The Seasonal Performance Factor (SPF) is a key indicator that describes the efficiency of a heat pump over an entire annual cycle. It represents the ratio between the total heat energy delivered and the electrical energy consumed over a year. For example, an SPF of 4 means that the heat pump produces an average of 4 kilowatt-hours (kWh) of heat using only 1 kWh of electricity. Therefore, the SPF provides insight into how efficiently a heat pump operates throughout the year.

Calculating SPF

The SPF is determined based on the actual operation of the heat pump over an entire year. It considers both the heating system performance at varying source temperatures, such as outdoor air temperatures, as well as the energy required for operating the heat pump, including power for pumps, fans, and control systems. Unlike the Coefficient of Performance (COP), which is measured under standardized laboratory conditions, the SPF reflects real-world efficiency and provides a realistic assessment of a heat pump system’s energy performance.

Typical SPF values

Modern heat pumps in well-designed and properly installed systems for domestic heating typically achieve SPF values between 3 and 5. This means that over the span of a year, they deliver three to five times more heat energy than they consume electricity. A high SPF indicates a particularly efficient heat pump, resulting in cost savings and lower environmental impact. The SPF for domestic heating depends on various factors, including the type of heat pump (air-to-water, ground-to-water, water-to-water), building insulation, outdoor temperatures, and the overall heating system efficiency.

For process heat applications, SPF values typically range between approximately 2 and 5. The efficiency of the heat pump in such applications primarily depends on the temperature difference between the return temperature of the heat source and the supply temperature of the heat sink, as well as the efficiency factor of the compressor.

Relevance in practice

The SPF is an important metric for users and planners to evaluate the economic and environmental performance of heat pump systems. A higher SPF reduces electricity costs and significantly improves economic viability. Additionally, many government subsidy and incentive programs require minimum SPF values to qualify for financial support for heat pump installations.

Conclusion

The seasonal performance factor is a crucial value for assessing the real-world efficiency of a heat pump. It provides insights into how well the system performs over the span of a year and helps determine the potential energy savings and economic benefits of a heat pump system. The higher the SPF, the more efficient and cost-effective the heat pump operation.