Heat pump for a block of flats
Heat pump for the “Maingold” block of flats
Bremen, GermanyEfficient and climate-neutral heating with the Ecodan air-to-water heat pump system
The “Maingold” construction project, an block of flats with 13 residential units in Bremen’s Neustadt district, is special in many respects. The building was erected between the foundation walls of a former air-raid shelter. In contrast to purely new buildings, the foundation and foundation walls of the old air-raid shelter were incorporated into the specialist planning carried out by Klaus Schierenbeck Gebäudeplanung. The result is a modern living culture that impresses with its harmonious façade structure, floor-to-ceiling windows, balconies and roof terraces. In addition, the building was completed in 2020 as a KfW Efficiency House 55 in accordance with EnEV. Even back then, the overall energy concept met the GEG requirements as of July 2021 for an Efficiency House EH 55 EE. The heat supply had to be planned in a correspondingly modern, efficient and future-oriented way.
Requirements
The challenge in terms of building technology for the construction project in the neighbourhood known as “Flüsseviertel” in Bremen’s Neustadt district was to develop a sustainable heat supply for the well-insulated block of flats. Moreover, climate protection, i.e. the supply of heat for the building with low CO2 emissions, was an absolute priority of this project. At the same time, the heat energy required for heating and DHW was to be produced in a climate-neutral manner. Other than that: Last but not least, all residential units were to have their own fresh water station and underfloor heating with individual room control.
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- Heating solution with low CO2 emissions
- climate-neutral production of heat and DHW
- separate fresh water station for each individual flat
- underfloor heating with individual room control
Which solution was chosen for the “Maingold” block of flats?
Heat pump cascadeEcodan air-to-water heat pumps with Zubadan inverter technology in a three-unit cascade
The building was designed by the Bremen-based Freudenberg/Mielke architects, who have already implemented several remodellings of air-raid shelters. The building project was implemented by M-Projekt, with architect Gunnar Neimke in charge. The overall energy concept and systems technology in this climate-neutral block of flats was developed by Klaus Schierenbeck, a planner and specialist in technical building equipment and energy efficiency expert for residential and non-residential buildings (Deutsche Energie-Agentur, DENA).
As a geothermal system was not possible, Schierenbeck recommended an Ecodan air-to-water heat pump system with Mitsubishi Electric Zubadan inverter technology to the building contractor. The heat pumps are installed in a three-unit cascade in the outdoor area and supplemented by a 4-pipe network with fresh water stations in each flat.
The technology has already successfully been used in more than 20 blocks of flats since 2016. However, also the energy costs from a comparable complex were very convincing. Each of the three Ecodan outdoor units has a heat output of 11.2 kW, enabling the heat pump cascade to easily cover the heating load for the building and to simultaneously provide sufficient heat for DHW production. The freely available heat in the ambient air serves as energy source and is extracted by the heat pumps. Moreover, the energy in the ambient air is considered to be 100 % environmental heat.
Advantages of the air-to-water heat pump solution
BenefitsHigher performance. More efficient. Safer.
Cascading of heat pumps offers numerous benefits over a single heat pump with a correspondingly high output. Operating the system within the very large modulation range of a cascade is much more efficient than running just one module at full load. This allows the units to operate simultaneously under partial load. A cascade control with auto-adapt function optimises the operating behaviour and automatically selects the best duty point for the system. In addition, a cascade offers a redundancy function when individual system units undergo maintenance, resulting in increased operational reliability. Moreover, the overall running times of the individual modules are being reduced, which increases their durability.
KfW Efficiency House level 55 and class EH 55 EE according to GEG 2020
The heat pump technology was an important component in fulfilling the requirements for the KfW Efficiency House level 55 in accordance with EnEV and GEG for a EH 55 EE Efficiency House. On top of that, a thermal insulation composite system with an external insulation of 20 cm was chosen for the building envelope. In combination with the mandatory triple-glazed windows and a ventilation system, which was necessary not least due to the internal bathrooms, the building achieves a final energy demand for heating and DHW of 12.9 kWh/(m2a) and a primary energy demand of 23.2 kWh/(m2a).
Operating range down to minus 28 °C ambient temperature
A special feature of the heating technology used here is the patented Zubadan compressor technology implemented in the heat pumps. The implemented injection method optimises the available heating output. 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 to ambient temperatures as low as minus 28 °C. This makes it possible to supply the building with heat and to go without the support of an electric heating rod or an additional heat generator even at low ambient temperatures.
Low flow temperature for heating and DHW
Also part of the system concept is the buffer tank – storing the heat until it is retrieved and bridging shut-off times of the electricity supplier – which can provide sufficient heat at all times. At the same time, the buffer tank provides energy for defrosting the outdoor modules in winter. Even heat distribution in the block of flats, which is considered extremely pleasant, is accomplished by underfloor heatings in each residential unit, being preadjusted via a dynamic valve for automatic hydraulic balancing and individually controlled via single room controllers. Low flow temperatures have a positive influence on the efficiency of the system. Since the underfloor heating is a low-temperature system, it is ideally suited to be combined with air-to-water heat pumps.
For theDHW productionof the 13 flats, an 800-litre stratified buffer tank is available in the plant room. At a DHW temperature of 53 °C, this buffer retains sufficient heat for domestic hot water production. Each residential unit has a dedicated fresh water station for DHW distribution alongside the heating distribution. The outlet temperature in each residential unit is 50 °C. The indirect heat transfer to the freshly tapped drinking water (continuous flow principle) eliminates the risk of legionella, and the requirements of the Drinking Water Regulation in accordance with worksheet B501 can be met in an energy-saving manner without high temperatures.
The operating principle of heat pumps is as simple as can be: To use the energy contained in the ambient air, the environmental heat absorbed by the heat pumps is transferred to a refrigerant circulating in a closed circuit. The pressure in the refrigerant compressor is increased, the temperature level rises, and a heat exchanger provides for the energy exchange from refrigerant to heating circuit water. A hydro module is available for each outdoor unit in the plant room in the basement. It is a simple way of hydraulically decoupling the heating and heat pump circuits from each other while ensuring a constant refrigerant flow rate.
The key points
Summary- The block of flats in Bremen’s Neustadt district meets the latest requirements in terms of comfort, furnishings and energy sustainability.
- The overall energy concept corresponds to the KfW Efficiency House 55 standard and fulfils the high GEG requirements for residential buildings.
- The heat requirement for heating and DHW is covered by air-to-water heat pumps in a three-unit cascade.
- Thanks to their comparatively low investment and installation costs, Ecodan outdoor units are a particularly economical alternative.
- The low flow temperature of the underfloor heating and the DHW production allow particularly economical and energy-efficient operation in the low temperature range.
- Thanks to the Zubadan compressor technology, the use of an electric heating rod or an additional heat generator is no longer necessary – even at particularly low outside temperatures.
- Hence, the entire system technology with its particularly low heating and DWH costs is extremely affordable for end users.
