Heat Pump Efficiency and Innovative Waste Heat Utilization Concepts

1. Introduction

Heat pumps are considered a key technology in the energy transition because they harness environmental heat from air, water, or the ground and achieve multiple heating or cooling energy yields with a small amount of electrical energy. Their efficiency is characterized by the Coefficient of Performance (COP), which typically reaches values ​​between 3 and 5. Nevertheless, waste heat utilization remains an underutilized potential for further efficiency improvements.

This article examines a multi-stage heat recovery concept that stores waste heat from heat pumps in water tanks and also channels it underground to enable continuous recovery.

2. Basics of Heat Pump Efficiency

The efficiency of a heat pump depends essentially on:

• Temperature difference between heat source and heat sink

• Quality of the heat exchangers (heat exchangers, pump systems)

• Storage options for energy required at a later time

Since waste heat often remains unused, especially during peak times or during cooling processes, Optimization potential through storage and geothermal recirculation.

3. Waste heat utilization concept

3.1 Directing waste heat upwards

The excess heat energy from the heat pump is initially fed into water tanks. These serve as short-term storage, allowing temperatures of 40–90°C to be achieved for domestic hot water heating or heating support. Thermodynamically favorable storage is achieved through layering in the tank.

3.2 Storing Heat in Tanks

The tanks act as buffer zones that absorb peak loads and smooth the heat pump's operating times. This reduces cycle losses (frequent switching on and off) and increases the system's service life.

3.3 Transferring Waste Heat Underground

Heat not directly needed can be coupled into underground storage layers (e.g., aquifers, geothermal probe fields, or seasonal aquifer storage). This process— Often referred to as Aquifer Thermal Energy Storage (ATES) or Borehole Thermal Energy Storage (BTES) – enables seasonal shifting: heat surpluses in summer are stored underground and reused in winter.

3.4 Continuous Recovery

The concept of continuous recovery is based on the fact that the heat pump is not exclusively dependent on "natural" sources in winter, but can access the waste heat temporarily stored underground. This reduces the temperature difference between source and sink, which significantly increases the COP value.

4. Efficiency Gains and System Integration

• Increase in the seasonal performance factor (SPF): By using stored waste heat, efficiency increases by 10–30%, depending on location and storage capacity.

• Load Management: Combination with photovoltaics enables a largely self-sufficient heat supply.

• Grid Serviceability: Waste heat storage smooths consumption peaks and reduces loads on the power grid.

• Ecological Benefits: Reduction in fossil heating energy demand and CO₂ emissions.

5. Challenges

• Investment costs: Underground storage facilities and tanks increase system costs.

• Hydrogeological conditions: Not every subsoil is suitable for heat storage.

• Regulatory aspects: Approval procedures for geothermal storage facilities can be complex.

• Material issues: Tanks and heat exchangers must withstand high temperature cycles.

6. Conclusion

The integration of waste heat utilization, short- and long-term thermal storage, and underground recirculation systems opens up considerable potential for increasing the efficiency of heat andHeat pump systems. Especially in combination with renewable electricity generation (photovoltaics, wind power), a virtually emission-free, year-round heat supply can be achieved.

Very exciting – so you want to combine the heat pump waste heat storage concept with a speculative combined heat and power (CHP) system to make solar cells more efficient at night. I have formulated an appendix for this, which is stylistically based on the scientific article:

Appendix A: Speculative combined heat and power generation to increase the efficiency of solar cells at night

A.1 Initial situation

Photovoltaic systems only generate electrical energy in direct or diffuse sunlight. At night or in heavy cloud cover, the output drops to zero. Existing storage solutions (batteries, chemical storage) are practical, but costly and associated with energy conversion losses.

A.2 Conceptual Idea

The waste heat stored in water tanks or underground can be converted back into electricity via a combined heat and power (CHP) system. This creates a thermoelectric bridge between the heat storage and the solar cells:

1. Thermal drive: The stored heat is converted into electrical energy in a Stirling or ORC (Organic Rankine Cycle) process.

