A novel heat pump system, the heat-source tower heat pump system (HSTHPS), has been developed in southern China, offering an alternative to traditional air-, water-, and ground-source heat pumps. The HSTHPS overcomes key limitations of existing technologies, including evaporator frosting in air-source heat pumps (ASHPS) and geological constraints of water- and ground-source systems (W/GSHPS). However, research on HSTHPS remains limited, affecting its wider adoption.
System Structure and Operation
The HSTHPS consists of a heat-source tower (HST) and a heat pump unit (HPU). In winter, an antifreeze solution extracts heat from ambient air before transferring it to the HPU's evaporator, where it undergoes a reverse Carnot cycle. This process captures both sensible heat and latent heat from air moisture condensation, making the system particularly suitable for humid climates. In summer, the system operates as a cooling unit, using water instead of an antifreeze solution to enhance heat dissipation.
HSTs are categorized into open and closed systems. Open HSTs function similarly to cooling towers, where antifreeze solution directly contacts air. While they offer low cost and high efficiency, they face challenges like solution loss, environmental pollution, and corrosion. Closed HSTs, in contrast, use finned tube heat exchangers to transfer heat indirectly, eliminating solution loss but reducing heat transfer efficiency. Hybrid designs aim to combine the strengths of both configurations.
Performance and Challenges
Studies have examined the heat and mass transfer characteristics of HSTHPSs, particularly the impact of air temperature and humidity. Open HSTs demonstrate strong heat absorption, but solution drifting and corrosion remain concerns. Closed HSTs require improvements in heat exchanger design and frost prevention strategies.
System performance is measured by coefficient of performance (COP) for the HPU and seasonal energy efficiency ratio (SEER) for the overall system. While the HPU exhibits high COP values, the SEER of the complete system remains only marginally better than traditional ASHPS. The primary reason is the high viscosity and pumping requirements of antifreeze solutions, which increase energy consumption.
Future Research and Applications
To enhance efficiency and sustainability, future research should focus on:
- Optimizing heat exchanger designs in closed HSTs, including tube types, fin arrangements, and surface modifications to prevent frost.
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Developing environmentally friendly antifreeze solutions to mitigate solution drifting in open systems.
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Exploring hybrid solutions, such as integrating HSTHPS with solar thermal systems to improve stability and reduce reliance on ambient air temperature.
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Refining operational strategies to minimize energy losses and enhance system reliability in various climatic conditions.
The HSTHPS represents a promising advancement in HVAC technology, particularly for regions with high humidity and moderate winter temperatures. Further research and technological refinements could make it a viable alternative to conventional heat pump systems in China and beyond.
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