D12, Vienna

The residential building D12 is a block of 7 buildings with 4-6 storeys each, commercial use on the ground-floor (GF) with 8 shops on 900 m2 and 213 flats on the upper levels. Seven heat pumps have been installed to cover the buildings energy supply in combination with PV, solar thermal and solar hybrid modules.

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Lessons learned 

  • The ground and groundwater coupled heat pumps supply the lion’s share of the heat, about four fifths of the total heat supplied was provided by these heat pump systems.
  • Air source heat pump (parking garage) could be used mainly during summer to provide high temperature heat, whereas ground source heat pump mainly during winter (highest source temperature)
  • The “multiple-heat source concept” of the overall energy system is approved to deliver a high redundancy and availability. Generally, no heat backup – like district heating – is required. Nevertheless, the district heating function as a thermal backup and guarantees high thermal comfort during heating season.

Key facts

BuildingHeat Pump and Source
LocationVienna, AustriaNumber of HP4 + 2 + 1
Construction2016Installed power4 x 144.1 kWh
2 x 65.1 kWh
1 x 57.8 kWh
Heat distributionunderfloor heatingOperation modemonoenergetic
Heated area19,080 m²Heat source4 x groundwater
2 x ground
1 x exhaust air
No. of apartments213
level of insulationvery good
Heating sytemDomestic Hot Water
Heat demand15.6 kWh / (m²a)DHW demand26 kWh / (m²a)
Heating
temperature
40 °CType of systemcentral
Max. temperature65 °C
Circulation system yes
Other information
PV & ST installationyesCOP4 x 3.57
2 x 4.47
1 x 3
Solar thermal90 kWthGround storage40 MWh th
PVT60 kWth / 16kWpelHot water storage6 x 2000l backup for SH and DHW
Photovoltaics20 kWp

Description of the technical concept

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The innovative energy supply system of the D12 is using several heat pump technologies combined with various sources (air, soil, groundwater, solar) and storage technologies. The control strategy operates the combinations of heat pumps with the most efficient heat source (based on demand and the external boundary conditions) and loads the thermal storage system. The connection between those plant components of the heat supply and the heat consumers is realized with two loops for high and low temperature supply of a set point of 65 °C for domestic hot water (DHW) and 40°C for space heating (SH). Using a so called ‘stratifier lance module’ the solar heat can be fed into high, middle and low temperature level storages, so that collector operating time and performance is maximized.

The heat generation systems are located in 6 building service rooms, each with SH and DHW buffer storages (6 X 2,000 l) connected with the two loops. The electrical energy demand of the HVAC system is supplied by the PV collectors, hybrid collectors and the battery storage and, if not available, from the public electricity grid.

As SH emission system, a floor heating system is installed. It is connected to the low temperature water loop and consists of 228 heating circuits. 17 main pumps circulate water to the ascending major distribution pipes with a total mass flow rate of 95 m³/h. The DHW production is provided by 5 freshwater modules connected to the high temperature loop. Each of these plate heat exchangers has a maximum heat transfer capacity of 315 kWth. The building complex is as well connected to the local district heating network with a capacity of 1.5 MWth. The heat system is operated in a holistic approach and the required/delivered energy is exchanged homogeneously over the hydraulic rings. However, the current water flow direction / frequency of the changes of direction cannot be determined explicitly. There are basically two operational modes depending on pressure difference:

1) Two or more active components operate the water network: The pumps produce the required pressure to direct the water flow, the pumps supply heat to the heating circuit and load the buffer tanks.

2) No heat generators running: The thermal water tanks are discharged and supply heat to the heating circuit.

AT003 D12 

  1. Pictures: IEA HPT Annex 49 “nZEB – Residential Building D12 – Aspern / Vienna / Austria” ↩︎
  2. ibid. ↩︎