Full-scale demonstration of thermal active building system - Supplementary grant

This project "Full-scale demonstration of thermo-active building system – Phase 3" has showed the way for new buildings (offices etc.) with increased requirements to energy performance due to the new building regulations. The project idea is to use prefabricated thermo-active structures as concrete slabs with embedded plastic pipes (PEX). The active concrete slabs are used both as cooling and heating system, peak load limiting (levelling out the peak load) and as energy storage.

Thermo-active building systems (TABS) contribute decisively to meet the new energy requirements and offer new exciting possibilities for the building design. The term "thermo-active structures" is used because the building structure is actively influenced inside by cooling/heating, while the heat and cooling accumulating capacity of the concrete is utilized. This technique ensures an energy-efficient building with pleasant indoor climate, since it acts as floor heating in the winter and cooling ceiling in summer. Dynamic activation of thermal mass is an optimal solution used in many countries for many years.

Based on results from a DTU pilot project, the building owner, Middelfart Sparekasse (a Danish bank), decided to use thermo-active structures for a new 5380 m2 large headquarter. The objective was to reduce electricity consumption for cooling and ventilation by 75-80 %, thereby making it easier to comply with the more stringent energy requirements. Following commissioning of the construction work, the project carried out technical monitoring and indoor climate satisfaction tests. Significant energy savings using this technology have been documented. Electricity consumption for cooling and ventilation was reduced by about 12-13 kWh/m²/year, corresponding to about 60%. The electricity savings have a potential to become even higher. The actual consumption is due to a number of factors. 1) The building has not only natural ventilation, but also mechanical ventilation, which has been in operation more than expected. 2) The building architecture contains a significant proportion of glass, causing increased cooling demand. 3) Commissioning of cooling and ventilation systems has been ongoing during the measurement period and is still ongoing. So in that light, 60% electricity saving is a good result. The design was evaluated and is now considered as fully developed. The production, PEX-pipes, installation and assembly methods are optimised as far as possible and the technology is commercialised and ready for use in the field.

The primary objective was to demonstrate the actual principle of thermo-active structures: The thermo-active slabs, that actively influences the building structure with an integrated system which cools the building e.g. by using outdoor air, groundwater or seawater as cooling source. During the night, this cooling water, which is typically at 19°C, removes the "excess temperature", which the structure has amassed over the course of the day. And because the plastic pipes are laid in the ceiling, cooling will not have a significant effect on the floor above. The thermo-active slabs can also be used for heating. The advantage is that the water only needs to be heated to 30°C, compared with approx. 60°C in radiator systems, although these can be used for supplementary heating.

It is documented that TABS can yield a constant cooling performance of at least 30 W/m² even with false ceiling covering 70-80% of the area under the thermo-active slabs. TABS are in many ways an optimal and indispensable solution, which not only minimizes electricity consumption for cooling and ventilation, but also has significant benefits in terms of improved indoor climate and in longer term large total economic gains. With the use of TABS in office buildings, the typical indoor climate discomfort associated with air cooling and ventilation (drag, noise, dust) are avoided, and in buildings with natural ventilation, the large temperature fluctuations throughout the day can be avoided. In both cases, this can result in increased productivity by the employees.

With thermo-active slabs it is possible to achieve lower construction costs than with conventional solutions, because the extra cost to floor structure and control system is compensated by savings on the technical installations (ventilation, cooling system, automation etc.). The building owner has more options at disposal regarding the building design, because energy savings make it easier to meet the energy performance requirements in the new building.