2. Power supply for the solar cell electronics: Even without solar radiation, the solar cells can continue to generate microcurrents by utilizing residual heat or artificially generated temperature differences (the principle of thermoradiative photovoltaics).

3. Hybrid operation: The interaction of PV and CHP makes it possible to generate a small but to achieve continuous base load coverage.

A.3 Thermoradiative Photovoltaics

Recent research approaches are investigating how solar cells can generate energy in the dark by radiating infrared heat (the difference from the cold night sky radiation). This process currently operates at a few milliwatts per square meter, but could be enhanced by combining it with heat storage.

A.4 Potential Benefits

• Nighttime electricity production: Even low power levels increase the overall efficiency of the PV system.

• Grid stability: By combining daytime PV generation and nighttime CHP output, the feed-in curve is smoothed.

• Sector coupling: An integrated system consisting of a heat pump, heat storage, and hybrid PV can supply the electricity and heat sectors connect.

A.5 Limitations and open questions

• The efficiency of thermoelectric systems is currently < 20%.

• Material issues (high-temperature resistance, thermoelectric materials).

• Economic viability compared to conventional batteries or hydrogen storage is unclear.

• Currently not regulated as a "renewable night-time power source" recognized.

👉 In short: This appendix presents a speculative vision in which waste heat and heat pump systems are not only used for heating purposes, but also indirectly keep solar cells alive at night by converting heat back into electricity.

Perfect 👍 Then I'll now build you an Appendix B that stylistically and scientifically follows Appendix A, but addresses your previously mentioned topic of "nightmares and distorted realities after time jumps." into an energy-technical, psychological-perceptual-theoretical context.

Appendix B: Perceptual Distortions and System Dynamics in Long-Term Storage and Time Jumps

B.1 Initial Situation

In the long-term thermal storage of energy – especially in geological underground storage – delayed feedbacks occur. Heat introduced in the summer is only available months later in the winter. This "time jump" of energy can be viewed analogously to cognitive phenomena such as memory fragmentation or dream distortion.

B.2 Distorted Realities After Time Jumps

In physics as well as in psychology, time shifts lead to paradoxical effects:

• Thermal distortion: The heat stored underground changes its temperature and quality on its way back (exergy losses).

• Cognitive distortion: People experience fragmented memories or "false" realities after long interruptions (e.g., sleep, anesthesia, cryogenesis).

• System analogy: An energy system based on seasonal shifting "dreams." in a sense: It stores real heat, but later only releases a transformed, distorted form.

B.3 Psychological-Technical Parallels

• Nightmares ↔ Storage Losses: Just as a nightmare is an exaggerated but distorted version of real experiences, a heat storage device in winter provides a distorted version of summer heat (lower temperature, higher losses).

• Reality Distortion ↔ System dynamics: When users expect stored heat to remain available unchanged, a "technical illusion" arises. In psychology, this corresponds to the misperception after time jumps.

• Continuity expectation: People and systems alike suffer from breaks in the timeline – Both memory and energy flows exhibit instabilities.

B.4 Practical Relevance

Understanding such distortion processes is crucial for both energy planning and user acceptance:

• Technical: Storage systems must be calculated with losses in order to realistically manage expectations for winter energy.

• Psychological: Communication to users must take into account that energy "comes back different than it went in."

• Interdisciplinary: Incorporating psychological metaphors can help better convey complex memory processes.

B.5 Speculative Extension

If wormholes or quantum time storage were to be researched as energy technologies in the future, distortions could become even more severe:

• Heat energy could be released "too early" or "too late." reappear.

• Paradoxical superpositions (superposition of summer and winter states) are conceivable.

• Analogous to the human psyche, an energy system would emerge that creates its own "nightmares." in the form of unpredictable energy flows.

👉 Appendix B thus links technical storage processes with psychological perceptual distortions and opens up a speculative outlook on the limits of time and energy.