Structural thermal energy storage in heavy weight buildings

October 27, 2016


Client:  CEMBUREAU – The European Cement Association
Period:  2016


To overcome the growing unbalance between energy demand and renewable energy generation, an increased flexibility is required from the demand side (i.e. the consumer). Orchestrated in a new energy infra- and market structure, e.g. so-called smart grids, buildings can play a significant role in demand side flexibility. Given the available inertia provided by heavyweight construction materials, and given the increasing electrification of heating and cooling systems, structural thermal energy storage (STES) in buildings can be one of the key actors for a successful demand response energy market, without additional investments in storage devices. However, the current version of the Energy Performance of Buildings Directive (EPBD) does not include the concept of structural thermal energy storage used for active-demand response (ADR).

Considering this absence, The Concrete Initiative commissioned a study to 3E to show the potential of using the structural thermal mass of heavyweight buildings, such as concrete buildings, in terms of potential increase of renewable energy penetration in the grid, avoiding grid peaks, and flexibility benefits in a smart grid context.

Scientific literature demonstrates a substantial benefit in pre-cooling and pre-heating of buildings under specific conditions, i.e. for a specific type of building, equipment, control setup, comfort range, time periods for pre-cooling or pre-heating, and limited season (heating and cooling season). Most studies focus on the benefits and possible limitations in term of energy consumption savings during grid peaks, and discuss the requirements to use thermal mass to create flexibility on grid level to its full potential.

In summary, those requirements are the sufficient thermal insulation of the building, an adapted fabric cover over the underfloor heating/cooling pipes, a suitable heating/cooling system providing flexibility such as electrical heat pump or a flexible district heating, a smart controlling, the possibility to aggregate individual loads, and adapted energy prices incentives.

When fulfilling these requirements, the flexibility provided by the thermal mass of the building fabric can lead to significant benefits such as the balancing of the grid infrastructure (e.g. peak reduction up to 50% of cooling load), investment and operating cost savings (operational savings up to 40%), higher RES penetration and CO2 emission reductions (up to 25% CO2-reductions per dwelling).

Schematic overview of the requirements related to the optimal use of Structural thermal energy storage

Nevertheless, different limitations are to be considered with pre-heating or pre-cooling strategies in buildings: a total electricity consumption increase due to storage losses, limited storage duration and utilization in mid-season, and comfort limitations. However, when the active demand response program is properly managed, those downsides of structural thermal storage can be addressed in order to tap the economic and environmental benefits.

Schematic overview of the benefits resulting from the optimal use of Structural thermal energy storage

The current review of the EPBD is an opportunity to raise ambitions with regards to the exploitation of structural thermal storage to its full potential with the following policy recommendations:

  • Evolve to new energy performance calculation models to take thermal energy storage into account.
  • Insist on new energy performance calculation models to take into account the dynamic use of thermal energy storage in a load shifting context.
  • Improve the recognition of the benefits of structural thermal storage by taking the “available structural storage capacity” into account in the Directive.
  • Promote the interoperability between building heating/cooling systems and the energy market in order to deploy ADR.
  • Encourage energy storage incentives in order to make it economically viable for end-users today.

The following policy recommendations would allow better use of the storage capacity but they are considered to be out of the scope of the EPBD.

  • Encourage experimental studies / pilot projects in real buildings to demonstrate the benefits of ADR using structural thermal energy storage in operation.
  • Encourage energy tariff structure reflecting the demand-supply unbalances in order to provide an incentive for ADR.
  • Align storages regulatory frameworks in order to maximize the storage opportunities, especially at peak.

The full fact sheet can be downloaded here