PlanEnergi is part of the consortium behind the FLEXYNETS project.

You can read more about the project by following this link.


Read the report on Large Storage Systems for DHC Networks here!

Project Period

2015 – 2018


FLEXYNETS: Low temperature 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, DHC systems often 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 which will reduce energy transportation losses by working at “neutral” (15-20 °C) temperature levels. Reversible heat pumps can be used to exchange heat with the DHC network on the demand side, thus providing the necessary cooling and heating for the buildings simultaneously.

The FLEXYNETS-principle is described in the video below:

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

This system does not substitute nor is opposed to the traditional district heating networks. It is expected that in urban areas not yet exploiting district heating , this new network generation can function as 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 is otherwise considered as waste heat by the network utility. This allows them to at the same time sell additional energy within the same infrastructure and make 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 circuit 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 managing the DHC network at centralized level and development of a strategy for integrating the devised DHC networks with the electric and the gas networks. Furthermore, 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 included is assessment of trading policies from the investigation of best practices on incentive schemes and regulations. 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).

To introduce and to discuss the concept with various experts, the 1st FLEXYNETS webinar was held on May 10th. Please find the recording of the webinar here: More information and registration at www.flexynets.eu/en/media.

Key PlanEnergi activities

PlanEnergi has analysed the potential roles of large-scale heat storages in the FLEXYNETS-concept. The results of this analysis are presented in a report, which is available for download here.

In WP2 concerning assessment of combinations of energy sources and heat/cold sinks, PlanEnergi is responsible of the evaluation of centralized and dispersed storages. Here three different possible options are 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 analysed, assessing the behaviour 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 storages, paying special attention to the dimensioning compared to the size of the building environment and regulations. Hence, the result will be a comparative analysis of these systems that will help evaluate the benefits and drawbacks of the storage technologies, assessing which is more suitable in different framework conditions.

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

Furthermore, in WP3 PlanEnergi is responsible for 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 as well as heating and cooling engineers. Based on the FLEXYNETS planning solutions an online pre-designed tool will be made available (WP6).

Moreover, PlanEnergi is a part of other WPs, which study control strategies and the DHC networks’ deployment into pilot plants.

For further information, please contact Daniel Trier.