With limited space for heating, Aggregate Industries were able to provide a innovative solution by incorporating an underground heat storage system to this exemplary development in Derby.



The goal was to provide heat for all the homes using on-site sources but there simply wasn’t enough roof space for all the PV panels needed to supply heating loads. Moreover, other heating solutions such as ground or air source heat pumps and biomass were also deemed unsuitable.


In the end, the solution was innovative yet simple: go underground. Each home was provided with a Thermastore system, essentially a thermal store under the ground floor. The store is filled with aggregate, which is heated over the summer using roof mounted solar thermal panels. The stored heat is released into the home as and when required during colder winter months.

Designed to minimise installation costs, the thermal store occupies the space between the foundations of each home. The ground between the footings was excavated and Insulating Concrete Formwork (ICF) was used for the main structural walls. The zone beneath the ground floor slab, that was to form the thermal store, was super insulated to prevent any heat losses. Each heat store measures 6m by 4m, is 1m deep and is filled with aggregate from recycled concrete and brick from the previous structure that occupied the site. The recycled material was graded and the fines removed, with pieces 50mm diameter and larger used for the thermal store fill.

Surplus heat generated from a roof mounted solar thermal array is transferred into the thermal store. Hot air is circulated through the aggregate stores ensuring an even distribution of heat throughout.

In the winter, heat is extracted from the thermal store and transferred to a conventional radiator based hot water heating system.

Project details

  • Housing


  • East Midlands Renewable Energy (EMRE)

    • Intelligent resourcefulness
    • Pro-active responsibility
    • All-round capability