Combined district heating (DH) systems have at least one base load heat plant and several peak-shaving heat sources, which can be installed in the primary network or in the heating substations. This article studies the combined DH system with peak-shaving gas-fired boilers in heating substations, where the peak boilers can be connected to the heat exchangers in series or parallel mode. We analyze the thermal balances for these two connection modes and obtain the analytical operational regulation formulas for them. Then we study the operational methods for each connection mode, considering the heat distribution control strategies in both primary and secondary networks. Adopted control strategies are (1) variable temperature (VT) control, (2) variable flowrate (VF) control, and (3) variable temperature and flowrate (VT-VF) control. The combinations of these three strategies in primary and secondary networks are compared in terms of pumping energy consumption. The results indicate that operational strategies should be phased into different periods according to whether the peak heating is needed or not. In addition, the pumping energy consumption for the parallel connection mode is less than that that for the series connection mode with the same operational strategy, and the VF control strategy shows better energy saving potential.

区域供热（DH）组合系统至少具有一个基本负荷供热厂和几个调峰热源，可以将其安装在主网络或供热变电站中。本文研究了供热变电站中带调峰燃气锅炉的组合DH系统，在该系统中，峰锅炉可以串联或并联连接到热交换器。我们分析了这两种连接方式的热平衡，并获得了它们的分析运行调节公式。然后，我们研究每种连接模式的操作方法，同时考虑一次和二次网络中的热量分配控制策略。采用的控制策略是（1）可变温度（VT）控制，（2）可变流量（VF）控制和（3）可变温度和流量（VT-VF）控制。在抽水能耗方面比较了初级和次级网络中这三种策略的组合。结果表明，根据是否需要峰值供热，应将操作策略分为不同的阶段。此外，在相同的运行策略下，并联模式的泵浦能耗要小于串联模式的泵浦能耗，变频控制策略具有更好的节能潜力。