Which Backup Generator for a Heat Pump?
Heat pumps are considered an efficient and future-proof heating solution. What is often overlooked in everyday life: Without electricity, even the best heat pump stops working. Especially in single-family homes, agricultural properties, or commercial buildings, the question therefore arises as to which backup generator is suitable to reliably operate a heat pump in the event of a power outage.
Key points at a glance
- A heat pump places higher demands on a backup generator than many simple household appliances.
- Not only the operating power, but above all the starting current of the compressor, is crucial.
- For three-phase heat pumps, the unbalanced load capability of the generator must be considered.
- Modern heat pumps require stable voltage and reliable frequency regulation.
- For safe sizing, the entire system should always be considered: heat pump, auxiliary heating, pumps, control system, and other consumers.
Table of Contents
Why heat pumps place special demands
A heat pump is not a simple consumer. It consists of several electrical components such as the compressor, circulation pumps, control system, and sometimes electric auxiliary heaters. The starting current of the compressor is particularly crucial here. This is significantly higher than the normal operating power and must be reliably supplied by the backup generator without voltage or frequency drops.
An undersized generator often leads to:
- the heat pump not starting
- protective mechanisms being triggered
- the electronics being disturbed or damaged
Correctly sizing power – more than just comparing kW
When selecting a suitable backup generator, it is not enough to just look at the rated power of the heat pump. More important are:
- starting power or starting current of the heat pump
- type of compressor, e.g., on/off or inverter
- additional consumers that should be supplied during emergency power operation
- simultaneity of loads
In practice, this means that a backup generator should be significantly more powerful than the pure electrical connection power of the heat pump suggests. Depending on the system type, a power reserve of 30 to 100 percent may be useful or even necessary.
Practical Tip: When sizing, not only the heat pump itself should be considered. It is crucial which consumers should run simultaneously in the event of a power outage – such as the control system, circulation pumps, refrigerator, lighting, or other important household consumers.
Single-phase or three-phase – crucial for practical use
Many heat pumps, especially larger systems, are operated three-phase with 400 V. Accordingly, the backup generator should also be three-phase. However, this often creates an underestimated issue: unbalanced load.
Unbalanced load in backup generators
An unbalanced load occurs when the three phases of a generator are loaded unevenly. In practice, this often happens when:
- the heat pump is operated three-phase
- single-phase household consumers such as lights, refrigerators, or sockets are connected to individual phases at the same time
Many generators have only limited unbalanced load capability. If one phase is loaded significantly more heavily than the others, the generator can shut down or be damaged.
For emergency power operation with a heat pump, it is therefore important to have:
- a high permissible unbalanced load of the generator
- a clean load distribution in the house network
- if necessary, a clear separation between the heat pump and other consumers
Especially for permanently installed emergency power solutions, this issue should be considered already in the planning phase.
Do not underestimate voltage and frequency stability
Modern heat pumps have sensitive electronics. A suitable backup generator must therefore:
- deliver stable voltage
- keep the frequency constant even with load changes
Inverter technology or high-quality conventional generators with good regulation, for example AVR, are clearly at an advantage here. Cheap or very simple generators are usually unsuitable for operating heat pumps.
Important: Heat pumps should not be connected to any small generators. If the voltage, frequency, or starting power are not suitable, this can lead to malfunctions, shutdowns, or damage to the electronics.
Conclusion: The right backup generator for heat pumps
A backup generator for a heat pump must be able to do more than just "supply power". Crucial factors are sufficient power reserves, clean voltage, stable frequency, and controlled handling of unbalanced loads in three-phase systems.
Those who also want to supply household consumers should consider the entire system as a whole and not just individual components. Properly sized, a backup generator ensures that heating, hot water, and important consumers continue to operate reliably even during extended power outages.