Thermally Activated Building Systems (Concrete Core Activation)

A water-carrying pipe network embedded in the concrete floor slab — cooling in summer at 16-20 °C, heating in winter at 26-30 °C. Ideal with a heat pump or free cooling.

How do thermally activated building systems work?

With thermally activated building systems (TABS), also known as concrete core activation, a water-carrying pipe network is embedded in the floor slab before the concrete is poured. The entire slab thus becomes a heating and cooling surface. In summer, water at 16 to 20 °C flows through the pipes and cools the concrete; in winter, 26 to 30 °C is sufficient for heating. The large surface area allows these small temperature differences, and the concrete acts as a store that balances load peaks over the day. The low flow temperatures make the system particularly efficient for heat pumps: in heating mode, seasonal performance factors (SPF, the ratio of heat delivered to electricity consumed over a year) of 5 and more are achievable. When cooling via ground probes in free cooling mode, only the circulation pump runs, which corresponds to an EER of 8 and above.

Which buildings benefit from thermally activated building systems?

TABS is a measure for new builds and deep refurbishments, because the pipe network is cast into the concrete slab. It requires a low-temperature heat source such as a heat pump or geothermal system and a steady occupancy pattern. Typical properties are new-build office buildings, hotels, care homes and residential buildings. Because the system responds slowly, it is not suitable for rooms with strongly fluctuating occupancy such as lecture halls or schools. In practice, TABS is usually designed as a base-load system and supplemented where needed by a fast-responding secondary system. The maximum output per square metre of slab is limited, so a well-insulated envelope is a prerequisite.

What do thermally activated building systems actually deliver?

Compared with conventional heating and cooling, final energy demand falls by 30 to 50 %. The calculation compares the demand of the old system (gas boiler with SPF around 0.95, split air conditioning with EER 3.5) with a heat pump plus TABS (SPF 5.5, EER 12 with free cooling). For a 4,000 m² office building this yields around 200,000 kWh/a of final energy and roughly 40 t CO2 saved per year. The additional cost over the standard installation is €30 to €60 per m² of gross floor area. With a service life of 50 years, the measure pays back in 10 to 18 years.

Energy carrier

Erdgas, Strom → Strom (WP) + Anergie/Erdwärme

Savings potential

30-50 % gegenüber konventioneller H+K

Worked example

A new 4,000 m² office building has a space heating demand of 200,000 kWh and a cooling demand of 120,000 kWh per year. The conventional option with a gas boiler (SPF 0.95) and split air conditioning units (EER 3.5) is compared with a heat pump and thermally activated building systems supplied via ground probes (SPF 5.5 in heating mode, EER 12 in free cooling mode). For heating this gives 200,000 / 0.95 − 200,000 / 5.5 = 210,526 − 36,364 = 174,162 kWh less final energy. For cooling it is 120,000 / 3.5 − 120,000 / 12 = 34,286 − 10,000 = 24,286 kWh. In total, the building saves around 198,500 kWh of gas and electricity, rounded to 200,000 kWh of final energy per year, which corresponds to roughly 40 t CO2. Heat meters for heating and cooling together with a separate electricity meter for the heat pump make the real performance factors traceable.

Investment & payback

Mehrkosten gegenüber Standardgewerk Heizen/Kühlen: 30-60 €/m² BGF; nur sinnvoll im Neubau oder Kernsanierung · Service life: 50 a · Payback: 10-18 a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

What is the difference between thermally activated building systems and underfloor heating?

In underfloor heating, the pipes sit in the screed close to the surface and respond within a few hours. In thermally activated building systems, they sit in the core of the concrete slab, which acts as a store and responds slowly over hours to days. TABS can both heat and cool, works with even lower flow temperatures, and can only be realised in new builds or deep refurbishments.

Can thermally activated building systems be retrofitted?

No, classic concrete core activation cannot be retrofitted, because the pipe network is placed in the formwork of the floor slab before concreting. It is a measure for new builds and deep refurbishments with new slabs. In existing buildings, near-surface alternatives such as ceiling sails or chilled ceilings are possible, but they exploit less thermal mass.

How much do thermally activated building systems cost in an office building?

The additional cost over a conventional heating and cooling installation is €30 to €60 per square metre of gross floor area. In return, radiators, split units and most of the ductwork are no longer needed. With a service life of 50 years, since the pipe network is part of the structure, the measure pays back in 10 to 18 years.

Which buildings are unsuitable for thermally activated building systems?

TABS is not suitable for rooms with high load fluctuations such as lecture halls, schools or event venues, because the system is too slow to respond to sudden full occupancy. Buildings with constant use such as offices, hotels, care homes and residential buildings are well suited. A poorly insulated envelope is also an exclusion criterion, since the surface output is limited.

Which standards apply to thermally activated building systems in Austria?

ÖNORM EN 15377 governs the design of embedded surface heating and cooling systems, including the sizing of thermally activated building systems. ÖNORM B 8110 sets the thermal insulation requirements that must be met for the low surface outputs of TABS. The usual efficiency requirements under ÖNORM EN 14511 additionally apply to the heat pump.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Wichtige Messpunkte: VL/RL TBA-Kreis, Wärmemengenzähler (Heizen+Kühlen), Raumtemperatur Stichproben, ggf. Lufttemperatur an Decke. WP-Strom getrennt. PUE-ähnliche Effizienz-KPI.

All measures