Example analysis of ground source heat pump design and operation costs

As a new development in heat pump technology, ground source heat pump systems have gained widespread popularity in recent years due to their energy efficiency and environmental benefits. These systems utilize the stable thermal properties of the ground to provide heating and cooling. In winter, the system absorbs heat from the underground through buried pipes filled with a heat transfer fluid, acting as a low-temperature heat source in a reversed thermodynamic cycle. This heat is then compressed and delivered to the building for heating. In summer, the cooler underground temperature allows the system to reject heat more efficiently, improving the refrigeration coefficient compared to traditional air conditioners that rely on ambient air for heat rejection. One of the key advantages of ground source heat pumps is that they primarily use electricity to operate, without requiring additional fuel sources like coal or gas. This makes them an environmentally friendly option for urban heating and cooling, eliminating the need for boiler rooms and reducing pollution associated with combustion. Additionally, these systems are particularly beneficial in remote or hard-to-reach areas such as highway toll stations, scientific research facilities, and border outposts where other heating and cooling methods may not be practical. This paper presents a detailed analysis of the ground source heat pump system at the Jingang Expressway toll station. The study covers load calculations, indoor and outdoor system design, and operational cost analysis. The Tianjin section of the expressway includes three toll stations, with the main toll station covering a total area of 871 square meters. Using the CLF cold load factor method recommended by ASHRAE, the cooling load was calculated at 120 W/m² for the main building and 220 W/m² for the toll booths. The maximum cooling load was found to be 113 kW, while the heat rejection capacity of the underground heat exchanger reached 146 kW. For heating, the system was designed to meet a load of 100 W/m² for the main building and 120 W/m² for the toll booths, resulting in a maximum heating load of 92 kW. The indoor system uses a fan coil setup, while the outdoor system employs vertical U-shaped ground loops. A total of 45 boreholes, each 100 meters deep, were required to meet the system’s thermal demands. The site had sufficient space, allowing for parking or landscaping without affecting the functionality of the system. In terms of operating costs, the system runs year-round, with 100 days of cooling and 120 days of heating. With two heat pump units, each consuming 13.3 kW, and considering time-of-use electricity rates, the annual operating cost was significantly lower than that of conventional air conditioning systems. At a COP of 4.5 in cooling mode and 4.1 in heating mode, the system saved approximately 63% in energy costs compared to traditional air conditioners. The study concludes that ground source heat pumps offer superior efficiency, environmental benefits, and cost savings, making them an ideal solution for sustainable heating and cooling in both urban and remote settings. Their ability to reduce reliance on fossil fuels and minimize environmental impact further highlights their importance in modern energy systems.

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