Study of the thermal performance of a distributed solar heating system for residential buildings using a heat-user node model

Abstract Most cities and towns in China have a high building density, which makes it difficult to realize conventional large-scale solar heating systems. One way to solve this problem is to use the roofs of already existing suitable buildings and create a distributed solar heating system (DSHS). These single-building users in a DSHS, the “prosumers” (which act as both energy-producers and -consumers), however, operate with largely unpredictable patterns. Therefore, analyzing the dynamic characteristics of the solar collection system for users is the key to establish a DSHS. The associated connection-components (between each heat-user and the heating network) can be treated as “heat-user nodes”. This study focuses on the bidirectional heat-transfer characteristics between the heating network and users in a DSHS. This is done through the analysis of the heat-balance relationship between the internal equipment of a user and the components between the user and the heating network, and a daily heat-profit index is proposed. Furthermore, a mathematical model is developed for a heat-user node in a DSHS, and a corresponding MATLAB/Simulink system-simulation model is created. Further, this study used a town in Lhasa, as a practical case study. The following three ways of connecting users to the heating network (DP-RS, DP-SS, SP) were considered. This research also takes into account the heating-network’s supply-water temperature, how the heat-medium flow affects the thermal performance of the system, daily heat-profit (and loss) for the users, and the heating network temperature fluctuations. The results show that the daily heat-profit for users with different connections to the heating network can be ranked in the following order (highest first): DP-SS, SP, and DP-RS. With the increasing water-supply temperature of the heating network, the users’ daily heat profit decreases. The suitable operating condition for DSHSs with the mentioned three connection types is a water-supply temperature of less than 70 °C. With increasing heat-medium flow in the heating network, the water-supply temperature for the three connection types decreases. The supply temperatures can be ordered as follows (highest first): SP, DP-RS, DP-SS. Furthermore, we found that the peak time for the single-pipe system occurs two hours earlier than for the double-pipe system. This study can provide a theoretical basis to help solve solar heating challenges in densely populated cities.