Operating heat pumps in cascades: When does that make sense?
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Stefano Fonseca is an energy and environment engineer with over six years of experience in technical building equipment (TGA). He combines technical expertise with a passion for understandable communication. For more than five years, he has been writing as a freelance editor about renewable energy and sustainable living, in particular about photovoltaics and heat pumps.
Large buildings place high demands on heating technology. A single heat pump is often not enough. The solution is usually based on a cascade circuit. This article explains when it makes sense to operate heat pumps in cascades and what advantages this technology offers.
What is a heat pump cascading?
A heat pump cascading is the interconnection of at least two heat pumps. These are hydraulically and control-connected to form an overall system. A central manager controls the individual devices as needed. In this way, the output can be flexibly adjusted to current heating requirements. The cascade works like a single, modulating large heat pump.
How do cascade heat pumps work?
Several heat pumps work together in a cascade. A cascade manager monitors the building's heat demand. When demand is low, only one heat pump runs in the optimum efficiency range. If demand increases, the manager gradually switches on additional devices. In this way, only the performance that is really needed is always provided. This avoids inefficient partial-load operation and frequent clocking.
What is a cascade manager?
A cascade manager is a special control and regulation device for heat pump cascades. It communicatively connects the individual heat pumps together. Its main task is to control the devices as required to cover the required heating load. It ensures efficient and wear-resistant operation by optimising the switching sequence and running times of the individual heat pumps.
When does a heat pump cascade make sense?
A heat pump cascade is particularly useful in buildings with high and highly fluctuating heat requirements. These include apartment buildings, commercial properties, hotels or public institutions. Starting at a heat load of around 20 to 30 kilowatts, a cascade is often more economical and efficient than a single large heat pump. It also offers greater reliability.
Can you also install a cascade in a single-family house?
Technically, it is also possible to install a cascade in a single-family home. However, it rarely makes economic sense. The heat requirement here is usually so low that a single, well-dimensioned and modulating heat pump is sufficient. The higher investment costs for two devices and the more complex control generally do not pay off.
What are the advantages of a heat pump cascade?
The cascade circuit offers significant advantages over a single large heat pump.
- Higher efficiency: The heat pumps often operate in the optimum output range. This increases the annual performance ratio (JAZ) and reduces operating costs.
- Maximum operational safety: If one heat pump fails, the other devices take over the supply. The heating does not completely fail.
- Flexible performance adjustment: The output can be adapted exactly to requirements. This avoids oversizing and inefficient clocking.
- Easier maintenance: The individual, smaller devices are more easily accessible and easier to maintain or replace than a single large system.
- Lower sound emissions: Several small appliances are often quieter than a single large, high-output heat pump.
Which heat pumps are suitable for a cascade?
In principle, all types of heat pumps are suitable for a cascade. Air-water heat pumps are the most flexible, as they do not require complex earthworks or permits. Ideally, identical models from the same manufacturer are used. This simplifies control and hydraulic integration. Monoblock devices are often a good choice for cascades due to their compact design.
What is the efficiency of a cascade?
A well-planned cascade is generally more efficient than a single large heat pump. The reason lies in better partial load behavior. Each heat pump can operate at its optimum output range for longer. Frequent switching on and off (clocking), which occurs with oversized individual systems and significantly reduces efficiency, is avoided. This results in a higher annual performance ratio (JAZ) and thus to lower operating costs.
How is the performance of a cascade dimensioned?
The sizing is based on the Heat load calculation of the building in accordance with DIN EN 12831. The total output of the cascade must be able to cover the maximum heating load on the coldest days of the year. This total output is then divided between several smaller heat pumps. A common practice is to split into a base load heat pump and one or more peak load heat pumps.
How do you correctly plan a heat pump cascade?
Careful planning is the key to the success of a cascade system.
- Heat load calculation: Determine the exact heating load of the building.
- Device selection: Select the number and output of individual heat pumps.
- Hydraulic concept: Create a detailed diagram for the hydraulic connection.
- Buffer tank: Size a suitable buffer tank for decoupling.
- Control engineering: Plan the use of the cascade manager and integration into building automation.
- Installation location: Determine the locations of outdoor units taking into account sound insulation and accessibility.
What is the role of the buffer tank in a cascade?
The buffer tank serves as a hydraulic switch and decouples the heat sources (cascade) from the heat consumer (heating circuits). It absorbs excess heat and releases it again when needed. This prevents the heat pumps from running frequently, extends their service life and ensures a uniform heat supply in the building.
Is a cascade quieter than a single large heat pump?
In most cases, a cascade of several small heat pumps is quieter than a single large system with the same total output. Smaller devices generally have a lower sound power level. In addition, not all devices run at the same time when the heat requirement is low. By cleverly positioning the outdoor units, sound pollution can be further minimized.
What are the installation site requirements?
The installation site must provide sufficient space for the installation of several outdoor units. The minimum distances to property boundaries, walls and each other must be maintained to ensure air circulation. The sound insulation requirements in accordance with TA Noise are particularly important. Careful planning of the installation site is crucial in order to to avoid conflicts with neighbors.
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