The building forms part of a cluster of five large renovated multi-family buildings from the 1960s within the Karlsruhe district Durlach, where an integrated energy system is demonstrated within the research project “Smart district Durlach”. The demonstrated heat pump technology features finned PVT collectors as single source for the heat pump system. Ultrafiltration are units are integrated in the drinking water circuit to allow low temperatures and maintain the hygienic requirements. 13 out of 150 radiators were exchanged to allow a heating temperature reduction to 55/45 °C.

The building was originally built in 1963 and renovated in 1995. The building features a heated floor area of 2112 m² on 5 floors with a total of 30 apartments. The building was renovated exchanging the windows with insulating glazing (Uwin = 1.7 W/m²K), and adding layers of thermal insulation (styrofoam, d = 60 mm, l = 0.035 W/mK) to the façade, cellar and to ceiling, thus reducing the overall U-value of the opaque envelope from Uenvelope = 1.71 W/m²K to  0.323 W/m²K.

Key facts

Building Heat pump and source
Location Karlsruhe, Germany
 Number of HP 1
Construction 1965 Installed power 55.4 kW
Heat distribution radiator heating Operation mode bivalent
Heated area 2112 m² living Heat source  PVT collectors
(solar+ambient)
Level of insulation good
(renovation in 1995) 
Heating system Domestic hot water
Heat demand 60 kW Type of system central
Heating temperature 55 / 45 °C
 Max. temperature 55 °C (with UF)
62 °C (without UF)
Circulation system yes

Description of the technical concept

Heat Pump Technology

  • 55.4 kWth brine-water heat pump
  • High temperature heat pump with
  • max. supply temperatures: 75 °C
  • Waterkotte IL EcoTouch
  • Tandem-Scroll with two power stages

Heat Source

  • Consolar Solink
  • PVT collectors with finned heat exchanger
  • 202 m2 collector area
    (East and west orientation)

→ Bivalent system with condensing gas boiler as back up (bivalent parallel operation)

→ Two drinking water storages (2x 850 l)

→ One heating buffer storage (850 l)

→ Heat pump integrated into district energy systems via SG ready to allow optimization of self-consumption of PV and CHP electricity

Low Ex Measures

Heat distribution system

  • Original radiators are mostly sufficient to allow a reduction of nominal heating temperatures
  • 13 of 150 radiators were identified as “bottleneck” radiators. These radiators are exchanged with radiators of larger heating power
  • Reduction of heating temperatures to 55/45°C
  • Hydronic balance

Domestic hot water distribution

  • Two external freshwater stations
  • Circulation
  • Ultrafiltration(UF) to reduce hot water temperatures from 62 °C to 55 °C
    (pilot project)

Karlsruhe-Durlach data sheet