To introduce and to discuss the concept with various experts, the 1st FLEXYNETS webinar will take place on May 10th (10:00-12:00). More information and registration at www.flexynets.eu/en/Webinar.


flexynetsJuly 2015 – July 2018


Flexynets: Fifth generation, low temperature, high exergy district heating and cooling networks

Traditionally, District Heating and Cooling (DHC) networks distribute energy from a centralized generation plant to a number of, in some cases, remote consumers. As such, actual DHC systems suffer from:

  • Heat losses
  • Highly unexplored integration potential of different available energy sources (e.g. renewables and waste heat) into the network
  • High installation costs.

The purpose of the Flexynets project is to develop, demonstrate and deploy a new generation of intelligent district heating and cooling networks that reduce energy transportation losses by working at “neutral” (15-20 °C) temperature levels. It is expected that reversible heat pumps will be used to exchange heat with the DHC network on the demand side, providing the necessary cooling and heating for the buildings contemporary.

Part of the concept is to utilize the heat that is normally rejected by buildings. The rejected heat will be fed into the network by heat pumps (which are working in “cooling mode”) and recycled by other heat pumps that are producing domestic hot water. In the same way, these networks allow to recover and recycle waste heat available along the network path, even at very low temperatures e.g. from supermarkets’ chillers, data centers and several industrial processes. Moreover, working at low temperatures reduces the heat losses to the ground, increasing the network efficiency.

This system does not substitute nor is opposed to traditional district heating networks. It is expected that in urban contexts not exploiting district heating yet, this new generation networks can represent the main heating and cooling system. In cities already making use of district heating, low temperature DHC networks can use thermal energy from the return pipes (in addition to waste heat), which otherwise is considered as waste heat by the network utility. This allows them contemporarily to sell additional energy with the same infrastructure and makes the network more efficient, reducing the return temperature.

Results and perspectives:

A range of Flexynets concepts will be developed in the project:

Flexynets Substations: a number of substation configurations that are suitable for the concept of Flexynets will be defined, simulated and tested.

Flexynets Loop: The concept will make it possible to modify the hydraulic circuitry associated to concentrating collectors’ loops, and to track more closely the ideal operating conditions. Furthermore, it will be easily adaptable to different uses, taking advantage of its variable configurations for different scenarios.

Flexynets Control: Development of low-level control strategies for prosumers’ substations, including the Flexynets-Loop control together with development of high-level control strategies for management of the DHC network at centralized level and development of a strategy for integrating the devised DHC networks with the electric and the gas networks. Besides this specific software will be elaborated and tested in a DHC pilot.

Flexynets Planning: based on the different analysis in the project, recommendations for the replication of such systems will be provided. The recommendations will be made public available via a pre-design tool uploaded on the project website.

Flexynets Trading: Among other inputs, the technical challenges will address the issue of net metering systems with particular focus on the cost benefit trade-off of their use for thermal applications. Also, trading policies assessment from the investigation of best practices on incentive schemes and regulations are included. The national, regional and local levels will be investigated at least across the four EU countries represented by the project partners (Italy, Germany, Denmark and Spain).

Key PlanEnergi activities:

In WP2 concerning assessment of combinations of energy sources and sinks, PlanEnergi is responsible of the evaluation of centralized and diffused storages. Here 3 different possible options will be studied, taking into account their advantages and disadvantages:

  • Centralized “daily” water storages
  • Large “seasonal” water pits
  • Surface near (<200 m) geothermal systems

Spatial requirements, energy performance and economic viability will be analyzed, assessing the behavior of the systems for different locations and weather conditions. TRNSYS simulation models of the considered storages will be elaborated and will be used to study the considered storages, paying special attention to the sizing compared to the one of the built environment and control procedures. Hence, a comparative analysis of these systems that will help to evaluate the benefits and drawbacks of the storage technologies, giving an idea of which one is more suitable under different boundary conditions.

WP3 is an assessment of DHC network topologies and pathways through the built environment. In this WP PlanEnergi is responsible of the analysis of reference towns. Three reference towns will be considered: a small village, a small city with integrated residential, commercial and industrial quarters and a large city with blocks differentiated by use. In this task, PlanEnergi will analyze and compare different networks’ layouts, in order to investigate the various possibilities for connecting heat sources and sinks as well as different storage options. Also the upgrade of installed 3rd generation networks’ pipelines to the Flexynets concept will be addressed.

Under WP3 PlanEnergi is further responsible of the Flexynets Planning concept that will provide recommendations for optimal configurations. Based on the analysis in this WP and other WPs the main objective is to extract simple but reliable, practical results that can be presented to urban planners and heating and cooling engineers. Based on the Flexynets planning solutions an online pre-design tool will be made available (WP6).

PlanEnergi is part of other WPs that look into control strategies and the DHC networks deployment into pilot plants.