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District Heating and Cooling

Annex IX Project 04

The Research / IEA DHC Annexes / 2008-2011 / Annex IX / Annex IX Project 04

Distributed Solar Systems Interfaced To A District Heating System That Has Seasonal Storage

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Privately constructed solar thermal buildings will become common as the technology evolves.  They will be built in the same area with conventional buildings, giving the effect of lower density to a district energy (DE) utility and having a negative impact on its payback on capital investment.

The challenge is: "How can district energy supply an interface to privately funded small/medium scale solar thermal systems with net billing for the benefit of both parties and to minimize fossil fuel consumption and peak loads on the network?"


  • To develop DE system-level design guidelines and methodologies for cost-effective integration of solar buildings by merging benefits of centralized and decentralized energy generation and storage.
  • To develop methodologies to estimate the optimum percentage and configurations of solar buildings to maintain utility stability and cost effectiveness in areas remote from a central DE plant.
  • Using experimental data from a house with a high-temperature solar system, to develop a bidirectional, net billing interface.  To evaluate control system interactions and establish guidelines for efficient system-level operation.

Target audience     

This information will be useful to the solar design industry and district energy engineers in any northern country doing planning for system expansion.  It will also be of interest to government energy policy officials who will be defining building standards and incentive programs to minimize fossil fuel consumption and greenhouse gas emissions.

General benefits

By using large scale storage together with solar input the renewable component of DE energy will be maximized, since surplus solar energy will be saved for later use. Any country with a DE industry and a significant number of solar buildings under planning or construction will benefit from the guidelines produced by this project.

Work progress

Start: November 2008
Status: Finished

Contractors & subcontractors

  • Gagest Inc. (Project Manager)
  • Benny Thomsen Kamstrup A/S
  • Lisa Aalto, Aalto Inc.