Distributed wireless control strategies for district heating substations

Sammanfattning: The overall fuel efficiency of district heating could clearly be improved by using new strategies for measurement and control. The potential for improvement is on the order of several percent. Keeping in mind that district heating makes up ~50% of the Swedish heating market (5 billion euro total turnover) which in turn is about 1% of the total world market, such improvements would be of global importance both from financial and environmental viewpoints.The energy transfer from the distribution network to space heating and tap water systems is done at a district heating substation. To maximize energy effciency in the district heating network and minimize primary fuel source usage, it is essential to have maximum utilization of produced heat. This means that a large temperature drop (Delta T) across the substation is of utmost importance. This is related to the fact that the same amount of heat energy can be transferred with a decreased flow, if the temperature difference (Delta T) between incoming and returning water is increased. This makes Delta T a very important factor in making district heating more effcient.Today, substation control systems focuses on indoor comfort and do not generally consider Delta T, since it is not measured by the control system, however, Delta T is measured by the energy meter used for billing.This thesis proposes an alternative way to control a district heating substation, wherein wireless sensor and actuator technology together with a service oriented architecture are used. This technology allows different devices, such as the energy meter, circulation pump, and control valve, to share information without restrictions and thus increase the control possibilities.To test the new control strategies, a complex thermodynamic computer model of a building with an included district heating substation was developed for simulation. The thermodynamic model was complemented with models of battery-powered wireless devices to predict the sensor lifetime. A field experiment was also carried out wherewireless platforms were retrofitted into commercially available components used in district heating substations. The complete setup is currently mounted in a villa for continued research.The results of my research so far have proved that there is great potential for increasingDelta T and for additional services if new sensor technology is applied.