Cycling (short cycling)

Cycling means that the heat pump frequently switches on and off for short periods. This reduces efficiency and lifespan, and often indicates that the unit is too large.

A heat pump runs best when it operates for long, steady periods. Cycling means that it does not run continuously, but starts and stops frequently. A compressor start is the moment of highest stress.

Why this is important for your house

The Bundesverband Wärmepumpe (German Heat Pump Association) counts frequent compressor starts among the consequences of overdimensioning. They lead to poorer efficiency and a shorter lifespan. klimaaktiv also states that an oversized heat pump has a negative impact on lifespan and efficiency, and explicitly aims to avoid cycling.

Where cycling comes from

• Oversized heat pump: During the transitional seasons, the house needs little heat. If the demand is below the minimum output of the device, it has to cycle. The outdoor temperature at which this happens is called the cycling point. According to the association, this should ideally be at +5 °C or above.
• On-off devices without storage: For heat pumps without capacity control, the klimaaktiv Wegweiser (guide) requires a sufficiently large heat storage tank.
• Too little water in the system: for example, when many thermostatic valves close at the same time.

What helps

• A standardised heating load calculation instead of a generous estimate.
• A modulating heat pump that adjusts its output.
• A proper hydraulic balancing.

Many devices display the number of compressor starts and operating hours. A very high number of starts with few operating hours is an indication that you should have the system checked.

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