Optimal schemes and benefits of recovering waste heat from data center for district heating by CO_2 transcritical heat pumps

摘要

Recovering waste heat from data center (DC) for district heating by CO2 transcritical heat pumps can effectively improve the performance of DC and reduce CO2 emission of district heating. However, the optimal design schemes, financial and environmental benefits, and market competitiveness of waste heat heating system are still unclear for different application scenarios. To realize the optimal system design and evaluate the benefits at different application scenarios, this work analyzed and compared the comprehensive performance of four system design schemes, considering two waste heat recovery locations and two cycle types. The maximum coefficient of performance (COP) was set as the optimization goal. Influences of electricity and heat prices on the optimal scheme and thermo-economic performance of waste heat heating system were analyzed. The direct electric-heating, coal-heating, gas-heating, air source heat pump, and ground source heat pump were selected as the comparative heating methods to evaluate the market competitiveness of waste heat heating system. Results show that using waste heat of cooling water from IT room achieves a better thermo-economic performance than that from chillers, which increases maximum COP by 18.2%-28.9% and reduces system investment cost by 4.2%-10.2%. The COP of IHE cycle (e.g., add an internal heat exchanger in the simple cycle) is larger, whereas the simple cycle has a lower investment cost. The cycle type with the shortest dynamic payback period depends on actual electricity and heat prices. The financial and environmental benefits of waste heat heating system are very attractive since it can reduce energy cost by 23.0%-75.0% compared with common heating methods and reduce CO2 emission by 12,880 tons annually compared with gas-heating. Furthermore, the energy efficiency of DC will be improved by waste heat reuse, and the annual energy reuse effectiveness (ERE) can decrease from 1.296 to 0.902 at the annual heating time of 121 days.