District heating networks are also faced with the task of optimising their energy consumption and carbon footprint. One effective way of doing this is to reduce the flow temperature. In order to still be able to provide consumers with a sufficient amount of heat, leaks in the network should be detected and eliminated as quickly as possible. Modern sensor and data transmission technology can make a decisive contribution to this.
Heat networks function fundamentally differently from electricity networks. Due to the inertia of the system, operators cannot respond to load changes by adjusting the feed-in at short notice. Instead, sufficient heat energy must be fed into the network at all times in order to be able to "buffer" short-term increases in consumption. Maintaining a buffer quantity of thermal energy is, of course, not ideal from an efficiency perspective, but it does ensure a reliable supply. At the same time, minimising the buffer quantity is in the economic interest of network operators. One factor influencing the size of the buffer is heat loss due to leaks – i.e. steam or water escaping – in the pipe network. These leaks not only cost thermal energy and heating water, but can also cause considerable damage to the operator's own infrastructure and to third-party property.
Modern sensor and data transmission technology saves costs
Because leaks are almost impossible to avoid completely in networks with hundreds of kilometres of pipes and thousands of manhole covers, the starting point must be to detect, locate and eliminate these leaks as quickly as possible.
Until now, "as quickly as possible" has been relative: conventional methods such as checking manhole covers with thermal imaging cameras – steam escaping from the supply channels causes a rise in temperature – have their limitations due to the nature of the technology. Given the dimensions mentioned above, even with considerable manpower, such checks can only be carried out at rough intervals – e.g. every two weeks. The result: in extreme cases, leaks remain undetected during this period.
The potential for improvement through automated leak monitoring is therefore evident. For this reason, the operator of a district heating network in a major Swiss city was unwilling to accept the situation and initiated a tender process. The subject of the tender: sensors for measuring humidity and temperature in the shafts. These sensors were also to transmit their data wirelessly, i.e. via radio, to the network operator's backend systems, where the measurement data would be integrated, evaluated and visualised for network-wide, automated leak monitoring.
Cost-effective solution with standard components
comtac AG was able to best meet these requirements. It measures and logs temperature and humidity values and transmits the data using an integrated transmission unit for data networks in accordance with the LoRa® standard. The "Long Range Wide Area Network" (LoRaWAN®) is a wireless low-power transmission method that, although it only allows comparatively low bandwidths, is designed for energy efficiency, long ranges and good penetration of buildings.
All these features make LoRa® – similar to a number of other low-power networks (LPN) – ideal for leak monitoring applications. Ultimately, sensor units using this technology can ensure reliable data transmission from the shafts under normal conditions. They take measurements every two hours and transmit the readings four times a day. In this mode, the product runs on battery power for well over five years, meaning that batteries can be replaced without any additional effort during scheduled on-site inspections.
Advantages in terms of energy efficiency and maintenance costs
The benefits of LPN-based leak monitoring are abundantly clear in the example network: leaks are normally detected reliably after just a few hours, while the labour-intensive manual inspection of manhole covers with thermal imaging cameras is no longer necessary. If the leaks are then repaired quickly, energy losses are reduced, which in turn has a positive effect on the overall efficiency of the district heating network, as described above. This mechanism works independently of location in all district heating networks of similar or larger dimensions.
The possibilities can be expanded even further with other hardware that is also available as standard. For monitoring and control tasks in all types of infrastructure networks, comtac AG offers "Cluey", a flexibly configurable monitor and controller. Equipped with the appropriate sensors and a radio module for LoRa® or other low-power networks, the device can not only perform monitoring tasks, but also trigger actions itself. These can be switching pulses or alarms, which are dispensable in the context of pure leakage monitoring, but enable additional functionalities in the context of broader solutions for infrastructure monitoring, including predictive maintenance.
