Project: Hybrid system in apartment building

Hybrid system in an apartment building

Apartment house modernisation

  • The building is heated with gas. Due to the already existing good insulation, the integration of environmental heat as a second heat generator would be possible.

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  • In addition to the highly fluctuating demand for heat for heating and hot water, the work is to be carried out in such a way that the tenants are directly affected as little as possible. This requires close coordination between the company carrying out the work, the landlords and the tenants.

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Trouble-free and simple renovation

The large apartment block contains 15 residential units and was built 15 years ago. As environmental protection is very important to the landlords, they wish to upgrade their property accordingly.

Low-fuss modernisation

A modern heating system that is as environmentally friendly as possible is important to the landlords. Therefore, they want to replace the current heating system and add renewable energy solutions.


They can do this by combining the new gas heating system with an environmentally friendly appliance. As a result, they can continue to use the existing radiators and piping. If they had chosen a heating system that was run solely on renewable energies, it may not have been feasible to use the present equipment.

Project challenges

The greatest challenge must surely be that the work is being conducted while the tenants are present. The construction work must kept within certain limits and preferably should be confined to the boiler room in the cellar.


Furthermore, hot water requirements and peak loads fluctuate very strongly due to the large number of tenants. So both heating systems must be capable of mitigating the effects of these high demands.


Last but not least, the insulation of the building is very good but there have been problems with mould in a few of the residential units in the past. This could be prevented by installing a ventilation system.


Reasons for using the proposed new components

The old gas heating boiler is 15 years old and is being replaced by a modern condensing appliance. Many owners use their heat generators for much longer than this, but they are considered to be technologically obsolete after 15 years. For this reason, the landlords can expect the new appliances to be more efficient. This alone saves fuel and reduces heating bills. The new boiler will also be less prone to malfunction.


A heat pump heating system is integrated at the same time. This updates the entire heating system and makes it more environmentally friendly. It also works particularly efficiently when used with heat distribution systems that only require low flow temperatures and if the walls are well insulated. The building already fulfils both of these requirements.

01. A combination system reduces the ecological impact

The heat pump heating system takes over part of the work of the new heating system without producing any emissions whatsoever. In this way, the combination of the two heat generators consumes less fuel and emits fewer harmful exhaust gases than if the heating system and hot water were run using the gas boiler alone.


As stated above, the combination of fossil and renewable energy consumes less fuel and so fuel bills are also slashed.

02. Low-maintenance and durable

Condensing appliances have proven themselves over many years. The users can trust that the new heating system will function reliably for a long time. This also applies to all other components of the new system. In addition, the new heat pump is a particularly low-maintenance model.


03. Heating supply around the clock

The heat pump heating system will mainly cover the DHW heating. As mentioned above, hot water demands can vary greatly, but this heating system works best when run continuously. For this reason, the landlords will also be installing a buffer cylinder.

04. Pleasant indoor environment

The landlords also decide to fit a decentralised ventilation system to improve the comfort of the homes, supply them with a constant flow of fresh air and prevent further mould formation. The system extracts polluted and moist air and supplies new fresh air. A bonus: as decentralised appliances do not require a system of air ducts, only limited installation work is needed in the apartments.

The following products were selected

All the appliances required for the project can be found in the range of the renowned heating and air conditioning technology manufacturer WOLF. The landlords sought advice from building services technology experts and so settled on these products.

WOLF Gas condensing boilers CGB-2 family

CGB-2 series of gas heating appliances

This appliance has an output of 55 kW and is intended for use in apartment blocks. The boiler is highly efficient.

This saves fuel and minimises emissions. The wall-mounted version of the appliance takes up very little space when installed.

WOLF combi storage tank

BSH high hygiene cylinder

The storage cylinder is primarily a supplementary product for renewable energy solutions and provides tenants with a continuous supply of hot water.

It compensates for the irregular demand for hot water that arises in buildings housing many occupants.

Sounds complicated? Not for us!

It can be complex and time-consuming to find the right solution for your home. We can help you to understand everything that is really relevant to your project in only a few minutes.

Additional comfort and environmental protection

The new condensing appliance combined with environmental heat reduces the consumption of fuel. In addition to lowering costs, this also produces fewer exhaust gases that are harmful to the climate.


The owners are considering adding a solar electricity system on the roof in the future. The heat pump heating system would then use only renewable energy sources and would further improve the ecological footprint of the entire system. So the landlords will have achieved their objective of modernising their building without the construction work inconveniencing the occupants too badly.

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