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ABSTRACT
In China, residential buildings have a high-volume ratio and density, which limit the amount of buried U-tube space available, thereby hindering the application of traditional ground-source heat pump systems (GSHPs). Due to the imbalance in heat transfer, the operating efficiency of GSHPs decreases annually in severe cold zones. To alleviate these issues, we assessed the feasibility of medium-depth U-tube GSHPs. An experimental platform in Fuxin City, China, was established, and a simulation model was designed with TRNSYS software. The area affected by the heating load was analyzed, and the proposed system was compared with solar-soil and medium-depth casing pipe GSHPs. The proposed system was found to be stable and efficient for long-term operations, delivering not only the lowest equivalent annual cost but also a 4.61% improvement in heating (compared to solar-soil GSHPs), an 81.54% improvement in cooling, and a 23.08% improvement in emission reductions (compared to medium-depth casing pipe GSHPs).The application of a special U-shaped pipe elbow and a dual-temperature switching valve allowed heat exchange conversion between the heating and cooling conditions. The results of the simulation model demonstrated that dual-temperature operation resulted in greater cooling performance and cheaper operating costs than did the single-temperature system.
Nomenclature
| = | Rated coefficient of performance of heat pump units | |
| = | Rated energy efficiency ratio of heat pump units | |
| = | Rated water inlet temperature of heat pump units | |
| = | Temperature on top of storage | |
| = | Surface temperature of storage volume | |
| = | Thermal gradient of storage volume | |
| = | Thermal conductivity | |
| N | = | Number |
| D | = | Distance |
| H | = | Depth |
| = | Diameter | |
| Ci | = | Investment cost |
| r | = | Discount rate |
| t | = | Life cycle |
| Cm | = | Management cost |
| MEC | = | Major equipment cost |
| DC | = | Drilling cost |
| BC | = | Backfill cost |
| = | Comprehensive borehole cost | |
| f | = | Unit fee |
| V | = | Volume |
| EC | = | Excavation cost |
| h | = | Excavation height of V-shaped channels |
| n | = | Number of boreholes in a single row |
| AOAC | = | Additional occupied area cost |
| A | = | Land area |
| OC | = | Operation cost |
| P | = | Total energy consumption |
| = | Estimate index | |
| = | Rated capacity | |
| = | Rated power | |
| = | Rated flow | |
| = | Rated head | |
| = | Area of collectors | |
| = | Collector efficiency | |
| = | Rate of heat loss rate | |
| ECI | = | Energy conservation index |
| ERI | = | Emission reduction index |
| EI | = | Economy index |
| = | Rate of energy conservation | |
| G | = | Annual cumulative reduction |
| Subscripts | = | |
| hp | = | heat pump |
| s | = | storage |
| f | = | fill |
| p | = | pipe |
| b | = | borehole |
| l | = | layer |
| o | = | outer |
| i | = | inner |
| ex | = | excavation |
| t | = | transaction |
| g | = | green land |
| el | = | electricity |
| H | = | heating |
| C | = | cooling |
| sp | = | Single-speed pump |
| c | = | collector |
| h | = | heat storage |
| O | = | outer pipe |
| I | = | inner pipe |
| sys | = | system |
| CO2 | = | carbon dioxide emission |
| SO2 | = | sulfur dioxide emission |
| dust | = | dust emission |
| Acronyms | = | |
| GSHPs | = | Ground source heat pump system |
| TRNSYS | = | Transient system simulation tool |
| GDP | = | Gross domestic product |
| tce | = | Ton of standard coal equivalent |
| tCO2 | = | Ton carbon dioxide |
| HVAC | = | Heating, ventilation and air-conditioning |
| Tp | = | Temperature penalty |
| COP | = | Coefficient of performance |
| EER | = | Energy efficiency ratio |
| BHE | = | Borehole heat exchanger |
| VGHE | = | vertical ground heat exchanger |
| Type557a | = | Mode of U-tube ground heat exchanger in TRNSYS |
| RTWD160HE | = | Ground source heat pump units of TRANE |
| Type 225 | = | Developed mode of heat pump in TRNSYS |
| Type 927 | = | Mode of heat pump in TRNSYS |
| Type 742 | = | Mode of variable pump in TRNSYS |
| Type 271 | = | Developed mode of variable pump in TRNSYS |
| Type 114 | = | Mode of single pump in TRNSYS |
| Type 557d | = | Mode of casing pipe ground heat exchanger in TRNSYS |
| EAC | = | Equivalent annual cost |
| DST | = | duct Ground Heat Storage |
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
Notes on contributors
Tingting Zuo
Tingting Zuo is an engineer in Integrated Energy Management Department of China Construction Carbon Technology Co., LTD. She received her Bachelor's degree from Tiangong University and her Master's degree from Dalian University of Technology. Her research interests are renewable energy applications and building energy efficiency.
Xiangli Li
Xiangli Li is an associate professor and doctoral supervisor of major Heating Ventilation and Air Conditioning in faculty of Infrastructure Engineering of Dalian University of Technology. He received his Ph.D. from Harbin Institute of Technology. His research interests include heat pump technology and building energy efficiency.
Lifan Wang
Lifan Wang is the chairman and founder of Fuxin Manulife New Energy Heating Co.. He and his company specialize in developing innovative technologies in construction technology. His research interest is in medium-depth geothermal energy apCang Tong is a researcher in Nanjing institute of future energy system, Sector heat exchange. He received his master's degree and PhD degree from Dalian University of Technology. His research interest is in thermal storage technology.
Shiwei Xue
Shiwei Xue is the chief executive officer of China Construction Carbon Technology Co.. He is responsible for the development of the company's integrated energy services and dual carbon research businesses. His research interest is in carbon reduction in the construction industry.
Zhijie Zhang
Zhijie Zhang is the vice general manager of China Construction Carbon Technology Co.. He received his master's degree from Tongji University and is currently studying for his PhD at Tianjin University. His research interest is carbon reduction in the construction industry.