Illustration Header Image Reference Steinbach Bremen

Heat Pump Cascade & Air-conditioning System for a Block of Flats

Reference for efficient and climate neutral heating and cooling

Bremen, Germany

Warm summers, long transition periods and security of energy supply are factors that building contractors have to consider when planning the heating system. The aim is to align the requirements for comfort, energy and cost efficiency as well as future security. In a new-build block of flats, these tasks have been implemented using energy-efficient heat pump technology. An air-to-water heat pumpcascade is used to providecomfortable room heating and domestic hot water. In the loft flat, an additionalair-to-air heat pump solution providescool temperatures in summer and can also be used for heating if a sudden heating demand occurs.

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Key Facts

Requirements:

sustainable, renewable heat supply
energy-saving, environmentally friendly building energy technology
cost-efficient and reliable heat technology
pleasant and comfortable temperatures in summer and winter

Requirements

The neighbourhood in Bremen known as “Viertel” essentially emerged during the city expansion from the middle of the 19th century. Many of the “Altbremer” houses typical of this building period have been preserved – especially in the side streets. Jürgen Steinbach has set up a modern residential project in a gap site on his parents’ former property which meets the current requirements in terms of energy efficiency and climate protection. The residential building with a living space of approx. 900 m² has an underground car park, eight residential units and a wrap-around balcony for the loft flat on the top floor.

A key challenge in this new-build project – as in all current new-build projects – was the building energy technology. According to the building contractor’s ideas, the aim was to develop a sustainable heat supply for the well-insulated block of flats and at the same time ensure a pleasant and comfortable temperature level in all flats all year round.

Which solution was chosen for the block of flats?

Heat pump cascade

Ecodan air-to-water heat pumps in a three-unit cascade

The heating supply 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 out of the question for various reasons, the consultant convinced the building contractors to opt for an air-to-water heat pump system with inverter technology in a three-unit cascade with fresh water stations for each residential unit. Due to the inner-city building density, another strong case was made for an air-to-water heat pump: Compared to all heat pump solutions, the least amount of construction work would be required if air is used as heat source. The (latent) heat in the ambient air serves as energy source and is extracted by air-to-water heat pumps.

Illustration: Steinbach block of flats in Bremen, Germany

Sustainable, renewable heat supply

The energy source provided by the ambient air is considered to be 100 % environmental heat, making it possible to use a monovalent and regenerative system that dispenses with fossil fuels. Heat distribution in the block of flats is accomplished by underfloor heatings in each residential unit, being preadjusted via a dynamic valve for automatic hydraulic balancing. 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.

Illustration: Air-to-air heat pump system in office at home

Energy-saving, environmentally friendly building energy technology

Three Ecodan air-to-water heat pumps manufactured by Mitsubishi Electric with Zubadan inverter technology with a total heat output of 33.6 kW were installed in a three-unit cascade on the roof of the building to provide environmentally friendly and energy-efficient space heating and domestic hot water. Each of the three Ecodan units has a heat output of 11.2 kW. This enables the heat pump cascade to easily cover the heating load for the building and to simultaneously provide sufficient heat for DHW production.

“We also opted for heat pump technology to show that it can be used to heat a building very economically without fossil energy carriers. Our tenants find that very attractive”,explains Jürgen Steinbach.

A cascade control with auto-adapt function optimises the operating behaviour of the Ecodan units and automatically selects the best duty point for the system. In addition, the cascade offers a redundancy function when individual units undergo maintenance, resulting in increased operational reliability.

Illustration: Ecodan air-to-water heat pumps on roof

Quote

Cascading the heat pumps offers several benefits over a single unit 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.

Torsten Koeppe // Sales engineer at Mitsubishi Electric for heating technology

Cost-efficient and reliable heat technology – even at ambient temperatures as low as -28 °C

A special feature of the heating technology used here is the Zubadan inverter technology implemented in the heat pumps. The patented injection method optimises the available heating output. This means that the heat pumps can still provide 100 per cent of their heating output even at ambient temperatures as low as -15 °C. At the same time, the lower operating range is extended to ambient temperatures as low as -28 °C. This makes it possible to go without the support of an electric heating rod or an additional heat generator even at low ambient temperatures.

Two buffers were integrated into the system concept for operation with reduced duty cycles. One buffer tank stores the heat on demand and provides the energy required for defrosting the outdoor modules in winter. This is used to bridge shut-off times of the electricity supplier in order to provide sufficient heat at all times. The second buffer is an 800-litre stratified buffer tank for DHW production for the eight residential units. At a DHW temperature of 53 °C, it retains sufficient heat for domestic hot water production. Each residential unit has a fresh water station for DHW distribution alongside the heating distribution.

