可以扩大积极影响。鉴于 HP 将水温提高到 55 °C(冬季可接受的最低阈值)的低性能,没有备用容量的单个 HP 会多消耗 23% 的能源。在燃煤热电联产的支持下,一次能源消费分布更加有利,即燃煤发电覆盖高峰。通过将部分热量需求从 HP 操作转换为更便宜的 HTDH 操作,可以扩大积极影响。

更新日期:2022-09-20
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