Experimental validation of the dynamic thermal network approach in modeling buried pipes

The transient behavior of buried pipe systems plays a significant role in many heating and cooling systems, particularly in thermal energy networks and ground heat exchangers. In this study, the dynamic thermal network (DTN) approach’s validity as a response factor method in modeling dynamic conduction heat transfer in a buried pipe system is experimentally validated. A lab-scale representation of a buried pipe system has been excited by step changes in boundary temperatures and heat fluxes measured up to times approaching steady-state conditions. This data is used to derive weighting factors and also evaluate the validity of numerical representations of the buried pipe and to verify that the DTN method can reproduce the heat flux responses. It is demonstrated that the weighting factors required in this method can be derived from both numerical and experimental step-response time series data. The DTN method is found to be both accurate in reproducing the heat fluxes in the validation experiments but also significantly more computationally efficient than a conventional numerical model when simulating long timescale responses in buried pipe systems

The future role of energy geostructures in fifth generation district heating and cooling networks

Energy geostructures are novel dual use engineering sub-structures that can be used for heat transfer and storage as well as original structural function. Their use is becoming increasingly popular in delivering cost-effective shallow geothermal energy. Currently, they are mostly used as a part of ground-source heat pump (GSHP) systems for supplying partial or full heating and cooling demands of different types of buildings. The recent introduction of fifth generation district heating and cooling (5GDHC) networks can pave the way for the exploitation of energy geostructures as ground-coupled low-temperature energy sources and stores for providing energy demands of a wider range of energy users in districts rather than single buildings. In this article, the capability and feasibility of the novel concept of integration of energy geostructures into the 5GDHC networks are evaluated through reviewing different aspects of thermal performance of operating energy geostructures and 5GDHC networks. The potential advantages and challenges along with the knowledge gaps in such integration are discussed, and some practical recommendations are provided concerning dealing with some implementation challenges. It is highlighted that the incorporation of energy geostructures in 5GDHC networks can enhance the sustainability, flexibility and resilience of the network. There is the potential to exploit a greater share of cost-effective geothermal energy, and the ability to act as both thermal energy sources and stores for efficiently supplying both heating and cooling demands. However, since the development of fifth generation thermal networks and energy geostructures, particularly energy walls and energy tunnels, are still in their infancy, further research is required to assess the magnitude of the opportunities and quantify the advantages of integrating energy geostructures into the 5GDHC networks

Modelling the dynamic thermal response of turbulent fluid flow through pipelines

The transient behaviour of pipe systems is important in many forms of thermal system such as domestic hot water, building heating, cooling and district thermal networks. In this study, different approaches to modelling the dynamic thermal response of pipelines are investigated through applying three forms of discretized one-dimensional flow and heat transfer model. These were further compared with fully three-dimensional finite volume method (FVM)calculations. Firstly, the models were examined to predict the pipe thermal response considering the thermal capacity and longitudinal dispersion of turbulent fluid flow to step changes in the inlet temperature of a ideally insulated pipe. A model is pro-posed combining features of plug-flow n-continuously stirred tanks and treatment of the nodes to take into account the effect of thermal capacitance of the pipe wall as well as the convective heat transfer from the pipe outer surface. The results elucidated that the proposed model is not only able to capture the out-let temperature changes due to a step change in the very good agreement against the detailed 3D model but also offers advantages in computational cost com-pared with the 3D model. The proposed model can be simply implemented in dynamic system simulation tools. The model is to be extended to include dynamic ground heat transfer effects