The working principle of air-to-water heat pumps

The working principle of Air-to-water 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, and the temperature level rises. The machines on the roof are connected to the heat exchanger via the refrigerant pipes that run through the building. A hydro module is available for each outdoor unit in the plant room in the basement of the residential house. This is where the energy exchange from refrigerant to heating circuit water takes place. It is a simple way of hydraulically decoupling the heating and heat pump circuits from each other while ensuring a constant refrigerant flow rate.

What project participants say

Project quotes

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Jürgen Steinbach, owner and Managing Director of KLK Klima-Lüftung-Kälte GmbH, explains:

“The tenants found it very attractive that the building is heated using cutting-edge air-to-water heat pumps. As we have a three-unit cascade, they were also positive about the operational reliability.

When it comes to combining heating and DHW, we recommend Mitsubishi Electric heat pumps, because the Zubadan technology can also be an economic DHW solution.”

Illustration: Three-unit cascade located in the cellar

Mitsubishi Electric cascade solutions

Ecodan cascade solutions make it possible to enjoy the unique benefits provided by Ecodan heat pumps even in larger complexes with higher heating outputs. They involve multiple Ecodan air-to-water heat pumps being interconnected in cascades, with Mitsubishi Electric once again providing preconfigured sets with suitable accessories.

Heat pump cascades

Air-to-air heat pump solution for the block of flats

Air-to-air system

Pleasant and comfortable temperatures in summer and winter

A very modern solution is on display in the top flat. As a penthouse style flat, it has generous window areas and large balconies on the south side. This can lead to relatively high heat loads in the warm season. In order to dissipate this heat and thus significantly increase living comfort, this residential unit is equipped with an additional Mitsubishi Electric M series air-conditioning systemand four MSZ-EFindoor units. However, the flat can not only be cooled in summer: On colder days, the system can also be used as an air-to-air heat pump system for heating. By this means, owner Jürgen Steinbach saves additional energy and costs, becauseM series air-conditioning systemsare also very energy efficient.

This is considered to be particularly comfortable in the study room while working from home. If required, it is possible to cool or heat at short notice at any time without the need to activate the underfloor heating straight away. One of the four wall-mounted units is located in the bedroom, another one in the study, and the other two in the living and dining area. The Mitsubishi Electric M series air-conditioning units are the ideal choice for greater living comfort in small to medium-sized rooms. The sleek design and the chosen “glossy white” model colour ensured harmonious integration into the appearance of the room. Moreover, the EF units are extremely quiet in operation due to their special “sleep mode”, which can be very important in the bedroom, for example.

They can also be controlled very conveniently. In addition to the room thermostats for the underfloor heating and the wireless remote controls for the air-conditioning system, both the heating and the indoor air-conditioning units can be easily operated via a tablet or mobile phone app using a WIFI adapter. “After all, this huge comfort benefit was not available with normal heating and cooling systems in the past. With Mitsubishi Electric technology, all this can be implemented very well”, concludes Steinbach.

The working principle of air-to-air systems for cooling and heating

Technically speaking, the design of split type air-conditioning systems corresponds to the design of air-to-air heat pumps. By selecting the function mode, the split type unit can switch from air-conditioning function to heating function. A refrigerant circulates in the heat pump which, in the case of the air-to-air heat pump, extracts heat from the ambient air and vaporises in the process. The vaporised refrigerant is compressed using an electrically driven compressor. This increases the temperature to such an extent that the heat can be released into the room air via a heat exchanger. The heat dissipation causes the refrigerant to liquefy again. It is then expanded to a lower pressure via an expansion valve and the cycle starts all over again. In cooling mode, this cycle works in reverse – heat is extracted from the rooms and released to the outside.

Split type air-conditioning systems / air-to-air heat pumps

Mitsubishi Electric M-series

IT RAC System

MUSY-TP

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The key points

Summary

In many respects, the block of flats in Bremen’s trendy neighbourhood known as “Viertel” reflects the cutting edge of technology and living comfort.
Being a modern block of flats, it makes use of particularly energy-saving building energy technology.
Along with being cost-orientated, this concept allows a reliable heat supply and ensures pleasant and comfortable temperatures in all flats all year round.
A Mitsubishi Electric Ecodan air-to-water heat pump system is used in a three-unit cascade. Thanks to its innovative Zubadan inverter technology, it provides comfortable room heating and domestic hot water in all eight residential units even at the lowest outside temperatures.
In addition, a Mitsubishi Electric M series air-conditioning solution was installed in the loft flat, which can be used to cool the rooms in summer and also to heat them if a sudden heating demand occurs.