Achieving primary side balance at the area substations is, however, just the beginning of the journey. Today a crude and inefficient basic balance is achieved on the secondary side of the area substations by operating with very large flow volumes and low temperature difference. Commonly the temperature difference on the secondary side of the area substations is ranging from 2-10°C, compared to 30-40°C in Scandinavian building heating systems. When keeping in mind that the only real control in current Chinese DH systems is typically at the area substations, which are supplying multiple buildings, there is inevitably an enormous energy saving potential waiting to be realized. The logical path, as occurred during the modernization process of Eastern European DH systems, is to continue the control level development shown in Figure 2. The next big modernization step will be moving from area substations to building level substations. The building level substations will enable significantly increased temperature difference in the distribution system, reduced pipe diameters as well as avoiding multiple distribution loops on the secondary side of the area substations when supplying high rise buildings. Experience from other markets have shown that building level substations enable significant reduction in the distribution heat losses as well as reduced oversupply at the building level. THE DIGITALIZATION OPPORTUNITIES IN THE CHINESE DISTRICT HEATING SECTOR As the social welfare philosophy and fixed payments for heating is rooted into the Chinese DH DNA, there is an enormous potential for new business models that take advantage of the rapid development in digital solutions. As an example, the currently accepted fixed payment structure provides a good opportunity for utilities to introduce innovative services in the transition from socialistic welfare system, with fixed payment per square meter, to market-oriented systems, with billing according to consumption. One of the potential innovative services could become selling temperature comfort. With a temperature comfort service contract, the utility would operate the residential control equipment to maintain the indoor environment within an interval specified by the consumer. This would allow the utility to optimize their system operation and drive down cost. The consumer will benefit from optimum indoor environment and does not need to maintain and operate the control equipment.
With the automatic controls migrating to the 2nd control level, the heating utilities become better equipped to address the past challenges of severe oversupply during the start and end of the heating season. Figure 3 shows an example of the actual, measured, heat supply dived by the heat demand degrees (HDD) in a Chinese utility. The figure underlines the general challenge that manually controlled systems are facing in adapting the heat supply to the demand during periods of high outdoor temperatures. Instead of the expected rapidly decreasing heat demand per HDD at warmer outdoor temperature (dotted red line), the heat delivery per HDD in Chinese system is increasing exponentially, leading to open window temperature regulation. Figure 2. The figure defines the district heating control levels and average heat savings realized during the transition from 1st to 5th level in European district heating systems.
Figure 3. Heat supply per heating degree for a given outdoor temperature in Chinese district heating system.
The actual oversupply is hard to estimate but by assuming that heat supply at 0°C is the ideal fit, the red dotted line would represent the ideal supply per heating degree across the different outdoor temperatures. The deviation of the measured supply compared to the ideal supply would in this case imply oversupply due to inefficient flow distribution at the area substation level of around 20 %, which could be avoided with the application of more advanced automatic controls.
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