Efficiency Improvements

The Organic Rankine Cycle (ORC) can improve first law efficiency (thermal efficiency) by up to 25% and second law efficiency (exergy efficiency) by up to 63%, making it highly effective for power generation from waste heat. The Vapour Absorption Refrigeration Cycle (VARC) offers a Coefficient of Performance (COP) up to 1.34 for cooling, with exergy efficiency ranging from 14% to 35%. The Ejector Refrigeration Cycle (ERC) has a COP up to 0.547 for cooling, with exergy efficiency up to 43.18%. These improvements depend on the system configuration and waste heat source temperature.

Cost Considerations

ORC systems typically have moderate to high initial costs but low operational costs when using waste heat. VARC systems have high initial costs and potentially high maintenance costs due to their complexity. ERC systems are simpler, with lower initial and operational costs, making them more economical for certain applications.

Best Option for Waste Heat Recovery

Given the versatility of power generation and high efficiency, ORC seems likely the best option for general waste heat recovery, especially for industrial applications needing power. However, if cooling is the primary need, VARC might be preferred for higher COP, though at a higher cost, while ERC offers a lower-cost alternative with reduced efficiency.

In conclusion, I would suggest that the Organic Rankine Cycle (ORC) is the best option for waste heat recovery when considering both efficiency and versatility, particularly for power generation. For cooling-specific needs, VARC offers higher efficiency than ERC but at a higher cost, while ERC is a cost-effective alternative with lower efficiency. The choice should be tailored to the specific waste heat source temperature, desired output, and budget constraints.

You appear to be asking about heat recovery from very low temperature sources: i.e. 60C or lower. If that is so, economics determines the best applications. In my experience, direct us of heat is the most economic use. This requires a large user of energy in the form of low temperatures. The best examples that I know of are market gardens, breweries and district heating. As heat pump technology improves, higher temperature applications like absorption refrigeration become more feasible.

The economics of low temperature heat recovery are rarely favourable, which has confounded energy analysts for generations..

This question can't be accurately answered unless you state the amount of heat to be recovered, i.e. the media and the DT in/out and what your objectives are. Depending on the heat recovery, steam cycle might be an option. There are some great ORCs now- look at the Durr, Germany range.