Annual Coefficient of Performance (JAZ — Jahresarbeitszahl)

Definition

The Annual Coefficient of Performance (JAZ) is the seasonally averaged efficiency of a heat pump and is regarded as the most important benchmark for both economic viability and funding eligibility. It is determined either by calculation according to VDI 4650 (design stage) or by measurement during operation (heat meter plus electricity meter). The calculation expresses annual heat output in kilowatt-hours divided by total electrical energy consumed, including all auxiliary energy such as circulation pumps, controls, defrost energy and any electric back-up heater. A JAZ of 3.5 means that on average 1 kWh of electricity produces 3.5 kWh of heat. In contrast to the COP, which represents a single operating point under laboratory conditions, the JAZ integrates all real-world influences such as the outdoor temperature profile, heating curve, heating limit and runtime behaviour. It is therefore the more honest efficiency figure and the basis of any economic assessment.

When is the term used?

Funding relevance: BAFA heating funding for air-water heat pumps currently requires a minimum JAZ of around 2.8 in existing buildings, while brine-water and water-water (ground-source / groundwater) heat pumps must reach roughly 3.5. Because these thresholds can change, we verify the currently applicable requirement during the funding check. For KfW efficiency house funding, the JAZ feeds into the primary energy balance. In renovation planning the JAZ is therefore doubly relevant: it determines ongoing electricity costs and decides about funding eligibility and the potential repayment subsidy (Tilgungszuschuss). High flow temperatures, insufficiently insulated building envelopes and oversized devices are the most common efficiency killers.

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