Heat pumps for the Bilker Bunker
Energy-saving heat supply for a listed building
DüsseldorfBilk is Düsseldorf’s most heavily populated district, with a thriving student community. The area is also known for its highly diverse culture, with countless restaurants, cafés and cultural institutions like the Bilker Bunker. Originally built as a civil defence bunker, the building was later sold and renovated over the course of the following two years. Today, the bunker is owned by KÜSSDENFROSCH Häuserwachküssgesellschaft mbH, which looks for interesting and unusual buildings worthy of preservation, purchases them, and finds the right economic purpose that preserves them for both the city and future generations.
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Requirements:
- Comprehensive redesign of the building services
- Energy-saving and future-proof heat supply
- Comfortable temperature level
- Controlled ventilation
Background
BackgroundThe renovation began with the construction of five maisonette apartments on the roof of the bunker with a total floorspace of 670 m². These luxury owner-occupied flats each have between 97 and 164 m² of floorspace. They are heated via an underfloor heating system that can also be used for cooling in summer. The second project phase saw the original bunker structure renovated in line with listed building protections. This focused mainly on opening up the indoor walls to create more space and transparency between the individual rooms. On top of this, some of the ceilings were removed and new steel girders installed that would allow larger items to be placed in the exhibition rooms. The Bilker Bunker was converted into a communal art and cultural space by Bilker Bunker gGmbH. This created a cultural institution that uses art to bring the community together, turning this former structure of war into an innovative space for art, culture and leisure for everyone.
Project quote
Project quote
“As architects and project developers, we work very closely together with citizens and local government to take everyone’s wishes into account. We plan and implement every stage of the conversion, from the design all the way to completion, which allows us to influence every little detail at all times.”
Challenges
Challenges
The vast majority of the heating requirement, however, was to be covered by cutting-edge technology that met the requirements of the modern building with its event, music, seminar and office spaces. “The listed building status meant that the German Building Energy Act (GEG) requirements for the heating systems did not apply to the bunker. They did apply to the five apartments built on top of the roof, however. Although a fossil fuel-based heating supply was considered, the idea was quickly dropped due to the political circumstances”, explains Peter Dukome, project manager at PBS-Energiesysteme GmbH from the nearby town of Haan.
The comprehensive overhaul of the building services was one of the main elements of the modernisation and conversion project in the bunker. The challenge here lay in developing and implementing a modern and energy-efficient heating supply for this unusual listed building. It had to provide comfortable temperatures all year round in both the bunker area and in the rooftop apartments that were subject to the requirements of the German Building Energy Act (GEG). The bunker’s listed status meant that it had virtually no windows on its outer shell, which created the need for controlled ventilation inside. This was achieved via a new central ventilation unit and a complete reinstallation of the air duct network.
Solution
SolutionThe bunker’s heating system uses fourEcodan air-to-water heat pumpsfrom Mitsubishi Electric in a cascade arrangement. Cascading of heat pumps offers numerous benefits over a single heat pump with a correspondingly high output. Cascades have a larger modulation range that ensures smoother operation with no interruptions. They are more efficient because the units work more effectively at partial load (greater energy efficiency). A control with auto-adapt function optimises the operating behaviour and automatically selects the best duty point. In addition, the cascade offers a redundancy function when individual units undergo maintenance, resulting in increased operational reliability.
The cascades consisting of four individual type PUD-SHWM140YAA units, each delivering 14 kW of rated heating capacity, provide the heat in the old civil defence bunker. Divided over seven floors (two basement floors and five above ground), the bunker has a total floorspace of around 2,300 m2 that is heated by the four air-to-water heat pumps and the heat recovery function of the central ventilation system. The heat pumps therefore cover the building’s heating load in monovalent operation. The heat is distributed via finned-tube heating elements whose crude steel look make them a good match for the character of the bunker.
Heating or cooling with reversible heat pumps
A pair of type PUZ-SHWM120YAA reversible Ecodan air-to-water heat pumps from Mitsubishi Electric work as two-unit cascades to supply the newly built apartments on the roof of the bunker. The outdoor units each deliver 12.1 kW of rated heating capacity or 12 kW of cooling capacity, and provide heat to the underfloor heating in cold outdoor temperatures. In hot summer months, the heat pumps are used to channel cool water through the underfloor heating. This surface temperature control indirectly cools the building structure in case of high outside temperatures: the heat load is dissipated outside via the underfloor heating, thus cooling the rooms down by a few degrees.
Major benefits
Benefits100% capacity at minus 15°C thanks to patented Zubadan technology
The outdoor units for both the bunker and the apartments are equipped with patented Zubadan technology. This makes it possible to keep the refrigerant mass flow and therefore the compressor speed constant. To achieve this, a two-part mixture is injected into the compressor head during the compression process. The flash injection circulation of the Zubadan compressor allows the unit to work at a higher speed at low outdoor temperatures, while keeping the amount of refrigerant in the heat pump system constant. This means that these heat pumps can still provide 100 per cent of their heating output even at ambient temperatures as low as minus 15 °C. At the same time, the lower operating range is extended down to minus 30°C outside temperature, at which the heat pumps can provide a usable temperature for heating operation. There is no need for an electrical heating element or further heat source.
Outdoor units on the outer facade
The outdoor units were installed on the outer facade in line with the local urban conditions. The four-unit cascade is mounted on a ledge above the gate entrance. The two-unit cascade for the apartments is installed above a utility area on the third floor. Both locations are easy to access for maintenance purposes, offer good air circulation, and are both optically and acoustically discreet. The heat pump cascades are hydraulically integrated into the various heat distribution systems via hydro boxes, in which the energy is transferred from the refrigerant to the heating water.
The system is augmented with two buffer storage tanks.
The indoor units for the four-unit cascade that supply the bunker are located in a technology room on the third floor. Each outdoor unit has a hydro box with heat exchanger. The system is augmented with two buffer storage tanks that store the pre-conditioned heating water until it is needed. They also help to bridge cut-off periods of the energy provider. At the same time, the buffer tanks constantly provide sufficient energy for defrosting the outdoor modules in winter. The technology room for the heat pump cascades for the five apartments is located on the fourth floor. It has two hydro boxes for energy transfer, along with a buffer tank for storing warm or cold water depending on the operating mode.
The key points
Summary- The former civil defence bunker in Düsseldorf’s Bilk district was recently converted into a cultural institution. In addition, five premium maisonette apartments were built on the bunker’s roof.
- A total of six Ecodan air-to-water heat pumps from Mitsubishi Electric are used to provide a modern, energy-efficient supply of heat for this unusual and partially listed building.
- The Ecodan air-to-water heat pumps are arranged as cascades with four or two units for heating and cooling the bunker or apartments respectively.
- The Ecodan air-to-water heat pumps provide energy-efficient heating and cooling and are the perfect solution for meeting the requirements of the new German Building Energy Act (GEG).
- All units are equipped with patented Zubadan technology, which allows the heat pumps to deliver 100 per cent of their heating capacity even at outdoor temperatures as low as minus 15°C.
- The lower operating range is extended down to minus 30°C outdoor temperature, in order to provide a usable temperature for heating operation as well.
- No electric heating element or additional heat source is required.
